Here’s a sound principle: When writing opinion pieces that criticise internationally renowned scientists, use the best possible information. Especially when the subject is energy, and the object of your criticism sits on the panel for the equivalent of the Nobel Prize for energy: the Global Energy Prize.
When Noel Wauchope criticised Barry Brook’s position on Integral Fast Reactor (IFR) technology (Answering Barry Brook on Australia's nuclear power future 12 June 2012), she didn’t adhere to this principle. While fast reactors are a general suite of technologies, the IFR is quite specific. Just a few months ago, the lead designers of this system, Charles E. Till and Yoon Il Chang from Argonne National Laboratory, published a comprehensive work for the non-specialist called Plentiful Energy. This book explains what the IFR is, how it works, how it was developed, and the host of advantages it brings. It makes it clear why the IFR design is special among fast reactors.
Wauchope’s piece is a litany of confusions and avoidable factual errors. This is dangerous, because bad information risks killing momentum for a technology that will be critical to solving a host of hitherto intractable problems.
Before getting into the details of the IFR, let’s start with a few points of fact. Nuclear energy, in all of its forms, currently supplies approximately 14% of global electricity demand. It is a mature energy source, with over 14,500 cumulative reactor-years of commercial operation in 32 countries. Numerous independent life-cycle greenhouse gas emissions analyses have been done on nuclear energy, from mining through to decommissioning. The verdict? The carbon footprint of nuclear energy is about the same as wind energy, and substantially less than solar photovoltaics, solar thermal and biopower (1). And of course, much, much less than coal. With the development of next-generation technologies, nuclear fission is an inexhaustible source of energy.
Enter the IFR. Developed at Argonne National Laboratory and demonstrated at the Argonne West site in Idaho, USA, from 1984to 1994,this technology was developed specifically to improve the safety, economy, fuel-fabrication process, fuel supply, and proliferation challenges of currently commercial reactors. The IFR is also able to use current stockpiles of nuclear “waste” and even depleted uranium as fuel, increasing the fuel efficiency of the nuclear cycle 150-fold. In fact, we have already mined enough uranium to power the world for hundreds of years using this technology.
Too good to be true? Not according to GE-Hitachi, which is proposing to build a commercial-scale (311 MW) version of the IFR called the Power Reactor Innovative Small Module(PRISM) in the UK right now, to deal with unwanted stockpiles of separated plutonium.
But Wauchope raised the spectre of many serious sounding problems. Is she on the money? She made much of the sodium coolant used in the IFR. True, liquid sodium reacts strongly with air and water. You might stop at the basic characteristic of “reacts with air and water”. Thank goodness the designers thought a bit harder, and relied on decades of hard-won engineering know-how.
Sodium’s advantages flow through the whole proposition. It is liquid from just under 100°C to beyond normal operating temperatures. So unlike water-cooled reactors, the reactor vessel does not need to be pressurised. This greatly improves safety, and lowers cost by simplifying the overall design and material requirements.
The lack of pressure also permits a roomier “pool and loop” configuration for the coolant. The primary sodium coolant sits in a pool around the reactor, in an inert argon-atmosphere room. A double-walled heat exchanger loop containing non-radioactive sodium flows through the primary coolant in the reactor vessel to absorb its heat, then is routed out of the reactor building to a nearby but separate structure housing the steam generator and turbine. So neither water nor air is ever in proximity to the reactor and its primary sodium pool. The Experimental Breeder Reactor II (EBR-II), the prototype fast reactor built at Argonne National Laboratory, used this cooling process and ran flawlessly for 30 years. How?
The unpressured sodium does not corrode either the stainless steel reactor vessel or the pipes for the coolant loop. Any flaw in the metal would cause a mere trickling leak, detected by sensors, into an inert environment (rather than flashing instantly to steam, as would occur in pipe breaks in highly pressurised water-cooled reactors). Sodium doesn’t react with the specially developed metal alloy fuel either. So if the fuel cladding is damaged somehow, no problem. There will be no blockages from build up of corrosion in the fuel. The test for this eventuality is called “Run Beyond Cladding Breach”. They ran the test at Argonne Lab, and after 223 days of varying power levels, the fuel was virtually unchanged.
It doesn’t stop there. The sodium coolant has a thermal conductivity far in excess of water. In the event of an emergency shutdown, all residual decay heat is removed completely passively, with no external power required. It is, as Wauchope concedes, as good as meltdown-proof. Emergency shutdown will also occur without any operator intervention. In the event of excess heat from an unexpected power build-up, the metal fuel expands. This causes neutron leakage that renders the chain reaction unsustainable, and once it powers down due to the laws of physics the sodium coolant passively takes it from there. This was tested by initiating the processes of the Three Mile Island and Chernobyl accidents. Nothing happened except quiet shut down. Just as predicted.
As far as Wauchope’s “volatile fission products evaporate from the molten salt”, this makes absolutely no sense since IFRs have no molten salt. She was confused about two very different nuclear reactor technologies. Gaseous fission products are produced when the metal fuel is irradiated, however. The pockets of gas expand in the metal fuel and eventually leaks to a sealed empty reservoir above the fuel pins called the plenum. Just to quote from the designers: “the plenum above the fuel column is sized so the fission gas pressures on the cladding are kept to reasonable levels”.