In the U.S., tritium for nuclear weapons was one of several products produced by the Atomic Energy Commission (AEC) and its successor, the Department of Energy (DOE), during the Cold War. The machines for tritium production were water-cooled, graphite-moderated production reactors in Hanford, Washington, and heavy water cooled and moderated production reactors at the Savannah River Plant (SRP, now Savannah River Site, SRS) in South Carolina. Lithium “targets,” containing enriched lithium-6 produced at the Y-12 Plant in Oak Ridge Tennessee, were irradiated in these reactors to produce tritium. Later, tritium was extracted from the targets, purified and packaged for use in nuclear weapons in separate facilities, initially at Hanford and Los Alamos and later at Savannah River.
Today, tritium for the U.S. nuclear weapons stockpile is produced in light water cooled and moderated commercial pressurized water reactors (PWRs) owned and operated by the Tennessee Valley Authority (TVA). Tritium is extracted from the targets, purified and packaged for use in nuclear weapons at the Savannah River Site (SRS).
The following three timelines provide details on tritium production activities in the Cold War nuclear weapons complex:
Under the Manhattan Project and through the Cold War, the U.S. developed and operated a dedicated nuclear weapons complex that performed all of the functions needed to transform raw materials into complete nuclear weapons. After the end of the Cold War (circa 1991), U.S. and Russian nuclear weapons stockpiles were greatly reduced. In the U.S., the nuclear weapons complex contracted and atrophied, with some functions being discontinued as the associated facilities were retired without replacement, while other functions continued at a reduced level, many in aging facilities.
In its current state, the U.S. nuclear weapons complex is struggling to deliver an adequate supply of tritium to meet the needs specified by the National Nuclear Security Administration (NNSA) for “stockpile stewardship and maintenance,” or in other words, for keeping the nuclear weapons in the current, smaller stockpile safe and operational. Key issues include:
There have been no dedicated tritium production reactors operating since 1988. Natural radioactive decay has been steadily reducing the existing inventory of tritium.
Commercial light water reactors (CLWRs) have been put into dual-use service since 2003 to produce tritium for NNSA while generating electric power that is sold commercially. The current tritium production rate needs to increase significantly to meet needs.
There has been a continuing decline in the national inventory of “unobligated” (i.e., free from peaceful use obligations) low-enriched uranium (LEU) and high-enriched uranium (HEU). This unobligated uranium can be used for military purposes, such as fueling the dual-use tritium production reactors.
There has been no “unobligated” U.S. uranium enrichment capability since 2013. The technology for a replacement enrichment facility has not yet been selected.
The U.S. domestic uranium production industry has declined to a small fraction of the capacity that existed from the mid-1950s to the mid-1980s. About 10% of uranium purchases in 2018 were from U.S. suppliers, and 90% came from other countries. NNSA’s new enrichment facility will need a domestic source of natural uranium.
There has been no operational lithium-6 production facility since the late 1980s.
There has been a continuing decline in the national inventory of enriched lithium-6, which is irradiated in “targets” to produce tritium.
Only one tritium extraction facility exists.
The U.S. nuclear weapons complex for tritium production is relatively fragile, with several milestone dates within the next decade that must be met in order to reach and sustain the desired tritium production capacity. There is little redundancy within this part of the nuclear weapons complex. Hence, tritium production is potentially vulnerable to the loss of a single key facility.
This complex story is organized in this post as follows.
Two key materials – Tritium and Lithium
Cold War tritium production
Hanford Project P-10 (later renamed P-10-X) for tritium production (1949 to 1954)
Hanford N-Reactor Coproduct Program for tritium production (1963 to 1967)
Savannah River Plant tritium production (1954 to 1988)
Synopsis of U.S. Cold War tritium production
The Interregnum of U.S Tritium Production (1988 to 2003)
New Production Reactor (NPR) Program
Accelerator Tritium Production (ATP)
The U.S. commercial light water reactor (CLWR) tritium production program (2003 to present)
Structure of the CLWR program
What is a TPBAR?
Operational use of TPBARs in TVA reactors
Where will the uranium fuel for the TVA reactors come from?
Tritium, or hydrogen-3, is naturally occurring in extremely small quantities (10-18 percent of naturally occurring hydrogen) or it can be artificially produced at great cost. The current tritium price is reported to be about $30,000 per gram, making it the most expensive substance by weight in the world today.
Tritium is a radioactive isotope of hydrogen with a half-life of 12.32 years. Tritium decays into helium-3 by means of negative beta decay, which also produces an electron (e–) and an electron antineutrino, as shown below.
Tritium is an important component of thermonuclear weapons. The tritium is stored in a small, sealed reservoir in each warhead.
With its relatively short half-life, the tritium content of the reservoir is depleted at a rate of 5.5% per year and must be replenished periodically. In 1999, DOE reported in DOE/EIS-0271 that none of the weapons in the U.S. nuclear arsenal would be capable of functioning as designed without tritium.
During the Cold War-era, the Atomic Energy Commission (AEC, and its successor in 1977, the Department of Energy, DOE) produced tritium for nuclear weapons in water-cooled, graphite-moderated production reactors in Hanford, Washington and in heavy water cooled and moderated production reactors at the Savannah River Plant (SRP, now Savannah River Site, SRS) in South Carolina. These reactors also produced plutonium, polonium and other nuclear materials. All of these production reactors were dedicated defense reactors except the dual-use Hanford-N reactor, which also could produce electricity for sale to the commercial power grid.
Tritium is produced by neutron absorption in a lithium-6 atom, which splits to form an atom of tritium (T) and an atom of helium-4. This process is shown below.
Natural lithium is composed of two stable isotopes; about 7.5% lithium-6 and 92.5% lithium-7. To improve tritium production, lithium-6 and lithium-7 are separated and the enriched lithium-6 is used to make “targets” that will be irradiated in nuclear reactors to produce tritium. The separated, enriched lithium-7 is a valuable material for other nuclear applications because of its very low neutron cross-section. Oak Ridge Materials Chemistry Division initiated work in 1949 to find a method to separate the lithium isotopes, with the primary goal of producing high purity lithium-7 for use in Aircraft Nuclear Propulsion (ANP) reactors.
Lithium-6 enrichment process development with a focus on tritium production began in 1950 at the Y-12 Plant in Oak Ridge, Tennessee. Three different enrichment processes would be developed with the goal of producing highly-enriched (30 to 95%) lithium-6: electric exchange (ELEX), organic exchange (OREX) and column exchange (COLEX). Pilot process lines (pilot plants) for all three processes were built and operated between 1951 and 1955.
Production-scale lithium-6 enrichment using the ELEX process was conducted at Y-12 from 1953 to 1956. The more efficient COLEX process operated at Y-12 from 1955 to 1963. By that time, a stockpile of enriched lithium-6 had been established at Oak Ridge, along with a stockpile of unprocessed natural lithium feed material.
The enriched lithium-6 material produced at Y-12 was shipped to manufacturing facilities at Hanford and Savannah River and incorporated into control rods and target elements that were inserted into a production reactor core and irradiated for a period of time.
After irradiation, these control rods and target elements were removed from the reactor and processed to recover the tritium that was produced. The recovered tritium was purified and then mixed with a specified amount of deuterium (hydrogen-2, 2H or D) before being loaded and sealed in reservoirs for nuclear weapons.
Tritium production at Hanford ended in 1967 and at Savannah River in 1988. The U.S. had no source of new tritium production for its nuclear weapons program between 1988 and 2003. During that period, tritium recycling from retired weapons was the primary source of tritium for the weapons remaining in the active stockpile. Finally, in 2003, the nation’s new replacement source of tritium for nuclear weapons started coming on line.
