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Atomic Insights

Atomic energy technology, politics, and perceptions from a nuclear energy insider who served as a US nuclear submarine engineer officer

Technical History Stories

ML-1 Mobile Power System: Reactor in a Box

February 1, 2019 By Rod Adams 11 Comments

This is a modest update of an article first published in November 1996. DOD’s recent issuance of an RFI for mobile, modest power output atomic power systems shows that the challenges that were clearly described in 1963 have not been addressed – yet. Now is a good time to start addressing them.

The ML-1 experimental reactor was unique. It was not a pressurized water reactor with a steam energy conversion system. Instead, ML-1 was the first nitrogen cooled, water moderated reactor with a nitrogen turbine energy conversion system. Its major design criteria was compactness.

The below video begins with a brief, illustrated explanation of the problems ML-1 was designed to address and alleviate. It makes a persuasive case that will inevitably beg the question – why was this nascent program halted so early in its development.

ML-1 could be packed into four transport packages – a trailer carrying two connected skids for the reactor and the complete heat conversion system, a shipping box for the control room, and two others for cabling, auxiliary gas storage and handling equipment and miscellaneous tools and critical supplies.

The two major containers weighed 15 tons each while the four additional containers each weighed between three and four tons. The complete system weight was about 38 tons. The systems were designed to fit into any of the Army’s transport systems including C-130 aircraft, standard Army trucks, and rail.

In order to reduce the weight of shielding needing transport, the reactor was designed to be installed with a human exclusion boundary of 500 feet.

Design Challenges

In order to minimize the engine volume and mass, the decision was made to operate the engine with nitrogen pressurized to approximately 9 bar – 9 times normal atmospheric pressure – at the compressor inlet. This decision, though it helped reduce the size of the heat exchangers and turbomachinery somewhat, made the design uniquely difficult.

Essentially every other gas turbine ever built has operated with air at atmospheric pressure as the working fluid. The designers of ML-1 had the difficult challenge of making the machine perform as desired with a high density working fluid. This requires the reduction of critical machine clearances and makes accurate balancing far more critical for long term, reliable operation.

A second design decision that made the engine construction more challenging than required was the decision to add a recuperator to the system. Though recuperators have proven that they can improve gas turbine efficiency by several percent in stationary applications, they are not normally used in mobile engines because the additional heat exchanger adds more weight and space than it is worth.

The reactor heat system also required a stretch of existing technology. In order to minimize the size of the reactor, designers decided to use water inside pressure tubes as the neutron moderator. In order to prevent boiling, the water in the tubes was circulated to maintain the temperature below 250 F.

The water tubes were interspersed throughout the core between the fuel bundles. The nitrogen gas flowed past both the water tubes and the fuel bundles and ranged in temperature from 800 F at the core inlet to 1200 F at the outlet. The physical distance between the inlet and the outlet was less than two feet; the temperature extremes made material selection very important.

Testing Experience

The designers of the ML-1 decided to test two different heat engines that could each be connected to the reactor heat source. Once of the machines had an 11 stage axial flow compressor designed and constructed by Fairchild-Stratos Corporation while the other included a two stage centrifugal flow compressor designed and built by Clark Brothers Company.

Neither heat engine was able to meet its designed power output because neither compressor was able to produce the required flow at the required differential pressure. Rather than achieving a power output of 300 kw the best that the tested system could achieve was less than 200 kw. Engineering evaluations were made indicating that some minor adjustments could be made that would raise the performance of the machine, but it is not apparent from the historical record that this kind of rework was ever completed.

A second problem that surfaced during the testing program was related to the moderator water tubes. The high thermal and temperature stress of the tubes combined with manufacturing flaws to cause cracking in the tube welds. The cracks allowed water to enter into the coolant system and required a lengthy hiatus in the test program to correct the problem.

A final problem that had a major effect on the system was the failure of the internal insulation of the regenerator. This was installed under the assumption that it would reduce heat losses and thus improve performance. The insulation consisted of a blanket of fine particles covered with a metal foil. The foil tore loose because of aerodynamic buffeting during testing, causing the distribution of the fine particles throughout the system. After the dust was removed from the engine, testing continued without the insulation.

Lessons Learned

Though the difficulties experienced by the ML-1 testers were the type that are common with the first of a kind of any complex piece of machinery, they proved to be fatal for the program and helped destroy any budding interest in nuclear gas turbines.

Because of the increasing amount of money needed to fight the Vietnam War, the Army’s research and development budget for non weapons items was severely constrained. There was little support for funding experimental nuclear systems in 1963, particularly experimental systems that seemed to have so many difficulties that needed fixing.

Now, however, after more than 30 years of technological developments, it is worth summarizing the lessons that can be learned for future closed cycle gas turbine development.

  • Pressurizing gas turbine cycles may be a good idea on paper, but there are practical engineering difficulties that must be overcome if it is to be used in a real system.
  • Recuperators are troublesome, particularly if space and weight are constraining factors in system design.
  • Water tube reactors are unnecessarily complex, particularly since there have been excellent results achieved by high temperature, graphite moderated reactors.
  • Any material that can potentially contaminate a closed cycle turbine system should be avoided.
  • If possible, well-proven components should be integrated into a complete system rather than designing each component from scratch.

