Liquid Metal Cooled Reactors

Photo credit: Wikipedia credited to U.S. DOE and in public domain.

Senator Carper (D-DE) asked each witness at a March 8 hearing about NEIMA – Nuclear Energy Innovation and Modernization Act – to give one suggestion for improving the bill. If asked, my answer would be to include findings that emphasize the importance of U.S. government-owned testing facilities that are capable of supporting the NRC licensing requirements for the types of reactors being developed by U.S. universities, the private sector and the National Laboratories.

If given the chance to make a second suggestion, I’d ask the Congress to include provisions that note the fact that there is a known gap in fast spectrum testing facilities and that there is a world class, lightly-used facility at the Hanford site in the state of Washington that is currently in a deactivated condition.

At least six entities in the United States or Canada (TerraPower, ARC, GE Prism, LeadCold, Oklo and Westinghouse) are investing significant sums of corporate or venture capital to pursue an elusive technical achievement; commercially viable nuclear power systems that achieve substantially greater fuel economy than conventional reactors. Though nuclear fuel is “cheap,” substantially better fuel use provides improved longevity and produces less waste material.

Efforts to achieve fuel economy objectives have reopened a discussion whose historical roots extend back more than 50 years into the middle of the 1960s. Given that there are United States entities that believe there is a need for advanced nuclear technology with fuel consumption characteristics that surpass those available from conventional reactors, those entities need a facility that can provide conditions for the fuel and materials testing required to support design, development and licensing.

Virtually all of the available facilities that can provide the necessary conditions are located in Russia. For obvious reasons, that fac adds an unnecessary level of cost and complication.

Conventional Light Water Reactors (LWR)

Conventional commercial nuclear reactors operate with slow [thermal] neutrons. They use materials like water, heavy water or highly purified graphite to moderate [slow] the high speed, high energy [fast] neutrons that are liberated when uranium or plutonium atoms are broken apart.

Thermal neutrons have a much higher probability of being absorbed and causing fission, thus they can work with fuel that is only slightly enriched to have a little more fissile material than natural uranium. The disadvantage of thermal spectrum reactors is that commercially proven configurations fission only 3-5% of the uranium in the fuel elements.

Thermal reactors obtain most of their heat from the 0.7% of natural uranium that is fissile U-235. Nearly all of the U-238 atoms that make up 99.3% of natural uranium are treated as if they were useless waste materials. In commercial fuel elements, natural uranium has been enriched so that 3-5% of the uranium is fissile U-235.

As the reactor operates, fissile U-235 is consumed. A small portion of the U-238 also fissions when nuclei are hit by neutrons with enough momentum. A portion of the U-238 that is smaller than the amount of consumed U-235 also absorbs a neutron and quickly decays into Pu-239, which is about as fissile as U-235.

In order for a reactor to be able to maintain heat producing operations, it much contain a certain amount of fissile material. Thus fuel elements removed from a core still contain a significant amount of fissile material; it cannot be consumed without separating the actinides from the rest of the material in the used fuel and adding enough fissile material to regain the 3-5% content needed in new fuel rods.

Towards the end of life for the loaded core, about a third of the produced power is coming from Pu-239. As a result, conventional reactors consume 3-5% of the loaded fuel, leaving 95-97% of the potential energy behind as waste if not recycled. To a reasonable level of provision, the process in a thermal reactor produces about as much energy from mined uranium as if the system only consumed U-235.

Inefficient? Yes. Is It A Major Cost Issue? Not Yet.

Many nuclear advocates or nuclear technology observers claim there is no immediate need to spend money to improve fuel cycle efficiency. Uranium is cheaper now in nominal dollars than it was in 1973 ($20-$24/lb versus $40/lb). The market is oversupplied to the point where mines are being closed for economic reasons, not because they have exhausted the known deposits. Storing used fuel [which some people insist on calling “nuclear waste”] is technically simple and not a major cost item, even though it can lead to heated political controversies.

Those objections do not prevent others from pursuing improvements because they seek other measures of effectiveness or have discovered ways to position their technology to compete in unique ways.