3. Cold War Tritium Production
3.1 Hanford Project P-10 (later renamed P-10-X) for tritium production (1949 to 1954)
The industrial process for producing plutonium for WW II nuclear weapons was conceived and built as part of the Manhattan Project. On 21 December 1942, the U.S. Army issued a contract to E. I. Du Pont de Nemours and Company (DuPont), stipulating that DuPont was in charge of designing, building and operating the future plutonium plant at a site still to be selected. The Hanford, Washington, site was selected in mid-January 1943.
Starting in 1949, the earliest work involving tritium production by irradiation of lithium targets in nuclear reactors was performed at Hanford under Project P-10 (later renamed P-10-X). By this time, DuPont had built and was operating four water-cooled, graphite-moderated production reactors at Hanford: B and D Reactors (1944), F Reactor (1945) and H Reactor (1949). Project P-10-X involved only the B and H Reactors, which were modified for tritium production.
Tritium was recovered from the targets in Building 108-B, which housed the first operational tritium extraction process line in the AEC’s nuclear weapons complex. The thermal extraction process employed started with melting the target material in a vacuum furnace and then collecting and purifying the tritium drawn off in the vacuum line. This tritium product was sent to Los Alamos for further processing and use.
Project P-10-X provided the initial U.S. tritium production capability from 1949 to 1954 and supplied the tritium for the first U.S. test of a thermonuclear device, Ivy Mike, in November 1952. Thereafter, most tritium production and all tritium extractions were accomplished at the Savannah River Plant.
DOE reported: “During its five years of operation, Project P-10-X extracted more than 11 million Curies (Ci) of tritium representing a delivered amount of product of about 1.2 kg.” For more details, see the report PNNL-15829, Appendix D: “Tritium Inventories Associated with Tritium Production,” which is available here:
3.2. Hanford N-Reactor Coproduct Program for tritium production (1963 to 1967)
This was a tritium production technology development program conducted in the mid-1960s. Its primary aim was not to produce tritium for the U.S. nuclear weapons program, but rather to develop technologies and materials that could be applied in tritium breeding blankets in fusion reactors. After an extensive review of candidate lithium-bearing target materials, the high melting point ceramic lithium aluminate (LiAlO2) was chosen.
Several fuel-target element designs were tested in-reactor, culminating in October 1965 with the selection of the “Mark II” design for use in the full-reactor demonstration. Targets were double-clad cylindrical elements with a lithium aluminate core. The first cladding layer was 8001 aluminum; the second (outer) cladding layer was Zircaloy-2.
During the N Reactor coproduct demonstration, four distinct production tests were run, the first two with small numbers of fuel and target columns being irradiated, and the last two runs with over 1,500 fuel and target columns containing about 17 tons LiAlO2. The last production test, PT-NR-87, recorded the highest N Reactor power level by operating at 4,800 MWt for 31 hours.
The irradiated target elements were shipped to SRP for tritium extraction using a thermal extraction process defined jointly by Pacific Northwest Laboratory (PNL, now Pacific Northwest National Laboratory, PNNL) and Savannah River Laboratories (SRL). The existing tritium extraction vacuum furnaces at SRP were used.
This completed the Hanford N Reactor Coproduct Program.
More details are available in PNNL report BNWL-2097, “Tritium Production from Ceramic Targets: A Summary of the Hanford Coproduct Program,” which is available at the following link:
This program provided important experience related to lithium aluminate ceramic targets for tritium production.
3.3. Savannah River Plant tritium production (1954 to 1988)
The Savannah River Plant (SRP) was designed in 1950 primarily for a military mission to produce tritium, and secondarily to produce plutonium and other special nuclear materials, including Pu-238. DuPont built five dedicated production reactors at the SRP and became operational between 1953 and 1955: the R reactor (prototype) and the later P, L, K and C reactors.
In 1955, the original maximum power of C Reactor was 378 MWt. With ongoing reactor and system improvements, C Reactor was operating at 2,575 MWt in 1960, and eventually was rated for a peak power of 2,915 MWt in 1967. The other SRP production reactors received similar reactor and system improvements. The increased reactor power levels greatly increased the tritium production capacity at SRP. You’ll find SRP reactor operating power history charts in Chapter 2 of “The Savannah River Site Dose Reconstruction Project -Phase II,” report at the following link:
Enriched lithium-6 product was sent from the Oak Ridge Y-12 Plant to SRP Building 320-M, where it was alloyed with aluminum, cast into billets, extruded to the proper diameter, cut to the required length, canned in aluminum and assembled into control rods or “driver” fuel elements.From 1953 to 1955, tritium was produced only in control rods. Lithium-aluminum alloy target rods (“producer rods”) were installed in the septifoil (7-chambered) aluminum control rods in combination with cadmium neutron poison rods to get the desired reactivity control characteristics.
Starting in 1955, enriched uranium “driver” fuel cylinders and lithium target “slugs” were assembled in a quatrefoil (4-chambered) configuration, which provided much more target mass in the core for tritium production.
Enriched uranium drivers were extruded in Building 320-M until 1957, after which they were produced in the newly constructed Building 321-M. Production rate varied with the needs of the reactors, peaking in 1983, when the operations in Building 321-M went to 24 hours a day. Manufacturing ceased in 1989 after the last production reactors, K, L and P, were shut down.
K Reactor was operated briefly, and for the last time, in 1992 when it was connected to a new cooling tower that was built in anticipation of continued reactor operation. K Reactor was placed in cold-standby in 1993, but with no planned provision for restart as the nation’s last remaining source of new tritium production. In 1996, K Reactor was permanently shut down.
3.4. Synopsis of U.S. Cold War tritium production
The Federation of American Scientists (FAS) estimated that the total U.S. tritium production (uncorrected for radioactive decay) through 1984 was about 179 kg (about 396 pounds).
DOE reported a total of 10.6 kg (23.4 pounds) of tritium was produced at Hanford:
About 1.2 kg (2.7 pounds) was produced at the B and H Reactors during Project P-10-X.
The balance of Hanford production (9.4 kg, 20.7 pounds) is attributed to N Reactor operation during the Coproduct Program.
The majority of U.S. tritium production through 1984 occurred at the Savannah River Plant: about 168.4 kg (371.3 pounds).
4. The Interregnum of U.S Tritium Production (1988 – 2003)
DOE had shut down all of its Cold War-era production reactors. Tritium production at Hanford ended in 1967 and at Savannah River in 1988, leaving the U.S. temporarily with no source of new tritium for its nuclear weapons program. At the time, nobody thought that “temporary” meant 15 years (a period I call the “Interregnum”).
DOE’s search for new production capacity focused on four different reactor technologies and one particle accelerator technology. During the Interregnum, the primary source of tritium was from recycling tritium reservoirs from nuclear weapons that had been retired from the stockpile. This worked well at first, but tritium decays.
4.1 New Production Reactor (NPR) Program
From 1988 to 1992, DOE conducted the New Production Reactor (NPR) Program to evaluate four candidate technologies for a new generation of production reactors that were optimized for tritium production, but with the option to produce plutonium:
Heavy water cooled and moderated reactor (HWR)
High-temperature gas-cooled reactor (HTGR)
Light water cooled and moderated reactor (LWR)
Liquid metal reactor (LMR)
Three candidate NPR sites were considered:
Savannah River Site
Idaho National Engineering Laboratory (INEL, now INL)
The NPR schedule goal was to have the new reactors start tritium production within 10 years after the start of conceptual design. Details on this program are available in DOE/NP-0007P, “New Production Reactors – Program Plan,” dated December 1990, which is available here: https://www.osti.gov/servlets/purl/6320732
The NPR program was cancelled in September 1992 (some say “deferred”) after DOE failed to select a preferred technology and failed to gain Congressional budgetary support for the program, at least in part due to the end of the Cold War.
DOE continued evaluating other options for tritium production, including commercial light water reactors (CLWRs) and accelerator tritium production (ATP).
