Why Hunterston B Nuclear Power
Station should not be Restarted
Presentation made to Paul Wheelhouse, Minister for Energy Connectivity and the Islands
Dr Ian
Fairlie and Dr David Toke
Feb
4 2019
Abstract
In our view, Hunterston B nuclear
power station needs to be closed for safety reasons, but this should not be lamented because
a)
there
is presently a surplus of electricity generation in Scotland, and more is in
the pipeline. Indeed there is so much renewable energy capacity being built
that Scottish electricity exports to England and Wales will continue to
increase,
b)
there
will be no significant job losses in Scotland, and
c)
Scottish
energy security will be improved as Hunterston B’s operation results in many
Scottish windfarms being turned off at certain times and periods.
The
two reactors (460 MW net each) at Hunterston B nuclear power station situated
near Ardrossan are 43 years old - the oldest reactors in Europe. Their
operating lifetimes have twice been extended at the request of the operators
EDF Energy - a UK subsidiary of EDF in France, and they are now scheduled to
close down for good in 2023.
They
have been off-line since March 2018 (R3) and October 2018 (R4) for safety
reasons. The decision as to whether these reactors will ever be allowed to
restart is for the Office of Nuclear Regulation (ONR). It is currently awaiting
a revised safety case for this from EDF Energy.
In
recent months, EDF Energy, the trade union GMB, some politicians and newspaper
editors have been pressing for the station to be allowed to restart. Quite a
few incorrect statements and
misrepresentations have been made: this briefing sets out to put the record
straight.
Need for Electricity?
Scotland
has a surplus of electricity generating capacity, and this surplus will
increase over the next decade regardless of whether Hunterston B, and even
Torness, were both to close. According to the Scottish Government (SG), renewable
electricity supplied 70 per cent of Scottish electricity consumption in 2017
and will supply around 87% in 2020.
On
top of this, sufficient wind power has already been given planning consent to
supply the equivalent of a further two-thirds of Scottish electricity consumption.
Much of this electricity will be sold to England and Wales. As renewable energy
costs continue to plummet, even more wind supplies will be forthcoming and
Scotland will become the main source of low carbon energy for the whole of the
UK, helping to meet both UK and SG targets for the reduction of greenhouse gas
emissions.
Moreover,
closing down Hunterston B will allow more wind power from Scottish windfarms to be supplied to the grid, thus improving
Scottish energy balance and security. The grid is currently overloaded partly
because the Scottish nuclear power stations (Hunterston B and Torness) will not/cannot
turn down their power to accommodate renewable energy, so windfarms have to be
switched off regularly. This wastes their capacity and causes newpaper controversies
over so-called ‘constraint payments’ paid to windfarm operators to compensate
their lost income.
It
would be ironic if Hunterston B were to be allowed to return to service,
because the electricity it produces is considerably more expensive than that
produced by the renewables. This is because the cost of nuclear fuel is high,
whereas fuel cost of solar and wind is effectively zero.
Jobs
Some
exaggerated claims have been made by a trade union as to the ‘thousands’ of
jobs that would be lost if Hunterston B were closed. The reality is that about
370 employees work there, and none would lose their jobs for at least two to three
years after closure. The reason is that
when a reactor is closed, radioactive decay heat is still produced in the
nuclear fuel – it cannot be switched off. This means the cooling circuits have
to be operated day and night for at least two to three years until the radioactive
decay rates have declined significantly. After that, the many decommissioning
jobs will employ most of the existing workers, just as occurred at the Dounreay
nuclear site in North Scotland. In fact, it is likely there will be more
decommissioning jobs at Hunterston B than there were operating jobs.
Safety
The most important matter is, of course, safety. Would it be
safe to turn the Hunterston B reactors back on?
In our view, the answer is, on balance, no. The vital issue is that the current
unstable state of the graphite moderator cores increases the possibility of a major
nuclear accident. Although the probability of such an accident remains low, the
consequences could be so severe, ie the radioactive contamination and
evacuation of both Glasgow and Edinburgh, that the risk should not be taken.
