Incidents and Events
The company’s management system implements the following principles relating specifically to the avoidance, reporting and mitigation of incidents and events:
- all reasonably practicable steps should be taken to identify and avoid the occurrence of initiating events which have the potential to lead to public harm
- maintenance practices, that underpin the sustained delivery of safe, reliable generation, are defined to prevent structures, systems, and components from degrading or failing and to ensure that actions are taken that promptly restore intended functions
- the conditions and limits necessary for the safety of operations are contained in Technical Specifications. All operations which may affect safety are carried out in accordance with written instructions in accordance with Nuclear Site Licence Condition 24 (Operating Instructions). These instructions comprise Technical Specifications, Environmental Specifications and Station Operating Instructions derived from Technical Specifications and Environmental Specifications
- high performance is established, maintained and improved through the careful selection, training and development of operational candidates, especially Shift Managers. Operators are trained and qualified to gain the necessary knowledge, skills and abilities to support safe and reliable operation
- all Nuclear Generation (corporate, station and contractor) personnel shall:
- identify conditions that have or could have an undesirable effect on performance of equipment, programmes or organisations.
- ensure necessary immediate actions are implemented to place the plant/situation in a safe and stable condition
- report the condition to a supervisor or the control room, as appropriate, including immediate corrective actions taken
- promptly initiate a Condition Report
- provide sufficient information so that the condition can be properly evaluated for operability, reportability, significance and disposition.
- symptom-based emergency response guidelines and accident management guidance should be available to control any accident, or mitigate the consequences, in the unlikely event of failure of any of the required engineered protective features
- the Emergency Preparedness Programme includes arrangements for working with other emergency services and Government bodies to provide countermeasure advice and actions to protect the public and environment from the consequences of any significant release of radioactive material from any of our power stations.
Our plant is designed to be operated without significant impact on the health and safety of its operating staff or of the public living around the stations. To this end it is subject to an extensive routine programme of inspection and maintenance. Its behaviour in normal operation and a wide range of abnormal circumstances have been analysed (the ‘Nuclear Safety Case’) to show that the station will either be able to continue operating safely or be brought to a safe shutdown condition. The resulting limits on the allowed operating parameters (such as temperature and pressure) and the availability of backup systems are incorporated into operating instructions which control all aspects of operation and direct the action to be taken if these limits are approached. Our staff are rigorously trained in the requirements of the safety case and operators in control are individually examined and authorised to the role. The adequacy of the safety case, the monitoring and maintenance regime and the control of operations is evaluated continually and is formally assessed in comparison to the latest standards every ten years.
To give early warning of any deterioration, whether in plant or operating standards, and to facilitate our goal of continuous improvement, every deviation from the expected plant status or the management system procedures is required to be reported into our Corrective Action Programme (CAP). Within the CAP each report is considered by a committee of experienced staff, categorised and allocated a priority. Notifications to affected parties, both inside and outside the company, are made according to the assigned category. The priority guides the depth of investigation: some events are simply recorded to allow a statistical evaluation of trends, while others are investigated in detail to find and eliminate the basic causes. Corrective actions are determined and assigned then followed up to ensure completion. The final step is an effectiveness review to check that the action has had the desired effect.
In addition to these routine processes the company has detailed plans for the action to be taken if, despite all these precautions, things should go wrong and the public should be threatened. We perform regular emergency exercises to test the procedures, facilities, systems and equipment, and enable everyone to practise their role. These are also the main way that we demonstrate the effectiveness of our emergency arrangements to external agencies and the public.
The application of the company's safety standards reduces to a very low level the chance of an accidental event which might lead to the release of even small amounts of radioactivity. Nevertheless we have plans and procedures for dealing with an accident or emergency and protecting both our workforce and members of the public. Many of our staff are assigned roles in the emergency organisation in addition to their normal job. They are trained in these roles, practise them regularly and periodically demonstrate them both to internal assessment teams and to the Office for Nuclear Regulation.
