Dropped rods investigation findings

1 March 2002

The investigation by the Nuclear Installations Inspectorate (NII) into the Chapelcross dropped rods incident is now complete.

On 5 July, 2001, a basket containing 24 irradiated fuel elements was dropped in a fuel discharge machine during normal defuelling operations at Chapelcross 3. BNFL declared a site incident when it emerged that 12 of these fuel elements had fallen 87 feet down the discharge well. NII also activated its Response Centre which operated until it was confirmed that the fuel elements in the discharge well were in the water-filled fuel flask at the bottom of the well and these had been recovered to the fuel pond.

Of the 24 original irradiated fuel elements, 12 remained in the fuel discharge machine on the reactor's pile cap. The recovery of this fuel was safely completed on 27 October, 2001, and has since been sent to Sellafield for reprocessing.

The NII carried out a wide-ranging investigation into this incident. The investigation focused on determining what caused the basket to become detached from the grab; why it took seven days to discover that not all of the fuel had remained inside the discharge machine; and whether there were grounds for health and safety enforcement action. The NII found a combination of "procedural and hardware deficiencies" were to blame.

The investigation has resulted in a series of recommendations, some of which are required to be completed before normal use of the fuel route is resumed:

• No worker or member of the public incurred any harm from the release of radioactive material as a result of the event.

• Such incidents can be prevented by implementing two plant modifications to the defuelling equipment.

• There was no deliberate attempt at deception with respect to reporting events or status of plant.

• Prosecution of BNFL was not appropriate and that their response to the identified recommendations should be monitored through NII's normal regulatory processes.

NII is regulating the return to normal operations of the fuel route through the nuclear site licence conditions. Defuelling mechanisms are also to be upgraded at Calder Hall, which is similar in design to Chapelcross.
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