Category Archives: Power Generating Technology – Nuclear

Radioisotope Thermoelectric Generators (RTG) for Spacecraft: History and Current U.S. Pu-238 Production Status

April 10, 2015All Posts, Chemical engineering, Power Generating Technology - Nuclear, Spacecraft and MissionsAdvanced Stirling Radioisotope Generator, Advanced Test Reactor, ASRG, ATR, Darlington, Department of Energy, DOE, HFIR, High Flux Isotope Reactor, Idaho National Engineering Lab, INEL, LANL, Los Alamos National Lab, Mars 2020 rover, Mars rover, MMRTG, Multi-Mission Radioisotope Thermoelectric Generator, NASA, Oak Ridge National Lab, Ontario Power Generation, ORNL, Perseverance, Pu-238, Radioisotope Thermoelectric Generators, RTGDrummer

Updated 5 March 2021

Peter Lobner

Radioisotope Thermoelectric Generators (RTG), also called Radioisotope Power Systems (RTS), commonly use non-weapons grade Plutonium 238 (Pu-238) to generate electric power and heat for National Aeronautics and Space Administration (NASA) spacecraft when solar energy and batteries are not adequate for the intended mission. In comparison to other RTG heat sources (Strontium-90, Cesium-137), Pu-238 has a relatively long half-life of 87.75 years, which is a desirable property for a long-life RTG.

Approximately 300 kg (661 lb) of Pu-238 was produced by the Department of Energy (DOE) at the Savannah River Site between 1959 – 1988. After U.S production stopped, the U.S. purchased Pu-238 from Russia until that source of supply ended in 2010.

Limited production of new Pu-238 in the U.S re-started in 2013 using the process shown below. This effort is partially funded by NASA. Eventually, production capacity will be about 1.5 kg (3.3 lb) Pu-238 per year. The roles of the DOE national laboratories involved in this production process are as follows:

Idaho National Engineering Lab (INEL):
- Store the Neptunium dioxide (NpO₂) feed stock
- Deliver feed stock as needed to ORNL
- Irradiate targets provided by ORNL in the Advanced Test Reactor (ATR)
- Return irradiated targets to ORNL for processing
Oak Ridge National Lab (ORNL):
- Manufacture targets
- Ship some targets to INEL for irradiation
- Irradiate the remaining targets in the High Flux Isotope Reactor (HFIR)
- Process all irradiated targets to recover and purify Pu-238
- Convert Pu-238 to oxide and deliver as needed to LANL
Los Alamos National Lab (LANL):
- Manufacture the Pu-238 fuel pellets for use in RTGs

Source: Ralph L McNutt, Jr, Johns Hopkins University APL, 2014

In 2015, the U.S. had an existing inventory of about 35 kg (77 lb) of Pu-238 of various ages. About half was young enough to meet the power specifications of planned NASA spacecraft. The remaining stock was more than 20 years old, has decayed significantly since it was produced, and did not meet specifications. The existing inventory will be blended with newly produced Pu-238 to extend the usable inventory. To get the energy density needed for space missions while extending the supply of Pu-238, DOE and NASA plan to blend “old” Pu-238 with newly produced Pu-238 in 2:1 proportions.

Since 2010, NASA’s RTG for spacecraft missions has been the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), which It is based on the SNAP-19 RTG flown on the two Viking Mars landers (circa 1975) and the Pioneer 10 and 11 deep space probes (circa 1972). At beginning of life, the current MMRTG can provide about 2,000 watts of thermal power and 110 watts of electrical power from eight General Purpose Heat Source (GPHS) modules that contain a total of 10.6 pounds (4.8 kilograms) of plutonium dioxide fuel. Electric conversion efficiency is about 6%.

Assembled MMRTG on a transport dolly. Source: NASA

MMRTG cut-away diagram. Source: NASA

You’ll find a NASA MMRTG Fact Sheet here: https://rps.nasa.gov/resources/86/multi-mission-radioisotope-thermoelectric-generator-mmrtg/?category=fact_sheets

NASA had a program to develop an Advanced Stirling Radioisotope Generator (ASRG), which was designed to produce about four times the power of the MMRTG per unit of Pu-238. Electric conversion efficiency was about 26%. The ASRG required a total of 2.7 pounds (1.2 kilograms) of plutonium dioxide in two GPHS modules. However, the ASRG would produce less waste heat, which can be used productively to warm electronics in the interior of a spacecraft, such as the Mars rover Curiosity. In November 2013, NASA announced that ASRG development had been discontinued because of budget cuts. You’ll find a NASA ASRG Fact Sheet at the following link: https://rps.nasa.gov/resources/65/advanced-stirling-radioisotope-generator-asrg/

