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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

Advanced Atomic Technologies

Will heavy nitrogen become a widely used fission reactor coolant?

November 17, 2020 By Rod Adams 42 Comments

Heavy nitrogen has the potential to become as important to the future of atomic fission power system development as heavy water has been up until now. That’s a bold statement, so let me explain why I believe it’s true.

Are any nitrogen cooled reactors being used today?

One nuclear fission power system – the US Army’s “reactor in a box” the ML-1 – is known to have used nitrogen as its primary coolant and working fluid.

Nitrogen has features that make it an intriguing coolant option in a closed, Brayton cycle fission system; its thermodynamic qualities are virtually identical to atmospheric air. The overwhelming majority of Brayton cycle machines in operation and production today have been designed to use air.

With few, if any, modifications, a conventional Brayton cycle compressor can push nitrogen through a high temperature nuclear reactor. The resulting hot, high pressure nitrogen can then turn a conventional gas turbine machine. The turbine can discharge its gas into a large, low pressure cooler to return the gas to the initial compressor inlet conditions.

Like helium and CO2, nitrogen is compatible with the graphite that is used as a moderator and structural material in gas cooled reactors. Unlike oxygen, it does not react with carbon (graphite).

All this has been well understood for decades and is the basis for choosing nitrogen for the Adams Engine.

Why have almost all other nuclear system designers dismissed the nitrogen alternative?

The main objection to using nitrogen as a reactor coolant is that nitrogen has a feature that makes it seem less useful than helium. That is the coolant gas selected by the overwhelming majority of those who believe gases have utility as reactor coolants in reactors capable of achieving gas temperatures higher than 700 ℃. (There are many nuclear reactor designers who dismiss all gas coolant options. Reasons for their dismissal are beyond the scope of this article.)

Unlike helium, nitrogen absorbs neutrons. In fact, its broad spectrum neutron absorption coefficient – a measure of probability for the reaction to occur – is fairly high at 1.83 ± 0.03 barns. That number is high enough that nitrogen is used as a secondary means of shutting down the British CO2-cooled Advanced Gas Reactors (AGR). (See pg. 21)

Nuclear reactor engineers work diligently to eliminate materials that absorb neutrons from their designs; neutrons absorbed by any material that is not fuel are wasted and reduce fuel efficiency. All else being equal, a reactor that contains more neutron absorbing materials will need more fissile material to be loaded to achieve the same operating cycle length.

Effects on fissile material efficiency are not the only reason to worry about putting neutron absorbers into fission reactors. When an atom absorbs a neutron it becomes a different isotope; that new isotope can create its own problems.

When atmospheric nitrogen is exposed to a neutron flux, it undergoes an N-P reaction. (That the shorthand for a reaction where an atomic nucleus absorbs a neutron and promptly emits a proton.) In the case of N-14, the most common nitrogen isotope, the N-P reaction creates carbon-14 (C-14).

C-14 decays with a low energy beta (nuclear electron) emission to become N-14. Essentially, one of the neutrons in radioactive carbon becomes a proton, producing stable nitrogen. That decay event is a lot slower than the N-P reaction that created the C-14 – after 5,730 years, only half of a mass of C-14 will have turned back into N-14.

C-14 is part of our earthly environment because it is constantly being created in the upper atmosphere where nitrogen is exposed to cosmic radiation. However, elevated quantities of C-14 are perceived to pose a risk to living organisms. Other nuclear reactors produce C-14, but releases of C-14 are tightly controlled. Production is avoided if at all possible.

Aside: There are valuable uses for C-14 today and more that are being developed. It is possible to turn the disadvantage of constantly producing C-14 into a revenue source that might even become a profit center, but that path isn’t within the scope of this article. End Aside.

One other difference between helium and nitrogen that sometimes enters the discussion about coolant alternatives for gas cooled reactors is the fact that helium has an attractively high specific heat transfer coefficient.

