Experts warn Glasgow and Edinburgh could be contaminated with radiation if EDF decide to reopen two nuclear reactors with 400 cracks in the core walls
- The cracks were found in March in reactor 3 at Hunterston B in North Ayrshire
- Almost 400 cracks were found, leading to the closure of the plant in October
- EDF Energy says it wants to reactivate the power plant with a limit of 700 cracks
- Two nuclear experts are now warning that the reactors should not be reopened
Nuclear experts have warned that two Scottish reactors should not be reopened because of cracks that could force both Glasgow and Edinburgh to be evacuated.
Earlier this year, worrying footage of almost 400 cracks 2mm-wide at Hunterston B in North Ayrshire were revealed.
Owners EDF Energy and trade union GMB want the reactors put back into service, after they were closed in October 2018.
But Dr Ian Fairlie, an independent consultant on radioactivity in the environment, and Dr David Toke, of the University of Aberdeen, are warning against attempts to reopen the reactors.
Although the probability of a meltdown is still low, both Glasgow and Edinburgh would need to be entirely evacuated if one was to occur.
However, both Dr Fairlie and Dr Toke have warned against the move and, when discussing the cracks in the reactors, said: ‘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.
‘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.’
The reactor was forced to shut the reactor after experts found the hairline fractures were growing faster than expected, in about one in every 10 bricks in a reactor core.
The limit for the latest period of operation was 350 cracks but an inspection found that allowance had been exceeded.
Now, EDF energy plans to ask the regulator for permission to restart with a new operational limit of up to 700 cracks.
One of the cracks found in the Hunterston B reactor which measure up to 2mm wide. Around 370 hairline fractures have been spotted at the site which has not produced any electricity since the flaw was uncovered
EDF energy had released the footage as evidence of their extensive efforts to fix the problem.
It revealed plans to restart Hunterston B after first proving that it is safe to the Office of Nuclear Regulation (ONR).
The rest of the site has remained below the upper safety threshold of 350 cracks and is still operational.
A video created by EDF Energy has revealed the site is undergoing strenuous tests in order to be passed fit for service.
It hopes to get the reactor back operational after more than 12 months offline.
A planned inspection of the graphite bricks that make up the core of reactor three in March last year uncovered new ‘keyway root cracks’.
The operational limit was 350 cracks but the inspection found this had been exceeded.
Cracks to the graphite blocks is known to occur but legislation is in place to ensure they do not threaten the structural integrity of the reactor.
EDF is now hoping to prove it is safe to use and would stand up to the most stringent tests and wants the ONR to increase the upper operational limit to 700 cracks.
Nuclear expert Professor Neil Hyatt from Sheffield University told BBC News: ‘The structural integrity of the graphite core has always been known to be the ultimate limiting factor to the lifetime of these reactors.
‘So, ultimately there may come a point in time where those reactors have to come offline and are not able to restart.’
The blocks form the vertical channels in the reactor and sit alongside the channels that control rods enter to limit the reaction.
Tests have taken place to ensure an earthquake would not stop the capabilities of the control rods.
EDF Energy said these have now grown to an average of 2mm wide.
The firm has released footage of the cracks, which was taken in 2017 and 2018.
Station director Colin Weir told BBC Scotland: ‘Nuclear safety is our overriding priority and reactor three has been off for the year so that we can do further inspections.
A video from EDF Energy revealed some of the cracks at the Hunterston B nuclear plant in Scotland. Around 400 hairline fractures have been spotted at the site which has not produced any electricity since the flaw was uncovered
The reactor (pictured) has not been operating since the cracks were discovered to be growing faster than expected
HOW DO NUCLEAR REACTORS WORK?
A nuclear reactor creates energy by splitting atoms of uranium.
The energy released from these atoms is then used to boil water.
This, in turn, drives a turbine.
A reactor core contains the uranium pellets and a 1000 megawatts (MWe) facility would have about 75 tonnes of enriched uranium.
Uranium-235 is bombarded with neutrons to split the atom, which then creates different elements or another isotope of Uranium.
Either way, it releases energy.
These often also undergo radioactive decay and a chain reaction is triggered – contributing to the net energy output.
Steam is produced, condensed and then recycled so the only waste products are often the radioactive compounds created from the fission.
Control rods can be added or removed from the reactor core to either increase or decrease the rate of reaction.
These are made of stable elements such as boron, silver, indium and cadmium that are capable of absorbing many neutrons without undergoing fission.
‘We’ve carried out one of our biggest ever inspection campaigns on reactor three, we’ve renewed our modelling, we’ve done experiments and tests and we’ve analysed all the data from this to produce our safety case that we will submit to the Office for Nuclear Regulation.
‘We have to demonstrate that the reactor will always shut down and that it will shut down in an extreme seismic event.’
Around 400 hairline fractures have been spotted at the site which has not produced any electricity since the flaw was uncovered.
EDF says it intends to prove the reactor can be shut down in all conditions and will then file to have it restarted.
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