Atomic Insights

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

Army Nuclear Program

Project Dilithium – Boldly going back to a place our ancestors visited and prematurely abandoned

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In January 2019, the Strategic Capabilities Office (SCO) of the U.S. Department of Defense officially informed the world that it was interested in learning more about small, mobile, nuclear generators.


The SCO said it wanted to find out if there was technology available that could supply a forward operating base with abundant, emission-free electricity for three or more years without new fuel.

The request for information is an intermediate step in an accelerated acquisition process for a solution that can provide U. S. forces with enhanced power production capacity in a future, energy-intensive contingency.

The RFI will help the SCO determine the current state of the art and potentially support a decision to move forward with a prototype. If successful, the program could produce mobile power sources that could substantially reduce the Army’s dependence on routine fossil fuel deliveries.

It doesn’t take much imagination to recognize that such a capability could be important in wider variety of applications. Nuclear generators could have reduced suffering following Hurricane Maria’s devastation of numerous island power systems, especially within the still tenuous system that powers Puerto Rico.

If such systems were in our inventory today, several might be on their way to Venezuela, where an entire nation in its 4th straight day of being blacked out.

I’ve been involved in a number of conversations since the SCO issued its formal request for information. Many of them have started off with “It’s high time…” The enabling technologies have all existed for decades and are reaching ever increasing states of maturity.

From about 1966 until now, however, the Department of Defense, with its more immediate needs and large resources, has been reluctant to make the needed commitment to purchase mobile nuclear systems if proven to be capable of being built to their specifications.

In the early part of the 1960s after learning logistics lessons from Korea and before becoming entangled in a lengthy, expensive conflict in Vietnam, the Army explored the potential of small nuclear power plants, both fixed and mobile. Our ancestors have been here before; Project Dilithium is a revisitation, not an exploration into the unknown.

The early visits were a modest success that could have supported a more expansive effort to increase mobility and independence from fossil fuel supply lines, but the “Guns and Butter” budgets of the Johnson and Nixon Administrations left little room left for research and development.

By the time the Vietnam war ended, there was a strong antinuclear movement, the Army had lost much of its credibility due to the missteps of the nation’s political leaders and the nation had elected an antinuclear President who claimed to have been a nuclear engineer in the U.S. Navy.

There might have also been some resistance from the key, native state supporters of both Johnson (Texas) and Nixon (California). After all, the Army’s relatively high cost of hydrocarbons and their logistics chains represent important sources of revenue for those who sell the fuels and transportation services.

As a result of some or all of the above, plans for small, manufactured nuclear powered generators were left on the shelf while the dust deepened on their binders.

It was terrific news when I learned about the SCO’s RFI. I remembered how many times I had heard about the vulnerability of our logistics supply lines and the high portion of casualties in Enduring Freedom and the Long War associated with the enemy’s logical focus on attacking those convoys.

I also remembered the multiple times I had reminded military colleagues in and around the five sided puzzle palace about the incredible capabilities energy-dense nuclear fission offered.

There are, not surprisingly, naysayers who are not as happy as I am about the potential development of nuclear generators that can be readily moved to places where power is needed, but unavailable via the normal wire delivery methods.

According to Ed Lyman, the current go-to representative of nuclear opposition from the Union of Concerned Scientists, people who have determined that small, transportable, durable, high endurance nuclear reactors can be built in the near future are guilty of “naive optimism.”

He also characterized the international alliances of nuclear professionals who have been patiently refining materials, improving designs, testing components and even building and operating demonstration systems as “nuclear lobbyists.”

I take personal offense.

Personal interest in small modular reactors, especially mobile ones

Though my role has been as a bit player or sideline cheerleader, I’ve been intensely interested in what I often call “atomic engines” since the early 1990s. It’s almost depressing to realize that means I’ve been pursuing this technology for nearly 30 years.

In January 1990, I’d just completed a 40 month tour as the Engineer Officer of a 27 year old nuclear submarine. I had spent the 1980s either learning about nuclear energy, operating small, factory-constructed nuclear propulsion plants in sealed, underwater ships, or earning an advanced degree in Systems Technology.

While at graduate school in Monterey, CA, my running partner, Mike LeFever, was a former Chief Engineer on a gas turbine powered destroyer. Being typical Navy geeks, we spent many hours during long runs along California’s scenic coast comparing our experiences and our favorite platforms.

We agreed that a nearly perfect ship propulsion plant would have characteristics of both gas turbines and nuclear steam plants.

With that background, there were current events in January 1990 that motivated me to learn more about the politics of nuclear energy. I began a self-directed study program designed to help me find the root causes of the gap between what I knew to be true about nuclear energy and the general lack of interest in using nuclear energy as a powerful tool that could address many of the world’s biggest challenges.

A nuclear steam plant had been my most valued shipmate on USS Von Steuben. It provided the motive force that enabled us to perform our vital mission of strategic deterrence while also giving us the electrical power to live in relative comfort in our underwater habitat.

Because we used nuclear fission instead of fossil fuel combustion, we had refrigeration, air conditioning, fresh water, capable weapons control systems, entertainment systems, and even continously scrubbed air supplemented by freshly manufactured oxygen.

We manufactured that oxygen by tearing apart some of the pure H2O we made by removing salt and other contaminants from sea water. From our point of view, the associated hydrogen was a dangerous waste product that needed to be released back int the sea before it accumulated in explosive quantities.

