The publication by Reuters on August 5, 2013 of a news report about the situation at the Fukushima Daiichi nuclear power plant (read) has revived questions concerning the management of the contaminated water on the site of Fukushima-Daiichi.

For IRSN, there was no sudden aggravation of the situation in recent days, but statements by the authority present at the site reminding the operator TEPCO of the need to put in place as quickly as possible corrective actions regarding the diffuse contamination of the Pacific Ocean.

Volumes of contaminated water at the site are estimated at several hundreds of thousands of cubic meter. The natural phenomena that led to the accident that affected TEPCO’s Fukushima Daiichi nuclear power plant on March 11, 2011 also led to flooding of the site leading to an accumulation of water in the basements of the power plant buildings. Furthermore, since the accident, the water used to cool the damaged cores of the reactors has been flowing into the basements of the buildings from where it is pumped in order to be re-used, after treatment, to cool the reactors.

However, the galleries below the plant are not completely sealed; there is a suspicion of contamination of groundwater. Tepco is trying to strengthen the leak tightness of the ground by injection of sealing products and by creating a first barrier between the facilities and the ocean (expected to be completed by mid-2014).

For more information on the situation, download the information notes by IRSN:

Fukushima Daiichi nuclear accident: Management of contaminated water from the damaged reactors (PDF)

Fukushima Daiichi nuclear accident: Contamination of the ground between the damaged reactors and the Pacific Ocean  (PDF)

IRSN and GRS are jointly developing the ASTEC software system dedicated to nuclear meltdowns in the different types of reactors currently in operation. A January 2013 meeting of the ASTEC Users Club in Aix-en-Provence in southeastern France bolstered its position as an international reference and consolidated its scope of applications, which has progressively been extended to include most types of reactors, existing and future.

Over the past decade, ASTEC has earned its status as an international reference in the simulation of core meltdown accidents in pressurized water reactors – including the Russian-designed VVER – with the help of the SARNET network [1] in particular.

Today, no fewer than 36 organizations use ASTEC, and three major events have just strengthened its position as the leading reference in this type of software:

• the selection of ASTEC by JRC/IET [2] for use in its core meltdown accident research laboratory,
• China Nuclear Power Engineering’s decision to acquire a five-year commercial user license for ASTEC,
• the beginning of the Code for European Severe Accident Management [3] project of the 7th FRDP.

The modular nature of ASTEC allows its scope of application to be extended to a wide range of reactors such as boiling water reactors, to enable a detailed analysis of the Fukushima Daiichi accidents and of the IPHWR [4] for collaboration with India’s BARC [5]. ASTEC is already being applied to naval propulsion reactors, but will benefit from certain improvements following IRSN-led development work as part of an agreement with the CEA/DAM [6].

For accidents in other types of reactors, ASTEC is being used to model accidents involving the ingress of air or water into the vacuum vessel of fusion facilities such as the ITER and is being adapted for sodium-cooled fast reactors as part of the 7th FRDP project entitled "Joint Advanced Severe Accidents Modelling and Integration for Na-Cooled Fast Neutron Reactors" coordinated by IRSN.

Notes:

1. Excellence network specialized in research on severe nuclear reactor accidents.
2. Institute for Energy and Transport of the Joint Research Centre of the European Union, located in Petten (the Netherlands).
3. Coordinated by GRS working closely with IRSN, this project brings 17 partners together to improve the modeling and functionality  of the ASTEC software for severe accident management.
4. Indian Pressurized Heavy Water Reactors (developed by India).
5. Bhabha Atomic Research Centre.
6. Military applications division of the French Alternative Energies and Atomic Energy Commission.

Created in 2006, the European Technical Safety Organisations Network ETSON [1] aims to contribute to the harmonization of nuclear safety in Europe and beyond. Today, the network publishes four technical guides to promote and disseminate best practices for the assessment of nuclear safety.

Since the launch of the EUROSAFE initiative in 1999, the French institute IRSN, the German GRS and the Belgian Bel V (formerly AVN) pursued the objective of advancing the harmonization of nuclear safety in Europe by comparing their methods to assess safety. In 2004, they published a "Guide for Safety Evaluation" with practical methods for performing common safety assessments.

Pursuing this approach, the European Technical Safety Organisations Network ETSON releases today four technical guides to promote and disseminate best practices for the assessment of nuclear safety at European and global level. The preparation of these guides relied on twelve thematic working groups in which experts have analyzed the different methods of evaluation of nuclear safety implemented in European countries.

A general document (Safety Assessment Guide) defines the scope of the methodology used in Europe during safety assessments, presents different requirements for the assessment of nuclear safety and also the technical elements required to complete an evaluation. It is supplemented by the first three thematic technical guides: Deterministic severe accidents analysis, Event review and precursor analysis, Human and organizational factors in nuclear facilities design and modification processes.