You can read a history of RTGs and more information on current U.S. Pu-238 production status in a 2014 presentation by Ralph L McNutt, Jr, at the following link: https://www.lpi.usra.edu/sbag/meetings/jan2014/presentations/08_1545_McNutt_Pu238_SBAG.pdf

9 February 2016 Update:

On 22 December 2015, DOE reported the first U.S. production in nearly 30 years of Pu-238. This production demonstration, which was partially funded by the NASA, was performed at ORNL and yielded 50 grams of Pu-238. The last U.S. production of Pu-238 occurred in the late 1980s at the Savannah River Plant in South Carolina.

DOE reported that it plans to set an initial production target of 300 – 400 grams (about 12 ounces) of Pu-238 per year. After implementing greater automation and scaling up the process, ORNL expects to reach the the production target of 1.5 kg (3.3 lb) Pu-238 per year.

The next NASA mission that will use an RTG is the Mars 2020 rover, which will use an MMRTG, as used on NASA’s Mars rover Curiosity.

You can read the ORNL announcement of initial Pu-238 production at the following link: https://www.ornl.gov/news/ornl-achieves-milestone-plutonium-238-sample

3 January 2019 Update:

In the past three years, ORNL has made scant progress in producing Pu-238. In a 13 December 2018 article, “NASA Doesn’t Have Enough Nuclear Fuel For Its Deep Space Missions,”author Ethan Siegel reports: “Although current production (at ORNL) yields only a few hundred grams per year (less than a pound), the laboratory has the eventual goal of ramping up to 1.5 kilograms (3.3 pounds) per year by 2023, at the earliest. Ontario Power Generation in Canada has also begun producing Pu-238, with the goal of using it as a supplemental source for NASA.” You can read the complete article on the Forbes website at the following link: https://www.forbes.com/sites/startswithabang/2018/12/13/nasa-doesnt-have-enough-nuclear-fuel-for-its-deep-space-missions/#1a73d47e1c18

The Canadian plans for becoming a source of Pu-238 was announced on 1 March 2017: “Ontario Power Generation (OPG) and its venture arm, Canadian Nuclear Partners, are participating in a project to produce isotopes in support of deep space exploration. Under the agreement, OPG would help create isotopes at the Darlington nuclear station east of Toronto that will help power space probes.” You can read the complete OPG press release here: https://www.opg.com/news-and-media/news-releases/Documents/20170301_DeepSpace.pdf

Also see the OPG public relations piece, “OPG looks to the stars,” here: https://www.opg.com/news-and-media/our-stories/Documents/20170802_OPG_Deep_Space.pdf

4 August 2020 Update:

The NASA Mars rover, Perseverance, was launched from Cape Canaveral on 30 July 2020, with an expected landing date of 18 February 2021 in the Jezero crater on Mars. Once on the surface, Perseverance will be powered by an MMRTG.

The Pu-238 and some other special materials for the Perseverence MMRTG were produced in the U.S. at ORNL, as described in the following short (2:03 minutes) video, “ORNL-produced tech fuels NASA’s Perseverance mission to Mars”:

In a 20 July 2020 news release, ORNL provided more information on the U.S. production process for Pu-238 and reported that, “the lab has been consistently increasing its Pu-238 production capabilities, aiming to produce 1.5 kilograms per year by 2026.” You can read this ORNL press release here: https://www.ornl.gov/news/ornl-produced-plutonium-238-help-power-perseverance-mars

At the planned U.S. production rate for Pu-238, NASA should be able to conduct an MMRTG mission at about four-year intervals. If NASA MMRTG missions will be more frequent than this, the U.S. will need to purchase additional Pu-238 from another source, perhaps Canada.

5 March 2021 Update:

The Perseverance rover landed on Mars on 18 February 2021, in the planned target area in Jezero Crater. Power from the MMRTG was nominal after landing. Perseverance will spend at least one Mars year (two Earth years) exploring the landing site region.

The next NASA mission with an MMRTG-powered spacecraft is the Dragonfly mission to Saturn’s moon Titan, which will launch in 2026 and arrive on Titan in 2034.

The Voyager 1 and 2 spacecraft were launched in 1977, each with three RTGs delivering a maximum of 470 watts of electrical power at the beginning of the mission. Both spacecraft have left the solar system (Voyager 1 in 2013 and Voyager 2 in 2018) and continue to transmit from interstellar space in 2021 with their RTGs operating at a reduced power level of about 331 watts after 44 years of Pu-238 decay during the mission. NASA plans to continue the Voyager missions until at least 2025.