One of the many reasons that the U.S. has not reached any long term agreement resulting in a successful and sustained program of final disposal for used fuel is that a significant group of nuclear-knowledgable scientists and engineers are professionally offended by the idea of permanently placing a vast source of potential energy into a location where it is as inaccessible as possible.

We believe that “final” disposal deep underground is an unnecessary barrier. Future generations will be smarter than we have been about making full use of the Earth’s endowment of actinides. They will not thank us for putting valuable material in places where it is difficult to retrieve.

Beyond LWRs

LWR “waste” material is capable of split and releasing just as much energy for each fission as splitting U-235. Uranium-238 can fission either directly with energetic fast neutrons [about 1 MeV of energy] or it can fission after absorbing a neutron, undergoing two beta decays to become Pu-239 and then being split by a second neutron.

In a reactor that has no or little moderation [either zero or a small portion of light materials like graphite or water in the core] neutrons retain high enough energy to either directly fission or to convert U-238 to fissile Pu-239. Doing so improves fuel economy by a factor that might approach 140. With fast neutrons, a fuel resource expected to last for a century with thermal reactors could conceivably last 14,000 years.

One of the primary technological rainbows that might lead to this pot of gold is to use reactors that are cooled by liquid metal, with the common choices being limited to sodium, lead, or a eutectic mixture of sodium and potassium called NaK.

Using liquid metals and fast neutron spectra requires materials and fuels whose characteristics are considerably different from those in conventional reactors. Doing this safely – and within the bounds of regulations – requires adequately testing and computer model validation.

United States Fast Breeder Reactor Program

In the mid 1960s, the U.S. Atomic Energy Commission shifted most of its nuclear technology investment expenditures away from projects that would improve on light water reactors. The general consensus was that those reactors had been commercialized to the point where private industry would invest the resources required for improvements.

In 1965, the Joint Committee on Atomic Energy (JCAE), the President and the AEC determined that the time was right to apply available resources to serious research and development of liquid metal cooled fast breeder reactors. That effort included the recognized need for a large-capacity, highly capable testing reactor.

A group of scientists, technologists, economic boosters and elected officials in the state of Washington joined forces and put together a proposal for a fast neutron test facility. Similar people associated with the Idaho National Reactor Testing station and the closely aligned Argonne National Laboratory in Illinois assumed that their site was the logical location for such a facility. After all, they had already hosted so many experimental, test and demonstration reactors. Their site was the National Reactor Testing Station before it was renamed as the Idaho National Laboratory.

Those loosely aligned individuals and corporate entities did not take into account the well-organized group in Washington. They did not understand the national government’s desire to soften the economic blow that had been dealt to eastern Washington with the winding down of the plutonium production reactors. They also failed to recognize the importance of Milton Shaw’s personal animosity towards Albert Crewe, then serving as the director of Argonne National Laboratory. Shaw was then serving as the director of AEC-Headquarters’ Division of Reactor Development and Technology; his opinion carried a great deal of weight in the AEC decision process.
(Source: Proving the Principle – A History of the Idaho National Engineering and Environmental Laboratory, 1949-1999 chapter 19)

The reactor that the Atomic Energy Commission designed, sited, built and operated at the Hanford Site in Eastern Washington to provide the proper environment for testing fast reactor fuels and materials operated from 1982-1992. That shutdown happened about 15 years after Presidents Ford and Carter had determined that the US would not pursue liquid metal breeder reactors.

The AEC took from 1967-1982 to move from conception to an operating test facility. Some of the delay was caused by the annual budget battles that questioned the need for the facility after the cancellation of the fast breeder reactor program. The design was reviewed and approved by the Nuclear Regulatory Commission (NRC), though regulation of the facilities construction and operation was retained by DOE.

That facility – the 400 MWth Fast Flux Test Facility (FFTF) – remains the highest capacity, most modern and least used test reactor in the U.S. DOE’s possession. It is still intact with its internals filled with an inert argon gas purge.

Though final environmental impact assessments have been conducted and a decision has been made to entomb the facility, budgets and preparation of detailed engineering plans move slowly at DOE; no destruction has begun yet. There is a pervasive myth floating around the DOE that actions taken during the George W. Bush administration to more completely remove the sodium coolant from the system has made it impossible for the system to be restored.

