Office for Nuclear Regulation

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Statement of nuclear incidents at nuclear installations

A statement of nuclear incidents at nuclear installations in Britain during the third quarter of 2001 is published today by the Health and Safety Executive (copy below). It covers the period 1 July to 30 September 2001.

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.

Statement of Nuclear Incidents at Nuclear Installations: Third Quarter 2001 Single copies of each free from the Information Centre, Health and Safety Executive, Room 004, St Peter's House, Stanley Precinct, Bootle L20 3LZ

Notes to Editors

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.

3. The locations of the installations mentioned in the statement are as follows:

Heysham 1 (British Energy Generation plc)
Sellafield (British Nuclear Fuels plc)
Chapelcross (British Nuclear Fuels plc)


The Health and Safety Executive 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.

INCIDENT 01/3/1 - HEYSHAM 1 (British Energy Generation Limited)

To meet the requirements of the nuclear site licence, each of the two reactors at Heysham 1 is shutdown periodically to enable examination, inspection, maintenance or testing of safety related components that cannot be accessed when the reactor is operating. Reactor 1 was subject to a periodic shutdown in August/September 2001.

Inspections of the reactor graphite core are carried out using remote TV cameras and equipment to measure the geometry of the core components. The aim of the inspections is to confirm that the core components are performing in accordance with the predictions assumed in the safety case. During the planned inspections of the Reactor 1 core fuel channels, BEGL found cracks in some of the graphite bricks. The cracking of reactor core bricks is a known and predicted ageing condition for irradiated graphite and has been observed at other AGR stations. BEGL responded to the inspection findings in a conservative way by revisiting and updating their existing core safety case for Heysham 1. Consideration was also given to the possible implications of the inspection findings to the other operating AGRs . The BEGL review considered the inspection results against the assumptions made in the existing safety case, which included the possibility of cracks in the core bricks, and concluded that the revised core safety case was valid for a further period of operation.

Specialist graphite inspectors from the HSE's Nuclear Installations Inspectorate carried out a detailed assessment of the revised core safety case, to ensure that the required safety functionality of the reactor core would be maintained for a further period of operation. NII's assessment focussed on ensuring sufficient safety margins were available in the safety case to allow for any further cracking of the core bricks. The NII assessment concluded that the safety case was adequate to support the return to service of Heysham 1 Reactor 1 and that the safety cases for other AGR stations remained valid.

The event was classified as Level 1 on the International Nuclear Events Scale (INES).

INCIDENT 01/3/2 - SELLAFIELD (British Nuclear Fuels plc)

During a rainstorm on 6 July 2001, localised flooding about 10-15 centimetres deep occurred outside a laboratory complex and overflowed an external door threshold into the building. The water entered an old laboratory which is currently being decommissioned. Historic plutonium (Pu) contamination, probably from under a floor lining, was re-suspended by the flooding and spread over part of the laboratory floor. The area has subsequently been cleaned up and decontaminated. There was no release of radioactivity from the building and no radiation dose received by the workforce.

BNFL reported the incident as a spill under the Ionising Radiations Regulations 1999 (IRR99). The estimated amount of activity involved was equivalent to 10MBq of 239Pu and 200MBq of 241Pu which is respectively 10 and two times the IRR reporting level. The incident was classified as Level 1 on the International Nuclear Event Scale (INES).

BNFL carried out remedial work on the building to prevent a reoccurrence of the water ingress, and additional work is in hand to strengthen these measures. HSE's Nuclear Installations Inspectorate investigated the incident, and is monitoring progress with the remedial work.

INCIDENT 01/3/3 - CHAPELCROSS (British Nuclear Fuels plc)

At 1.20 am on 5 July, during routine discharge operations on Reactor 3 at BNFL's Chapelcross nuclear power station, a basket containing 24 irradiated magnox fuel elements dropped. It fell about 5 feet onto a door in the pile cap floor, but was still contained within the discharge machine. BNFL stood down its Emergency Control Centre at about 6pm when it concluded that the fuel was stable and that no radioactivity had been released.

On the eveni2011-10-26 detailed remote TV examination, and found that 12 fuel elements were missing from the basket. After further checks, BNFL concluded that the door the basket had been resting upon must have been opened during discharge operations, and that the missing elements must have fallen about 80 feet, down the discharge shaft through which the elements are normally lowered in the baskets.

BNFL declared a site incident on 12 July in order to be better able to co-ordinate its activities. The NII set up its Response Centre and dispatched a team of inspectors to the site. NII focused upon ensuring that BNFL took appropriate steps to locate and recover the missing fuel. They recovered it safely on 17 July, and the NII was able to stand down its Response Centre as it was satisfied that no member of the public or employees had incurred any harm from the incident.

Subsequently, priority was given to regulating BNFL's recovery of the 12 irradiated fuel elements still within the discharge machine. This was achieved safely on 27 October.

BNFL has embargoed routine refuelling operations at Chapelcross, and will have to provide a safety case to satisfy the NII that it can return to routine refuelling safely. Similar measures have been taken at its sister station at Calder Hall.

The NII is producing a report, which will be available to the public on this incident which was classified as Level 1 on the International Nuclear Event Scale (INES).