(December 1, 2000) BNFL have dismissed rumors that they are planning to use 1,000 workers in a desperate attempt to repair faulty boiler welds inside both Wylfa reactors. Serious doubts remain about how else they could properly repair the suspect welds and yet keep the dose to each worker below the legal dose limits.
(539.5224) WANA - Taking on temporary staff (usually students) to carry out high radiation exposure maintenance tasks in American reactors enables regular staff to keep their own radiation exposure down. The casual workers are known as 'glowboys' because of their cavalier attitude to radiation exposure.
Ultrasonic techniques have revealed defects in all 64 welds where pipes penetrate the Reactor Pressure Vessel. Having decided that 14 of the suspect superheater welds required 'bracing' to limit the amount of movement in the event of a weld failure, BNFL have thrown their own plans back into the melting pot.
A recent submission to the Nuclear Installation Inspectorate has put forward three alternatives for tackling the problem. The first solution is to re-do the welds. However for this, BNFL would need to employ hundreds of skilled welders, and it is not clear where they could find them. The second solution is to apply external bracing to the pipes where they enter the reactor pressure vessel. The third solution is to apply internal bracing to the pipes on the inside of the concrete reactor pressure vessel. Bracing would not stop weld bursts from happening, but it is supposed to stop a cascade of knock-on weld bursts in adjoining pipe penetrations.
The NII were said to be surprised that BNFL have yet to decide how to tackle the faulty welds that have put the Wylfa reactors out of action since April.
The 'bracing' that has been talked about for months is intended to prevent superheater pipes 'popping out' of the reactor pressure vessels in the event of a weld burst.
Such a weld burst would be likely to affect other vulnerable welds leading to further weld bursts. The consequences of steam being injected into the reactor core at twice the pressure of the carbon dioxide coolant go way beyond popping the superheater steam pipes out of the reactor. The pressure relief valves cannot cope with more than one pipe burst.
A pressure shock would be created within the reactor by the differential between the steam pressure at the top and the coolant pressure at the base of the reactor. This would put great stress on the reactor core, exerting downward loading on the graphite blocks and their steel support structure. Given that the volume of the graphite has been reduced by radiolytic corrosion, in the worst affected areas by up to 45%, failure of the graphite core is likely.
Displacement of graphite, let alone collapse, could block the cooling channels causing overheating and preventing all the control rods from shutting the reactor down, which could eventually lead to a meltdown. Even a single channel fire and melt-down would be beyond the ability of the operators to control.
A meltdown at Wylfa would burn through the steel lining to the reactor pressure vessel into the concrete, which contains enough oxygen to sustain the combustion of the uranium fuel.
John Large Calls 'Time' on Wylfa
A public meeting at Llangefni on Oct 27th heard Dr John Large, the independent nuclear expert call for the immediate closure and decommissioning of Wylfa nuclear power station. Large warned of the effects of ageing on Wylfa, designed to last 20 years, and which BNFL want to keep going until it is 45 or 50 years old. The BNFL proposals for reinforcing the faulty superheater welds were described as impractical, and would not stop the problem of weld bursts spreading. Dylan Morgan of People Against Wylfa B (PAWB) described Wylfa as 'a disaster waiting to happen'.
A BNFL spokesman commented (to the Daily Post): "These people are not willing to discuss, listen or learn the true situation with an open mind. They are totally anti-nuclear."
The next move in the campaign to prevent Wylfa from restarting is likely to be the launch of a detailed analysis by John Large of the faults in the old Magnox stations.
One of the critical concerns that is emerging from this work is that, in the event of welds bursting, steam pressure in Oldbury and Wylfa Magnox stations might be sufficient to cause the failure of the three metre thick post-tensioned concrete reactor pressure vessel.
Greenpeace, who have commissioned this report, are to brief the National Assembly for Wales on the dangers that now face both north and south Wales from Wylfa and Oldbury. Trawsfynydd closed within a year of John Large's warnings in 1992. Hinkley Point A closed within a year of his intervention in 1999.
Public puts pressure on regulators
The NII site inspectors at both Oldbury and Wylfa are reported to have been inundated with letters from concerned members of the public. The Oldbury inspector has reported to the local community liaison committee that this is having a bad effect on his ability to inspect the station and therefore on nuclear safety.
Nuclear Inspectors like other industrial regulators stand between the public and the industry that they regulate. At Oldbury a member of the local liaison committee assured the meeting that he had heard not one expression of concern from local residents. This confirms what we have long suspected, these committees are unrepresentative and are stuffed with people who unquestioningly accept reassurances from BNFL. There are acknowledged dangers in regulators getting too close to the industry that they regulate. One antidote to this would be for the NII to engage far more closely with the fears and anxieties of the public.
It is difficult to 'learn the true situation' when the documents upon which public safety rest (the 'safety case') are kept secret. That secrecy may reflect safety, or conceal dangerous assumptions about the continuing safety of operating aging Magnox stations.
One restricted document, to which access has been gained, has given us a glimpse of 'the true situation'. This refers to predictions of graphite 'failure' before Oldbury and Wylfa are 35 years old. The question arises: how long before? Oldbury is aged 32 years and Wylfa is just under 30 years old.
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