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Des accidents nucléaires partout

Angleterre : Hartlepool : Système de refroidissement de secours défectueux




22 février 2011


Le 22 février 2011, lors d’un essai, une soupape ne s’est pas complètement ouverte. Trois pompes ont été déclarés indisponibles. Cet incident a montré une faille dans les systèmes de refroidissement de secours.

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The High Pressure Back Up Cooling System provides post trip cooling to the boilers in the event of loss of normal boiler feed water

The High Pressure Back Up Cooling System provides post trip cooling to the boilers in the event of loss of normal boiler feed water. The system has three diesel driven pumps that draw water from dedicated HPBUCS tanks through a common suction header. This suction header can be isolated by closing a valve in the event of damage to the dedicated tanks and feed lines to allow the pumps to be fed from the Reserve Feed Tanks (RFTs). Under normal operation, it is a requirement of the Technical Specifications that this valve is fully open.

On 22 February 2011 flow tests revealed that a valve was not fully open and therefore all three HPBUCS pumps were declared unavailable. This represents a reduction in the diversity of the cooling systems and the Technical Specifications require the reactors to be shut down within 4 hours.

In response to this event BEGL switched the feed supply to the RFTs within 20 minutes thus avoiding shutting down the reactors. The Valve was returned to the fully open position shortly afterwards.

BEGL has carried out a full and prompt investigation into this event and this has addressed the wider aspects of this event including the level of maintenance and subsequent testing on this valve and similar valves on other systems. BEGL is currently completing remedial actions to address the findings.

ONR has carried out its own investigation. Our preliminary conclusions are that the licensee’s investigation was thorough and that it has identified the root causes of this event and extended the findings to other systems that may have single point vulnerabilities. In addition BEGL has placed actions to ensure that valve indications are robust, that maintenance standards are adequate and return to service testing demonstrates that safety related plant will deliver its safety function. ONR is currently monitoring the Licensee’s progress on closing out the actions from the investigation

https://www.hse.gov.uk/nuclear/quarterly-stat/2011-1.htm


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