A statement of nuclear incidents at nuclear installations in Britain during the third quarter of 2002 is published today by the Health and Safety Executive (HSE). It covers the period 1 July to 30 September 2002. There is one installation mentioned in the statement, Torness (British Energy)
The statement is published under arrangements that came into effect from the first quarter of 1993, derived from the Health and Safety Commission's powers under section 11 of the Health and Safety at Work, etc. Act 1974.
1. The arrangements for reporting incidents were announced to Parliament by the Parliamentary Under Secretary of State for Energy on 30 April 1987 (Hansard col. 203-204). A minor modification to arrangements for reporting on nuclear incidents was announced in HSE press notice E108:93 of 30 June 1993.
2. Normally each incident mentioned in HSE's Quarterly Incident Statements will already have been made public by the licensee or site operator either through a press statement or by inclusion in the newsletter for the site concerned.
Statement of Nuclear Incidents at Nuclear Installations: Third Quarter 2002 - single copies of each free from the Information Centre, Health and Safety Executive, Room 004, St Peter's House, Stanley Precinct, Bootle L20 3LZ.
The Health and Safety Executive (HSE) presents the attached statement of nuclear incidents at nuclear installations published under the Health and Safety Commission's powers derived from section 11 of the Health and Safety at Work, etc. Act 1974.
The sudden and extensive failure of a gas circulator at Torness in May 2002 was thought, from forensic evidence, to be linked to the development of an unexpected fatigue related crack in part of the impeller. In August, another gas circulator on the other Torness reactor showed signs of increasing vibration and was promptly shut down by the operators. Its subsequent disassembly revealed a fully developed fatigue related crack in a similar position to the first failure, but the prompt shutdown had prevented consequential damage.
Following the initial failure, British Energy (BE) increased the attention given to circulator vibration monitoring. As a result of the second failure, more extensive routine monitoring of circulator characteristics is being undertaken and more extensive circulator monitoring equipment is being fitted to allow efficient, cross-fleet monitoring of circulator behaviour. Activities in this area are being brought up to best practice standards.
Inspectors from HSE's Nuclear Installations Inspectorate (NII) monitored the recovery of the first failed circulator and its examination by BE specialists, and BE's examination of the fixed structure for any signs of damage. Agreement to replace the failed generator was given by HSE when it was satisfied that there was no structural damage to the reactor. As the second failure did not result in the disintegration of the circulator impeller there was no damage to the reactor structure.
With the discovery of a systematic and comparatively frequent failure mechanism, safety concerns increased and NII required a revised and extended safety case to cover operations. This incorporated forewarning of failure by early and effective detection of changes in vibration patterns together with recognition of the need to shut down any affected circulators before major failure and consequential challenge to the circulator casing occurs.
BE has inspected all gas circulator impellers in service at Torness and found no evidence of developing defects. Only a limited number of impellers have been inspected at Heysham 2, but again no defects have been found. BE has provided acceptable interim safety cases justifying continued operation of the reactors at Torness and at its sister station Heysham 2, and will produce, in the spring of 2003, final safety cases incorporating all the findings from its inquiry into the failures and changes introduced in the light of the events at Torness.