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Sellafield: Waste tanks incident

Nuclear Monitor Issue: 

(February 16, 2001) An incident at Sellafield's High Level Waste tanks on 26 January 2001 was kept secret for two weeks, only being revealed in BNFL's Sellafield Newsletter on 9 February. The incident caused suspension of a number of Sellafield's operations, including reprocessing at THORP.

(543.5242) WISE Amsterdam - Ironically, the incident happened as a result of improvements intended to increase safety and reduce radioactive discharges into the atmosphere. The ventilation system for dealing with the gases given off by the highly radioactive liquid waste in the tanks had just been improved. However, an electrical wiring fault in part of this system cuased the system to malfunction, leading to a build up of explosive gases. Alarms warned that the system was malfunctioning, but staff ignored the alarms for nearly three hours before taking action to solve the problem. The incident has been provisionally classified as Level 1 on the International Nuclear Event Scale (INES).

Government Ministers were informed several days after the event by inspectors from the Nuclear Installations Inspectorate (NII), Britain's nuclear safety authority, which is part of the Health and Safety Executive (HSE). However, an HSE press release dated 31 January 2001, announcing an NII order to BNFL to reduce the quantity of waste stored in the same tanks, made no mention of the incident that had happened five days previously.

The highly radioactive liquid in the tanks, known as Highly Active Liquor (HAL), is essentially a solution of fission products in nitric acid. This radioactive liquid, which remains after plutonium and unused uranium have been extracted during reprocessing, is initially stored in tanks which must be actively cooled and ventilated 24 hours a day. Failure of cooling and ventilation systems can have disastrous consequences: when a similar tank blew up in Kyshtym in the Russian area of Chelyabinsk in 1957, the resulting nuclear accident was second only to Chernobyl in magnitude, devastating an area the size of central London.

Because of this, the NII has been pressing BNFL for years to convert the waste to a more stable form as soon as possible. BNFL set up a Waste Vitrification Plant (WVP) to convert the waste to glass blocks, which are safer because they do not need active cooling. However, the throughput achieved by the first two waste vitrification lines has been lower than expected, with particular problems in the 1995/96 and 1996/97 periods. The plant was also sabotaged last year (the culprits remain undetected). BNFL declared in 1995 that it would have a third vitrification line ready in 1999, but failed to meet this target.

The order made to BNFL on 31 January, as mentioned in the HSE press release, took the form of a "Specification" - a legally binding requirement - reducing the maximum permitted storage of HAL at Sellafield. The current storage limit is 1,575 cubic metres, and the Specification states that this is to be reduced by 35 cubic metres a year until 2012, when it will be rapidly reduced to the minimum needed to feed the vitrification plant (the "buffer stock"). In order to reduce HAL stocks, the HAL must be vitrified at a faster rate than reprocessing produces more of it. 2012 is the planned closure date of Sellafield's B205 Magnox reprocessing plant (see article elsewhere in this issue), and the planned rapid reduction of HAL stocks from this date is clearly related to B205's closure.

However, the NII states that the major contribution to the hazard potential comes from HAL derived from the Thermal Oxide Reprocessing Plant (THORP). Laurence Willams, head of the NII, said in the press release: "We will not hesitate to use our regulatory powers to halt THORP reprocessing, should that be necessary, in order to keep BNFL within the Specification". It is now clear that Williams did hesitate to inform the public of the incident of 26 January. A spokesman for the Nuclear Free Local Authorities said: "Days after this potential disaster occurred the Nuclear Installations Inspectorate still pressed ahead with a feeble plan to give BNFL to July 2015 to clear the waste backlog. At the time we said the plan was totally inadequate and information about the build up of explosive gases on 26 January now demonstrates the dangers."

The staff reaction to the incident, ignoring the alarm for nearly three hours, once more demonstrates BNFL's "serious safety culture problem", as the NII described it following last year's investigation into BNFL's management of safety systems at Sellafield. However, the quickest way to reduce Sellafield's stock of high level radioactive liquid waste is to stop reprocessing, so that no more is produced and the existing stocks can be vitrified.

Sources: Contact:


  • HSE Press Release E015:01, 31 January 2001
  • CORE News Briefing, nos. 05/01 (2 February 2001) and 06/01 (12 February 2001)
  • "The storage of liquid high level waste at BNFL Sellafield: an updated report of safety", NII, February 2000
  • Nuclear Free Local Authorities press release, 12 February 2001
  • The Observer, 11 February 2001

Contact: Cumbrians Opposed to a Radioactive Environment (CORE), 98 Church Street, Barrow, Cumbria LA14 2HJ, UK
Tel: +44 1229 833851. Fax: +44 1229 812239.