From a curious nuclear submarine engineer’s perspective, it seemed rather strange to realize that the world was still fighting bitterly over control of oil producing regions. After all, my reliable boat engine had been built in the early 1960s in a manufacturing spurt that produced more than 100 submarines and about a dozen surface ships in less than a decade.

In every one of those ships, the alternative propulsion plant was an oil burner. Why weren’t there more ships, both Navy and civilian running on uranium? Why weren’t there smaller generators powering islands and other places still burning diesel fuel?

Why were the Army and the Air Force still dependent on diesel generators with their large and vulnerable supply infrastructure?

I realized, of course, that part of the answer might lie in the fact that steam cycles, like the one that my submarine had used, were bulky and sometimes ornery beasts that would be a bit challenging to operate in places that were not well supplied with water. (That still didn’t explain the relatively low use of nuclear propulsion on ships.)

As part of my self-study program, I haunted the Naval Academy’s extensive library collections on atomic energy. That was when I learned that there had once been a much broader interest in using atomic fission to address the applications I envisioned.

The early enthusiastic explorations included working demonstrations of small base-sized generators for the Army, small power plants for Air Force radar sites and barge mounted generators for ports and waterfront installations. It turned out that the Air Force had even developed several conceptual designs for plane engines as part of an extensive, billion dollar investigation of aircraft nuclear propulsion.

I found out that one of the Army’s plants and a couple of the Air Force concepts/prototype efforts used primitive versions of the combination of nuclear heat and Brayton Cycle gas turbines that Mike and I had casually chatted about as the “perfect” power plant.

Though the demonstrations had been reasonably successful, especially considering the fact that no two systems were alike and each had its own first of a kind (FOAK) challenges, neither the Army nor the Air Force had persevered or flourished like the Navy’s Nuclear Power Program. The most frequently offered explanation for this contrast rested on the slight shoulders of one man – Admiral Hyman G. Rickover.

To be continued…

ML-1 Mobile Power System: Reactor in a Box

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This is an August 2022 update of an article first published in November 1996 and updated in February 2019. The first update was stimulated by discussions associated with DOD’s issuance of an RFI for mobile, modest power output atomic power systems. That RFI resulted in Project Pele, which has now selected BWXT to build a first of a kind mobile reactor to meet requirements recognized in the 1950s. 

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 promotional video used mockups to illustrate what the completed system might look like. It 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 were required to weigh <= 15 tons each while the four additional containers each could weigh between three and four tons. The complete system weight would be 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.

Though the Army lost interest in the program, the Atomic Energy Commission (AEC), which was in charge of the technical development of the reactor power system, was interested in continuing the research and development program to solve the technical problems described above. They created a program and a budget to move the system to the point where it might be ready for a field test.

That program was not funded. There were some who suggested a more modest program and an early field test of the system, but that proposal was also not implemented, partly as a result of well deserved caution about field testing products too early. (The SL-1 experience was fresh in the minds of AEC leaders.)

During AEC authorization hearings for FY1967, Milton Shaw, head of AEC reactor development, submitted a description of the ML-1 program and the reasons the Commission had decided to cancel the program and was only requesting sufficient funds to wind it down. Through the modern magic of Google Books and a probing search by Nick Touran of What is Nuclear, I can share that submitted testimony with you.

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.

Treasure trove of documents about the ML-1, the US Army’s trailer-mounted, nitrogen-cooled, atomic fission-heated generator

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I recently published an article featuring a video from the Army Nuclear Power Program that focused on the Army’s mobile, low power closed cycle nitrogen cooled nuclear reactor designated the ML-1. The article generated a good discussion that indicated a strong desire for more information about the program. My initial searches didn’t turn up a […]

McMurdo Station – the New York of the Deep Freeze South

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(Note: If you are impatient and do not want to watch cute photos of penguins, skip to 19:06 to learn more about the reasons why the PM-3A, a 1,500 kilowatt nuclear electricity generator and process heat supply system, was such a valuable contributor to sustained Antarctic research.) Nearly all of the images that are used […]

Camp Century – Nuclear plant designed, manufactured, constructed & tested in less than 2 years

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Under current rules and assumptions, anyone who claims that they can design and build a power-producing nuclear reactor in less than 10-15 years is considered to be naive or hopelessly unrealistic. However, there is no reason to believe that everyone with the technical capacity for completing the task will follow the same rules. Even in […]

McMurdo veterans’ cancers FAR more likely to be caused by cigarettes that by Nukey-poo

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Note: (This story corrected on March 8, 2011) The world’s ignorance regarding the health effects of radiation is occasionally incredible. I just came across a story from New Zealand titled Health fears around polar nuke leak that attempted to implicate the Naval Facilities Engineering Command’s PM-3A, a small nuclear plant that supplied heat and electricity […]

Small Reactors, Safety Culture, Safe Design, and Lessons Learned From SL-1

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The United States has been operating small nuclear power plants continuously since the early 1950s. These reactors have been used for research and development, power generation, and ship propulsion. There have been tens of thousands of people associated with the design, development, manufacture and operation of these smaller reactors. The enterprise has accumulated an admirable […]

The Atomic Show #133 – Todd Tucker, Author Atomic America

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Atomic America has a thought provoking subtitle – “How a Deadly Explosion and a Feared Admiral Changed the Course of Nuclear History”. The unifying story through the book is one that most nuclear trained people know a little about – the accident at the Army’s SL-1 that took place on January 3, 1961. In Atomic […]

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