Each ETSON members will appropriate the harmonised methods described in the TSAGs, decline them in their countries for their own safety studies assessment and, then, share the experience feedback.

Download the ETSON guides (PDF files) on the ETSON website www.etson.eu​

• Safety Assessment Guide
• Technical Safety Assessment Guide : Event review and precursor analysis
• Technical Safety Asessment Guide : Human and organisational factors in nuclear facilities design and modification processes
• Technical Safety Assessment Guide : Deterministic severe accidents analysis

Note:

1- The ETSON network currently comprises eight members (IRSN - France, GRS - Germany, Bel V – Belgium, UJV - Czech Republic, VTT – Finland, LEI – Lithuania, VUJE – Slovakia, PSI - Switzerland) and 3 associate members (JNES – Japan, SSTC - Ukraine, SEC NRS – Russia)

For several years, IRSN has been conducting researches on the economical costs of nuclear accidents involving radioactive releases in the environment. A short presentation of these studies took place during the Eurosafe Forum in November 2012.

Preparing for a nuclear accident implies understanding potential consequences. While many specialized experts have been working on different particular aspects, surprisingly little effort has been dedicated to establishing the big picture and providing a global and balanced image of all major consequences.

IRSN has been working on the cost of nuclear accidents, an exercise which must strive to be as comprehensive as possible since any omission obviously underestimates the cost. It therefore provides (ideally) an estimate of all cost components, thus revealing the structure of accident costs, and hence sketching a global picture.

On a French PWR, it appears that controlled releases would cause an “economical” accident with limited radiological consequences when compared to other costs; in contrast, massive releases would trigger a major crisis with strong radiological consequences. The two types of crises would confront managers with different types of challenges.

More information:

Download the paper by Patrick Momal and Ludivine Pascucci-Cahen presented during the Eurosafe Forum: Massive radiological releases profoundly differ from controlled releases (pdf)

On February 12, 2013, a roof and a section of wall of the turbine hall of the C​hernobyl reactors collapsed. IRSN publishes an information note about this event which, given the available evidence, has no impact on the environment.

The collapse was caused by an accumulation of snow on the roof structural steelwork. The area is near the sarcophagus that was installed over the damaged reactor in 1986. The photos below show a view of the outer wall of the turbine hall, locally destroyed, and a view of the roof partially collapsed.

Download the information note from IRSN

Following the accident that occurred on the Fukushima Daiichi nuclear power plant on 11th March 2011, the French prime minister asked the French nuclear safety authority (ASN) to carry out an audit on the safety of French nuclear facilities.

On 5th May 2011, ASN required the French nuclear operators to perform Complementary Safety Assessments (CSAs) of their facilities. The CSAs evaluate the capacity of French nuclear facilities to withstand extreme situations beyond design basis assumptions. In 2011, these evaluations included the power reactors in operation or under construction, as well as certain nuclear facilities considered by ASN to be priority.

The operators submitted their CSAs reports to ASN on 15th September 2011. IRSN’s review and of these reports was transmitted to ASN and to the Nuclear Safety Advisory Committees on 4th November 2011.

Based on IRSN's critical assessment, the Nuclear Safety Advisory Committees met the 8th, 9th and 10th November 2011 to review these Complementary Safety Assessments and the relevance of the improvements proposed by the operators to enhance the safety of their facilities in the event of extreme situations (earthquake, flood, loss of electrical power supply, loss of heat sinks).

On 17th November 2011, during a conference jointly organised by ASN and IRSN, IRSN presented its analysis and conclusions to the press and made public its CSAs report. And on 3rd January 2012, ASN’s report on the CSAs was submitted to the Prime Minister and made public.

The review conducted by IRSN of the CSAs reports submitted by operators revealed three main observations:

1. A small number of nuclear facilities have compliance gaps in terms of requirements, which weaken their safety within the framework of events taken into account for their design. Corrective actions are already in progress and are to be accelerated.
2. Developments in knowledge must lead to some requirements being re-examined in advance. This is especially the case with the integration of earthquakes, for which knowledge has advanced massively over the last years.
3. The issue of the behaviour of nuclear facilities in the event of a conceivable extreme natural disaster is raised since, in the current situation, this could have unavoidable consequences, ending up in core meltdown and radioactive release.

To confront these exceptional - but nonetheless conceivable - scenarios, IRSN recommends adopting an additional safety requirement level, entitled “hardened safety core”, which would guarantee that the vital basic functions of nuclear facilities are sustained over several days, thus enabling off-site resources to intervene.

More information:

IRSN information notice of 17th November 2011: IRSN analysis and conclusions following the expert review of the Complementary Safety Assessments submitted to ASN by the operators at the request of the Prime Minister after the Fukushima accident

Technical summary of IRSN review of CSAs report: Post-Fukushima Complementary Safety Assessments: behaviour of French nuclear facilities in the event of extreme situations and relevance of the proposed improvements