Per unit of mass, helium will transfer 5 times as much heat as nitrogen. But, helium is a light, monatomic gas. Its molecular weight is 4 atomic units. In comparison, nitrogen is a stable diatomic gas with a molecular weight of 28. Since all gases have the same molar volume, at the same temperature and pressure, nitrogen is 7 times as heavy as helium.

A volume of nitrogen has about 40% more capacity for moving heat as the same volume of helium. Compressors and turbines move volumes, not masses.

Partly out of habit and partly because of the challenges associated with managing C-14, virtually all high temperature gas cooled reactor designers have stuck with helium as their choice of coolant. Even though many reactor-decades worth of operational experience has been accumulated with CO2 as a coolant, that gas breaks down at the temperatures envisioned for HTGRs.

Choosing helium has forced gas cooled nuclear power system designers to deal with the considerable challenge of designing and fabricating special purpose helium machinery. Reactors heat sources tend to work well with helium as their cooling medium. It’s a much more difficult gas to move with compressors or circulators and to use to spin turbines.

But the engineers who design reactors are usually not well versed in heat engine design and manufacturing processes. They choose the gas that seems best for their part of the power system. They are often in charge in nuclear power plant design organizations.

Enter heavy nitrogen

Atmospheric nitrogen consists of a predictable ratio of two stable isotopes. 99.67% of them are N-14, an atom that contains 7 neutrons and 7 protons. But 0.36% (36 atoms out of 10000) are N-15, an atom that contains 7 protons and 8 neutrons.

That extra neutron makes the atom extremely reluctant to allow another neutron into the nucleus. The broad spectrum cross-section for neutron absorption for N-15 is roughly 8,000 times lower than it is for N-14. N-15’s absorption cross section is even lower than helium.

Aside: I need to credit Atomic Insights participants for teaching me that heavy nitrogen might be a good solution to a difficult problem. Cyril R. first introduced N15 into a discussion about the NGNP project in March 2013. As you might notice if you review the comment thread, I resisted the idea at the time. John ONeill reintroduced the idea in an Atomic Insights comment posted on Nov. 6, 2018. Those discussions have been running around inside my mind for years, with periodic efforts to learn more. I admit it. I’m slow. End Aside.

Closed Brayton cycle machines using a reasonably pure form of N-15 as the fluid for both turning turbines and transferring heat from a high temperature gas reactor should overcome two obstacles that have stopped nuclear gas turbines from being developed.

They would be using a gas whose thermodynamic properties are virtually identical to atmospheric air. That allows the use of a broad spectrum of refined compressors and turbines that are in production today. Those machines have fully established supply chains for various components. The machines are accompanied by blueprints, maintenance manuals, operating manual and experienced technicians.

There will be some refinements required in bearings and ductwork, but those are largely external to the main parts of a turbo machine.

A small portion of N-14 will remain in an inventory of gas that is vastly enriched in N-15. It will still require some management. But reactor designers and operators inevitably must deal with impurities.

An interesting aspect of making this design choice is the fact that the reactor will be most reactive when its coolant is pure. Any event that results in a reduction in coolant purity will tend to make the reactor less reactive and may even result in halting the fission reaction.

If there is a major loss of coolant event, there will be provisions for refilling the system with available gases, likely either conventional nitrogen or atmospheric air. A major loss of coolant would likely be accompanied by shutting down the reactor for repairs, so there will not be a significant neutron flux and the replacement gas will not accumulate a substantial quantity of C-14 during the repair period before the system is again filled with an inventory of N-15.

There are current uses for N-15 on a laboratory scale. It’s a useful isotope for tracing biological processes like fertilizer uptake. According to current suppliers, the world market for high purity N-15 is less than $1 M annually. And that is for a gas where one supplier’s catalog lists a 5 L bottle as being available for $2,190.00.

There are existing production facilities and several different available processes that can separate N-15 from atmospheric nitrogen. A patent for one of the processes was granted to Taiyo Nippon Sanso Corporation in 2010 (US Patent Number 7,828,939 B2).

Aside: Soon after the original version of this post was published and shared, @Syndroma pointed out that there is serious interest in using N15 for nitride fuels for fast reactors. Nuclear Engineering International published an article titled Russia looking at isotope-modified nitride nuclear fuel about that application for heavy nitrogen. End Aside.