4.2 Accelerator Tritium Production (ATP)
A candidate ATP design developed by Los Alamos National Laboratory (LANL) was based on a 1,700 MeV (million electron volt) linear accelerator that produced a 170 MW / 100 mA continuous proton beam. The ATP total electric power requirement was 486 MWe. The general arrangement of the ATP is shown in the following diagrams.
In this diagram, beam energy is indicated along the linear accelerator, increasing to the right and reaching a maximum of 1,700 MeV just before entering a magnetic switch that diverts the beam to the target/blanket or allows to beam to continue straight ahead to a tuning backstop.
The Target / Blanket System operates as follows:
The continuous proton beam is directed onto a tungsten target surrounded by a lead blanket, generating a huge flux of spallation neutrons.
Tubes filled with Helium-3 gas are located adjacent to the tungsten and within the lead blanket.
The spallation neutrons created by the energetic protons are moderated by the lead and cooling water and are absorbed by Helium-3 to create about 40 tritium atoms per incident proton.
The tritium is continuously removed from the Helium-3 gas in a nearby Tritium Separation Facility.
The unique feature of on-line, continuous tritium collection eliminates the time and processing required to extract tritium from the target elements used in production reactors.
ATP ultimately was rejected by DOE in December 1998 in favor of producing tritium in a commercial light water reactor (CLWR).
After the end of the Cold War, both the U.S. and Russia greatly reduced their respective stockpiles of nuclear weapons, as shown in the following chart.
The decommissioning of many nuclear weapons created an opportunity for the U.S. to temporarily maintain an adequate supply of tritium by recycling the tritium from the reservoirs no longer needed in warheads being retired from service. However, by 2020, after 32 years of exponential decay at a rate of 5.5% per year, the 1988 U.S. tritium inventory had decayed to only about 17% of the inventory in 1988, when the DOE stopped producing tritium. You can check my math using the following exponential decay formula:
y = a (1-b)x
y = the fractional amount remaining after x periods
a = initial amount = 1
b = the decay rate per period (per year) = 0.055
x = number of periods (years) = 32
Recycling tritium from retired and aged reservoirs and precisely reloading reservoirs for installation in existing nuclear weapons are among the important functions performed today at DOE’s Savannah River Site (SRS). But, clearly, there is a point in time where simply recycling tritium reservoirs is no longer an adequate strategy for maintaining the current U.S. stockpile of nuclear weapons. A source of new tritium for military use was required.
5. The U.S. commercial light water reactor (CLWR) tritium production program (2003 to present)
In December 1998, Secretary of Energy Bill Richardson announced the decision to select commercial light water reactors (CLWRs) as the primary tritium supply technology, using government-owned Tennessee Valley Authority (TVA) reactors for irradiation services. A key commitment made by DOE was that the reactors would be required to use U.S.-origin low-enriched uranium (LEU) fuel. In their September 2018 report R45406, the Congressional Research Service noted: “Long-standing U.S. policy has sought to separate domestic nuclear power plants from the U.S. nuclear weapons program – this is not only an element of U.S. nuclear nonproliferation policy but also a result of foreign ‘peaceful-use obligations’ that constrain the use of foreign-origin nuclear materials.”
5.1 Structure of the CLWR program
The current U.S. CLWR tritium production capability was deployed in about 12 years, between 1995 and 2007, as shown in the following high-level program plan.
Since early 2007, NNSA has been getting its new tritium supply for nuclear stockpile maintenance from tritium-producing burnable absorber rods (TPBARs) that have been irradiated in the slightly-modified core of TVA’s Watts Bar Unit 1 (WBN 1) nuclear power plant, which is a Westinghouse commercial pressurized water reactor (PWR) licensed by the U.S. Nuclear Regulatory Commission (NRC).
The NRC’s June 2005 “Backgrounder” entitled, “Tritium Production,” provides a good synopsis of the development and nuclear licensing work that led to the approval of TVA nuclear power plants Watts Bar Unit 1 and Sequoyah Units 1 and 2 for use as irradiation sources for tritium production for NNSA. You find the NRC Backgrounder here:
The CLWR tritium production cycle is shown in the following NNSA diagram. Not included in this diagram are the following:
Supply of U.S.-origin LEU for the fuel elements.
Production of fuel elements using this LEU
Management of irradiated fuel elements at the TVA reactor sites
PNNL is the TPBAR design authority (agent) and is responsible for coordinating irradiation testing of TPBAR components in the Advanced Test Reactor (ATR) at the Idaho National Laboratory (INL). Production TPBAR components are manufactured by several contractors in accordance with specifications from PNNL, with WesDyne International responsible for assembling the complete TPBARs in Columbia, South Carolina. When needed, new TPBARs are shipped to TVA for installation in a designated reactor during a scheduled refueling outage and then irradiated for 18 months, until the next refueling outage. After being removed from the reactor, the irradiated TPBARs are allowed to cool at the TVA nuclear power plant for a period of time and then are shipped to the Savannah River Site.
SRS is the only facility in the nuclear security complex that has the capability to extract, recycle, purify, and reload tritium. Today, the Savannah River Tritium Enterprise (SRTE) is the collective term for the facilities, people, expertise, and activities at the SRS related to tritium production. SRTE is responsible for extracting new tritium from irradiated TPBARs at the Tritium Extraction Facility (TEF) that became operational in January 2007. They also are responsible for recycling tritium from reservoirs of existing warheads. The existing Tritium Loading Facility at SRS packages the tritium in sealed reservoirs for delivery to DoD. You’ll find the SRTE fact sheet at the following link:
Program participants and their respective roles are identified in the following diagram.
5.2 What is a TPBAR?
The reactor core in a Westinghouse commercial four-loop PWR like Watts Bar Unit 1 approximates a right circular cylinder with an active core measuring about 14 feet (4.3 meters) tall and 11.1 feet (3.4 meters) in diameter. The reactor core has 193 fuel elements, each of which is comprised of a 17 x 17 square array of 264 small-diameter, fixed fuel rods and 25 small-diameter empty thimbles, 24 of which serve as guide thimbles for control rods and one is an instrumentation thimble.
Rod cluster control assemblies (RCCAs) are used to control the reactor by moving arrays of small-diameter neutron-absorbing control rods into or out of selected fuel elements in the reactor core. Watts Bar has 57 RCCAs, each comprised of 24 Ag-In-Cd (silver-indium-cadmium) neutron-absorbing rods that fit into the control rod guide thimbles in selected fuel elements. Each RCCA is controlled by a separate control rod drive mechanism. The geometries of a Westinghouse 17 x 17 fuel element and the RCCA are shown in the following diagrams.
To produce tritium in a Westinghouse PWR core, lithium-6 targets, in the form of lithium aluminate (LiAlO2) ceramic pellets, are inserted into the core and irradiated. This is accomplished with the tritium-producing burnable absorber rods (TPBARs), each of which is a small-diameter rod (a “rodlet”) that externally looks quite similar to a single control rod in an RCCA. During one typical 18-month refueling cycle (actually, up to 550 equivalent full power days), the tritium production per rod is expected to be in a range from 0.15 to 1.2 grams. The ceramic lithium aluminate target is similar to the targets developed in the mid-1960s and used during the Hanford N-Reactor Coproduct Program for tritium production.
A TPBAR “feed batch” assembly generally resembles the shape of an RCCA, but with 12 or 24 TPBAR rodlets in place of the control rods. The feed batch assembly is a hanging structure supported by the top nozzle adapter plate of the fuel assembly and the TPBAR rodlets are hanging in the guide thimble tubes of the fuel assembly. The feed batch assembly does not move after it has been installed in the reactor core.