According to a 2007 detailed study funded by DOE as part of the Global Nuclear Energy Partnership (GNEP) the action taken was to drill a 3/4″ carefully engineered hole in a non pressure barrier. The study determined that adequate recovery from that action would add a little less than $1 M to the $500 M facility restoration cost estimate. (See pages 56-57 of the linked PDF)

What Kind Of Reputation Did The FFTF Earn?

During the 15 years following the 1976-77 turn away from developing fast breeder reactors as a national priority, the FFTF was completed, put through an extensive start-up testing program and used operationally for the next 10 years. Because FFTF’s primary mission of supporting an expansive breeder reactor program had been cancelled before the facility ever started up, its supporters were put into the position of existence justification before they even opened for business. The facility was used for materials testing, medical isotope production, and was proposed for use as a plutonium burner, a source for Pu-238 for space missions and as a prototype liquid metal power reactor.

One of the test series conducted at the FFTF validated the system’s passive safety claims. The unvalidated nature of those claims was a major objection raised by the project’s more vocal opponents, including Arthur Tamplin and Thomas Cochrane, both of the Natural Resources Defense Council (NRDC).
(Source: Moore, T.G. Fast Breeder Reactors Fueling Controversy, Pittsburgh Post Gazette, Aug 3, 1979)

During its operational life, the FFTF demonstrated the value of having been built with a view towards longevity and reliable operation. At times, it could run for many months without reducing power. That is valuable when operating to “burn up” fuel or highly irradiate materials with neutrons.

In 1990, President George H. W. Bush and his Secretary of Energy, James Watkins determined that the FFTF was no longer needed and could be sacrificed in the name of budget cutting. They justified the decision by claiming that the US was no longer pursuing fast reactor technology. Apparently, the staff people who supplied this budget cutting recommendation and justification ignored the Integral Fast Reactor (IFR) project in Idaho, which was then in its 18th year and still going strong.
(Source: Nation’s Most Modern Reactor Scheduled For Closing; DOE Cites Costs, Los Angeles Times Feb 11, 1990, Pg A28)

In 1993, the FFTF was ordered to be placed in standby by President Clinton and Hazel O’Leary, his first Secretary of Energy. On Jan 19, 2001, the last day of the Clinton Administration, Bill Richardson, then serving as the Secretary of Energy, signed the Record of Decision (ROD) on the Final Environmental Impact Statement for closing and decommissioning the facility. In December 2001, President George W. Bush and his Secretary of Energy, Spencer Abraham ordered that the facility be permanently shutdown by completing the sodium removal.

In 2007, as part of the Global Nuclear Energy Partnership, the Department of Energy funded a study to determine if the facility could be economically restored on a usefully short schedule. With a 20% contingency and conservative schedule assumptions, that study indicated that restoration would take about 5-6 years and cost $500 million. The study ended up in a room known to insiders as the abandoned room, a place where all of the GNEP Environmental Impact Statement paperwork accumulated with no consideration given to reviewing the documents and making a final decision.

Mission And Requirements Justification For Fast Test Facility

At the end of the Obama Administration, DOE began identifying the mission need and requirements for a new fast reactor testing facility. Though the documents produced as part of that effort only mention the FFTF in passing, it now appears that the process for meeting user demands for fast neutron testing capability will include evaluating the option of restoring the FFTF.

With a more diverse and less politically vulnerable user base compared to the 1970s vintage fast breeder reactor program, the FFTF should finally get the chance to perform its primary mission for a lengthy period of time.

As the US DOE has found with the Advanced Test Reactor (ATR), a 50 year-old facility initially built to serve a single customer, there is a wide range of potential customers and a sustainable demand for a well run neutron irradiation user facility that might last for numerous decades.

It’s time to move from repeated bipartisan efforts to permanently kill the FFTF to a broad-based effort to recognize value and restore the facility that our parents built and carefully put away in case we might need it.

Supporting advancements in nuclear energy seems to be an area of agreement in a sharply divided Congress. It is an improvement program where there are so many potential benefits that everyone – with the possible exceptions of Bernie Sanders and Ed Markey, two relics who cannot seem to discard their 1960s point of view – in the House and Senate can find reasons to favor supportive legislation.