- 184 - groundwater by liquid radioactive releases, is in progress. This examination, which began before Fukushima as part of the reactor operating life extension beyond 40 years, takes account of the opinion of the Advisory Committee which met in June 2009 on this subject and which was followed by ASN requests. As part of the complementary safety assessments subsequent to the Fukushima accident, EDF decided to speed up the studies in response to the ASN requests, in relation to the schedule initially stipulated by ASN following the 2009 Advisory Committee meeting. These studies, which are specific to each site, comprise hydrogeological surveys based on in-situ measurements and feasibility studies concerning the technical measures, such as geotechnical or equivalent containments, designed to delay the transfer of contamination to the groundwater. EDF undertook to provide these studies in 2012 or 2013 depending on the sites. Given their unfavourable conditions in the event of pollution, ASN considers that the sites of Fessenheim, Bugey and Civaux are priorities. ASN will require that EDF speed up the submission of the hydrogeological surveys. Furthermore, the possibility of implementing countermeasures to basemat melt-through and soil pollution are among the topics being examined as part of the more general ten-yearly safety reviews framework. In this context, ASN will be asking EDF to send it a feasibility study on the implementation of technical arrangements to prevent the transfer of radioactive contamination to the groundwater in the event of a severe accident leading to melt-through of the basemat by the corium. For the particular case of the Fessenheim reactors, the 1.50 m thickness of the basemat is the lowest in the fleet (3 to 4 metres for most reactors in the fleet). In the current situation, EDF considers that the time to melt through the basemat following a severe accident with fuel melt and vessel melt-through could be about one day in the worst case (malfunction of all safeguard systems). In July 2011, for the continued operation of Fessenheim reactor n°1 beyond 30 years, and without prejudice to the conclusions of the CSAs, ASN asked EDF to reinforce the Fessenheim basemat before 30th June 2013 in order to significantly increase its corium resistance in the event of a severe accident. The dossier, which has been submitted by EDF on 9th December 2011, will be examined by ASN in 2012. 6.3.6 Supply of electricity and compressed air for operation of the equipment used to preserve the containment integrity The ASN specifications required that EDF also adopt a stance on the electrical systems used by the equipment designed to preserve the integrity of the reactor buildings containment. In the CSA reports, EDF mentions that a limited number of items are needed for directly managing preservation of the integrity of the containment in the event of a reactor "severe accident". These are the containment isolation valves and the wide-range containment pressure measurement system which outputs information determining when to open the U5 filter if necessary. Following the CSAs, EDF decided to back-up the electrical power supply to all this equipment with an Ultimate Backup Diesel Generator (DUS) to be added to each reactor. Pending the implementation of this modification, an electrical back-up (mobile diesel generator) will be installed by the FARN, except for the containment isolation valves. An ITS (temporary safety instruction) to request manual closure of these valves before entering the GIAG phase will be proposed by EDF. This is considered by ASN to be satisfactory. 6.3.7 Instrumentation required to protect the integrity of the containment The pressure in the containment is managed by monitoring the wide-range containment pressure measurement. This monitoring system helps determine the moment at which to open the U5 device when the pressure in the reactor building exceeds a threshold. In the CSA reports on the reactors in the fleet, EDF states that the primary pressure measurement on all plant series, as well as the wide-range containment pressure measurements at Fessenheim, the CPY and N4 plant series, are backed-up electrically via the LLS turbine generator set. In addition, following the CSAs, EDF undertook to conduct a feasibility study on short-term electrical back-up (less than 24 hours) of the containment pressure for the reactors of the Bugey NPP and the 1300 MWe plant series by the end of 2012.
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