Since lithium-6 is a strong neutron absorber, the TPBAR functions in the reactor core in a manner similar to fixed burnable absorber rods, which use boron-10 as their neutron absorber. The reactivity worth of the TPBARs is slightly greater than the burnable absorber rods.
In 2001, Framatome ANP issued Report BAW-10237, “Implementation and Utilization of Tritium Producing Burnable Absorber Rods (TPBARS) in Sequoyah Units 1 and 2.” This report provides a good description of the modified core and TPBARs as they would be applied for tritium production at the Sequoyah nuclear plant. Watts Bar should be similar. The report is here:
The feed batch assembly and TPBAR rodlet configurations are shown in the following diagram.
TPBARs were designed for a low rate of tritium permeation from the target pellets, through the cladding and into the primary coolant water. Tritium permeation performance was expected to be less than 1.0 Curie/one TPBAR rod/year. With an assumed maximum of 2,304 TPBARs in the reactor core, the NRC initially licensed Watts Bar Unit 1 for a maximum annual tritium permeation of 2,304 Curies / year.
5.3. Operational use of TPBARs in TVA reactors
NRC issued WBN 1 License Amendment 40 in September 2002, approving the irradiation of up to 2,304 TPBARs per operating cycle.
For the first irradiation cycle (Cycle 6) starting in the autumn of 2003, TVA received NRC approval to operate with only 240 TPBARs because of issues related to Reactor Coolant System (RCS) boron concentration. Actual TPBAR performance during Cycle 6 demonstrated a significantly higher rate of tritium permeation than expected; reported to be about 4.0 Curies/one TPBAR/cycle.
TVA’s short-term response was to limit the number of TPBARs per core load to 240 in Cycles 7 and 8 to ensure compliance with its NRC license limits on tritium release. In their 30 January 2015 letter to TVA, NRC stated, “….the primary constraint on the number of TPBARs in the core is the TPBAR tritium release per year of 2,304 Curies per year.” This guidance gave TVA some flexibility on the actual number of TPBARs that could be irradiated per cycle. This NRC letter is available here: https://www.nrc.gov/docs/ML1503/ML15030A508.pdf
PNNL’s examinations of TPBARs revealed no design or production flaws. Nonetheless, PNNL developed design modifications intended to improve tritium permeation performance. These changes were implemented by the manufacturing contractors, resulting in the Mark 9.2 TPBAR, which was first used in 2008 in WBN 1 Cycle 9. PNNL also is conducting an ongoing irradiation testing programs in the Advanced Test Reactor (ATR) at INL, with the goal of finding a technical solution for the high permeation rate. You’ll find details on this program in a 2013 PNNL presentation at the following link: https://www.energy.gov/sites/prod/files/2015/08/f26/Senor%20-%20TMIST-3%20Irradiation%20Experiment.pdf
In October 2010, the General Accounting Office (GAO) reported: “no discernable improvement in TPBAR performance was made and tritium is still permeating from the TPBARs at higher-than-expected rates.” This GAO report is available here: https://www.gao.gov/products/GAO-11-100
In response to the high tritium permeation rate, the irradiation management strategy was revised based on an assumed permeation rate of 5.0 Curies per TPBAR per year (five times the original expected rate). Even at this higher permeation rate, WBN 1 can meet the NRC requirements in 10 CFR Part 20 and 10 CFR Part 50 Appendix I related to controlling radioactive materials in gaseous and liquid effluents produced during normal conditions, including expected occurrences.
The many NRC license amendments associated with WBN 1 tritium production are summarized below:
In License Amendment 40 (Sep 2002), the NRC originally approved WBN 1 to operate with up to 2,304 TPBARs.
Cycle 6: TVA limited the maximum number of TPBARs to be irradiated to 240 based on issues related to Reactor Coolant System (RCS) boron concentration. Approved by NRC in WBN 1 License Amendment 48 (Oct 2003).
Cycles 7 & 8: WBN 1 continued operating with 240 TPBARs.
Cycle 9: First use of TPBARs Mark 9.2 supported TVAs request to increase the maximum number of TPBARs to 400. Approved by NRC in WBN 1 License Amendment 67 (Jan 2008)
Cycle 10: TVA reduced the number of TPBARs irradiated to 240 after discovering that the Mark 9.2 TPBAR design changes deployed in Cycle 9 did not significantly reduce tritium permeation.
Cycles 11 to 14: NRC License Amendment 77 9May 2009) allowed a maximum of 704 TPBARs at WBN 1. TVA chose to irradiate only 544 TPBARs in Cycles 11 and 12, increasing to 704 TPBARs for Cycles 13 & 14.
Cycles 15 & beyond: NRC License Amendment 107 (Aug 2016) allows a maximum of 1,792 TPBARs at WBN 1.
The actual number of TPBARs and the average tritium production per TPBAR during WBN 1 Cycles 6 to 14 are summarized in the 2017 PNNL presentation, “Tritium Production Assurance,” and are reproduced in the following table.
The current tritium production plan continues irradiation in WBN 1 and starts irradiation in Watts Bar Unit 2 (WBN 2) in Cycle 4, which will start after the spring 2022 refueling. Tritium is assumed to be delivered six months after the end of each cycle.
As of early 2020, TVA and DOE are not delivering the quantity of tritium expected by NNSA. In July 2019, DOE and NNSA delivered their “Fiscal Year 2020 – Stockpile Stewardship and Management Plan” to Congress. In this plan, the top-level goal was to “recapitalize existing infrastructure to implement a plan to produce no less than 80 ppy (plutonium pits per year) by 2030.” To meet this goal, NNSA set a target for increasing tritium production to 2,800 grams per two 18-month reactor cycles of production at TVA by 2027. This means two TVA reactors will be producing tritium, and each will have a target of about 1,400 grams per cycle. This will be quite a challenge for TVA and DOE.
5.4 Where will the uranium fuel for the TVA reactors come from?
The tritium-producing TVA reactors are committed to using unobligated LEU fuel. That means that the uranium is not encumbered by international obligations that restrict its use for peaceful purposes only. Unobligated uranium has a very special pedigree. The uranium originated from U.S. mines, was processed in U.S. facilities, and was enriched in an unobligated U.S. enrichment facility.
Today, that front-end of the U.S. nuclear fuel cycle has withered against international competition, as shown in the following chart from the Energy Information Administration (EIA).
Since the U.S. has not had an unobligated uranium enrichment facility since 2013, when the Paducah enrichment plant was closed by the Obama administration, there currently is no source of new unobligated LEU for the tritium-producing TVA reactors.
The impending shortage of unobligated enriched uranium eventually could affect tritium production, Navy nuclear reactor operation and other users. This matter has been addressed by the GAO in their 2018 report GAO-18-126, “NNSA Should Clarify Long-Term Uranium Enrichment Mission Needs and Improve Technology Cost Estimates,” which is available here:
The solution could be a mixture of measures, some of which are discussed briefly below.
Downblend unobligated HEU to buy time
Currently, the LEU for the TVA reactors is supplied from the U.S. inventory of unobligated LEU, which is supplemented by downblending unobligated HEU. In September 2018, NNSA awarded Nuclear Fuel Services (NFS) a $505 million contract to downblend 20.2 metric tons of HEU to produce LEU, which can serve as a short-term source of fuel for the tritium-producing TVA reactors. This contract runs from 2019 to 2025. Beyond 2025, additional HEU downblending may be needed to sustain tritium production until a longer-term solution is in place.
Build a new unobligated uranium enrichment facility and re-build the associated domestic uranium mining, milling and conversion infrastructure
NNSA is in the process of selecting the preferred technology for a new unobligated enrichment plant. There are two competing enrichment technologies: the Centrus AC-100 large advanced gas centrifuge and the Oak Ridge National Laboratory small advanced gas centrifuge, both of which are designed to enrich gaseous uranium hexafluoride (UF6).
