- 146 - to avoid a breach at the RCP seals in a situation of total loss of the external and on-site electrical supplies for the reactors in service, EDF has started examining the implementation of robustness tests on the new high-temperature seals installed on the reactors in service in place of the O-rings; a programme will be defined in April 2012; EDF will examine the devices existing or under development across the world to ensure sealing of the RCP shaft seals at shutdown; on the basis of the results, EDF will adopt a position at the end of the first half of 2012 on a design modification allowing simultaneous injection at the seals on the two neighbouring reactors of the 900 MWe series; EDF will carry out a study of operation with accelerated cooling to reach a state where injection at the RCP seals is no longer necessary; as with the 1300 MWe and N4 series, EDF will shortly install on the 900 MWe series a motor-driven pump that ensures adequate make- up of the primary system when the latter is sufficiently open; in the short phase of direct opening of the reactor vessel with the closure head loosened, EDF will check - for March 2012 on the reactors in service - that this motor-driven pump can be used for make-up operations, pending installation of the "ultimate backup diesel generator" which will supply power to a means of make- up the primary system; for the EPR reactor, EDF will present an analysis of the situations of generalised electrical power failure by the end of 2012, and decide whether additional provisions are necessary; To define the requirements of the hard core equipment, EDF will consider diversification and independence, and will verify the risks of common mode failure in particular. ASN considers that the electrical power supply reinforcement objectives proposed by EDF must be implemented. In order to set the objectives for these reinforcements and the corresponding deadlines, ASN will issue an instruction governing the implementation of an additional hazard-resistant electrical power supply means and, pending this, the implementation of a temporary generator sets on each reactor. EDF has undertaken to determine whether the output of the CVCS system charging pump is sufficient for the injection at the RCP seals on the two neighbouring reactors simultaneously. If the pump output cannot be demonstrated as being sufficient, ASN considers that EDF should in the short term define a modification that makes simultaneous injection at the seals of the two neighbouring 900 MWe series reactors possible. Moreover, if a breach at the RCP seals cannot be avoided in a situation of loss of a site's off-site and on-site electrical power supplies, ASN considers that means for managing the breach must be deployed to prevent this situation degrading into a severe accident. ASN considers that the principle of EDF's commitment to take diversification and independence into account as means of achieving the hard core requirements, and to verify the minimising of common mode failure risks, is satisfactory. 5.2 Loss of the cooling systems / heat sink The heat sink provides the water to remove the thermal power from the nuclear fuel, to cool the systems of the nuclear or conventional facilities, and it supplies certain specific systems such as the fire-fighting system or water for industrial use. A reactor needs to be permanently connected to a heat sink, even after shutdown. The water is taken directly from the natural environment, that is to say the sea for coastal NPP sites, or a waterway for NPP's situated on the banks of a river. The water intake structures and the pumping station pump and filter the raw water which, once collected and filtered, is used to cool the systems via heat exchangers. The pumping station is connected directly to the intakeoutfall structure. Each site usually has one pumping station for two plant units. Each pumping station has two redundant and geographically separated channels.
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