Anticipated operational occurrences

The safe operating limits proposed for the RBMK-1000 and RBMK-1500 reactors are shown in Table 4. 

Safety factor for critical power of fuel channels Non-dimensional 1.0 1.0 

Water flow rate in a CPS channel with an inserted rod mVh 2.0 3.0 

Reactivity margin in the effective manual control rods Number of effective control rods a 0 

The acceptance criteria applicable for analyses of DBAs are listed in Table 5 [9]. 

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The Millstone Unit 1 PRA contains component failure and maintenance unavailability data, and initiating event frequency data, including typical BWR anticipated operational occurrences and LOSP. 

In the United States, commercial nuclear power plant operators are required to monitor and report any detectable quantities of radioactive materials released to the environment (NRC 1996). Table 6-1 summarizes releases of radiostrontium isotopes with half-lives >8 hours to the atmosphere and water for 1993 from PWR and BWR nuclear power plants. Nearly all of the radioactive material reported as released in effluents are from planned releases from normal plant operation or anticipated operational occurrences. The latter includes unplanned releases of radioactive materials from miscellaneous actions such as equipment failure, operator error, or procedure error, and are not of such consequence as to be considered an accident (NRC 1993b). 

Top-Level Regulatory Criteria Anticipated Operational Occurrences Design Basis Events Emergency Planning Basis Events... 

Anticipated Operational Occurrences (AOOs) These are families of... 

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

The structural effects of the five postulated anticipated operational occurrences (AOOs) on the reactor core are discussed in this section. The... 

The control assemblies shall incorporate features which ensure that the control rods and reserve shutdown material enter their designated channels for all reactor configurations resulting from anticipated operational occurrences (AOOs) and design basis events (DBEs). 

The plant anticipated operational occurrences (AOOs) are described in detail in Section 11.6. For the AOOs in which the outer control rods are tripped, the trip occurs quite early in the event, before there can be a significant temperature transient or environmental change affecting the equipment. For AOO-5 the trip may occur long after the event is initiated and there is no significantly detrimental transient Imposed on the CRDs prior to the time when they are signalled to release the rods. 

The plant anticipated operational occurrences (AOOs) are described in Section 11.6. Those which affect the reactor Internals are discussed below. 

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 are off-normal events, usually plant transients, which can be coped with by the plant protection systems and normal plant systems but which could have the potential to damage the reactor if some additional malfunction should happen. Their typical frequency of occurrence may be more than 10 year Some of the anticipated occurrences (PIEs - postulated initiating events) are due to the increase of reactor heat removal (as might occur for an inadvertent opening of a steam relief valve, malfunctions in control systems, etc.). Some are due to the decrease of reactor heat removal (such as for feed-water pumps tripping, loss of condenser vacuum and control systems malfunctions). Some are due to a decrease in reactor coolant system flow rate, as in the case of a trip of one or more coolant pumps. Some are connected with reactivity and power distribution anomalies, such as for an inadvertent control rod withdrawal or unwanted boron dilution due to a malfunction of the volume control system for a PWR. Events entailing the increase or decrease of the reactor coolant inventory may also happen, due to malfunctions of the volume control system or small leaks. Finally, releases of radioactive substances from components may occur. 

Cr.l2 Suppression of reactor power oscillations III Protection and Reactivity Control Systems Cr.29 Protection against anticipated operational occurrences... 

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. 

Criterion 29 - Protection against anticipated operational occurrences. The protection and reactivity control systems shall be designed to assure an extremely high probability of accomplishing their safety functions in the event of anticipated operational occurrences. 

Criterion 60 - Control of releases of radioactive materials to the environment. The nuclear power unit design shall include means to control suitably the release of radioactive materials in gaseous and Uquid effluents and to handle radioactive solid wastes produced during normal reactor operation, including anticipated operational occurrences. Sufficient holdup... 

Criterion 64 - Monitoring radioactivity releases. Means shall be provided for monitoring the reactor containment atmosphere, spaces containing components for recirculation of loss-of-coolant accident fluids, effluent discharge paths, and the plant environs for radioactivity that may be released from normal operations, including anticipated operational occurrences, and from postulated accidents. 

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. 

A system important to safety, i.e., provided to ensure the safe shutdown of the equipment or otherwise control an operation or to limit the consequences of anticipated operational occurrences and design basis incidents. Safety systems consist of the protection system, the safety actuation systems, and the safety system support features. Components of safety systems may be provided solely to perform safety functions, or may perform safety functions in some plant operational states and non-safety functions in other operational states. Safety system support features are considered the collection of equipment that provides services such as cooling, lubrication, and energy supply required by the protection system and the safety actuation systems. 

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