NNSA failed to meet its goal of making the selection by the end of 2019. Regardless of the choice, it will take more than a decade to deploy such a facility. Perhaps a mid-2030’s date would be a possible target for initial operation of a new DOE uranium enrichment facility.
In the meantime, the atrophied / shutdown US uranium mining, milling and conversion industries need to be rebuilt to once again establish a reliable, domestic source of feed material for DOE’s uranium enrichment operations. This will be a daunting task given the current sad state of the US uranium production industry.
In May 2020, the US Energy Information Administration (EIA) released its 2019 Domestic Uranium Production Report. Mining uranium ore or in-situ leaching from underground uranium ore bodies, followed by the production of uranium (U3O8) concentrate (”yellowcake”), are the first steps at the front-end of the nuclear fuel cycle. The following EIA summary graphic shows the decline of US uranium production, which has been especially dramatic since 2013.
A key point reported by the EIA was that total US production of uranium concentrate from all domestic sources in 2019 was only 170,000 pounds (77,111 kg) of U3O8, 89% less than in 2018, from six facilities. In the graphic, you can see that US annual production in 1996 was about 35 times greater, approximately 6,000,000 pounds (2,721,554 kg). This EIA report is available at the following link: https://www.eia.gov/uranium/production/annual/
Conversion of U3O8 to UF6 is the next step in the front-end of the nuclear fuel cycle. Honeywell’s Metropolis Works was built in 1958 to produce UF6 for US government programs, including the nuclear weapons complex. Therefore, the Metropolis Works should be an unobligated conversion plant and, as such, is an important facility in the nuclear fuel cycle for the US tritium production reactors operated by TVA. In 2020, the Metropolis Works is the only US facility that can receives uranium ore concentrate and convert it to UF6.
In 1968, Metropolis Works began selling UF6 on the commercial nuclear market. However, since 2017, operations at the Metropolis Works have been curtailed due to weak market conditions for its conversion services and Honeywell has maintained the facility in a “ready-idle” status. In March 2020, the NRC granted the Metropolis Works a 40-year license renewal, permitting operations until March 24, 2060. When demand resumes, the Metropolis Works should be ready to resume operation.
Recognizing the US national interest in having a viable industrial base for the front-end of the nuclear fuel cycle, President Trump established a Nuclear Fuel Working Group in July 2019. On 13 April, 2020, the DOE released the “Strategy to Restore American Nuclear Energy Leadership,” which, among other things, includes recommendations to strengthen the US uranium mining and conversion industries and restore the viability of the entire front-end of the nuclear fuel cycle. You’ll find this DOE announcement and a link to the full report to the President here: https://www.energy.gov/articles/secretary-brouillette-announces-nuclear-fuel-working-groups-strategy-restore-american
Reprocess enriched DOE and naval fuel spent fuel
A large inventory of aluminum clad irradiated fuel exists at SRS, with a smaller quantity at INL. The only operating chemical separations (reprocessing) facility in the U.S. is the H-Canyon facility at SRS, which can only process aluminum clad fuel. However, the cost to operate H-Canyon to process the aluminum-clad fuel would be high.
There is a large inventory of irradiated, zirconium-clad naval fuel at INL. This fuel started life with a uranium enrichment level of 93% or higher. In 2017, INL completed a study examining the feasibility of processing zirconium-clad spent fuel through a new process called ZIRCEX. This process could enable reprocessing the spent naval fuel stored at INL as well as other types of zirconium-clad fuel.
In 2018, the U.S. Senate approved $15 million in funding for a pilot program at the INL to “recycle” irradiated (used) naval nuclear fuel and produce high-assay, low-enriched uranium (HALEU) fuel with an enrichment between 5% to 20% for use in “advanced reactors.” It seems that a logical extension would be to also produce LEU fuel to a specification that could be used in the TVA reactors.
In 2018, Idaho Senator Mike Crapo made the following report to the Senate: “HEU repurposing, from materials like spent naval fuel, can be done using hybrid processes that use advanced dry head-end technologies followed by material recovery, which creates the fuel for our new advanced reactors. Repurposing this spent fuel has the potential of reducing waste that would otherwise be disposed of at taxpayer expense, and approximately 1 metric ton of HEU can create 4 useable tons (of HALEU) for our new reactors.”
Perhaps there is a future for closing the back-end of the naval fuel cycle and recovering some of the investment that went into producing the very highly enriched uranium used in naval reactors. Because of the high burnup in long-life naval reactors, the resulting HALEU or LEU will have different uranium isotopic proportions than LEU produced in the front-end of the fuel cycle. This may introduce issues that would have to be reviewed and approved by the NRC before such LEU fuel could be used in the TVA reactors.
More information on options for obtaining enriched uranium without acquiring a new uranium enrichment facility is provided in Appendix II of GAO-18-126.
5.5 Where will the enriched lithium-6 target material come from?
A reliable source of lithium-6 target material is needed to produce the TPBARs for TVA’s tritium-producing reactors.
The U.S. has not had an operational lithium-6 production facility since 1963 when the last COLEX (column exchange) enrichment line was shutdown. COLEX was one of three lithium enrichment technologies employed at the Y-12 Plant in Oak Ridge, TN between 1950 and 1963. The others technologies were ELEX (electrical exchange) and OREX (organic exchange). All of these processes used large quantities of mercury. At the time lithium-6 enrichment operations ceased at Y-12, a stockpile of enriched lithium-6 and lithium-7 had been established along with a stockpile of unprocessed natural lithium feed material.
There has been a continuing decline in the national inventory of enriched lithium-6. To extend the existing supply, NNSA has instituted a program to recover and recycle lithium components from nuclear weapons that are being retired from the stockpile.
In May 2017, Y-12 lithium activities were adversely affected by the poor physical condition (and partial roof collapse) of the WW II-vintage Building 9204-2 (Beta 2).
Shortly thereafter, NNSA announced the approval of plans for a new Lithium Production Facility at Y-12 to replace Building 9204-2. The NNSA’s Fiscal Year 2020 – Stockpile Stewardship and Management Plan set an operational date of 2030 for the new facility.
5.6 Where is the tritium recovered?
Tritium is extracted from the irradiated TPBARs, purified and loaded into reservoirs at the Savannah River Site (SRS). These functions are performed by “Savannah River Tritium Enterprise” (SRTE), which is the collective term for the tritium facilities, people, expertise, and activities at the SRS.
The first load of irradiated TPBARs were consolidated at Watts Bar and delivered to SRS in August 2005 for storage pending completion of the new Tritium Extraction Facility (TEF). The TEF became fully operational and started extracting tritium from TPBARs in January 2007. The tritium extracted at TEF is transferred to the H Area New Manufacturing (HANM) Facility for purification. In February 2007, the first newly-produced tritium was delivered to the SRS Tritium Loading Facility for loading into reservoirs for nuclear weapons.
From 2007 until 2017, the TEF conducted only a single extraction each year because of the limited quantities of TPBARs being irradiated in the TVA reactors. During this period, the TEF sat idle for nine months each year between extraction cycles.
In 2017, for the first time, the TEF performed three extractions in a single year using the original vacuum furnace. Each extraction typically involved 300 TPBARs.
In November 2019, SRTE’s capacity for processing TPBARs and recovering tritium was increased by the addition of a second vacuum furnace.
In their “Fiscal Year 2020 – Stockpile Stewardship and Management Plan,” the NNSA’s top-level goal is to “recapitalize existing infrastructure to implement a plan to produce no less than 80 ppy (plutonium pits per year) by 2030.” This goal will drive tritium production demand, which in turn will drive demands for unobligated LEU to fuel TVA’s tritium-producing reactors and enriched lithium-6 for TPBARs.