It seems reasonable to believe that production processes could be scaled to meet any substantial demand for the product. It’s also worth noting that this is not a material that will be consumed. It will be continuously cycled through closed loop systems. Any leaks from those systems will return the gas back into the atmosphere.

Opportunities, not predictions or guarantees

Closed Brayton turbo machinery using a fission heat source has been an elusive goal for a small number of people since the earliest days of atomic energy development. Nothing in this post is new information, so it’s entirely possible that its publication will not make any difference.

But the potential for addressing some of the world’s energy needs with a power system that combines an emission-free, abundant, affordable and reliable heat source with refined Brayton cycle heat engines is too attractive to ignore completely.

It is the Brayton cycle that makes natural gas power plants so quick and easy to erect. It is the Brayton cycle that makes them responsive and thermally efficient.

I’ll close with one final thought. When natural gas fired gas turbines are shut down because there isn’t enough demand for electricity or other power, they cool down quickly. Operators don’t purposely keep them warm because that consumes fuel.

A fission-heated Brayton cycle machine will stay warm for many hours as a result of radioactive decay heat generation. That might be a feature that makes the system even more attractive in applications where flexibility has a market value.

Filed Under: Advanced Atomic Technologies

Atomic Show #287 – Darren Gale, VP Commercial Operations, X-Energy talks about Xe-100

November 12, 2020 By Rod Adams 2 Comments

X-Energy is the lead recipient for one of two industry groups selected to receive $80 M in Department of Energy (DOE) funding as part of a public-private partnership program to demonstrate advanced nuclear power plants on an aggressive time table.

Its primary partner in the endeavor is Energy Northwest, which currently owns and operates the Columbia Generating Station in eastern Washington. Energy Northwest will be the owner and operator of the demonstration power station, which will consist of a four-unit installation of X-Energy’s Xe-100 high temperature gas cooled reactor.

Each unit is designed to produce 80 MWe, resulting in a power station output of 320 MWe.

Advanced Reactor Demonstration Program

The award is part of the Advanced Reactor Demonstration Program, which also includes two additional development pathways with longer horizons. The $80 M in FY 2021 funds is a down payment that will provide funds for completing detailed design work and beginning the licensing process.

Future appropriations will be required to complete the projects; the funding opportunity announcement for the program included an award ceiling of $4 B to be shared among three different development pathways.

For Atomic Show #287, I spoke with Darren Gale, X-Energy’s Vice President for Commercial Operations. Darren is the company executive with direct responsibility for executing the company’s contract with the Department of Energy and delivering on the promise to design, license and construct an advanced nuclear reactor power plant.

The ADRP has an aggressive target date for beginning to deliver electricity to the grid is the end of 2027. During our conversation, Darren explained how his company is positioned to deliver on its promise.

Xe-100 Design history

We spoke about how X-Energy has been working on its high temperature pebble bed reactor design for more than a decade. X-Energy was founded in 2009 by Kam Ghaffarian, a successful entrepreneur who founded Stinger Ghaffarian Technologies (SGT) in 1984. Dr. Ghaffarian remains the owner of X-Energy, but is being joined by additional investors.

The design is mature and the company has been engaging with the NRC for several years. It expects to be able to submit a license application within the next year or two; part of the uncertainty includes determining the most appropriate and streamlined licensing pathway.

The Xe-100 is a helium-cooled, high temperature pebble bed reactor that has a number of similarities to the Chinese HTR-PM. They share a common heritage tracing back through the South African HTGR program and to the German AVR demonstration reactor.

As Darren explains, the Xe-100 includes a number of refinements in its fuel design and in its fuel handling system that enable more efficient fuel use.

Another design difference is that each Xe-100 reactor/steam generator modules are connected to its own Rankine cycle steam turbine. In the HTR-PM design, two reactor/steam generator modules feed a single larger turbine.

