Stop Hinkley Press Release

16th May 2008

Hinkley 'scrammed' last week

One of the reactors at Hinkley 'B' was 'scrammed' by an automatic trip on Thursday 8th May, it emerged today. At the time British Energy said the reactor shut down had been due to an electronic problem on the conventional side and was not serious, refusing to give details. The news emerges after it was revealed Hinkley is missing its last-resort safety system.

But campaigners say this was just spin to say the problem wasn't serious. Although the problem turned out to be with a turbine and not the reactor itself, it would have impacted on nuclear safety. Moreover the rapid shut down itself may have damaged the ageing reactor.

If the reactor had not been automatically shut down its safety would have been in jeopardy through overheating. But on the other hand dumping huge volumes of heat during the 'scram' could have meant exposing the brittle boiler tubes to greater stress.

A turbine speed-limiter had failed meaning the turbine had to be stopped. Reactor turbines are essential to removing heat from the reactor which would quickly overheat without them so the reactor tripped automatically at that point. But the aged boiler tube system may have struggled to cope with the big changes in temperature while still under high pressure and may now have been further impaired after its eight month major repair work last year.

When asked about the shut-down today a British Energy press-officer initially said the reactor had been shut down manually but would not give any details. Shortly afterwards he called back to correct his message and say the reactor had tripped automatically when a turbine governor had failed. When put to him this had nuclear safety implications he said: "You have to make your own interpretation."

The reactor had been restarted on Tuesday. It was not clear whether an inquiry had been held with the nuclear regulators in this short space of time. Normally regulators would come from their Bootle headquarters to investigate a shut-down then examine its potential consequences. It would be too serious a matter for just the Site Inspector.

Last week it was also revealed that Hinkley has been operating without its last-line defence system, known as the boron beads system.

Jim Duffy spokesman for Stop Hinkley said: "This kind of spin gives the industry its deserved reputation for secrecy. This was ultimately a nuclear safety issue with public implications. What's more the corroded reactor may have been damaged by the shut-down but, with possible new defects, was started in a worryingly short time."

"Given the baffling absence of its last-resort shut-down system I can't see how anyone can justify running this dangerous power station."

Jim Duffy, Stop Hinkley. 07968 974805 

Note:

Hinkley 'B' graphite reactor core bricks are known to have 26-26% weight loss in the worst affected areas, with potential safety consequences through localised overheating leading to a nuclear fuel fire.

The control rod channels could also become obstructed making shut-down more difficult.

Boiler tubes within the reactor pressure vessel were found to be extensively corroded and cracked in September 2006 leading to an eight month outage for repairs to the brittle welds. Hinkley has operated at 60-70 % output since then with an expectation to return to 100% output last March. It still operates at 60-70 % output.

The Scottish Daily Mail revealed Hinkley has no tertiary safety system known as 'boron beads' found in other AGRs and possibly originally fitted at Hinkley and later removed. Other shut-down systems using nitrogen or water would fail if the reactor was losing pressure due to a leak.

 

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Note:

The term 'SCRAM' originally meant 'Safety Control Rod Axe Man' when early reactors had a rope cut by an axe in an emergency to allow the (single) control rod to fall into the reactor to shut it down. It now applies to automatic shut-downs with gravity control rods in nuclear reactors.


 

 

 

Click here for the Stop Hinkley Press Release on missing safety system, dated 9th May 2008:

 

 

 

 

 

 

 

Page Updated 16-May-2008