Integrating six decades of learning about fast reactors

John Sackett and Yoon Chang (seated at left) and Jack Spencer (standing). GABI's Florence Lee-Lowe seated at right.

John Sackett and Yoon Chang (seated at left) and Jack Spencer (standing). Florence Lee-Lowe seated at right.

I learned some important new concepts yesterday from two of the leaders of the Integral Fast Reactor (IFR) project – John Sackett and Yoon Chang.

Among other things, they informed me — as a member of a group of about 35 other attendees at a workshop titled Sustainable Nuclear Energy for the Future: Improving Safety, Economics, and Waste Management organized by the Global American Business Initiative — that the “Integral” part of their project’s name refers to the fact that the IFR creators were aiming to produce a highly evolved system that integrated lessons from a number of separate fast reactor learning experiences.

It also meant that the leaders believed an important part of their project’s success was creating a situation where all of the disciplines required for a complete reactor power plant system were in one place where their special knowledge could be integrated with that of other specialists to produce the best possible system concepts.

Though I’ve written and thought quite a bit about the IFR project over the years, I had a mistaken impression about the reason that “Integral” was chosen to be part of the project’s name.

Because the project combined the Experimental Breeder Reactor 2 (EBR-2) with a closely associated fuel recycling facility that used pyroprocessing to produce new metallic fuel elements, I thought that ‘Integral’ meant that the project leaders envisioned that each IFR installation would include both reactors and a fuel recycling facility.

Rod Adams exercising his questioning attitude

Rod Adams exercising his questioning attitude

That never made economic sense to me; it would substantially increase the initial capital cost and eliminate some economies of scale that would accrue if recycling was done at a specialized, regional facility for a large number of power plants. It also seemed to inherently limit the potential market reach of the system; many potential customers for a safe, reliable nuclear power plant would not want — or be allowed — to get into the fuel recycling business.

Now that I have a better understanding of the ‘I’ in IFR, I’m a stronger fan of the concept and of the various system design iterations that fall under the umbrella of Integral Fast Reactors.

There are several key choices that make the IFR different from other fast reactors that have met with mixed success or outright failure. These choices were made as a result of a focused effort to apply lessons learned, something that happens more quickly and permanently as a result of evaluating a failure. Systematic learning can be inhibited in a situation where moderate successes more firmly establishes a path that has inherent limitations.

An IFR includes the following:

  • Metal alloy fuel vice oxide fuel
  • Fuel element design that provides space for gaseous fission products to accumulate without damaging cladding
  • Low/no pressure sodium coolant
  • Pool vice loop for sodium coolant
  • Inert gas blanket
  • Double walled tank to hold the coolant and provide leak detection in inert environment
  • Double walled steam generator tubes

Within those basic choices, there are a wide variety of iterations that can provide specific solutions to customer needs.

It is important to recognize that the IFR design choices are not just conceptual. They were proven through 30 years worth of experience with an operating [not paper] power plant (EBR-2) and pilot scale fuel recycling facility. The system was reliable, experienced few sodium related challenges, demonstrated passive safety through a well planned series of physical experiments, and produced low worker radiation exposures. That last advantage was a result of the virtually non-existent corrosion of internal surfaces even after 30 years in a hot, sodium-bathed environment.

As Sackett and Chang informed the workshop, the commonly held perception of sodium as being a difficult and dangerous coolant has been proven wrong by experience. Despite the fact that sodium reacts violently when exposed to water or air, no one has ever been injured as a result of sodium leaks. All instances of sodium and water interactions in steam generators have been readily contained and all instances of sodium leaks from piping have been mitigated by standard response processes made easier by the fact that there is no pressure forcing the material out of piping or tanks. If there is a leak, it is a drip or a steady stream, not a gusher.

As I listened, I could not help but compare the experiences Sackett and Change described of working with low pressure sodium to the experience of working with high pressure, “live steam.” Even though water is not normally thought of as explosive, steam explosions were the cause of numerous fatalities in the era before the American Society of Mechanical Engineers and the Hartford Steam Boiler Inspection and Insurance Company joined forces to develop pressure vessel codes and standards.

Even in recent years, after we have had 150 years to become quite skilled at producing high quality piping, valves and pressure vessels, there are instances where people are severely injured or killed by accidental exposure to live steam. Pipes that start as high quality, high integrity components can deteriorate as a result of corrosion or erosion, and valves can either fail or be mispositioned.

One of my former shipmates had the life changing experience of being the commanding officer of a ship that experienced a steam line rupture. Unfortunately, some of the sailors involved experienced a life-ending experience.

We may all be more comfortable with water than with liquid sodium, but power plants don’t use benign, well-behaved forms of H2O, they use high temperature, high pressure forms that are at least as hazardous as hot, low pressure sodium.

Sackett pointed out a maintenance advantage to sodium that I had never thought much about. Since sodium freezes at 98 degrees C, maintainers can easily create a freeze plug to isolate a valve or a pipe section when the plant is shutdown for maintenance.

From my water-cooled reactor experience, I’m familiar with using freeze plugs, but they are not easy or cheap to create or maintain. They require a continuos supply of refrigerant to keep the water well below room temperature. In a sodium reactor, freezing happens naturally as long as there is no effort to add the heat required to maintain sodium well above room temperature.

In the 21 years since President Clinton and current Secretary of State John F. Kerry (who was then a Senator) joined forces to kill the IFR project, creative scientists, engineers and administrators have managed to continue to develop and prove out some of the planned innovations — especially in fuel recycling — that had not yet been completed. People who recognized the unique value of the IFR have also continued to refine their designs, publish papers, publish books [ex: Plentiful Energy and Prescription for the Planet] and give talks around the world to increase understanding of the potential for nearly infinitely sustainable nuclear energy.

GE-Hitachi’s PRISM reactor is one of the more well known commercial variations on the IFR concept, but Terrapower’s current iteration of the traveling wave reactor seems to qualify.

Another intriguing variation is the ARC-100, a small, simple, long-fuel life (20 years between refueling) version that I first learned about when I was preparing to retire from the Navy in 2009-2010. I plan to learn more about its current status and the company’s development plans in the coming weeks.

Despite the impression that the above photos might provide, yesterday’s audience was fairly diverse and included a number of people young enough to make IFRs a reality. I’m more optimistic about our future energy choices today than I have been for quite a while. GABI sustainable nuclear 3 I’m looking forward to the next GABI workshop and want to express my appreciation for their continuing efforts to provide excellent learning opportunities that make it worthwhile to drive to DC every once in a while.

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