For more information:

“Plutonium-238 Production for Space Exploration – A National Historic Chemical Landmark,” American Chemical Society: https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/plutonium-238-production.html
Plutonium (Pu) 238 Radioactive Isotope Decay Calculator: https://www.easycalculation.com/chemistry/Pu-238.html

Efficiency in Electricity Generation

March 17, 2015All Posts, Power Generating Technology - Alternate, Power Generating Technology - Fossil, Power Generating Technology - Nuclearelectrical generation efficiency, EURELECTRIC, Siemens, Union of the Electricity Industry, VGB PowerTechDrummer

Peter Lobner

On 9 March 2015, Siemens announced that it had achieved a generation efficiency record at the Cengiz Enerji Samsun combined-cycle gas turbine power plant in Turkey. With an installed capacity of 600 MWe, this plant achieves a net efficiency of almost 61%. This makes Cengiz Enerji Samsun the most efficient fossil-fired 50 Hz power plant in 2015, not only in Turkey, but in the world.

You can read more at the following link:

http://www.globalenergyworld.com/news/15838/Siemens_Achieves_Record_Efficiency_With_The_Samsun_H-class_Power_Plant.htm

If you wonder how this level of generation efficiency compares to other types of electric power generators, then I recommend that you read the July 2003 report, “Efficiency in Electric Power Generation,” drafted by Union of the Electricity Industry – EURELECTRIC (Brussels, Belgium) and VGB PowerTech (Essen, Germany).

While this report is 12 years old, I think it remains one of the best single sources of comparative efficiency information on a very wide range of generator types. You can download a pdf version of this report by doing an Internet search for:

Efficiency in electricity generation – Eurelectric

The link you need should be at or near the top of your search results.

One of the key results presented in this report is a chart showing comparative efficiencies. The new Cengiz Enerji Samsun power plant raises the bar a few percentage points for “Large gas fired CCGT power plant”.

5 July 2016 update: New record for fossil plant efficiency

On 17 June 2016, General Electric (GE) and Électricité de France (EDF) began operating the first ever combined-cycle power plant equipped with GE’s 9HA large gas turbine. GE advertises the 9HA as the “world’s largest and most efficient heavy duty gas turbine”. There are two models, 9HA.01 and 9HA.02 that have claimed simple cycle outputs and net efficiencies of 397 MWe @ 41.5% net efficiency, and 510 MWe @ 41.8% net efficiency, respectively. In a combined cycle application, the power outputs and efficiencies increase substantially. GE claims the 9HA.01 delivers 592 MWe @ 61.6% net efficiency, while the 9HA.02 delivers 755 MWe @ 61.8% net efficiency. You can download a GE specification sheet on the 9HA at the following link:

https://powergen.gepower.com/content/dam/gepower-pgdp/global/en_US/documents/product/gas%20turbines/Fact%20Sheet/9ha-fact-sheet-oct15.pdf

With regard to the new 605 MWe combined cycle 9HA.01 power plant at Bouchain, France, GE announced that this plant has been recognized by Guinness World Records as the world’s most efficient combined-cycle power plant, with a demonstrated net efficiency of 62.22% (better than advertised by GE). You can read the GE announcement at the following link:

https://powergen.gepower.com/about/insights/bouchain-grand-opening.html

History of the DOE National Laboratories

March 11, 2015All Posts, Engineering, Nuclear Arms & Arms Control, Physics, Power Generating Technology - NuclearDepartment of Energy, DOE, national laboratories, Office of Scientific & Technical Information, OSTIDrummer

Peter Lobner

Many at SAIC worked at or for one or more DOE national laboratories at some point in their careers. The following link to the DOE Office of Scientific & Technical Information (OSTI) web site provides links to other web sites with historical information on the various national labs.

http://www.osti.gov/accomplishments/nuggets/historynatlabs.html

For example, on this OSTI web page, you can select the Idaho National Laboratory link, and a pop-up menu will display the available documents. If you select, “Proving the Principle: A History of the Idaho Engineering and Environmental Laboratory, 1949 – 1999,” this will take you to an INL web site that includes a 25 chapter history + a 2000 – 2010 addendum, all organized for chapter-by-chapter web access.

I hope you find some something of interest via the OSTI website.