The 80 MWe power output selection was influenced, in part, by the availability of off-the-shelf steam turbine power plants. Unlike light water reactors, the Xe-100 will produce steam at temperatures (565 ℃) and pressures (16.5 MPa) used in modern supercritical steam systems.

Like the HTR-PM, Xe-100 reactors are continuously fueled while operating, eliminating the need to schedule refueling outages. There will still be a need to periodically shut down the reactor for inspections and steam turbine maintenance. X-Energy expects that there will be more requirements during the early years of operation while the company and the regulator gain experience and understanding of operational effects.

Eventually, though, the company expects to achieve somewhat higher than average availability than conventional reactors that require unavoidable outages for refueling.

Project location

The project will be built in eastern Washington at WNP-1, a site that was licensed for construction of a nuclear power plant in 1975. Using a site that has already been reviewed and approved for use as a nuclear plant greatly reduces the amount of time and effort required for long lead time environmental impact reviews, seismic surveys, and site pre construction surveys.

Though the original plant was never completed, certain civil structures, including a water intake system and pump house were completed before the project was cancelled. Darren explained that the existing infrastructure at the site would require refurbishment, but it enables a more rapid timeline than a greenfield.

Employment opportunities

X-Energy is in the hiring mode. The Xe-100 team head count is approximately 50. Some of the necessary tasks will be completed by contractors. But Darren expects that the permanent team will expand to include 200 or more people within the next year or two.

Most of the project design work is taking place at X-Energy’s Rockville headquarters, but current restrictions related to COVID-19 have required some creative uses of remote work, multiple buildings, and video conferencing. As a result of the learning that has come with that experience, X-Energy will be somewhat flexible in allowing some employees with key skills to work from remote locations.

The Xe-100 demonstration project is an exciting opportunity for advanced reactor designers and supporters to turn ideas and concepts into functioning equipment that generates real power and heat.

I hope you enjoy this episode and participate in the comment threads, especially if you have questions that are not addressed. As you will hear towards the end of the show, Darren expects to be able to return several times during the course of the construction project.

https://s3.amazonaws.com/AtomicShowFiles/atomic_20201111_287.mp3

Podcast: Play in new window | Download (Duration: 40:19 — 46.3MB)

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Filed Under: Advanced Atomic Technologies, Gas Cooled Reactors, Graphite Moderated Reactors, New Nuclear, Pebble Bed Reactors, Podcast, Small Nuclear Power Plants

Atomic Show #285 – MMR at Illinois

November 3, 2020 By Rod Adams 6 Comments

The University of Illinois at Urbana-Champaign has a stretch goal of completing its next research and test reactor by the end of 2025. It has assembled a team that includes several other major universities, national labs, and industrial partners. It has selected the MMRTM, a product that is being developed by USNC (Ultra Safe Nuclear […]

Filed Under: Advanced Atomic Technologies, Atomic education, New Nuclear, Podcast

Atomic Show #278 – Micro-Modular Reactor (MMR) project partners USNC, GFP and OPG

June 21, 2020 By Rod Adams 14 Comments

Global First Power (GFP), Ultra Safe Nuclear Corporation (USNC) and Ontario Power Generation (OPG) recently announced that they had formed a joint venture called Global First Power Limited Partnership. That venture will build, own and operate an installation called the Micro Modular Reactor (MMR™) at the Chalk River Laboratories site. Mark Mitchell and Eric MGoey […]

Filed Under: Advanced Atomic Technologies, Atomic Entrepreneurs, Business of atomic energy, Gas Cooled Reactors, New Nuclear, Podcast, Small Nuclear Power Plants, Smaller reactors

Transcript: Atomic Show #278 – Micro-Modular Reactor (MMR) project partners USNC, GFP and OPG

June 21, 2020 By Rod Adams Leave a Comment

Atomic Show #278 transcript, lightly edited for clarity. Intro music (00:15): Rod Adams (00:21):This is Rod Adams and it’s time for Atomic Show show number 278. Yes, these Atomic Shows are coming almost regularly these days. I guess it helps to have not only myself, but all of my guests, working from home. Today I […]

