## 150 Years Is Not Enough

At a recent meeting on ‘Coastal Processes’ at Sizewell held at Snape Maltings on the of 29^{th} February Colin Taylor (Environment Manager (Marine), New Nuclear Build, EDF Energy) stated that they had 150 years of data for the coastal processes at Sizewell.

He also said that their ‘models’ can predicted what has happened in the past. I shall not go into this anymore in this blog although it was a bit disconcerting that he said that their models had lots of problems with storm surges and that ‘waves were a bit tricky’.

He did assure me that they were confident about the 1/10,000 flood risk – again he called this 10^{-5}pa risk when it is in fact 10^{-4}pa risk.

What is the probability that we would see a 10^{-4}pa event in 150 years. For details of how to work out this sort of problem see my previous post. So the probability of seeing this sort of event in 150 years is:

p_{150} = 1-(1-p_{yr})^{150}

This works out as a 1.5% chance of seeing such an event. So it is extremely unlikely that their 150 years of data would have covered such an event.

How many years of data would we need to have a reasonable probability of seeing such an event. Since Sizewell C (if built) will contain massive amounts of radioactive spent fuel (see here) we want to have quite a good chance of seeing such an event to test any model. Lets say a probability of 0.95 (95%). Let us call that probability p_{t}. Then rewriting the formula above

p_{t} = 1- (1-p_{yr})^{t}

where t is the period of time that we are looking for. So we rearrange the above equation:

(1-p_{t})=(1-p_{yr})^{t}

take the logs of both sides

ln(1-p_{t})=t ln(1-p_{yr})

t = ln(1-p_{t})/ln(1-p_{yr})

If we put the numbers in this means that we would need nearly 30,000 years of data to have a 95% probability of seeing a 10^{-4}pa event.

As pointed out by Colin Taylor the coast of the UK has changed quite considerably over that period. In fact 10,000 years ago the UK was connected to the continent via a land bridge. Incidentally that land bridge may have been destroyed by a massive tsunami^{1}.

I am sure that Colin Taylor and others would argue that having their models tested over such time periods is impossible and unreasonable. I agree it is impossible but considering the risks involved it is not unreasonable. The only conclusion is that there should not be a nuclear power plant at Sizewell.

^{1} Storegga Slide, Wikipedia (http://en.wikipedia.org/wiki/Storegga_Slide)

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