Jake DeWitte and Caroline Cochran, the cofounders of Oklo, a start up company that is developing a 1-2 MWe nuclear reactor-based power system for remote areas, have been credited with drawing attention to a problem that can be solved by a government policy decision.
“Nearly all advanced reactors have a need for low enriched fuel greater than 5%,” Cochran recently wrote in an email.
Oklo is the chair of the Fast Reactor Working Group (FRWG), an industry-led effort focused specifically on future nuclear technology.
Current U.S. Nuclear Regulatory Commission licenses in the fuel supply chain specify a limit of 5% enrichment. Since there is currently no commercial demand for material with higher levels of enrichment, there is no commercially significant supply available.
The U.S. is party to an international agreement to keep enrichment less than 20% for all commercial uses. Material with fissile isotope content greater than 5% and less than 20% is known as high assay low enriched uranium (HALEU), the material that advanced reactors have been designed to use.
There is a small quantity of HALEU produced each year from down blended HEU. The quantity is just large enough to fuel research reactors in the U.S. and in countries where the U.S. has agreed to supply fuel.
What’s Being Done to Address Gap?
NEI and the Nuclear Innovation Alliance have formed a working group to explore ways to address the need for HALEU.
A potential domestic source for a starter quantity of HALEU fuel to prime the demand pump is the U.S. Department of Energy’s stock of surplus HEU.
For more than two decades, DOE has been selling LEU to the commercial market. It removes HEU from either Russia or its own inventory, contracts with private companies to blend the HEU with either natural or depleted uranium and produces a material that competes with freshly enriched LEU used for commercial nuclear fuel.
Due to criticality prevention considerations, the process begins with a relatively large tank of natural uranium in solution. HEU in the same chemical solution is carefully added from small diameter containers to bring the isotopic mix to just under 5% U-235 with the remainder being U-238.
The system as configured is designed and licensed for a maximum of 5% enrichment; an investment of several tens of millions of dollars plus several years of design, licensing and installation would be required for a different enrichment level.
Efforts to identify a source of HALEU have included discussions with legislators who are working on the Nuclear Energy Innovation and Modernization Act, which passed out of the Senate Energy and Public Works Committee in March.
During a recent hearing held by the Senate Energy and Natural Resources Committee, Sen. Deb Fischer (R-NE) addressed the HALEU issue with Dr. Ashley Finan, the Nuclear Innovation Alliance policy director. Here is an excerpt from the conversation:
Fischer: Dr. Finan, I understand that there are several advanced reactor technologies that need uranium enriched to 20% and this is higher than the standard 5% enrichment currently used in operating reactors. Can you tell me more about the situation?
Finan: Sure. Thank you for the question. There are many of the advanced reactor companies who will need to use enriched uranium that is low enriched, but is between 5 and 20%. We currently do not have a supply chain for that fuel because there hasn’t been a demand. That’s essentially the situation. It’s possible that they could obtain the material internationally, but that is not the preferred option.
Can Commercial Suppliers Meet Needs?
Though there is wide experience in the world’s nuclear enterprise with fuel enrichments that vary from 3% to < 90%, knowledge isn’t sufficient.
Safely handling material with higher enrichment level requires facility provisions to avoid accidental criticality, a condition in which nuclear fuel material begins a nuclear reaction when it isn’t supposed to.
Specifics are way beyond the scope of this piece, but HALEU licensees will require different machinery capacities, different piping systems, different storage containers and special shipping containers. Each stage in the fuel supply chain could be affected.
Procedures and control systems need revisions to accommodate the new material’s characteristics. Safety regulators have to review and approve all of these components to overall system of handling.
None of that comes cheaply. Fortunately, none of the changes require any inventions or material discoveries.
During the hearing mentioned above, Sen. Fischer asked NEI CEO Maria Korsnick how long it would take to develop a commercial supply of HALEU.
Korsnick replied that the supply chain for the material could be established within 7-10 years after customers place firm orders for a sufficient quantity of material to justify the necessary investments.
Before advanced reactor developers can place firm orders, they must be able to develop a solid order book from credible customers.
It is unlikely that any will succeed in that sales effort unless they build and operate demonstration power plants.
Improving Performance Vectors
Advanced reactor technology developers are aiming to improve nuclear energy performance along many vectors. An area of intense interest is waste reduction.
One part of the answer to the inevitable question, “What do you do with the waste?” is to make less of it.
Another is to create ways to reuse the materials that have traditionally been called waste.
The material removed from current reactors often contains 95% or more of the initial potential energy; if some of that can be consumed in a second or third pass through operating reactors, a smaller volume of material will ultimately need to be permanently protected.
Being able to start reactors with fuels that have higher enrichment levels and being able to add new fuel with higher enrichment during various stages of operation is roughly analogous to using high quality dry wood, or even lighter fluid to keep a fire burning hot enough and long enough to consume large, possibly damp logs.
Urenco Might Be Initial Source
During the recently completed 7th Annual International SMR and Advanced Reactor Summit hosted by Nuclear Energy Insider in Atlanta, there was a spontaneous discussion about supply sources for HALEU.
NEI’s Marcus Nichol, who attended the session where the topic came up, reported that a representative from Urenco said his company would be able to supply the material needed.
Urenco can enrich uranium to needed levels in its European facilities. Its U-Battery is one of the reactor designs under development that will need HALEU, so it will need to develop a complete fuel supply chain to meet its own needs.
Apparently, scaling the capacity of that supply chain to meet the needs of other developers fits within Urenco’s business model for future growth.
Of course, this is not the domestic source that some might prefer, but it would be sufficient to enable advanced reactors to prove their worth and market acceptability.
A version of the above was first published in the April 7, 2017 edition of Fuel Cycle Week. It is republished here with permission.