The Prototype Fast Reactor (PFR) sodium tank farm houses four tanks that contain sodium residues from the operation of the reactor.
On October 6, following operations in the PFR sodium tank farm to remove the residue sodium from a redundant tank, the tank was left overnight under surveillance.
In the early hours of October 7, the Dounreay fire brigade was alerted by an alarm from the tank farm. About the same time, an operator undertaking surveillance heard banging noises and saw smoke, and also called the on-site fire brigade.
The fire brigade arrived promptly and quickly extinguished the fire. The area was monitored by the fire brigade until it was deemed that there was a low probability of re-ignition. We continued to monitor the situation and the area was kept under surveillance, until the residues from the fire were cleared up.
The NDA and the regulators were informed and an investigation was convened. A brief was also posted on our website (based on our understanding at that time).
The initial investigation confirmed the probable mechanism for the initiation of the fire and concluded radioactivity may have been released, via an unauthorised route. SEPA were informed.
It also indicated that there were a number of aspects that required further investigation. The level of the investigation was increased to ensure that the full picture of the reasons for this incident were understood.
The investigation thoroughly checked each aspect of the work and identified procedural non-compliances and behavioural practices that were factors in the incident, and fell short of the values and standards expected of our people. It also confirmed the release of radioactivity via an unauthorised route.
The detailed report was reviewed as draft in the action review meeting. The same report was shared with NDA and regulators.
On November 11, the Office for Nuclear Regulation (ONR) served DSRL with an Improvement Notice relating directly to the tank farm incident.
Direct action has been taken to stabilise the situation and stop work in the tank farm area. It will not be re-started until the ONR are satisfied with DSRL’s improvements.
A dedicated team led by a senior manager will be responsible for a safety improvement plan focused on learning lessons from this and other incidents and ensuring there is improvement in the way we undertake work. This improvement plan will be wide ranging and ensure the whole site recognises the improvements that must be made.
Managing Director of DSRL, Mark Rouse, said: “We have accepted the Improvement Notice and will co-operate fully with the regulators.
“Our investigation identified unacceptable behaviours and practices that fell well short of our values and standards. It is important to take the time to ensure as many lessons are learned from this incident as possible.
“We are determined to improve our behaviours and compliance to ensure that we always meet the high standards expected on a nuclear site.”