Both at-power and shutdown conditions should be addressed in the SFP PSA, however different operating modes for a SFP PSA may not be as relevant as for the reactor core. During shutdown conditions the plant configuration typically varies more and POSs that cover all these different configurations should be defined. The definition is made in the same way as for the reactor core shutdown PSA (for instance regarding system availabilities), but for the SFP PSA the following specific conditions also need to be taken into consideration: transfer canal (if applicable) between SFP and reactor building pool; opened, closed, amount of fuel offloaded to the SFP; complete core offload, partial core offload, reloading of new fuel; fuel movement complete; amount of cooling in the SFP. Note that this section covers issues that can be of interest for the SFP PSA for a plant to be commissioned or already in operation. In principle the types of accidents in SFP PSA can be divided into two categories: events/ sequences, loss of cooling events/ sequences (or non-draining IEs). Draining events may be caused by inappropriate operator action, seismic induced structural failures, heavy load drops, loss of coolant accidents (LOCAs), and reactor-related phenomena causing structural failure (e.g. steam explosion, hydrogen detonation). For non-draining events, the set of initiating events can be derived from an analysis of the situations leading to the temperature increase, i.e. to the loss of the cooling system, which may be due either to malfunctions in the cooling system itself or its support functions including electrical supply or the cooling chain. In L1 PSA, it is necessary to study each plant state (POS) because of the different configurations or characteristics of structural failures and support systems of electrical supply or cooling chain. Also, the timing of the release is very dependent on the sequence/ initiating event. This is also important for operator actions. However in L2 PSA it is almost irrelevant which particular combination of initiating event and failure has led to loss of cooling or draining and loss of coolant. The following spent fuel pool events leading to fuel damage should be taken into account: loss of cooling to the SFP (including failure of support systems and loss of coolant inventory loss from the SFP; heavy load drops, loss of coolant accidents (LOCAs), reactor-related phenomena causing structural failure, reactivity accidents;
Both at-power and shutdown conditions should be addressed in the SFP PSA, however different operating modes for a SFP PSA may not be as relevant as for the reactor core. During shutdown conditions the plant configuration typically varies more and POSs that cover all these different configurations should be defined. The definition is made in the same way as for the reactor core shutdown PSA (for instance regarding system availabilities), but for the SFP PSA the following specific conditions also need to be taken into consideration: transfer canal (if applicable) between SFP and reactor building pool; opened, closed, amount of fuel offloaded to the SFP; complete core offload, partial core offload, reloading of new fuel; fuel movement complete; amount of cooling in the SFP. Note that this section covers issues that can be of interest for the SFP PSA for a plant to be commissioned or already in operation. In principle the types of accidents in SFP PSA can be divided into two categories: events/ sequences, loss of cooling events/ sequences (or non-draining IEs). Draining events may be caused by inappropriate operator action, seismic induced structural failures, heavy load drops, loss of coolant accidents (LOCAs), and reactor-related phenomena causing structural failure (e.g. steam explosion, hydrogen detonation). For non-draining events, the set of initiating events can be derived from an analysis of the situations leading to the temperature increase, i.e. to the loss of the cooling system, which may be due either to malfunctions in the cooling system itself or its support functions including electrical supply or the cooling chain. In L1 PSA, it is necessary to study each plant state (POS) because of the different configurations or characteristics of structural failures and support systems of electrical supply or cooling chain. Also, the timing of the release is very dependent on the sequence/ initiating event. This is also important for operator actions. However in L2 PSA it is almost irrelevant which particular combination of initiating event and failure has led to loss of cooling or draining and loss of coolant. The following spent fuel pool events leading to fuel damage should be taken into account: loss of cooling to the SFP (including failure of support systems and loss of coolant inventory loss from the SFP; heavy load drops, loss of coolant accidents (LOCAs), reactor-related phenomena causing structural failure, reactivity accidents;
ASAMPSA_E-WP40-D40-7-vol4-L2PSA-RD-and-SFP-1.docx