The U.S. nuclear fuel cycle for the production of tritium currently is incomplete. It is able to produce tritium by using temporary measures that are not sustainable:
Downblending HEU to produce LEU
Recycling tritium as the primary means for meeting current demand
Recycling lithium components
The next 15 years will be quite a challenge for the NNSA, DOE and TVA as they work to reestablish a complete, modern nuclear fuel cycle for tritium production. There are several milestones on the critical path that would adversely impact tritium production if they are not met on schedule:
Higher tritium production goals for the TVA reactors: deliver 2,800 grams of tritium per two 18-month reactor cycles of production in TVA reactors by 2027
New Lithium Facility at Y-12 operational by 2030
New uranium enrichment facility operational, perhaps by the mid-2030s
There is a general lack of redundancy in the existing and planned future nuclear fuel cycle for tritium production. This makes tritium production vulnerable to a major outage at a single non-redundant facility.
“National Nuclear Security Administration Needs to Ensure Continued Availability of Tritium for the Weapons Stockpile,” Report GAO-11-100, General Accounting Office, October 2010: https://www.gao.gov/assets/320/311092.pdf
Sean Johnson, “Making the invisible engineer visible: DuPont and the recognition of nuclear expertise,” Technology and Culture, Volume 52, Number 3, July 2011, pp. 548-573: https://muse.jhu.edu/article/447781/pdf
For more information on Cold War-era Hanford tritium production:
Johnson AB, Jr., TJ Kabele, and WE Gurwell, “Tritium Production from Ceramic Targets: A Summary of the Hanford Coproduct Program,” BNWL-2097, Pacific Northwest National Laboratory, 1976: https://www.osti.gov/servlets/purl/7125831
Johnson AB, Jr., TJ Kabele, and WE Gurwell, “Tritium Production from Ceramic Targets: A Summary of the Hanford Coproduct Program,” BNWL-2097, Pacific Northwest National Laboratory, 1976: https://www.osti.gov/servlets/purl/7125831
On 19 January 1942, US President Franklin D. Roosevelt approved the production of an atomic bomb. At that time, most of the technology for producing an atomic bomb still needed to be developed and the US had very little infrastructure in place to support that work.
The Manhattan Engineer District (MED, aka the “Manhattan Project”) was responsible for the research, design, construction and operation of the early US nuclear weapons complex and for delivering atomic bombs to the US Army during World War II (WW II) and in the immediate post-war period. The Manhattan Project existed for just five years. In 1943, 75 years ago, the Manhattan Project transitioned from planning to construction and initial operation of the first US nuclear weapons complex facilities. Here’s a very brief timeline for the Manhattan Project.
13 August 1942: The Manhattan Engineer District was formally created under the leadership of U.S. Army Colonel Leslie R. Groves.
2 December 1942: A team led by Enrico Fermi achieved the world’s first self-sustaining nuclear chain reaction in a graphite-moderated, natural uranium fueled reactor known simply as Chicago Pile-1 (CP-1).
1943 – 1946: The Manhattan Project managed the construction and operation of the entire US nuclear weapons complex.
16 July 1945: The first nuclear device was successfully tested at the Trinity site near Alamogordo, NM, less than three years after the Manhattan Project was created.
6 & 9 August 1945: Atomic bombs were employed by the US against Japan, contributing to ending World War II.
1 January 1947: The newly formed, civilian-led Atomic Energy Commission (AEC) took over management and operation of all research and production facilities from the Manhattan Engineer District.
25 August 1947: The Manhattan Engineer District was abolished.
The WW II nuclear weapons complex was the foundation for the early US post-war nuclear weapons infrastructure that evolved significantly over time to support the US mutually-assured destruction strategy during the Cold War with the Soviet Union. Today, the US nuclear weapons complex continues to evolve as needed to perform its critical role in maintaining the US nuclear deterrent capability.
2. A Closer Look at the Manhattan Project Timeline
You’ll find a comprehensive, interactive timeline of the Manhattan Project on the Department of Energy’s (DOE) OSTI website at the following link:
The Atomic Heritage Foundation is dedicated to “supporting the Manhattan Project National Historical Park and capturing the memories of the people who harnessed the energy of the atom.” Their homepage is here:
The Manhattan Project National Historical Park was authorized by Congress in December 2014 and subsequently was approved by the President to commemorate the Manhattan Project. The Manhattan Project National Historical Park is an extended “park” that currently is comprised of three distinct DOE sites that each had different missions during WW II:
Los Alamos, New Mexico: Nuclear device design, test and production
Oak Ridge, Tennessee: Enriched uranium production
Hanford, Washington: Plutonium production
On 10 November 2015, a memorandum of agreement between DOE and the National Park Service (NPS) established the park and the respective roles of DOE and NPS in managing the park and protecting and presenting certain historic structures to the public.
You’ll find the Manhattan Project National Historical Park website here:
Following is a brief overview of the three sites that currently comprise the Manhattan Project National Historical Park.
3.1. Los Alamos, New Mexico
Los Alamos Laboratory was established 75 years ago, in early 1943, as MED Site Y, under the direction of J. Robert Oppenheimer. This was the Manhattan Project’s nuclear weapons laboratory, which was created to consolidate in one secure, remote location most of the research, design, development and production work associated producing usable nuclear weapons to the US Army during WW II.
The first wave of scientists began arriving at Los Alamos Laboratory in April 1943. Just 27 months later, on 16 July 1945, the world’s first nuclear device was detonated 200 miles south of Los Alamos at the Trinity Site near Alamogordo, NM. This was the plutonium-fueled, implosion-type device code named “Gadget.”
During WW II, the Los Alamos Laboratory produced three atomic bombs:
One uranium-fueled, gun-type atomic bomb code named “Little Boy” was produced. This was the atomic bomb dropped on Hiroshima, Japan on 6 August 1945, making it the first nuclear weapon used in warfare. This atomic bomb design was not tested before it was used operationally.
Two plutonium-fueled, implosion-type atomic bombs code named “Fat Man” were produced. These bombs were very similar to Gadget. One of the Fat Man bombs was dropped on Nagasaki, Japan on 9 August 1945. The second Fat Man bomb could have been used during WW II, but it was not needed after Japan announced its surrender on 15 August 1945.
The highly-enriched uranium for the Little Boy bomb was produced by the enrichment plants at Oak Ridge. The plutonium for Gadget and the two Fat Man bombs was produced by the production reactors at Hanford.
Three historic sites are on Los Alamos National Laboratory property and currently are not open to the public:
Gun Site Facilities: three bunkered buildings (TA-8-1, TA-8-2, and TA-8-3), and a portable guard shack (TA-8-172).
V-Site Facilities: TA-16-516 and TA-16-517 V-Site Assembly Building
Pajarito Site: TA-18-1 Slotin Building, TA-8-2 Battleship Control Building, and the TA-18-29 Pond Cabin.
You’ll find information on the Manhattan Project National Historical Park sites at Los Alamos here:
Land acquisition was approved in 1942 for planned uranium “atomic production plants” in the Tennessee Valley. The selected site officially became the Clinton Engineer Works (CEW) in January 1943 and was given the MED code name Site X. This is where MED and its contractors managed the deployment during WW II of the following three different uranium enrichment technologies in three separate, large-scale industrial process facilities:
Liquid thermal diffusion process, based on work by Philip Abelson at Naval Research Laboratory and the Philadelphia Naval Yard. This process was implemented at S-50, which produced uranium enriched to < 2 at. % U-235.
Gaseous diffusion process, based on work by Harold Urey at Columbia University. This process was implemented at K-25, which produced uranium enriched to about 23 at. % U-235 during WW II.
Electromagnetic separation process, based on Ernest Lawrence’s invention of the cyclotron at the University of California Berkeley in the early 1930s. This process was implemented at Y-12 where the final output was weapons-grade uranium.
