The discharge was made on 23 October 2001 without a representative sample of the effluent being taken, as required by British Energy's authorisation.
In February 2002, the Scottish Environment Protection Agency responded by serving an enforcement notice requiring the company to improve its procedures to avoid a repetition of the incident. SEPA acknowledged that the release was "very unlikely" to have caused environmental damage or a breach of discharge limits.
On 15 January, British Energy appeared at Haddington sheriff court over the incident. It was fined £15,000 after pleading guilty to offences under sections 13(1) and 32(1)(a) of the Radioactive Substances Act 1993.
According to a British Energy spokeswoman, the discharge consisted of waste water from a variety of sources, including a laundry used to wash overalls, floor drains and showers. Two or three such discharges are typically made per week, after testing.
The company said that on the day of the offence, human error led to water in one tank being tested and untested water from another being discharged.
British Energy responded to the incident initially by locking the tank outlets so that only tested water could be discharged, Torness operations manager Mike Lavelle explained. An improvement plan was later agreed with SEPA which included an improved control room, and new control and locking systems. This was under way when the enforcement notice was served.
British Energy has been reducing staff numbers to cut costs. The process has raised concerns at the Nuclear Installations Inspectorate. In early 2000, it ordered the company to halt plans for personnel cuts "until they can demonstrate that the process will not adversely affect the safety of nuclear power stations" (ENDS Report 301, p 25 ).
But British Energy figures reveal that staff cuts at Torness continued. At the time of privatisation in 1996, 627 people worked at the site. The number then declined to 513 in 1999/2000 and 474 in 2001/02.
British Energy denies that the cuts played any part in the discharge incident. The number of people trained to do the testing had not been reduced, Mr Lavelle said, and last year the NII approved staffing levels at the plant.