Offsite power

Two types of initiators are internal and external. Internal initiators result from failures within a plant or the plant s support utilities. Thus, vessel rupture, human error, cooling failure, and loss of offsite power are internal events. All others are external events earthquakes, tornados, fires (external or internal), and floods (external or internal). Event trees can be used to analyze either type of initiator. 

An obvious example is the situation which can occur such that a loss of offsite power makes some power buses unavailable for RCS heat removal. In addition, this loss-of-power mitiator affects the availability of the remaining systems, because emergency power becomes the only source of electric power. 

Issue Resolution, JCOs, Plant Modifications EOOS performs sensitivity analyses to determine the significance of e. Ihe removal of offsite power or decay heat removal equipment. 

Loss of offsite power at nuclear power plants is addressed in EPRI NP-2301, 1982 giving data on the frequency of offsite power loss and subsequent recoveiy at nuclear power plants. Data analysis includes point estimate frequency with confidence limits, assuming a constant rate of occurrence. Recovery time is analyzed with a lognormal distribution for the time to recover. 

Select 1 and type a title for the problem the default title is "Siation Blackout from l ss of Offsite Power, unless you want to use this enter your title. 

Valve Arrangement of Auxiliary Feedwater System and Main Steam System during Shutdown - the auxiliary feedwater system has six MO Vs in the flow path to the steam generators and the main steam nonreturn valves are normally closed during shutdown. These valves depend on offsite power and are difficult to manually open. 

Four onsite power diesel generators that start automatically on loss of offsite power to reduce the frequency of the loss of station AC by an order of magnitude compared with ( , NDl 1 -6. This with the diesel driven auxiliary feedwater pump provides ample recovery imie... 

The loss of all AC power initiator includes both commercial (offsite) power and all three diesels, including the normally-running diesel. Local fault events include localized flow blockages in iho core and localized fuel faults. A lobe power imbalance initiator occurs if the individually-controlled core section powers (lobe powers)... 

The ESDs were then translated into associated event trees. A generic event tree was developed for all initiators not involving LOCA. The generic transient event tree for each category of the transient initiators and loss of offsite power were specialized by the impact of the initiators on the safety and support systems, from the success criteria of the mitigating systems, and the initiator-specific human actions which were modeled in the fault trees. 

Ten front line systems and 5 support systems were modeled using about 700 basic events. A generic transient event tree with 215 sequences was developed and quantified for 14 different transients and three loss-of-offsite-power events. Four LOCA event trees were de I and... 

In April 1982, a data workshop was held to evaluate, discuss, and critique data in order to establish a consensus generic data set for the USNRC-RES National Reliability Evaluation Program (NREP). The data set contains component failure rates and probability estimates for loss of coolant accidents, transients, loss of offsite power events, and human errors that could be applied consistently across the nuclear power industry as screening values for initial identification of dominant accident sequences in PRAs. This data set was used in the development of guidance documents for the performance of PRAs. 

Automatic and manual initiation demands In addition to test demands, equipment may be activated or deactivated by intended or spurious signals. These signals include losses of offsite power and normal shutdowns or startups. Different components react to different signals or sets of signals, depending on their functions for each system. The... 

Vessels and Ducts 5.2 NSSS Control 7.3.2 Offsite Power, Main Generator 8.4... 

The operability of the systems as a whole and, under conditions as close to design as practical, the full operation sequence that brings the systems into operation, including operation of applicable portions of the protection system and the transfer of power between the offsite power system and the on-site power system,... 

Suitable redundancy in components and features, and suitable interconnections, leak detection, and isolation capabilities shall be provided to ensure that for on-site electric power system operation (assuming offsite power is not available) and for offsite electric power system operation (assuming... 

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. 

The base scenarios are classified by initiating events or safety system availability which may impact on an accident progression. Left hand side of Fig. 2 represents sample database structure of analysis results for a loss of offsite power initiating event which can be applied to the OPR-1000 plant. There are 12 base scenarios depending on the operation status ofplant safety features. The operation status of safety systems are ... 

As the German nuclear power plants are designed to withstand the impact of external explosions and aircraft crashes, loads due to high winds are not expected to he important risk contributors. Nevertheless, outdoor switchyards and transformers are susceptible to wind driven missiles. If such equipment fads, loss of offsite power event sequences (transients typically analyzed as part of the plant internal events) might result. Similar simations can also arise fiwm an increased rainwater, sea salt spray, sand, or dust loading. 

The possible consequences of a flooding depend on the question whether it is hmited to the outdoor plant area or water actually penetrates into buildings. In the first case, the dominant consequence is apotential loss of offsite power. In case water should penetrate into safety related huildings/rooms, there is additionally a potential for a radioactive release or even a loss of the residual heat removal system. 

The operation of the affected plants has primarily been impaired by loss of offsite power and by short-circuits due to increased moisture ingress. 

In the case of a bush or forest fire, there is generally sufficient time for the operators to bring the reactor into a safe state and to take appropriate protection measures. The potential impacts of external fires are the intake of smoke via the ventilation system and a loss of offsite power. 

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