A Story In Irony: The Rise And Fall Of Fast Breeder Reactors

Many FBRs were built for power generation and research in the U.S., Russia, the UK, France, Japan, China, and India. Of these, only two remain operational today and both are located in Russia

In the early 1950s, the world was swept by the promise of atomic power. Fuelled by optimism, Lewis Strauss, then head of the U.S. Atomic Energy Commission, famously envisioned a future where electrical energy would be “too cheap to meter.” The hope was that nuclear power would revolutionise energy production, relegating fossil fuels to transportation.

Central to this vision were breeder reactors. In conventional water-cooled reactors, the fuel comprises 3-5 per cent of uranium-235 (U-235), with uranium-238 (U-238) making for the remainder.

Energy generation is primarily through the fission of U-235 in the fresh fuel bundles. After spending some time inside the reactor core, the U-238 nuclei in the fuel absorb neutrons and transmute to plutonium-239 (Pu-239). Pu-239 is a fissile fuel like U-235, and undergoes fission and contributes to about 30 per cent of the total energy generated by the reactor.

The conversion ratio in a reactor is defined as the ratio of new fissile atoms produced to fissile atoms consumed. All nuclear reactors experience some degree of conversion. Light water reactors (LWRs) have a conversion ratio of approximately 0.6 while pressurised heavy-water reactors (PHWRs) that use natural uranium fuel have a conversion ratio of 0.8. This phenomenon, where fresh fuel is produced while the original fuel is burned, is a unique phenomenon seen only in nuclear reactors.

When the conversion ratio is greater than one, the reactor produces more fuel than it consumes. There are some special reactors where this can be achieved, which are called breeder reactors.

The first nuclear reactor to produce electricity-the Experimental Breeder Reactor I (EBR-I)-constructed at Argonne National Lab, was a fast breeder reactor. On December 20, 1951, it became one of the first electricity-generating nuclear power plants, illuminating four light bulbs and later powering the entire facility.

The success of EBR-I sparked a wave of optimism throughout the 1950s and 60s about nuclear power’s ability to meet global energy needs sustainably without a significant environmental impact. Imagine that you set out for a drive in your car and find that the fuel gauge reading at the end of the drive is higher than when you started.

There was a boom in constructing nuclear reactors in the 1960s and 1970s. It turned out that water-cooled reactors like the LWRs and PHWRs were simpler and cheaper to build compared to other reactor designs. More than four hundred LWRs and PHWRs have been constructed worldwide for power generation and marine propulsion. With very few exceptions, they have operated safely and reliably.

The history of fast breeder reactors (FBRs) is more chequered. Many had anticipated that they would quickly match the economic viability of water-cooled reactors. However, the engineering challenges turned out to be too daunting. Many FBRs were built for power generation and research in the U.S., Russia, the UK, France, Japan, China, and India. Of these, only two remain operational today and both are located in Russia.

The FBR’s compact design and high power capacity make it suitable for submarines. Both the US and the then USSR built FBRs for submarine propulsion. The Soviet Alfa class submarine, the fastest submarine ever built, was powered by a Lead Bismuth-cooled fast reactor. Eventually, both countries abandoned FBRs for submarine propulsion because they were too expensive to build and challenging to maintain.

India had based its long-term nuclear energy strategy on transmuting its abundant thorium reserves to fissile uranium-233 (U-233) in FBRs. A beginning was made by constructing a sodium-cooled Fast Breeder Test Reactor (FBTR) based on the French reactor, RAPSODIE. This reactor went critical in 1985 and was used for research and gaining operating experience on the FBR.

The FBTR design was then scaled to a 500 MWe Prototype Fast Breeder Reactor (PFBR). However, this project has been delayed and is over a decade behind schedule.

The main engineering challenge with FBRs is the liquid metal coolant. Except for nuclear power, there is no other industrial process application for liquid metal. So, all the major components of this type of reactor are custom-built and quite expensive. Most FBRs use liquid sodium coolant, which has intrinsic safety issues. Sodium burns in contact with air and explodes in contact with water. If the liquid metal coolant solidifies for any reason, the reactor can never be repaired. Corrosion is an issue in Lead Bismuth-cooled reactors. Of all countries, Russia has had the maximum experience and success with FBRs. They planned to start building a commercial 1200 MWe FBR in 2014, but the plant’s construction is yet to commence.

The nuclear energy community is still optimistic about building fast reactors. Four of the designs shortlisted for the next generation of reactors, the so-called Gen IV reactors, were fast reactors. All the proposed Gen IV reactors are supposed to be safer, cheaper, more proliferation-resistant and more reliable than the existing power reactors. Only time will prove if any of these proposed designs can live up to the promise.

(The writer is a nuclear engineer who was involved in India’s strategic submarine program. He is currently Director of the School of Engineering at DY Patil International University, Akurdi in Pune)