ASN requires EDF to comply with additional requirements for implementation of the "hardened safety core"

On 21st January 2014, the ASN Commission adopted 19 resolutions setting out additional requirements for implementation of the post-Fukushima “hardened safety core” in EDF’s NPPs. These resolutions specify the objectives and the contents of this “hardened safety core”, which shall comprise measures to:

• Prevent a severe accident affecting the core of the reactor or the spent fuel pool;
• Limit the consequences of an accident which could not be avoided, with the aim of preserving the integrity of the containment without opening the venting system. This aim of mitigating the consequences of an accident applies to all the phases of an accident;
• Enable the licensee to perform its emergency management duties.

 This “hardened safety core” must be as independent as possible from the existing systems, more specifically with regard to I&C and electrical power supplies. The ASN resolutions specify the design rules to be adopted for the “hardened safety core” equipment. These rules must comply with the most demanding nuclear industry standards, used for the design and construction of installations requiring a high level of safety. Finally, they will lead EDF to determine the maximum hazards to be considered for the “hardened safety core” equipment, in particular for earthquake, flooding.

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The creation of a “hardened safety core” was prescribed by ASN on 26th June 2012, following the analysis of the conclusions of the stress tests that were ordered to take account of the lessons learned from the Fukushima Daiichi accident of 11th March 2011. The concept of the “hardened safety core” aims to create structures and equipment able to withstand extreme events and perform functions that are vital to the safety of the reactor. The aim is to provide the equipment necessary for controlling the safety functions with protection from hazards, more specifically those greater than the hazards adopted for the general design of the facility, in order to ensure ultimate protection of the facilities against them.

At the request of ASN, the “hardened safety core” proposed by EDF was analysed by IRSN and the conclusions of this analysis were presented to the Advisory Committee for nuclear reactors (GPR) on 13th and 20th December 2012.

Based on the recommendations made by the Advisory Committee, ASN prepared draft resolutions which determine the additional prescriptions specifying certain requirements relative to the “hardened safety core” proposed by EDF for its NPPs. From 18th November to 9th December 2013, the public were invited to consult the draft ASN resolutions concerning the additional prescriptions applicable to EDF for the “hardened safety core” in the NPPs and submit their comments on the content of these drafts.

These resolutions will apply to all the NPPs in operation, as well as to the Flamanville 3 EPR reactor currently under construction.

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ASN recalls the other measures concerning EDF NPPs decided on further to the stress tests.

 In its opinion of 3rd January 2012, further to the stress tests, ASN underlined the fact that it would be requiring the licensees to comply with a range of measures and reinforce the safety requirements concerning the natural risks (earthquake and flooding), the prevention of risks linked to the other industrial activities, to subcontractor oversight and to processing of deviations. These measures were imposed by 32 ASN resolutions, each setting out about thirty additional prescriptions applicable to EDF’s NPPs, to AREVA’s facilities and to certain CEA reactors. The corresponding measures should lead to a significant increase in the safety margins beyond the design-basis margins of the facilities. Over and above the “hardened safety core”, EDF is required to comply with the following prescriptions:

• the “Nuclear rapid intervention force (FARN)”, which ASN confirmed was able to intervene by late 2012 and which will be fully operational no later than the end of 2014. This force can provide assistance to a damaged site by providing specialised teams to back up those of the plant concerned and mobile equipment to supply additional water and electricity. A number of modifications were therefore made to the reactors to make it easier to connect this equipment brought on-site by the FARN;
• pending the deployment of the 58 ultimate backup diesel generator sets for all the reactors, medium-power generator sets were added to each reactor before 30th June 2013;
• additional training to its staff for intervention in the event of an earthquake and a severe accident.

 In its opinion of 3rd January 2012, ASN also recalled that social, organisational and human factors were a key aspect of safety. Over and above the requirements in this field imposed by the ASN resolutions of 26th June 2012 (improving and reinforcing operator training, taking account of intervention conditions in an emergency situation, considering the psychological stress on staff working in these situations, etc.), ASN set up a pluralistic working group on these subjects, the Social, organisational and human factors steering committee (COFSOH). In 2013, two plenary meetings of this committee produced an inventory of the work initiated by three working groups on the following topics:

• subcontracting in a normal operating situation: organisation and intervention conditions;
• the use of subcontracting: legal questions;
• management of emergency situations.

 In its opinion, ASN also recommended that the draft order setting out the general rules concerning BNIs, which it had prepared jointly with the Ministries responsible for nuclear safety, be signed as rapidly as possible. This order was signed on 7th February 2012 and will make a significant contribution to improving safety; in more specifically sets new requirements concerning:

• oversight of external contractors by the nuclear licensees;
• taking account of combinations of situations when demonstrating nuclear safety;
• detecting and processing deviations;
• management of the technical capabilities of the licensees and any modifications to them;
• the competence and qualification of persons performing potentially hazardous activities;
• the development of a policy, which must also be implemented by the contractors, confirming the priority given to the prevention of the potential risks generated by the facility.

 In 2013, ASN focused on verifying correct implementation of the provisions of this order. ASN will clarify some of the requirements of this order by means of regulatory resolutions (the first was published in 2013 and several others will appear in 2014).

 Finally, on the basis of the in-depth experience feedback from the Fukushima accident, ASN announced in its opinion of 3rd January 2012 that it would be reinforcing the baseline safety requirements for the nuclear facilities. For this purpose, in 2013, ASN published its guide No.13 “concerning the protection of BNIs against external flooding”, which details recommendations aimed at assessing and quantifying the external flooding risks affecting these facilities, and at defining appropriate means of protection to counter them.

In 2014, ASN intends to finalise guidelines for implementation of new provisions introduced by the order of 7th February 2012 concerning the processing of deviations affecting NPPs, in order to explicitly determine the time within which facilities must be restored to conformity once a deviation has been discovered.

With regard to the baseline safety requirements concerning the consideration of seismic risks, the prescriptions setting out the additional requirements for deployment of the “hardened safety core” significantly reinforce the ability of the NPPs to withstand this risk^[1]. Finally, together with IRSN, ASN has begun to examine an update of the baseline safety requirements concerning the other external hazards. The following table summarizes demands which apply to each NPP:

  A English version of ASN resolution is provided for Gravelines NPP (GRA) and Flamanville NPP (FLA, including the EPR FLA3).

[1] Following on from this work, ASN will be initiating a revision of basic safety rule 2001-01 concerning determination of the seismic risk for the safety of BNIs.