Scientists Used Natural Cosmic Radiation to Peer Inside Fukushima’s Mangled Reactor

March 8, 2015All Posts, Physics, Power Generating Technology - Nuclearcosmic radiation tomography, Fukushima, imaging damaged reactor, LANL, Los Alamos National Lab, muography, muon tomography, TEPCODrummer

Peter Lobner, updated 4 March 2023

Introduction

A muon is an unstable elementary subatomic particle in the same class as an electron (they’re both leptons), but with a much greater mass (207 times greater). A useful property of muons is that they can penetrate matter much further than X-rays with the added benefit of causing essentially zero damage to the matter it passes through. Muons scatter and lose energy as they pass through matter, slowing down and eventually decaying, typically into three particles: an electron and two types of neutrinos. The higher the average density of the matter encountered along the muon’s flight path, the more quickly the muon slows down.

Muons are created by the interaction of high-energy cosmic rays with the upper regions of Earth’s atmosphere and they account for much of the cosmic radiation that reaches the Earth’s surface. This means that the existing flux of muon radiation at the Earth’s surface (about 10,000 muons/square meter/sec) is a free resource for clever researchers.

Muon tomography uses this free muon flux and the muon’s characteristic of slowing down more quickly in denser matter to create a density map of the field-of-view available to a muon detector. There are two types of muon imaging, transmission and scattering. The differences are addressed in LA-UR-15-24802, listed below. In both types of muon imaging, denser objects and structures in the detectors field of view appear as shadows (muon shadows) that are darker (fewer muons getting thru to the detectors) than less dense areas.

Muon tomography at the Fukushima Nuclear Power Plant

Tokyo Electric Power Company (TEPCO) supported the use of muon tomography at the Fukushima Nuclear Power Plant to help determine what damage was done to the reactor cores at Units 1, 2 and 3 during the 11 March 2011 accident, which was precipitated by a 9.0 magnitude earthquake followed by a 15-meter (49.2-ft) tsunami.

A 2013 muon tomography feasibility study (Hauro Miyadera, et al.) reported: “Muon scattering imaging has high sensitivity for detecting uranium fuel and debris even through thick concrete walls and a reactor pressure vessel. Technical demonstrations using a reactor mockup, a detector radiation test at Fukushima Daiichi, and simulation studies have been carried out. These studies establish feasibility for the reactor imaging. A few months of measurement will reveal the spatial distribution of the reactor fuel.”

At Reactor #1, two 22 ton (20 metric ton), 21-foot by 21-foot (6.4 m by 6.4 m) muon detectors were installed and used to collect data over periods of months to develop high-resolution images of the damaged reactor core and surrounding areas. Placement of the muon detectors and the general scan geometry is shown in the following diagram.

Source: LA-UR-12-20494

Reactor #1 muon scan results

In March 2015, TEPCO announced that its muon tomography scanning efforts at Fukushima were successful, and confirmed that the nuclear plant’s Reactor #1 suffered a complete meltdown. The muon scans showed no corium (i.e., the lava-like product of a reactor core meltdown containing the melted nuclear fuel, fission products, control rods, and structural materials) remained in the reactor pressure vessel (RPV). The muon scans did not show the distribution of the corium that flowed out of the bottom of the reactor vessel into the primary containment vessel (PCV).

*Muon tomography scan of Reactor #1. The corium, if present in the*
*RPV, should have been visible as a dark shadow inside the RPV.*
*Source: TEPCO via ExtremeTech (2015)*

*Muon tomography scan of Reactor #1, focusing on the RPV.*
*Source: TEPCO via ExtremeTech (2015)*

Reactor #2 muon scan results

World Nuclear News (WNN) reported (2016 & 2017), “TEPCO said analysis of muon examinations of the fuel debris shows that most of the fuel has melted and dropped from its original position within the core (and resolidified)…..Measurements taken between March and July 2016 at unit 2 showed high-density materials, considered to be fuel debris, in the lower area of the RPV.”

*A muon tomography image of Reactor #2.*
*Source: TEPCO via WNN (2016)*

Reactor #3 muon scan results

In 2017, WNN reported, “Some of the fuel in the damaged unit 3 of the Fukushima Daiichi plant has melted and dropped into the primary containment vessel, initial results from using a muon detection system indicate. Part of the fuel, however, is believed to remain in the reactor pressure vessel.”

*Muon tomography image of Reactor #3.*
*Source: TEPCO via WNN (2017)*

Summary of fuel debris status at Fukushima

Based on the results of the muon tomography program and other means of investigation, TEPCO created the following graphic summary showing the estimated distribution of core and containment vessel fuel debris in Fukushima Units 1, 2 & 3.