The emergency organisation is assigned activities and responsibilities to achieve the following objectives:
- to activate the site emergency arrangements
- to issue appropriate warnings at the correct time and ensure the safe withdrawal of all persons on site to pre-arranged assembly points
- to notify rapidly all persons and external organisations concerned with implementing remedial actions
- to assemble and deploy, when necessary, emergency teams to assess and minimise the consequences of the accident
- to assess the risk and extent of any potentially hazardous situation, ensure that timely advice is given on appropriate measures to safeguard the public, and ensure that appropriate measures are taken to safeguard station personnel
- to protect the environment. Steps taken to protect public health may also provide environmental benefits; nevertheless, attention is paid to the environmental harm which could result from emergency intervention activities
- to minimise and then terminate any release of radioactivity and make the affected plant safe
- to provide authoritative specialist advice to the police, local authorities and other organisations responsible for taking the necessary action to protect the public. This advice will be provided initially by the Emergency Controller and subsequently by either the EDF Energy Nuclear Generation Ltd Company Adviser or (until relieved of the responsibility) the Government Technical Adviser
- to provide accurate and timely information for the local authority to inform the public via the news media
- to maintain an accurate record of events for later analysis
- to ensure the safety of unaffected plant.
If an event should ever occur resulting in a release to the environment of significant quantities of radioactive material then, in addition to our own staff, many off-site organisations would be involved and called upon to take actions to protect the public. These organisations include the police and other emergency services, local authorities, Government departments and agencies, each of which has its own emergency responsibilities and procedures. These procedures are co-ordinated in the Off-Site Emergency Plan by the local authority, which fulfils the requirements under the Radiation Emergency Preparedness and Public Information Regulations (REPPIR).
Over the last five years, the reactors operated by EDF Energy Nuclear Generation have seen an overall safety improvement linked to a major effort to upgrade the facilities and a strong emphasis on further improving equipment reliability and operational focus. The rate of occurrence of events related to the above indicators is less than one event per reactor-year of operation, and represents minor failures in very reliable plant and management systems to protect safety and maintain legal compliance. Fluctuations in the number of such events from year to year are expected and efforts to improve our arrangements and reduce the incidence of these events further are continuing.
Number of Nuclear Safety Events
The International Nuclear Event Scale (INES) is a rapid alert system used for consistent communication of events across the nuclear industry. These are categorised between Level 1, which is an anomaly with no impact on the safety of the general public or workforce, and Level 7, which represents a major accident. There have been no nuclear safety events rated above INES Level 2 at EDF Energy Nuclear Generation’s power stations.
During 2009 we had one nuclear safety event rated INES Level 2 which is classed as an incident with minor consequences to people or facilities, but where the measures put in place to prevent or cope with accidents did not operate as intended.
The INES Level 2 incident occurred at our Dungeness B power station during the construction of a new fuel assembly. Whilst a fuel assembly is the completed series of fuel components used in the core of an advanced gas-cooled reactor power station, the incident did not concern the reactor in any way. In the process of connecting a new fuel assembly to the supporting fuel plug unit a piece of rubber was, on a procedural check, found trapped in the coupling preventing the two sections from joining correctly. As part of the recovery process polyurethane foam was injected below the suspended fuel assembly to minimise the potential drop height in the event of a de-latch. Subsequent analysis of the foam showed that its use was not permitted under the power station's operating arrangements. The foam did not come into contact with the fuel assembly and the coupling did not fail.
There was no impact on the safety of the workforce at the station or the public at large. There was no release of radioactivity or any damage to the plant. This incident was reported to the safety Regulator, with which the operator has co-operated, and has been thoroughly investigated. Company wide improvements have since been made.
Nuclear Reportable Events
Our site licences require comprehensive arrangements for reporting and investigating incidents occurring at our power stations to our regulator, the Office for Nuclear Regulation (ONR). The most significant of these are known as Nuclear Reportable Events (NRE).
The NRE and the events rated at Level 1 or 2 on the INES are distinct but overlapping sets of events. Within EDF Energy Nuclear Generation a vast number (~50,000) of 'conditions adverse to quality' are reported each year. Each of these reports is categorised and sentenced either to immediate action, to further investigation or for data trending. A very small number of events are identified as requiring formal reports to the ONR under our site licence compliance arrangements or the reporting requirements of responsible Government departments. These are the 'Nuclear Reportable Events'. Each such event will be rated on the INES, but because the reporting is determined by the type of event rather than its severity, some may be rated at INES Level 0. A wider range of events are reported to the ONR and/or other interested parties and all such events whose descriptions are potentially public receive an INES rating. This means that some events which are not 'Nuclear Reportable' may nevertheless be rated at INES Level 1.
