Formal–statistical methods - Probabilistic Safety Assessment for Optimum Nuclear Power Plant Life Management (PLiM) - page 69

basis of objectives of the study and preliminary analysis of the structure
and composition of the object, its purpose and process of operation. As
the hazardous developments become more extensive and detailed, the
corresponding integral index R becomes more representative. It is
important to match the selected dangerous events with 'qualitative leaps'
in changing the state of the object, the staff and operators, the nature and
magnitude of the effect of damaging factors on the population and the
environment. For example, for nuclear power plants dangerous events in
the first approximation include an uncontrolled nuclear reaction (nuclear
explosion), the destruction or explosion of a reactor core with the release of
fissile material and radioactive substances, core meltdown, depressurisation
of the nuclear installation circuits with emission of radioactive substances,
etc.
Thus, the risk according to [2.8]-[2.10] quantifies the risk of the whole
'nuclear facility - individual - environment' complex and, strictly speaking,
is an integral indicator of the dangers of this global complex. Under certain
fixed characteristics of a nuclear facility, the environment, personnel and
population, the integral indicator can be regarded as one of the most
important indicators of the safety of the nuclear facility and is used for
comparison and selection of preferred (as regards the level of hazard)
options of the scheme-design version of the object, the organisation of its
operation and protection from accidents and disasters.
The algorithm for risk assessment for nuclear facilities includes the
following basic procedures.
1. Analysis of the structure and composition of the nuclear facility
and determination on this basis of a limited list of catastrophic outcomes
(hazardous events associated with a significant negative impact from a
nuclear facility on the environment). Ranking of catastrophic outcomes from
nuclear facilities on the basis of the reasons (mechanisms) for occurrence
and the degree of severity. Allocation of payment options for catastrophic
outcomes from a nuclear facility that are significantly different in severity
and mechanisms.
2. Life cycle analysis of a nuclear facility. Allocation of stages (substage,
fragments) of the life cycle which differ significantly in means and methods
of operation, the placement of the nuclear facility, and according to other
parameters determining the probability of catastrophic outcomes, and the
magnitude of the damage resulting from them.
3. Estimating the probability p i of occurrence of each calculated
disastrous outcome from nuclear facilities at each of the selected stages
(substage, fragments) of the life cycle of the nuclear facility by:
- Determining the list of possible ad-hoc situations in the nuclear
facilities (including damage, failures, human error, natural anomalies,
malicious and terrorist acts, etc.), their probabilities and the most important
characteristics (levels, combinations, the duration of the primary anomalous
effects on nuclear objects from the environment, the types and combinations

￿ ￿ ￿ ￿ ￿