The Little Boy atomic bomb used 92.6 pounds (42 kg) of highly enriched uranium produced at Oak Ridge with contributions from all three of these processes.
The nearby township was named Oak Ridge in 1943, but the nuclear site itself was not officially renamed Oak Ridge until 1947.
The three Manhattan Project National Historical Park sites at Oak Ridge are:
X-10 Graphite Reactor National Historic Landmark
Y-12 complex: Buildings 9731 and 9204-3
The S-50 Thermal Diffusion Plant was dismantled in the late 1940s. This site is not part of the Manhattan Project National Historical Park.
Following is a brief overview of X-10, K-25 and Y-12 historical sites. There’s much more information on the Manhattan Project National Historical Park sites at Oak Ridge here:
X-10 was the world’s second nuclear reactor (after the Chicago Pile, CP-1) and the first reactor designed and built for continuous operation. It was intended to produce the first significant quantities of plutonium, which were used by scientists at Los Alamos to characterize plutonium and develop the design of a plutonium-fueled atomic bomb.
X-10 was a large graphite-moderated, natural uranium fueled reactor that originally had an continuous design power rating of 1.0 MWt, which later was raised to 3.5 MWt. Originally, it was intended to be a prototype for the much larger plutonium production reactors being planned for Hanford. The selection of air cooling for X-10 enabled this reactor to be deployed more rapidly, but limited its value as a prototype for the future water-cooled plutonium production reactors.
The X-10 reactor core was comprised of graphite blocks arranged into a cube measuring 24 feet (7.3 meters) on each side. The core was surrounded by several feet of high-density concrete and other material to provide radiation shielding. The core and shielding were penetrated by 1,248 horizontal channels arranged in 36 rows. Each channel served to position up to 54 fuel slugs in the core and provide passages for forced air cooling of the core. Each fuel slug was an aluminum clad, metallic natural uranium cylinder measuring 4 inches (10.16 cm) long x 1.1 inches (2.79 cm) in diameter. New fuel slugs were added manually at the front face (the loading face) of the reactor and irradiated slugs were pushed out through the back face of the reactor, dropping into a cooling water pool. The reactor was controlled by a set of vertical control rods.
The basic geometry of the X-10 reactor is shown below.
Site construction work started 75 years ago, on 27 April 1943. Initial criticality occurred less than seven months later, on 4 November 1943.
Plutonium was recovered from irradiated fuel slugs in a pilot-scale chemical separation line at Oak Ridge using the bismuth phosphate process. In April 1944, the first sample (grams) of reactor-bred plutonium from X-10 was delivered to Los Alamos. Analysis of this sample led Los Alamos scientists to eliminate one candidate plutonium bomb design (the “Thin Man” gun-type device) and focus their attention on the Fat Man implosion-type device. X-10 operated as a plutonium production reactor until January 1945, when it was turned over to research activities. X-10 was permanently shutdown on 4 November 1963, and was designated a National Historic Landmark on 15 October 1966.
K-25 Gaseous Diffusion Plant
Preliminary site work for the K-25 gaseous diffusion plant began 75 years ago, in May 1943, with work on the main building starting in October 1943. The six-stage pilot plant was ready for operation on 17 April 1944.
The K-25 gaseous diffusion plant feed material was uranium hexafluoride gas (UF6) from natural uranium and slightly enriched uranium from both the S-50 liquid thermal diffusion plant and the first (Alpha) stage of the Y-12 electromagnetic separation plant. During WW II, the K-25 plant was capable of producing uranium enriched up to about 23 at. % U-235. This product became feed material for the second (Beta) stage of the Y-12 electromagnetic separation process, which continued the enrichment process and produced weapons-grade U-235.
As experience with the gaseous diffusion process improved and additional cascades were added, K-25 became capable of delivering highly-enriched uranium after WW II.
You can take a virtual tour of K-25, including its decommissioning and cleanup, here:
Construction on the second Oak Ridge gaseous diffusion plant, K-27, began on 3 April 1945. This plant became operational after WW II. By 1955, the K-25 complex had grown to include gaseous diffusion buildings K-25, K-27, K-29, K-31 and K-33 that comprised a multi-building, enriched uranium production chain collectively known as the Oak Ridge Gaseous Diffusion Plant (ORGDP). Operation of the ORGDP continued until 1985.
Additional post-war gaseous diffusion plants based on the technology developed at Oak Ridge were built and operated in Paducah, KY (1952 – 2013) and Portsmouth, OH (1954 – 2001).
Y-12 Electromagnetic Separation Plant
In 1941, Earnest Lawrence modified the 37-inch (94 cm) cyclotron in his laboratory at the University of California Berkeley to demonstrate the feasibility of electromagnetic separation of uranium isotopes using the same principle as a mass spectrograph.
The initial industrial-scale design agreed in 1942 was called an Alpha (α) calutron, which was designed to enrich natural uranium (@ 0.711 at.% U-235) to >10 at.% U-235. The later Beta (β) calutron was designed to further enrich the output of the Alpha calutrons, as well as the outputs from the K-25 and S-50 processes, and produce weapons-grade uranium at >88 at.% U-235.
The calutrons required large magnet coils to establish the strong electromagnetic field needed to separate the uranium isotopes U-235 and U-238. The shape of the magnet coils for both the Alfa and Beta calutrons resembled a racetrack, with many individual calutron modules (aka “tanks”) arranged side-by-side around the racetrack. At Y-12, there were nine Alpha calutron “tracks” (5 x Alpha-1 and 4 x Alpha-2 tracks), each with 96 calutron modules (tanks), for a total of 864 Alpha calutrons. In addition, there were eight Beta calutron tracks, each with 36 calutron modules, for a total of 288 beta calutrons, only 216 of which ever operated.
Due to wartime shortages of copper, the Manhattan Project arranged a loan from the Treasury Department of about 300 million Troy ounces (10,286 US tons) of silver for use in manufacturing the calutron magnet coils. A general arrangement of a Beta calutron module (tank) is shown in the following diagram, which also shows the isotope flight paths from the uranium tetrachloride (UCl4) ion source to the ion receivers. Separated uranium was recovered by burning the graphite ion receivers and extracting the metallic uranium from the ash.
Construction of Buildings 9731 and 9204-3 at the Y-12 complex began 75 years ago, in February 1943. By February 1944, initial operation of the Alpha calutrons had produced only 0.44 pounds (0.2 kg) of U-235 @ 12 at.%. By August 1945, the Y-12 Beta calutrons had produced the 92.6 pounds (42 kg) of weapons-grade uranium needed for the Little Boy atomic bomb.
After WW II, the silver was recovered from the calutron magnet coils and returned to the Treasury Department.
3.3. Hanford, Washington
On January 16, 1943, General Leslie Groves officially endorsed Hanford as the proposed plutonium production site, which was given the MED code name Site W. The plan was to construct three large graphite-moderated, water-cooled plutonium production reactors, designated B, D, and F, in along the Columbia River. The Hanford site also would include a facility for manufacturing the new uranium fuel slugs for the reactors as well as chemical separation plants and associated facilities to recover and process plutonium from the irradiated uranium slugs.
After WW II, six more plutonium production reactors were built at Hanford along with additional plutonium and nuclear waste processing and storage facilities.
