The Silver Bullet for Climate Stabilizationo

In 1994, the Clinton administration induced Congress to terminate development of the Integral Fast Reactor (IFR) at Argonne National Laboratory, describing it as unnecessary, and told its developers to shut up about it.  Thus a technology that has been called the silver bullet we need to stop global warming disappeared into a memory hole.

What is this technology about?

As World War II ended, the US started researching civilian uses of nuclear fission, specifically to heat water for steam turbines that generate electricity.  The research proceeded on two tracks: (1) “thermal” reactors that consume their fission fuel—uranium enriched by increasing the proportion of its “fissile” (readily fissionable) isotope, U‑235, from less than one percent to about four percent; and (2) breeder reactors that optionally replenish their fission fuel— plutonium bred from the “fertile” isotope, U-238, that comprises 99 percent of natural uranium.  While thermal reactors create plutonium as a byproduct and fission it, plutonium is the primary fission fuel of breeder reactors while uranium is their breeding fuel.

Thermal reactors “moderate” the speed of the neutrons created by fission because slow neutrons do a better job at fissioning U-235 than fast neutrons.  Breeder reactors don’t moderate because fast neutrons produce more (fast) neutrons in fissioning plutonium than slow neutrons do and accordingly produce a higher breeding ratio.  Of the neutrons produced by a fission, all but the one that is needed to perpetuate the fission chain reaction are potentially available for breeding, which occurs when U‑238 “captures“ a neutron and becomes (through transmutation) fissile plutonium Pu‑239.

What emerged as the standard for commercial nuclear power was the “2^nd generation” thermal Light Water Reactor (LWR), the first of which was installed at Shippingport, PA in 1957.  LWR uses uranium oxide as a fuel and light (ordinary) water as both a coolant and a moderator.  Today more than 350 commercial reactors are operating in 27 countries, including 100 in the US that produce 20 percent of the electricity.

Meanwhile, breeder development continued at Argonne.  In 1964 the Experimental Breeder Reactor II (EBR-II) started up to test what eventually became the IFR and kept going for 30 years.  Instead of a water coolant, IFR uses liquid metal sodium, which doesn’t moderate neutron speed.  As a fission fuel it settled on a solid metal alloy consisting of uranium enriched with plutonium and mixed with zirconium in something like a 70-20-10% ratio, with uranium used by itself as a fertile “blanket” around the fuel assemblies when IFR is operating as a breeder.

The choice of metal fuel is unique among current “4^th generation” breeder technologies and has important advantages.  Foremost among them is its inherent safety, which in the last analysis means not letting any radiation escape into the outside world.

Metal expands when heated by fission, and when it gets too hot the expansion allows more neutrons to run away, thus “passively” reducing or even stopping fission and lowering the temperature.  In public tests conducted in 1986, neither loss of the internal coolant flow nor loss of the heat sink transferring heat to the steam turbine—the causes of all three of the operating LWR accidents at Chernobyl, Three Mile Island and Fukushima—made EBR-II fail.  Given “a couple of chances to melt down” and release radiation, as one of the nuclear engineers commented, “It politely refused both times.”

Another advantage is pyroprocessing, IFR’s technique for reprocessing its metal fuel and fuel assemblies through standard electro refining to cleanse them of impure fission products.  Performed remotely in a highly radioactive “hot cell” that no one can enter, electro refining mixes the reprocessed fuel in a mixture that makes the plutonium element too impure for use in weapons.  Thus, unlike oxide fuel reprocessing, pyroprocessing poses no risk of nuclear proliferation.

The slow process in IFR operations is breeding—upwards of a decade is needed for an IFR reactor to produce enough surplus plutonium to start up another IFR reactor.  Which raises the question, where will the first commercial IFR reactors get their start-up plutonium?  Although it’s a natural element like uranium, plutonium has no mineable sources.

Bit LWRs have left a large amount of radioactive spent fuel containing plutonium that’s waiting to be buried in some tomb like Yucca Mountain NV for hundreds of thousands of years.  And what’s toxic waste to the LWR is potential fuel to the IFR.  With the addition of a facility to reduce oxide fuel to metal, pyroprocessing can reprocess it and save the US government hundreds of million dollars a year in waste handling costs.

Counting both the uranium that is “depleted” by stripping it of the U-235 that enriches LWR fuel and the fuel itself, LWRs use only one percent of the uranium they mine.  IFR, by contrast, keeps reprocessing its fuel until all of the longest-lasting radioactive elements including plutonium are used up, leaving a much smaller amount of much less toxic waste that needs to be sequestered for only 300 years.  And since depleted uranium is still fertile, IFR can use it, too.

While uranium resources are plentiful, they’re not unlimited.  But IFR extracts a hundred times more energy out of uranium than LWRs.  If IFR reactors supplied all of the world’s electricity needs, uranium would last as long as the planet.  In this sense IFR is as “renewable” an energy source as solar, wind, water and geothermal power.

The economics of IFR as a base load power producer have yet to be established.  But given the intermittence and geographic limitations of these alternative non-carbon energy sources, and the high cost of LWR waste, IFR should be very competitive.  And compared to fossil fuel power, if the negative externalities of their greenhouse gases and toxic emissions are properly accounted for, IFR should be like Secretariat at the Belmont in 1973—a runaway winner.

IFR generates power safely and efficiently and is the key to climate stabilization.  The problem is political: how do we get it back on track?