For more information

Hauro Miyadera, et al., “Imaging Fukushima Daiichi reactors with muons,” published in AIP Advances, published online 24 May 2013: https://aip.scitation.org/doi/10.1063/1.4808210
Fukushima Daiichi NPS Prompt Report (Feb 09, 2015) – Recent topics: Cosmic “muon” rays to look inside Fukushima reactors as TEPCO begins testing,” TEPCO, 9 February 2015: https://www.tepco.co.jp/en/press/corp-com/release/2015/1248057_6844.html
“Muon Tomography – Imaging the core of Fukushima reactors with muons,” LA-UR-15-24802, Los Alamos National Laboratory, 2015: https://www.lanl.gov/org/ddste/aldps/physics/_assets/docs/muon-tomography.pdf
Graham Templeton, “Scientists Are Using Cosmic Radiation To Peer Inside Fukushima’s Mangled Reactor,” Motherboard, 2 March 2015: https://www.vice.com/en/article/kbzk89/scientists-are-using-cosmic-radiation-to-peer-inside-fukushimas-mangled-reactor
Haruo Miyadera, et al., “Our Next Two Steps for Fukushima Daiichi Muon Tomography”, LA-UR-12-20494, Los Alamos National Laboratory, 2015:https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-12-20494
“Muon Scan Finds No Fuel In Fukushima Unit 1 Reactor Vessel,” SimplifyInfo.org, 19 March 2015: https://simplyinfo.org/2015/03/muon-scan-finds-no-fuel-in-fukushima-unit-1-reactor-vessel/
Joel Hruska, “Muon scans confirm complete reactor meltdown at Fukushima Reactor #1,” ExtremeTech, 20 March 2015: https://www.extremetech.com/extreme/201706-muon-scans-confirm-complete-reactor-meltdown-at-fukushima-reactor-1
“Detectors confirm most fuel remains in unit 2 vessel,” World Nuclear News, 29 July 2016: https://world-nuclear-news.org/Articles/Detectors-confirm-most-fuel-remains-in-unit-2-vess
“Muons suggest location of fuel in unit 3,” World Nuclear News, 2 October 2017: https://www.world-nuclear-news.org/RS-Muons-suggest-location-of-fuel-in-unit-3-0210174.html
“The Status of Fuel Debris Retrieval,” TEPCO: https://www.tepco.co.jp/en/hd/decommission/progress/retrieval/index-e.html
David Adams, “Muography offers a new way to see inside a multitude of objects,” PNAS, Vol. 118, No. 14, 31 March 2021: https://www.pnas.org/doi/10.1073/pnas.2104652118

60 Year Anniversary of “Underway on Nuclear Power”

Peter Lobner

Updated 10 January 2020

60 years ago, on 17 Jan 1955, CDR Eugene Wilkinson, the first CO of the USS Nautilus, SSN-571, ordered the following message sent as his nuclear-powered sub got underway for the first time in New London, CT.

Source: U.S. Navy CDR Eugene Wilkinson and Nautilus. Source: U.S. Navy

You’ll find an interesting, short backstory to this message at the following link:

http://ussnautilus.org/blog/underway-on-nuclear-power/

Wilkinson retired from the Navy as a Vice Admiral in 1974, died in 2013, and is buried in Fort Rosecrans National Cemetery in San Diego, CA.

There’s a short history of the early Navy nuclear power program and Nautilus at the following link:

http://www.navalhistory.org/2014/09/30/60-years-ago-today-uss-nautilus-and-the-u-s-navy-get-underway-on-nuclear-power

Admiral Rickover. Source: U.S. Navy

We owe a debt of gratitude to Admiral Hyman G. Rickover for the success of the Naval Nuclear Power Program, which is quite visible here in San Diego, with nuclear-powered aircraft carriers based at North Island and submarines operating from Ballast Point in Point Loma.

10 January 2020 update:

In July 2018, I completed a set of eight resource documents collectively titled, “Marine Nuclear Power: 1939 – 2018,” and comprising over 2,100 pages formatted as slide presentations. The eight parts are:

Part 1: Introduction
Part 2A: United States – Submarines
Part 2B: United States – Surface Ships
Part 3A: Russia – Submarines
Part 3B: Russia – Surface Ships & Non-propulsion Marine Nuclear Applications
Part 4: Europe & Canada
Part 5: China, India, Japan and Other Nations
Part 6: Arctic Operations

All of these can be accessed through my 25 July 2018 “Marine Nuclear Power 1939 – 2018” post at the following link:

https://lynceans.org/all-posts/marine-nuclear-power-1939-2018/