Postscript – When I wrote this article in 1996, I had been working on a direct cycle, low pressure, nitrogen-cooled, pebble bed heated atomic engine for about five years. I was the founder of a struggling 3-year old company called Adams Atomic Engines, Inc.

I’d started publishing Atomic Insights as a paper newsletter in an attempt to widely share what I knew about nuclear energy.

At that time, natural gas was plentiful and cheap, no one was very concerned about climate change, the established US nuclear industry was competing for the business of destroying the existing power plants as they approached the end of their initial 40 year operating licenses, and no one thought that the US would continue being involved in power-hungry expeditions overseas.

Aside: During a 33 year career serving in the US Navy and Naval Reserves, I had a multitude of personal experiences with the Military Industrial Complex. I’ve also participated actively in the early lives of six grandchildren.

I now know enough to want to do everything in my power to ensure that US overseas activities are focused on enabling prosperity, not on expanding our role as a “superpower.” There are so many better ways to invest most of the money that we currently spend on offensive wars. End Aside.

Filed Under: Army Nuclear Program, Atomic Insights Nov 1995, Small Nuclear Power Plants, Technical History Stories

Sad-ending story of EBR-II told by three of its pioneers

August 24, 2015 By Rod Adams

During the period between 1961 and 1994, an extraordinary machine called the Experimental Breeder Reactor 2 (EBR-II) was created and operated in the high desert of Idaho by a team of dedicated, determined, and distinguished people.

In 1986, that machine demonstrated that it could protect itself in the event of a complete loss of flow without scram and a complete loss of heat sink, also without a scram. Those tests were conducted carefully, with an expanded supervisory and operating staff while being witnessed by dozens of internationally respected scientists and engineers.

A few weeks later, at a nuclear power plant behind the Iron Curtain, a small, poorly led operating crew made up of people with little nuclear power plant experience conducted an ill-conceived experiment to see how long the steam turbine at a nuclear plant would keep spinning with enough momentum to supply electricity after the reactor was tripped. Before conducting the turbine momentum test, plant operators inadvertently — or purposely — put the reactor into its most unstable possible state.

That reactor blew up and caught fire. It stole the world’s attention away from the experiments at EBR-II proving that nuclear reactors could be designed to be automatically safe using well-developed physical principles. One result of the attention-getting explosion was to begin a long period of visceral distrust of nuclear energy. In too many cases, the distrust has been extended to all of the people who have devoted their professional lives to understanding, developing, building and operating the technology.

Instead of being reassured by the highly successful, extensively witnessed tests in the open and free United States, the world was subjected to overblown scare stories and dire future predictions as the result of events at a reactor in the opaque, somewhat mysterious world of the Soviet bloc.

Instead of moving steadily towards a future society supplied with virtually unlimited power from emission-free nuclear fission energy, the world has experienced nearly three decades of increasing dependence on natural gas, coal and oil. Those decades have seen periods of incredible transfers of wealth from the world’s energy consumers into the pockets of the world’s fossil fuel producers as people have been told that supplies of low cost fuel were running out.

Fossil fuel exports to European nations frightened away from nuclear energy by the events at Chernobyl have been a primary source of revenue for Russia, the dominant member of the former Soviet union. Control of the world’s fossil fuel markets has been a major source of power, wealth, and conflict with numerous U.S. companies in the hydrocarbon and military equipment industries accumulating substantial, sustained profits.

In 1994, the U.S. Senate — following the lead of Senator John F. Kerry and President Bill Clinton — decided to eliminate all funds for operations and research associated with the Integral Fast Reactor (IFR) project. The vote was close, only 52 senators, a small majority, voted in favor of removing the funds.

That complete nuclear power plant and fuel cycle project included the EBR-II reactor. During President Clinton’s 1994 State of the Union address, he had characterized the valuable research being conducted on advanced nuclear energy systems as an unnecessary waste of money that should be stopped as part of a program of spending reductions.

Below is a poignant piece of recorded history told by three leading members of the team.

Spoiler alert — you know you are a problem-solving patriot if you are moved by John Sackett’s final soliloquy.

Making a Contribution: The Story of EBR-II (Full Version) from ComDesigns, Inc. on Vimeo.

Note: The above video was recorded not long before EBR-II was demolished. A sadly ironic end of the tale is that the funds for the destruction came from the American Recovery and Reinvestment Act of 2009. Somehow, it doesn’t seem right that the Department of Energy chose to use funds from a program that was supposedly designed to help America recovery from a terrible recession to destroy a machine that should have been proudly preserved as an inspiration for its prosperous future.

