Myth VIII – Yes, you’ve highlighted several problems but you see once we get these new fast reactors working all these problems will be solved

If there’s one thing that constantly worries me (if not scares me) about the nuclear industry and its cheerleaders, its they’re undying enthusiasm for (so-called) fast “breeder” reactors (or their stable mate the fast neutron reactor). Anyone with half a brain, who knows the sordid history of these boondoggles (part III here), would have to conclude that they represent a series of failed white elephants – and would generally try to change the subject when anyone brought the matter up.

These “breeder” reactors have been under development for that last 50 years and you will struggle to find an example that has not run vastly over budget, proven to be unreliable (off more often than its on) or suffered a string of serious accidents. Indeed the majority of these plants tick all of the previous boxes and yet despite 60 years of research and tens of billions of dollars worth of money spend on them, they still count as experimental in every sense of the word.

The most recently built Monju in Japan is a classic example. It has already suffered 2 coolant leaks and fires, the last of which forced it off-line for several years. It cost a staggering $ 5.9 Billion and took 10 years to complete, despite its tiny 280 MW output (that’s about $21,000 per installed kW! 3 times the cost of PV at the time of its installation, 7 times the cost at current market prices!). It has, like most Fast Reactors, spend more of its life off than on and been subject to repeated modifications and changes, not least due to those leaks of radioactive coolant.                                                          

The problem with Fast-breeders reactors (FBR’s) is that they basically try to do several things at once that are very technically challenging. The high heat flows and operating temperatures required by fast reactors usually means the use of liquid metal coolants like Sodium. Which aside from the technical difficulty of it being a liquid metal (i.e has to be kept circulating and above its 98’C melting point at all times – unless you want to turn the reactor into a solid block of metal!) there’s also the fact that sodium catches fire if exposed to air and burns vigoursly in the presence of water (where it will also begin to generate hydrogen risking an explosion). This latter point means the heat exchangers, where the sodium transfers its heat to water to make steam, are often a major stumbling block as they tend to be quite complex and maintenance hungry. The lifetime load factor of the French Superphenix Fast Breeder was just 7.79% with the Dounreay FBR managing a slightly better 10% (see chapter 10, here) . Heat exchanger problems played a large role in this poor performance in both cases.

The high neutron flux of a fast reactor core also creates problems, as these neutrons bombard the reactors structural elements with intense doses of radiation. Eventually parts of the reactor itself become radioactive and undergo transmutation themselves, causing them to loose their structural strength or suffer a degradation in their physical properties. This would be bad enough it weren’t for the very high operating temperatures fast reactors must operate at, which often requires special high temperature alloys to survive such temperatures and pressures, not to mention corrosive attack by the liquid metal coolant. These factors means huge margins of safety need to be factored into an FBR design and many parts need to be replaced at regular intervals.

Obviously weighting all these factors up and building a fast reactor capable of operating reliably over a lengthy service life is quite challenging, even today. Needless to say its also expensive and there’s no reason to doubt that any of this will change at any time in the near future.

About daryan12

Engineer, expertise: Energy, Sustainablity, Computer Aided Engineering, Renewables technology
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8 Responses to Myth VIII – Yes, you’ve highlighted several problems but you see once we get these new fast reactors working all these problems will be solved

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