The Manhattan Project National Historical Park sites at Hanford are:
B Reactor, which has been a National Historic Landmark since 19 August 2008
The previous Hanford High School in the former Town of Hanford and Hanford Construction Camp Historic District
Bruggemann’s Agricultural Warehouse Complex
White Bluffs Bank and Hanford Irrigation District Pump House
A brief overview of the B Reactor and the other Hanford production reactors is provided below. There’s more information on the Manhattan Project National Historical Park sites at Hanford here:
The Manhattan Project National Historical Park does not include the Hanford chemical separation plants and associated plutonium facilities in the 200 Area, the uranium fuel production plant in the 300 Area, or the other eight plutonium production reactors that were built in the 100 Area. Information on all Hanford facilities, including their current cleanup status, is available on the Hanford website here:
The B Reactor at the Hanford Site was the world’s first full-scale reactor and the first of three plutonium production reactor of the same design that became operational at Hanford during WW II. B Reactor and the similar D and F Reactors were significantly larger graphite-moderated reactor than the X-10 Graphite Reactor at Oak Ridge. The rectangular reactor core measured 36 feet (11 m) wide x 36 feet (11 m) tall x 28 feet (8.53 m) deep, surrounded by radiation shielding. These reactors were fueled by aluminum clad, metallic natural fuel slugs measuring 8 inches (20.3 cm) long x 1.5 inches (3.8 cm) in diameter. As with the X-10 Graphite Reactor, new fuel slugs were inserted into process tubes (fuel channels) at the front face of the reactor. The irradiated fuel slugs were pushed out of the fuel channels at the back face of the reactor, falling into a water pool to allow the slugs to cool before further processing for plutonium recovery.
Reactor cooling was provided by the once-through flow of filtered and processed fresh water drawn from the Columbia River. The heated water was discharged from the reactor into large retention basins that allowed some cooling time before the water was returned to the Columbia River.
Construction of B Reactor began 75 years ago, in October 1943, and fuel loading started 11 months later, on September 13, 1944. Initial criticality occurred on 26 September 1944, followed shortly by operation at the initial design power of 250 MWt.
B Reactor was the first reactor to experience the effects of xenon poisoning due to the accumulation of Xenon (Xe-135) in the uranium fuel. Xe-135 is a decay product of the relatively short-lived (6.7 hour half-life) fission product iodine I-135. With its very high neutron cross-section, Xe-135 absorbed sufficient neutrons to significantly, and unexpectedly, reduce B Reactor power. Fortunately, DuPont had added more process tubes (a total of 2004) than called for in the original design of B Reactor. After the xenon poisoning problem was understood, additional fuel was loaded, providing the core with enough excess reactivity to override the neutron poisoning effects of Xe-135.
On 3 February 1945, the first batch of B Reactor plutonium was delivered to Los Alamos, just 10 months after the first small plutonium sample from the X-10 Graphite Reactor had been delivered.
Regular plutonium deliveries from the Hanford production reactors provided the plutonium needed for the first ever nuclear device (the Gadget) tested at the Trinity site near Alamogordo, NM on 16 July 1945, as well as for the Fat Man atomic bomb dropped on Nagasaki, Japan on 9 August 1945 and an unused second Fat Man atomic bomb. These three devices each contained about 13.7 pounds (6.2 kilograms) of weapons-grade plutonium produced in the Hanford production reactors.
From March 1946 to June 1948, B Reactor was shut down for maintenance and modifications. In March 1949, B Reactor began the first tritium production campaign, irradiating targets containing lithium and producing tritium for hydrogen bombs.
By 1963, B Reactor was permitted to operate at a maximum power level of 2,090 MWt. B Reactor continued operation until 29 January 1968, when it was ordered shut down by the Atomic Energy Commission. Because of its historical significance, B Reactor was given special status that allows it to be open for public tours as part of the Manhattan Project National Historical Park.
The Other WW II Production Reactors at the Hanford Site: D & F
During WW II, three plutonium reactors of the same design were operational at Hanford: B, D and F. All had an initial design power rating of 250 MWt and by 1963 all were permitted to operate at a maximum power level of 2,090 MWt.
D Reactor: This was the world’s second full-scale nuclear reactor. It became operational in December 1944, but experienced operational problems early in life due to growth and distortion of its graphite core. After developing a process for controlling graphite distortion, D Reactor operated successfully through June 1967.
F Reactor: This was the third of the original three production reactors at Hanford. It became operational in February 1945 and ran for more than twenty years until it was shut down in June1965.
D and F Reactors currently are in “interim safe storage,” which commonly is referred to as “cocooned.” These reactor sites are not part of the Manhattan Project National Historical Park.
Post-war Production Reactors at Hanford: H, DR, C, K-West, K-East & N
After WW II, six additional plutonium production reactors were built and operated at Hanford. The first three, named H, DR and C, were very similar in design to the B, D and F Reactors. The next two, K-West and K-East, were of similar design, but significantly larger than their predecessors. The last reactor, named N, was a one-of-a kind design.
H Reactor: This was the first plutonium production reactor built at Hanford after WW II. It became operational in October 1949 with a design power rating of 400 MWt and by 1963 was permitted to operate at a maximum power level of 2,090 MWt. It operated for 15 years before being permanently shut down in April 1965.
DR Reactor: This reactor originally was planned as a replacement for the D Reactor and was built adjacent to the D Reactor site. DR became operational in October 1950 with an initial design power rating of 250 MWt. It operated in parallel with D Reactor for 14 years, and by 1963 was permitted to operate at the same maximum power level of 2,090 MWt. DR was permanently shut down in December 1964.
C Reactor: Reactor construction started June 1951 and it was completed in November 1952, operating initially at a design power of 650 MWt. By 1963, C Reactor was permitted to operate at a maximum power level of 2,310 MWt. It operated for sixteen years before being shut down in April 1969. C Reactor was the first reactor at Hanford to be placed in interim safe storage, in 1998.
K-West & K-East Reactors: These larger reactors differed from their predecessors mainly in the size of the moderator stack, the number, size and type of process tubes (3,220 process tubes), the type of shielding and other materials employed, and the addition of a process heat recovery system to heat the facilities. These reactors were built side-by-side and became operational within four months of each other in 1955: K-West in January and K-East in April. These reactors initially had a design power of 1,800 MWt and by 1963 were permitted to operate at a maximum power level of 4,400 MWt before an administrative limit of 4,000 MWt was imposed by the Atomic Energy Commission. The two reactors ran for more than 15 years. K-West was permanently shut down in February 1970 followed by K-East in January 1971.
N Reactor: This was last of Hanford’s nine plutonium production reactors and the only one designed as a dual-purpose reactor capable of serving as a production reactor while also generating electric power for distribution to the external power grid. The N Reactor had a reactor design power rating of 4,000 MWt and was capable of generating 800 MWe. The N Reactor also was the only Hanford production reactor with a closed-loop primary cooling system. Plutonium production began in 1964, two years before the power generating part of the plant was completed in 1966. N Reactor operated for 24 years until 1987, when it was shutdown for routine maintenance. However, it never restarted, instead being placed in standby status by DOE and then later retired.
Four of these reactors (H, DR, C and N) are in interim safe storage while the other two (K-West and K-East) are being prepared for interim safe storage. None of these reactor sites are part of the Manhattan Project National Historical Park.
The Federation of American Scientists (FAS) reported that the nine Hanford production reactors produced 67.4 metric tons of plutonium, including 54.5 metric tons of weapons-grade plutonium, through 1987 when the last Hanford production reactor (N Reactor) was shutdown.
4. Other Manhattan Project Sites
There are many MED sites that are not yet part of the Manhattan Project National Historical Park. You’ll find details on all of the MED sites on the American Heritage Foundation website, which you can browse at the following link:
Another site worth browsing is the interactive world map created by the ALSOS Digital Library for Nuclear Issues on Google Maps to show the locations and provide information on offices, mines, mills, plants, laboratories, and test sites of the US nuclear weapons complex from World War II to 2016. The map includes over 300 sites, including the Manhattan Project sites. I think you’ll enjoy exploring this interactive map.
Hanford site, plutonium production reactors and processing facilities:
“Hanford Site Historical District: History of the Plutonium Production Facilities 1943-1990,” DOE/RL-97-1047, Department of Energy, Hanford Cultural and Historical Resources Program, June 2002 https://www.osti.gov/servlets/purl/807939