External corrosion affecting multiple systems on a power reactor

Print View Posted on: 17 January 2019

Event Date: 31 December 2018 Event Type: Power Reactor
Event Location: United Kingdom, DUNGENESS B INES Rating: 2 (Final)

In September 2018, as part of a regulatory intervention on external corrosion management, the UK nuclear safety regulator (Office for Nuclear Regulation (ONR)) issued a direction for Dungeness B nuclear power station to carry out a review and reassessment of safety addressing the corrosion of concealed systems that fulfil a safety function. Inspections carried out by the site nuclear licence holder (licensee) in response to this direction identified that seismic restraints, pipework and storage vessels associated with several systems providing a safety function were found to be corroded to an unacceptable condition. This condition would have been present whilst the reactor was at power, although, the affected systems were not called upon to perform their safety function.

Rectification of the degradation has now been undertaken whilst the units have been shut down for maintenance. The rectification work required more than 300m of pipework associated with reactor cooling systems to be renewed, along with renewal of numerous seismic pipework supports and remediation of carbon dioxide storage vessels. Both reactors at Dungeness B are currently (January 2019) shutdown as part of the licensees ongoing recovery program. The licensee has identified a number of additional commitments that will be fulfilled prior to returning either reactor to service. ONR continues to engage with the licensee to monitor progress against commitments. The licensee has an on-going investigation underway to establish the causes of this issue.

There were no safety consequences to people or the environment as a result of this event. The event related to the erosion of the normal levels of defence in depth associated with the operation of a nuclear power station in the UK.

INES Rating: 2 - Incident (Final) as per 31 December 2018
Release beyond authorized limits? No
Overexposure of a member of the public? No
Overexposure of a worker? No

Contamination spread within the facility? No
Damage to radiological barriers (incl. fuel damage) within the facility? No

Degradation of Defence In-Depth Yes

Person injured physically or casualty? No
Is there a continuing problem? No

James Francis
Office for Nuclear Regulation (ONR)

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