The main problem is what is called keyway root-cracking in
the graphite moderator cores of the reactors. These cores consist of about 3,100
graphite barrels stacked ~10 m high by ~10 m wide and ~10 m long. These are
normally locked together rather like a three dimensional jigsaw, by means of
shims inserted into keyway slots. The difficult problem is that over 100
barrels have been observed to be split from top to bottom because of cracks in
the keyway slots. And that is with only 28% of the barrels being examined. EDF
has estimated that about 370 barrels are cracked, ie about 12% of the total
number.
This is a serious matter because if an untoward incident
were to occur – for example an earth tremor, gas
excursion, steam surge, sudden outage, or sudden depressurisation, the barrels could become dislodged and/or
misaligned. According to John Large, the late independent nuclear engineer, this could in turn result in the following happening:
(a)
control rods
could be blocked from dropping into the reactor core by the resulting
displaced graphite barrels. (Only 12 of the 81 control rods in R3 are
articulated).
(b)
coolant gas channels could become partly blocked by misaligned barrels, and
(c)
fuel assemblies
could become stuck and not be able to be withdrawn. Large explicitly mentioned
this in the BBC programme “Costing the Earth” at the end of 2017. https://www.bbc.co.uk/programmes/b080t880
These
events could in turn lead to large emissions of radioactive gases. Further, if
hot spots were to occur and if nuclear fuel were to react with the graphite
moderator they could lead to explosions inside the reactor core. In the very
worst case,
the hot graphite core could become exposed to air and ignite
leading to radioactive contamination of large areas of central Scotland,
including the metropolitan areas of Glasgow and Edinburgh.
This
does not bear thinking about. In our view, it should not be allowed to occur.
Research
In
more detail, the decision as to whether to allow the Hunterston B reactors to
restart is a matter for the ONR to decide. This is a difficult and complex decision
as Probabilistic Risk Analyses are necessary and these require much research
effort and are time-consuming. Hundreds
of computer programs and dozens of researchers are involved.
Barry
Marsden, Professor of nuclear graphite technology at the University of
Manchester has stated “The thing which will close (these reactors) down in the
end will be the cost of ensuring safety. It is possible to make a safety case
for a significant amount of cracked bricks but it takes time and costs money.” https://uk.reuters.com/article/uk-britain-nuclear-edf-analysis/cracks-in-british-nuclear-reactor-ring-power-alarm-bells-idUKKBN1IA2P0
But even this may be an optimistic view. Under the
ONR’s rules (see a,b,c below), in the case of high consequence, low frequency events of beyond design basis, operators
of nuclear power stations are required to conduct Probabilistic Safety Analyses
(PSAs). These are expected to look hard at low
frequency events. In judging the adequacy of safety cases, inspectors are
required to especially consider the effects of very low frequency events, eg
seismic events.
At the end of the day, EDF’s forthcoming
revised safety case will have to demonstrate to ONR that its computer models
indicate there is a less than one in ten million chance (ie 1 in 10,000,000 or
10-7) of such an accident occurring given its estimated number of
graphite barrel cracks. Will EDF’s
models be able to show this? One needs to keep in mind that EDF’s computer
models so far have not accurately predicted the numbers and locations of the
cracked barrels at reactor 3.
And if the EDF models were to show this and if
the ONR were to accept it, should the Scottish public necessarily accept it?
Given that the reactors are very old, well past their sell-by dates, are not
needed, and that closure would not threaten jobs, the public may well ask why
they should be exposed to such an existential threat even if the chances of it
occurring were very low.
Put another way, since the station is to
close anyway in 2023, do we need to run the risk?
References
ONR (Office for
Nuclear Regulation) (2018a) Safety Systems, Nuclear Safety Technical Assessment Guide,
NS-TAST-GD-003 Revision 8, Bootle: ONR, http://www.onr.org.uk/operational/tech_asst_guides/ns-tast-gd-003.pdf
ONR (2018b) Guidance on the
Demonstration of ALARP (As Low As Reasonably Practicable), Technical Advice
Guidance 5, (NS-TAST-GD-005 Revision 9) Bootle: ONR, http://www.onr.org.uk/operational/tech_asst_guides/ns-tast-gd-005.pdf
ONR (2018c) ONR Guide External Hazards, Technical Advice Guidance 13, NS-TAST-GD-013 Revision 7, Bootle: ONRhttp://www.onr.org.uk/operational/tech_asst_guides/ns-tast-gd-013.pdf
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