E. GIL LOPEZ, IAEA Radiation Safety Regulator, Austria

Abstract: Despite nuclear facilities being designed, constructed and operated according to the most stringent safety regulations, accidents, human failures, extreme external events or malicious acts can occur that require the implementation of adequate emergency actions. Since the Chernobyl accident in 1986, many efforts have been devoted to improving the nuclear emergency response at national and international levels, and emergency planning and preparedness have become a significant activity of the safety provisions needed to put in service a nuclear power plant. National regulations, usually based on international standards, establish the technical requirements for emergency planning and allocate responsibilities to plant operators and governmental bodies in charge of its implementation. Giving a suitable response to a nuclear accident requires efficient coordination among intervention organizations, emergency coordination centres are operated to facilitate such coordination, and regular exercises are performed to train intervention staff and improve emergency plans and procedures at every level.

Key words: emergency plans, emergency response, coordination centres, intervention organizations, international standards and recommendations.

12.1 Introduction

Nuclear and radiological emergencies can occur in a wide range of facilities, including fixed and mobile nuclear reactors; facilities for the mining and processing of radioactive ores; facilities for fuel reprocessing and other fuel cycle facilities; facilities for the management of radioactive waste; the trans-

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port of radioactive material; sources of radiation used in industrial, agricul­tural, medical, research and teaching applications; facilities using radiation or radioactive material; and satellites and radio-thermal generators using radiation sources or reactors. The common characteristic of nuclear and radiological emergencies is that both involve hazards associated with ion­izing radiation. In coherence with the rest of this book, this chapter is specifically aimed at emergency planning at nuclear power plants.

Nuclear facilities contain large amounts of nuclear material that can generate radioactive material by a chain reaction or by activation of stable nuclides that have been exposed to high neutron flux. Nuclear reactors can accumulate a large amount of radioactive materials, depending on their thermal power, the fuel burn-up and the time elapsed since the last shut­down. Multiple barriers contain these radioactive materials and prevent their radiation from damaging facility workers and the environment. Some critical components of a nuclear facility, such as the reactor core, need per­manent cooling because radioactive decay of fission products generates a large amount of energy that could damage them if it is not extracted effi­ciently. An accident or an intentional action could disable the reactivity control systems, the cooling systems or the barriers containing radioactive materials. In this case, large amounts of these materials could escape to the environment. The energy accumulated within the facility can contribute to the spreading of radioactive materials into the environment over a wide area.

The fundamental safety objective in the use of nuclear and radiation techniques is to protect people and the environment from harmful effects of ionizing radiation. This objective has to be achieved without unduly limit­ing the operation of facilities or the conduct of activities that give rise to radiation risks. To reach this objective all reasonable efforts must be made to prevent nuclear or radiation accidents and mitigate their consequences.

The most harmful consequences arising from nuclear facilities and activi­ties have come from loss of control over the nuclear reactor core, nuclear chain reaction or radioactive source. Consequently, in order to ensure that the likelihood of an accident having harmful consequences is extremely low, measures have to be taken:

• To prevent the occurrence of abnormal conditions, including breaches of security, that could lead to such a loss of control

• To prevent the escalation of any such failures or abnormal conditions that do occur

• To prevent the loss of control over radioactive sources.

Taking measures towards achieving these goals by undertaking interven­tions, which are defined as any action intended to reduce or avert exposure or the likelihood of exposure to sources which are not part of a controlled practice or which are out of control as a consequence of an accident, is governed at all times by the principles of justification and optimization recommended by the International Commission on Radiological Protection, ICRP (ICRP, 1991, 1993). According to the ICRP, any proposed interven­tion that does more good than harm is justified, and the form, scale and duration of any intervention shall be optimized so that the net benefit is maximized.

Every nuclear facility is designed to prevent any accident that can occur according to the applicable regulation. Two approaches are commonly used to demonstrate the compliance with regulation: the deterministic approach is used to demonstrate that the design is enough to prevent all regulated design-basis accidents and mitigate their consequences if they were to occur; the probabilistic methodology is used to verify that the accidents behind the design basis, that is the so-called severe accidents, should have a very low probability of occurrence and their consequences should be mitigated by dedicated design features. In addition, every nuclear facility has an emergency plan to be activated in case of an accident or malicious act to prevent severe damage to the facility and uncontrolled release of radioactive material, which could produce direct or delayed health effects on facility workers and the population that could be affected by radioactive material released.