Filed Under: Advanced Atomic Technologies, Atomic Show Transcript, Gas Cooled Reactors, International nuclear, New Nuclear, Small Nuclear Power Plants

Atomic Show #277 – Simon Wakter, pro-nuclear engineer in an ambivalent country

May 30, 2020 By Rod Adams 1 Comment

Simon Wakter is a strongly pro-nuclear engineer in a country that passed a referendum officially phasing out nuclear energy since several years before he was born. He has to round up to be called a thirty-something. Simon works in the nuclear energy branch of AFRY, a well-established 17,000 employee, all-of-the-above. engineering company that recently adopted […]

Filed Under: Advanced Atomic Technologies, Atomic history, Atomic politics, Podcast, Small Nuclear Power Plants, Smaller reactors

Atomic Show #276 – HolosGen Claudio Filippone and Chip Martin

May 19, 2020 By Rod Adams 17 Comments

HolosGen has attacked the nuclear power plant cost and schedule challenge from the opposite direction chosen by many nuclear reactor developers. Claiming to be agnostic about the reactor specifics – as long as it produces reliable heat in a small-enough configuration – HolosGen founder Claudio Filippone decided to focus on radical improvements to the “balance […]

Filed Under: Advanced Atomic Technologies, Atomic Entrepreneurs, Gas Cooled Reactors, Podcast, Small Nuclear Power Plants, Smaller reactors

Atomic Show #275 – Managing advanced nuclear development during pandemic

May 12, 2020 By Rod Adams 10 Comments

Managing any business is hard work, especially during a global pandemic with stay-at-home orders in place. It requires creativity and flexibility along with some amount of prior preparation. On May 11, 2020, I gathered a group of representatives from several start-up companies that are developing advanced nuclear technologies to talk about how they are making […]

Filed Under: Advanced Atomic Technologies, Atomic Entrepreneurs, Business of atomic energy, Podcast

Atomic Show #274 – Thomas Jam Pedersen, Copenhagen Atomics

April 30, 2020 By Rod Adams 1 Comment

Copenhagen isn’t the first city name that comes to mind as the place to start a nuclear company. Denmark has decommissioned its last research reactor and has never had a nuclear power plant. That hasn’t deterred Thomas Jam Pedersen and his colleagues at Copenhagen Atomics. Starting a decade or more ago, they began learning about […]

Filed Under: Advanced Atomic Technologies, International nuclear, Podcast

Atomic Show #273 – Liz Muller, Deep Isolation

April 23, 2020 By Rod Adams 7 Comments

Liz Muller is a co-founder and the CEO of Deep Isolation, a company that makes the modest claim of having invented a solution to nuclear waste. The politically unsolved waste issue has plagued nuclear energy development since the mid 1970s. That was when it became abundantly clear that the original plan to recycle used fuel […]

Filed Under: Advanced Atomic Technologies, Innovation, Nuclear Fuel Cycle, Nuclear Waste, Podcast

Atomic Show #270 – Fastest Path to Zero

March 27, 2020 By Rod Adams 5 Comments

Fastest Path to Zero logo

Suzanne (Suzy) Hobbs Baker serves as the Creative Director for Fastest Path to Zero. I recently spoke with Suzy and Steve Aplin, a consultant to the Canadian nuclear industry and frequent Atomic Show guest, about the work that Fastest Path to Zero has done and plans to do in the near future. Fastest Path to […]

Filed Under: Advanced Atomic Technologies, Alternative energy, Clean Energy, Climate change, Podcast, Smaller reactors

Oklo has filed first combined license application (COLA) with the NRC since 2009

March 18, 2020 By Rod Adams 15 Comments

Oklo, Inc. announced yesterday that its combined license application (COLA) to build and operate an Aurora at INL was undergoing acceptance review at the Nuclear Regulatory Commission. Key project specifics Oklo’s Aurora is a 1.5 MWe liquid metal fast reactor with heat pipes to move fission heat out of the reactor core and into the […]

Filed Under: Advanced Atomic Technologies, Liquid Metal Cooled Reactors, New Nuclear, Smaller reactors

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