- 268 - nature of the hypotheses used for the calculation. The flow rates are similar to those calculated for the Monteynard dam burst scenario. The licensee has therefore assessed the risks of water entering the reactor building taking 216.2 m NGF as the reference water height. It indicates that at this height of 216.2 m NGF, the consequences on the facility would be: flooding of level C of the reactor building via the large doors (truck door and courtyard door), loss of all the electrical power supplies. For information, the normal operations control room is situated on the 4th floor of building ILL4, above the 216.20 m NGF level. Yet operation from this room requires the off-site electrical power supplies or, the backup diesel generators situated at level 210.50 m NGF or the batteries situated on the 1st floor of building ILL4, i.e. at the level 214.20 m NGF. loss of the emergency control station (PCS), which allows control of the gaseous effluents (EG) system and the emergency water make-up system (CES); the associated electrical power supply consists of a backup diesel generator that is watertight up to the level 210.50 m NGF. Given this information it can be considered that monitoring and control of the facility is only maintained up to level 210.50 m NGF. The ILL points out that these failures do not however lead to an accident, as the reactor core and the fuel elements cooling in the pool are always correctly cooled by natural convection. It is important to underline the fact that in the event of a risk of site flooding, safe reactor shutdown can be carried out very rapidly, since the moment the reactor is shut down the residual power can be removed by simple natural convection which is established completely passively (via three natural convection valves, the opening of just one of them being sufficient) from the moment the cooling pumps that provided a forced downward flow stop functioning. On this basis it can be considered that, on condition that there is an effective flood risk alerting system, the licensee will be capable of shutting down the facility. Proposed measures to reinforce the robustness of the facility to the flood risk In view of which is presented above, the ILL has undertaken: during the winter 2013-2014 shutdown, to reinforce all the enclosure penetrations and openings situated below the level 216.20 m NGF. The items concerned are: the courtyard door, the truck door, the level C airlock, the penetration opening D2O and the secondary water penetration opening. During the examination ILL undertook to examine the possibility of starting work to reinforce the water-tightness of the reactor building openings as of the winter 2012-2013 shutdown, with priority being placed on the courtyard door which is situated at the lowest level (207 m NGF). put in place, during the winter 2011-2012 shutdown, a diesel generator set outside the floodable zone to energise the systems that guarantee reactor monitoring after flooding and deployment of initial aid means, such as a motor driven pump. It has also undertaken to build a new control station called PCS that can implement and control all the backup systems (CES, CRU, CDS, CEN) up to a water height reaching the 216.20 m NGF level. This point is developed in the "Severe accident management" section. Requests from ASN to reinforce the robustness of the facility On completion of its review of the ILL's CSA report, ASN considers the licensee's procedure satisfactory. In the coming months it will perform and in-depth examination of the licensee's proposed improvements, some of which could become requirements.
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