Accident Analysis . ACADs (08-006) Covered Keywords Description Supporting Material. Emergency Classification. L evel of risk to the public. 4 emergency classifications: Notification of Unusual Event Alert Site Area Emergency General Emergency . Accident Analysis. Assessment :
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ACADs (08-006) Covered
According to the probability of its occurrence and potential consequences, an event may be classified as:
A postulated accident that a nuclear facility must be designed and built to withstand without loss to the systems, structures, and components necessary to ensure public health and safety.*
Accident sequences that are possible but were not fully considered in the design process because they were judged to be too unlikely.
Complementary methods of safety analysis are used jointly in evaluating the safety of an NPP:
Deterministic safety analysis:
Probabilistic safety analysis (PSA) combines
Two classes of radiation exposure effects:
1. Deterministic effects
2. Stochastic effects
1. set of actions during the evolution of a beyond design basis accident:
(a) To prevent the escalation of the event into a severe accident;
(b) To mitigate the consequences of a severe accident;
(c) To achieve a long term safe stable state.
2.severe accident management:
mitigate the consequences of a severe accident
Accident management is essential to ensure effective defense in depth
Factors that affect protective action decisions include:
“A restriction or range placed upon important process variables that are necessary to reasonably protect the integrity of the physical barriers that guard against the uncontrolled release of radioactivity.” *
Settings for automatic protective devices related to those variables having significant safety functions. Where a limiting safety system setting is specified for a variable on which a safety limit has been placed, the setting will ensure that automatic protective action will correct the abnormal situation before a safety limit is exceeded.
if any safety limit is exceeded:
after appropriate evaluation
in accordance with established plant procedures.