Anticipated operational occurrences conditions

Following anticipated operational occurrences (e.g. fire, flooding, overheating or power excursions) acceleration of ageing effects may occur. It is advisable to investigate and to take corrective actions to stop accelerated ageing. Table II summarizes information on these conditions and induced ageing mechanisms. 

Radiation Change of properties - chemical decomposition - strength change - ductility change - colour change - swelling - resistivity change - bumup 

Stress (pressure) Creep - changes of geometry (e.g. break, collapse) 

Cycling of temperature, flow and/or load Flow induced vibrations Motion - displacement - change of position or set point - loose connections 

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Graphite Core Component Allowable Stress Limits Anticipated Operational Occurrence Performance Design Basis Event Performance "Safety-Related" Design Condition Performance Interfaces... 

SSCs that prevent imsafe conditions or that mitigate the consequences of anticipated operational occurrences and accident conditions ... 

A. 19. Operating procedures. A sampling review of operating procedures should be performed, including all the procedures for normal operations, anticipated operational occurrences and accident conditions. Inspections should be focused on the operating personnel s adherence to procedures, including operational limits and conditions. The usability and adequacy of the procedures should also be evaluated. This may necessitate sustained observations in the control room. The inspection programme in this area may necessitate sustained observation to cover 24 hour operation as necessary, in particular shift turnovers. The inspectors should check the availability of safety systems and the presence of alarm systems, and the way in which they are handled by the operations staff... 

The surveillance of safety systems should cover systems and components provided to shut down the reactor and keep it shut down, and to ensure that safety limits are not exceeded either owing to anticipated operational occurrences or during the initial operation of systems that are required in order to mitigate the consequences of accident conditions. Such mitigation could be done through ... 

DOE 5480,27, EQUIPMENT QUAE IEI CAT IONS (EQ) EOR NUCEEAR FACILITIES AND OPERATIONS 1-15-93, which establishes the environmental conditions under which equipment must perform their safety function during normal operations, anticipated operational occurrences, and DBAs they are required to operate during and after. 

Anticipated operational occurrences. Anticipated operational occurrences mean those conditions of normal operation which are expected to occur one or more times during the life of the nuclear power unit and include but are not limited to loss of power to all recirculation pumps, tripping of the turbine generator set, isolation of the main condenser, and loss of all offsite power. 

Criterion 10 - Reactor design. The reactor core and associated coolant, control, and protection systems shall be designed with appropriate margin to assure that specified acceptable fuel design limits are not exceeded during any condition of normal operation, including the effects of anticipated operational occurrences. 

Criterion 13 - Instrumentation and control. Instrumentation shall be provided to monitor variables and systems over their anticipated ranges for normal operation, for anticipated operational occurrences, and for accident conditions as appropriate to assure adequate safety, including those variables and systems that can affect the fission process, the integrity of the reactor core, the reactor coolant pressure boundary, and the containment and its associated systems. Appropriate controls shall be provided to maintain these variables and systems within prescribed operating ranges. 

Criterion 20 - Protection system functions. The protection system shall be designed (1) to initiate automatically the operation of appropriate systems including the reactivity control systems, to assure that specified acceptable fuel design limits are not exceeded as a result of anticipated operational occurrences and (2) to sense accident conditions and to initiate the operation of systems and components important to safety. 

A postulated initiating event is an event identified during design as capable of leading to anticipated operational occurrences or accident conditions. The primary causes of PIEs may be credible equipment failures or operator errors (both within and external to the facility), and human induced or natural events. 

The levels at which protective devices are automatically actuated in the event of anticipated operational occurrences or incident conditions, to prevent safety limits from being exceeded. 

The starting point for the safety analysis is the set of PIEs that need to be addressed. A PIE is defined in Ref. [1] as an identified event that leads to anticipated operational occurrences or accident conditions . PIEs include events such as equipment failure, human errors and human induced or natural events. The deterministic safety analysis and the PSA should normally use a common set of PIEs. 

The plant conditions considered in the design basis analysis include anticipated operational occurrences and design basis accidents (DBAs). The division is based on the frequency of the occurrence. 

An event should not generate a subsequent more serious plant condition without the occurrence of a further independent failure. Thus an anticipated operational occurrence by itself should not generate a DBA, and such an accident by itself should not generate a beyond design basis accident. 

Expected in the life of the plant) Expected Anticipated operational occurrences Anticipated transients, transients, frequent faults, incidents of moderate frequency, upset conditions, abnormal conditions No additional fuel damage... 

The word emergency is used in many different contexts and different areas of human activity. In Ret [4] emergency is defined in part as A nonroutine situation or event that necessitates prompt action primarily to mitigate a hazard or adverse consequences for human health and safety, quality of life, property or the environment . In IAEA safety assessment publications the following terms have been established for identification of different operational states and accident conditions of a nuclear power plant normal operation, anticipated operational occurrences (AOOs) (abnormal operation), design basis accidents (DBAs), beyond design basis accidents (BDBAs) and severe accidents. 

In IAEA pubhcations, e.g. in Ref. [8], accident conditions are defined as deviations from normal operation more severe than anticipated operational occurrences, including design basis accidents, beyond design basis accidents and severe accidents. Examples of such deviations include loss of coolant accidents (LOCAs), complete loss of residual heat removal from the core, and anticipated transient without scram. 

Postulated initiating event. An event identified during design as capable of leading to anticipated operational occurrences or accident conditions. 

Anticipated operational occurrence. An operational process deviating from normal operation which is expected to occur at least once during the operating lifetime of a facility but which, in view of appropriate design provisions, does not cause any significant damage to items important to safety or lead to accident conditions. 

Accident conditions. Deviations from normal operation more severe than anticipated operational occurrences, including design basis accidents and severe accidents. 

The hazards associated with external events (and combinations of events) that are to be considered in the design of the reactor shall be determined. The combination of external events with anticipated operational occurrences or DBA conditions shall be considered for those cases in which an anticipated operational occurrence or a DBA condition is caused by the external event and where there is a need to consider long lasting external events (such as flooding) or long post-event recovery times. 

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