Firstly let’s establish some criteria with which to judge the relevant “fit for purpose” strengths of the IV generation reactors we will review.
- Cost, Any alternative to the LWR must be cheaper. Nuclear energy is already more expensive than renewables at current prices (I sumarise these factors in a past article here), nevermind future prices. So if nuclear has a future its overall costs must be lower. Its possible, as I will show, than some of these reactors proposed will have higher capital costs than existing nuclear power, but if the overall cost picture is better (i.e construction, operation, decommissioning, waste storage) we still get to tick this box. Even if the reactors we review come out more expensive than the LWR there is still some merit in these designs if they can tick a couple of these other boxes below. We’ll be paying more, but getting a better quality product for our money. Obviously, though more expensive reactors means a good deal less of them…or possibly none depending on the pace of renewables roll out.
- Safety, As I said before, the LWR has numerous inherent safety flaws. The number one barrier to public acceptance of nuclear energy is safety. Argue all you want about it, but the LWR design amounts to an elaborate attempt at trying to make a silk purse out of a sow’s ear. Our preference would therefore be for a reactor that is not just safer, but inherently safer. Not least because this might well feed into our 1st criteria above – lower costs…at least that’s the theory! An inherently safer reactor for example won’t need that vastly over designed concrete containment dome. Much of the cost overruns and time delays to new nuclear build has revolved around getting these containment domes built.
- Fuel efficiency, the global stockpiles of fissile material are limited. We could probably maintain the existing stock of reactors going for 50-80 years or so, but given that they only represent 5% of global energy output, that leaves us with the question of where does the other 95% of our energy come from and the obvious question as to whether nuclear energy is just more trouble than its worth. Better fuel economy would mean more reactors and greater market penetration. One promising idea is to raise the working temperatures of the reactors to avail of the Brayton cycle (giving our reactors a thermal efficiency of 50-60% v’s the 30-40% achieved via the Rankine cycle). Better thermal efficiency and higher operating temperatures means reduced fuel requirement and higher rates of fuel burn-up (and thus reduced nuclear waste).
- Thorium, there is much debate about Thorium as a potential nuclear fuel. The experts at IEER seem to pour cold water over it (see here) but a rebutal to their comments can be found here. I’m an engineer not a physicist, so I’ll be glossing over this one by and large, but yes it would be handy if these new nuclear plants could make use of Thorium, but I’m not going to slap it down as an ironclad requirement that they can, as its possible (if the IEER are correct) that if I do I’d be setting a criteria that’s impossible to meet, which would be grossly unfair.
- Reduced nuclear waste, the elephant in the room for nuclear energy is the ever growing waste mountain. We’ve yet to come up with a comprehensive solution to nuclear waste and until we do the argument of environmentalists is “if you’re in a hole, stop digging!” While again, I’m going to gloss over this one, but needless to say if the reactors we now review can generate a lot less waste that would make them a much more attractive proposition to the LWR. Obviously, if the opposite proves to be true, that’s a potential black mark against them.
- Scalability, when embarking on this program of “megatron” LWR’s the industry was probably hoping the greater economies of scale provided by building big would allow greater market penetration. In practice, the opposite has proven true. These large LWR’s are simply too big and unwieldy for the electricity grid of most of the world’s smaller country to utilise them. Only a handful of larger nations can use these mega-LWR’s, and even then for only a small portion of their energy needs. Smaller reactors, might therefore allow greater market penetration and larger use. This also feeds into the next criteria…..
- ……Modular design & Mass production, there is another way of lowering costs other than building big – mass production. If we could run the reactors off a production line then the costs would come down and the pace of roll out would accelerate. The whole reason why renewable are now chafing at nuclear’s heels is due to the fact that they are being mass produced in ever growing quantities. If nuclear energy is to remain competitive it must do the same. But mass production, as I will show in part 10 of this article often requires some degree of “dumbing down” of our design so again, I’m not going to make this an ironclad requirement, but something that would be “handy”.
If we can prove that any of the reactors we examine can tick all (or most) of these boxes then maybe the nuclear industry has some future, beyond its current walking dead routine.
Before we turn our attention to the reactor design’s I’m going to briefly introduce the concept of failure mode and effects analysis
A brief note on FMEA
I will be occasionally making reference to the engineering technique known as “failure mode and effects analysis” or FMEA. This is an engineering management technique by which potential “failure modes” in a system are identified, prioritised and corrected. http://en.wikipedia.org/wiki/Failure_mode_and_effects_analysis
The process breaks down into three phases, firstly identify any possible failure modes in a component and classify the probability of such a failures likely occurrence. Secondly, what are the likely consequences of such a failure or hazard? Minor? Serious? Catastrophic? Finally we ask, what is the likelihood of the fault being detected? A fault that is easily detectable is less of a threat to life and limb than a defect that is harder, or indeed impossible to diagnose, at least until it fails.
FMEA, originally developed by the Aviation Industry in the 1950’s, has revolutionised the standards of safety and quality control in many industries. The high safety standards we now see in the aviation industry are largely a consequence of FMEA. The auto industry, despite the fact that the number of cars on our roads is increasing, that motorway speeds are rising, that the age and experience of drivers is falling, indeed that ever indicator that suggests that accidents and deaths on our road should be going up, instead road death rates are going down. This is largely thanks to the benefits of FMEA.
Unfortunately the nuclear industry has a bit of torrid relationship with FMEA. After a series of serious near misses in the 1970’s at nuclear plants around the US (in a one year period alone the AEC recorded 3,333 incidents in the US, 98 of these being rated as “serious”) the newly formed NRC commissioned the 1975 Rasmussen Report into nuclear safety. Using FMEA the Rasmussen engineers identified at least 78 ways that relatively minor operator errors could lead to a core meltdown scenario. One of these very meltdown scenarios was eerily similar to the sequence of events that led to the Three Mile Island accident 4 years later. They also calculated the probability of a catastrophic core meltdown as being in the order of 1:20,000 per core year, at a time when the nuclear industry claimed it was more like 1:10 Billion. It was this application of FMEA since TMI that has led to the current LWR “death spiral” of ever increasing new design iterations and rising costs.
So while some nuclear scientists will inevitably groan at its mention, the fact is everything we build these days from fridge freezers to children’s toys has to go through the FMEA firewall and the general public will not accept nuclear power if these new reactors can’t stand up to appropriate safety scrutiny.
Before exploring these alternative design concepts, we will undertake abrief discussion of various high temperature materials.