Figure 1. Clunky but instructive model of the ABWR. The feedwater is pumped into the RPV(Reactor Pressure Vessel) through the blue pipes, then flows down the outside annulus of the RPV, then up through the fuel elements in the center, boiling in the process. The steam is extracted from the top of the RPV, and flows out the red pipes to the turbine hall. It's a simple process, almost magical.
In 2013, GE-Hitachi (GEH) began the process of getting their 1350 MW Advanced Boiling Water Reactor (ABWR) licensed by the UK Office of Nuclear Regulation (ONR). This was in anticipation of building two ABWR's at the Wylfa site in Wales. Four ABWR's were already operating in Japan.
Requirement 73 of the IAEA's Safety of Nuclear Power Plants:Design mandates the plants "to control gaseous radioactive releases to the environment below the authorized limits on discharges and to keep them as low as reasonably achievable",\cite{iaea-2016a}[p 53] The ONR in implementing ALARA requires HEPA filters on all HVAC vents including the turbine building.1 The Japanese required HEPA filters only on the radioactive waste building. The other buildings were allowed medium efficiency filters. The ONR also required Bag In/Bag Out protection for the filter change outs.2
It turned out that complying with the UK rules required a fairly complete redesign of the ABWR HVAC system including the ducting. This in turn meant reanalyzes for all the impacted spaces. To avoid this, GEH went to great pains to show that the changes would reduce the Most Exposed Person(MEP) dose from the vent releases from 2.2 to 2.1 microsieverts per year. 0.1 microsieverts is approximately the dose that a human gets from eating a banana. The ONR did not dispute the calculation, but was unmoved. ALARA required the reduction.
In defense of the ONR, I don't think they had much choice. Other designs had complied with their requirement. The requirement was obviously reasonably achievable. If the ONR had disowned ALARA, those vendors would have a legitimate claim of favortism. The legal implications must have been frightening.
Much more fundamentally, if we start allowing the cost of a requirement to be a factor, the whole regulatory apparatus starts to fall apart. GEH's analysis showed that the UK vent requirement obviously reduces societal welfare. The cost of the UK vent requirement vastly outweighed the benefit, avoiding a banana dose for a hypothetical person who exists only as a bounding case.
The vent requirement should be changed to simply require the HVAC system to keep the Most Exposed Person dose rate profile to less than a legally acceptable cancer incidence level, say 10 in a million, using a reasonably realistic radiation harm model. But if we start applying that test to vents, we would need to do the same to all our requirements. That would put us on the slippery slope back to should-cost nuclear.
As it turned out, GEH finally got the UK version of the ABWR approved in 2019; but the ABWR’s at Wylfa were never built. In 2020, GEH backed out citing "financial reasons". The UK government would not offer GEH the Regulated Asset Base subsidy it wanted. Regulated Asset Base(RAB) is the new name for the good old American regulated monopoly, in which the more money the utility spends, the more money the investors make.
GEH had seen all it needed to see of UK's independent regulatory agency. Under RAB, the ratepayer bears all the costs of regulatory changes and uncertainty. Regulators are happy. Investors are happy. And the ratepayers are screwed. The Labour government has recently revived the RAB idea. That's how Labour represents the common man.
HEPA stands for High Efficiency Particulate Air. This gibberish means the filter will capture 99.97% of 0.3 micron particles.
Bag In/Bag Out was developed for labs handling infectious micro-organisms. Think Yuhan. It involves a complicated bagging system, which, if done properly, isolates a contaminated filter from the environment during filter change outs. But for nuclear the bag only protects from alpha particles and electrons. It has nil impact on photon dose. If the workers are wearing bunny suits and respirators, they are already protected from alphas and electrons. The extra change out time required by Bag In/Bag Out increased the worker photon dose.
Outstanding as always, thank you. One minor quibble though. The Regulated Asset Base model was introduced by the previous Conservative government a couple of years after Wylfa fell through.
You are of course right that the new Labour government has adopted it without demur and it is the funding model for the second major reactor being built at Sizewell C.
The first one, Hinkley Point C, was funded by EDF and the government. Both are eyewateringly expensive at c. $14m per MW, despite Kepco apparently being around $2.5m per MW.
Rolls Royce are the preferred bidder for a fleet of SMRs, coming in at a chunky 470MW, but they're FOAK so it will be at least 10 years to first completion.
The existing fleet (c. 5GW)are due to be closed by 2030, with numerous extensions already, with one exception at Sizewell B. But the graph is pointing down not up at the moment, despite all the recent hype.
When you get in the weeds of everything the ONR has done, it all sounds superficially reasonable. It's only when your step back and look at the whole package that you can see how ridiculous the multiple layers are.
Anyway, more power to your elbow and thanks for all your insights.
One thing LNT'ers feel comfortable with is using collective dose. The ICRP warns people against using it for risk assessment since it leads to alarmist predictions. However, the ICRP is OK to use it for risk comparison.
In the ABWR example, the dose to the most highly exposed person (usually someone who stands by the fence all year round, and in the location with highest dose) is 0.1 micro-Gy. The collective dose to people living in their homes is probably less than 1 micro-Gy from the HEPA. Compare this to the collective dose LNT considers to cause one fatal cancer, which is 20-50 Gy.
We need the government to change the mandate for the regulator. In the long term we would prefer a new dose-response model (SNT). In the short term the regulator must be forced to compare the societal cost of any requirement to the expected results of a release given its collective dose, probability, and the LNT estimate of harm (20-50 Gy required for a single fatal cancer).
I spent 4.5 hours on the NRC town-hall mtg on LNT just a few weeks ago. I can see It will be a steep climb to replace LNT with a better dose response model. Right now politicians hear that all of their constituents may get a lethal dose from something like a LLW site. That is horrible. Tell them that the most conservative model possible predicts 0.0001 of a single fatal cancer. That is obviously zero.