Letter to Sizewel SSG Members
While carrying out routine inspections in the early hours of Saturday 3rd September, an operative noted unexpected plant indications and upon investigation, discovered water escaping from a cracked flow meter in the site’s active effluent treatment plant (AETP). The meter forms part of a section of the system which returns treated water to the used fuel storage pond and as such the activity in the liquid was very low. The plant was shut down before the loss initiated our early warning alarms.
Our physical safety defences performed exactly as expected. All the treated water except a small amount which remained on the floor in the AETP was captured by the system and there was no impact on personnel or the environment.
You will recall the far more significant event in our AETP, in January 2007, which led to a complete review and overhaul of the plant’s design and safety systems. I want to reassure you that this event does not provide any indication that improvements we made then are ineffective now.
Among the enhancements was the installation of early warning alarm and plant protection systems. Our nuclear maintenance schedule ensures all these systems are checked frequently and rigorously.
These systems were not required in this case because the fall in pond levels was not enough to trigger any of the alarms. Our investigations show that the pond level reduced by 1.4cm (in a total depth of 6.75m) which equates to a loss of 7m3 of treated water. In total approximately 13.3m3 of treated water was captured by our secondary containment, over a period of four and a half hours.
We are currently carrying out our own investigations to identify any lessons to be learned from this event and we will share them with you in due course. Both the Office for Nuclear Regulation and the Environment Agency have been informed. Inspectors from both organisations have declared their intention to carry out their own investigations and we will support them in doing so.
This event will be reported at the next Sizewell A and B Stakeholder Group quarterly meeting. If there are any further significant developments I will write to you again but please feel free to contact us if you have any specific questions in the meantime.