Filed Under: Advanced Atomic Technologies, Atomic history, Atomic Pioneers, Atomic politics, Breeder Reactors, Fuel Recycling, Liquid Metal Cooled Reactors, Politics of Nuclear Energy, Pro Nuclear Video, Technical History Stories

The first Critmass, December 2, 1942

December 2, 2013 By Rod Adams

Seventy one years ago — on December 2, 1942, at 3:25 pm — Enrico Fermi and his team achieved the first controlled, man-made, self sustaining chain reaction in a simple reactor. In recognition of that historical event, several of my nuclear colleagues refer to December 2 as “Critmass” (short for critical mass). The first nuclear […]

Filed Under: Atomic history, Atomic Pioneers, Graphite Moderated Reactors, Technical History Stories

JFK’s “Best of the Above” speech at Hanford, WA on September 26, 1963

September 23, 2013 By Rod Adams

Almost exactly 50 years ago today, President John F. Kennedy, Jr. visited Hanford, Washington to give a speech about the importance of electrical power and the role that he expected nuclear technology would play in the future. (HT to the TriCity Herald for posting the video provided by the Department of Energy and to Martin […]

Filed Under: Atomic history, Graphite Moderated Reactors, Politics of Nuclear Energy, Pro Nuclear Video, Technical History Stories

San Onofre steam generators – honest error driven by search for perfection

March 9, 2013 By Rod Adams

Mitsubishi Heavy Industries (MHI), the supplier that sold four new steam generators to Southern California Edison (SCE) for the San Onofre Nuclear Generating Station (SONGS), has issued a redacted version of its root cause analysis of the u-tube failures that have kept both of the station’s 1100 MWe units shut down since January 31, 2012. […]

Filed Under: Nuclear workforce, Politics of Nuclear Energy, Technical History Stories

Rockwell’s perspective on the history of nuclear power regulation

January 28, 2013 By Rod Adams

Ted Rockwell has been an active participant in the development of nuclear energy production in the United States since the very earliest days of the technology. He started his nuclear career as an engineering troubleshooter in 1943 at the site that is now Oak Ridge National Laboratory during the Manhattan Project. He was one of […]

Filed Under: Atomic history, LNT, Nuclear regulations, Politics of Nuclear Energy, Technical History Stories

Ten months to obtain an AEC construction permit

December 7, 2012 By Rod Adams

I’m doing a little history reading today and came across a passage worth sharing. The source is Glenn Seaborg’s “The Atomic Energy Commission Under Nixon” St. Martin’s Press, NY 1993 pg 101-102. In December 1965, the management of Northern States Power Company (NSP) reached an internal decisions that a new generating unit in the 500-electrical-megawatt […]

Filed Under: Nuclear Cost Data, Technical History Stories

Atomic Show #191 – 70th Anniversary of CP-1, the First Controlled Fission Chain Reaction

December 2, 2012 By Rod Adams

On Sunday, December 2, 2012, I gathered together a group of nuclear professionals to talk about the impact to human history of the construction and operation of Critical Pile 1 (CP-1). That simple assembly of graphite, uranium, and uranium dioxide was built in about 6 weeks. When measurements taken during construction indicated that the system […]

Filed Under: Atomic history, Atomic Pioneers, Podcast, Technical History Stories

December 2, 1942 – Two pioneers present at dawn of fission era

December 2, 2012 By Rod Adams

In the summer of 2012, Argonne National Laboratory recorded the first hand memories of two members of the group of 49 engineers, scientists and students who were present when mankind first proved that it could control a fission chain reaction. Just imagine – you can watch a very recently recorded account from people who were […]

Filed Under: Atomic history, Atomic Pioneers, Technical History Stories

Reed College has a nuclear reactor operated by undergraduate liberal arts majors

May 9, 2012 By Rod Adams

Reed College is perhaps best known among technologists as the place where Steve Jobs learned about calligraphy – among a number of other useful topics. It is also the only liberal arts college that owns a research reactor that is operated primarily by undergraduates. I hope you enjoyed Will and Norm’s visit to the Reed […]

Filed Under: Atomic Advocacy, Pro Nuclear Video, Technical History Stories

Pursuing the unlimited energy dream – history of the Integral Fast Reactor

February 8, 2012 By Guest Author

Photo of Experimental Breeder Reactor I group

Note: Len Koch, whose participation in nuclear energy research started in the 1940s, wrote the below open letter to colleagues who are striving to restore interest in the progress that they made in research and development of the Integral Fast Reactor during the period from 1954-1994 the year that President Clinton and Hazel O’Leary, his […]

Filed Under: Breeder Reactors, Fuel Recycling, Guest Columns, Liquid Metal Cooled Reactors, Nuclear Fuel Cycle, Plutonium, Technical History Stories

Kirk Sorensen – Why didn’t molten salt thorium reactors succeed the first time?

December 23, 2011 By Rod Adams

Kirk Sorensen is the founder of Flibe Energy. He has been prospecting in libraries for years to learn more about a path not taken (yet). He is convinced that the way forward for energy in the United States and around the world is the molten salt thorium reactor that can produce an almost unlimited amount […]

Filed Under: New Nuclear, Politics of Nuclear Energy, Technical History Stories, Thorium

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