European stress tests: ASN publishes the update of its national action plan which covers all the measures decided on by France

On 26 April 2012, one year after the Fukushima Daiichi accident, a joint statement by ENSREG^[1] and the European Commission concluded the stress tests conducted on the European nuclear power plants. This statement emphasised the need to implement an overall action plan to ensure that these stress tests would be followed by safety improvement measures implemented in a consistent manner in each country.

The ENSREG global action plan provided for the nuclear safety regulator of each member country to publish a national action plan by the end of 2012. ASN published the action plan for France in December 2012^[2]. The national action plans then underwent a peer review, which was concluded by a seminar organised by ENSREG, held in April 2013 in Brussels. For France, the seminar summary report emphasized in particular the comprehensive nature of the action plan presented, the importance that ASN attached to the transparency of the stress tests, the ambitious nature of the content and the implementation times for the measures to improve safety in the nuclear power plants decided further to the Fukushima Daiichi accident, and the taking into account of organisational and human factors, including subcontracting conditions.

Further to this seminar it was decided to assess the situation of implementation of the actions in each country after two years. ASN therefore updated its action plan applying the ENSREG recommendations. Two aspects have implications that are particularly important:

Lightbox

• taking into account by the licensee of ASN's additional demands aiming to clarify certain design provisions of the hardened safety core. These demands are part of a defence in depth approach. As such they concern measures to prevent and mitigate the consequences of an accident that exceeds the initial design basis limits for all the facilities on a site. This approach involves the deployment of external mobile means which will be completed at the end of 2015. France has also decided to supplement these provisions by implementing substantial fixed means ensuring increased robustness against extreme external hazards;
• ASN's commitment to the pan-European work on the management of radiological emergency situations with the aim of harmonising population protection measures on either side of national frontiers. It is in this context that the associations HERCA (Heads of European radiological Protection Competent Authorities) and WENRA (Western European Nuclear Regulators' Association) adopted a joint position^[3] at the end of 2014 aiming to improve management and cross-border coordination in emergency situations.

As in the preceding exercise, the updated national action plans will be examined by all the European safety regulators. ENSREG will organise a seminar in April 2015 at which each safety regulator will present its national action plan and answer questions raised by its counterparts and the public.

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

At the end of the stress tests, ASN underlined in its opinion of 3rd January 2012 that it was going to oblige the licensees to take measures to reinforce protection against natural risks (earthquakes and flooding) or risks associated with other industrial activities and control the accident situations that could result therefrom (loss of electrical power supplies, loss of heat sinks, severe accidents). These requirements oblige EDF more specifically:

• to implement a "hardened safety core" comprising a limited number of equipment resources that can ensure the safety functions in extreme situations.
  This "hardened safety core" must be as independent from the existing systems as possible, particularly regarding the instrumentation and control and the electrical power supply. On 21 January 2014, the ASN Commission adopted 19 resolutions specifying the objectives and the constituents of this "hardened safety core".EDF proposes setting up this hardened safety core in two phases:
  • a first phase comprising the setting up of the fundamental elements of the hardened safety core, and more specifically, for each reactor, a large-capacity ultimate back-up diesel generator set necessitating the construction of a dedicated building, a dedicated ultimate water source and ultimate water makeup, and the construction on each site of a local emergency response centre capable of withstanding extreme external hazards. These provisions will be implemented gradually, starting in 2015 and completed for the most part by 2022;
  • a second phase will supplement the first to improve the level of coverage of the potential accident scenarios considered, particularly with respect to the potential consequences of severe accidents. These means include the finalising of the ultimate makeup connections to the reactor, the installation of an ultimate instrumentation & control system and the definitive instrumentation of the hardened safety core, the setting up of an ultimate containment cooling system to avoid opening the filtered venting system of the reactor containment, the setting up of a system for flooding the reactor pit to prevent basemat melt-through by the corium These means have also been defined by EDF with a view to continuing reactor operation, as they correspond to the objectives set by ASN in this context. EDF therefore plans implementing them under the next periodic safety reviews.

• the deployment of the "FARN" (nuclear rapid intervention force), which can come to the aid of a site with 4 accident-stricken reactors by providing specialised teams who can back up the teams of the nuclear power plant (NPP) concerned and bring mobile equipment to ensure the water makeups and provide electrical power. In this context, several modifications have been applied to the reactors to facilitate the connection of the equipment brought by the FARN. ASN checked that this was operational at the end of 2014.
• the implementation of a set of temporary or mobile measures to reinforce protection against transient situations of total loss of the heat sink or electrical power supplies: These measures include, for example, the installation of medium-power generator sets on each reactor, the reinforcing of the local emergency response means (pumps, generator sets, hoses, etc.), the installation of connection tappings for mobile equipment, notably that of the FARN the reinforcing of the resistance to earthquakes (safe shutdown earthquake - SSE) and flooding (thousand-year flood safety level) of the emergency management premises. Implementation of these provisions is well advanced and should be completed in 2015.

The update of the ASN action plan on the follow-up of the French NPP stress tests and the synthesis table tracking the actions prescribed by the ASN resolutions of 26th June 2012 show EDF's progress with their implementation.

EDF has met all the regulatory deadlines of the resolutions of 26th June 2012, and has notably implemented the modifications they required for 31st December 2014, particularly with respect to the seismic risk, the flood risk, the limitation of discharges in the event of an accident, the maintaining of the water inventory of the pools in exceptional external hazard situations and the improving of the instrumentation.

In its opinion of 3rd January 2012, ASN also underlined that the social, organisational and human factors represent a key element of safety. The ASN resolutions of 26th June 2012 contain requirements in this area (improvement and reinforcing of operator training, consideration of intervention conditions in emergency situations, consideration of the psychological pressure on the persons intervening in these situations, etc.). ASN has moreover set up a pluralistic working group on these subjects called the COFSOH (Social, organisational and human factors steering committee). This committee has held six plenary meetings since 2012. The meetings have addressed the following subjects: conditions of subcontracting and relations between the ordering customer and subcontractors, the relationship between "managed security" and "regulated security", management of skills in a context of staff renewal, and the evaluation of the organisation or the use of appropriate Human and Organisational Factors (HOF) indicators to assess safety.