1977 shaft explosion
During the night shift of May 10, 1977 an explosion occurred at the shaft which caused severe damage to the superstructure.
No personnel or flasking equipment were involved directly and no-one was hurt.
Subsequent investigations concluded that there had been an explosion due to a build-up of hydrogen in the upper shaft air space. It was thought that sodium present in the waste had reacted, causing a build-up of gas that was ignited by a spark from a water pump. Waste operations ceased after this event.
The area around the shaft, including outside the nearby site fence, was progressively surveyed and cleared of contamination. Short-term and longer term measures were taken to create an inert atmosphere within the shaft.
The incident was reported later the same day by UKAEA to the Scottish Office regulatory division and to the Nuclear Installations Inspectorate in line with the then arrangements.
The report was categorised as an “unauthorised discharge” as defined in the 1960 Radioactive Substances Act.
The public relations consequences of the incident in 1977 were muted – articles about the event in local and national media at the time were low-key – but renewed interest in the explosion during the 1990s generated extensive media and public interest in the fate of the shaft.
In 1995, research on the health physics implications of the incident concluded that the significant ground contamination, which then remained in the vicinity of the shaft, resulted from the methods of waste disposal used in the 1960s.
The research found it was possible, but not absolutely certain, that the 1977 explosion added some permanent contribution to this pre-existing contamination, but it found no evidence that radioactive material was ejected by the explosion from within the volume of waste deposited in the shaft.