​Fukushima in 2016

Fukushima in 2016: Lessons learned in France
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Fukushima Daiichi in 2016:

Lessons learned in France

​The Fukushima accident has led to stricter safety measures and to improving the forecasting tools designed to help governments in a crisis situation and in the management of contaminated areas after an accident.

Lessons learned in France

Fukushima Daiichi in 2016:

Lessons learned in France

​The Fukushima accident has led to stricter safety measures and to improving the forecasting tools designed to help governments in a crisis situation and in the management of contaminated areas after an accident.

Lessons for the safety of facilities

The Fukushima accident has shown the vulnerability of nuclear facilities in the event of extreme and multiple natural aggressions. On an international level and in France, it has led to stricter safety measures and to the launching of new research programmes.

It is in this context that the French authorities have established a "post-Fukushima hardened safety core" aimed at equipping French facilities with operational resources in order to strengthen the prevention of accidents, limit their consequences and manage the related crisis for extreme levels of aggressions exceeding those of the standards in force.

EDF announced the gradual implementation of "post-Fukushima" measures at all of its power plants, increasing the safety level at each stage:

Phase 1. During this phase, which was completed in 2015, EDF set up material and organisational resources, in some cases temporary, essentially enabling the water and electricity supply capacity to be increased. Organizationally, one of the major measures was the establishment of the Nuclear Rapid Intervention Force (Force d'Action Rapide du Nucléaire, FARN), which is aimed at deploying additional resources at an accident site within less than 24 hours.Phase 2. With its deployment currently underway, the goal of this phase is to supplement and strengthen, between 2016 and around 2020, the means set up in Phase 1 by implementing final material and organisational means that are robust to extreme aggressions. These means constitute the first elements of the hard core.Phase 3. The modifications associated with this phase, whose deployment will begin in 2019, will complement and reinforce earlier measures so that the entire "hardened safety core" will be installed and operational at the end of this phase. The definition by EDF of the ultimate means necessary for achieving the objectives of Phase 3 is underway. It requires studies, some of which are already being reviewed by the IRSN since they are of a structural nature.

Definition of the levels of extreme natural hazards

The hardened safety core equipments must withstand aggressions whose severity exceeds that considered in the facility safety requirements, particularly with regard to earthquakes, floods (including heavy rain), extreme winds, lightning, hail and tornadoes.

Moreover, the hardened safety core must remain operable in the event of a combination of such aggressions and total loss of electrical power not belonging to the hard core, as well as the loss of the cooling source not belonging to the hard core.

Deployment for other nuclear facilities

The CEA research reactors.
The findings of the review conducted by IRSN led ASN to require operators to define a hardened safety core for four reactors: Phenix (currently being dismantled), Osiris (shutdown since late 2015), Orphée (operating) and RJH (under construction).
The ILL High Flux Reactor (HFR).
The operator has proposed significant changes to the facility aimed at strengthening its capacity to withstand extreme aggressions. The HFR hardened safet core will be fully operational in the first half of 2016.
The fuel cycle facilities.
This activity is characterised by a wide variety of facilities and of materials and processes used. In addition, Areva has defined, on a case by case basis, the hard core measures. This has been analysed in detail by IRSN. Moreover, Areva has initiated actions to strengthen the crisis management means.

 

Download "Lessons learned from the Fukushima accident for the safety of French facilities"  (PDF, 285 Ko)

​Deflector spike zone: view of the floating drome. This dam protects the inlet channel of the Cruas nuclear power plant (on the right in the image) by stopping the large blockages carried by the Rhone (left). © Noak/Le bar Floréal/IRSN

Lessons for the safety of facilities

Lessons for the safety of facilities

​Deflector spike zone: view of the floating drome. This dam protects the inlet channel of the Cruas nuclear power plant (on the right in the image) by stopping the large blockages carried by the Rhone (left). © Noak/Le bar Floréal/IRSN

The Fukushima accident has shown the vulnerability of nuclear facilities in the event of extreme and multiple natural aggressions. On an international level and in France, it has led to stricter safety measures and to the launching of new research programmes.

It is in this context that the French authorities have established a "post-Fukushima hardened safety core" aimed at equipping French facilities with operational resources in order to strengthen the prevention of accidents, limit their consequences and manage the related crisis for extreme levels of aggressions exceeding those of the standards in force.

EDF announced the gradual implementation of "post-Fukushima" measures at all of its power plants, increasing the safety level at each stage:

Phase 1. During this phase, which was completed in 2015, EDF set up material and organisational resources, in some cases temporary, essentially enabling the water and electricity supply capacity to be increased. Organizationally, one of the major measures was the establishment of the Nuclear Rapid Intervention Force (Force d'Action Rapide du Nucléaire, FARN), which is aimed at deploying additional resources at an accident site within less than 24 hours.Phase 2. With its deployment currently underway, the goal of this phase is to supplement and strengthen, between 2016 and around 2020, the means set up in Phase 1 by implementing final material and organisational means that are robust to extreme aggressions. These means constitute the first elements of the hard core.Phase 3. The modifications associated with this phase, whose deployment will begin in 2019, will complement and reinforce earlier measures so that the entire "hardened safety core" will be installed and operational at the end of this phase. The definition by EDF of the ultimate means necessary for achieving the objectives of Phase 3 is underway. It requires studies, some of which are already being reviewed by the IRSN since they are of a structural nature.

Definition of the levels of extreme natural hazards

The hardened safety core equipments must withstand aggressions whose severity exceeds that considered in the facility safety requirements, particularly with regard to earthquakes, floods (including heavy rain), extreme winds, lightning, hail and tornadoes.

Moreover, the hardened safety core must remain operable in the event of a combination of such aggressions and total loss of electrical power not belonging to the hard core, as well as the loss of the cooling source not belonging to the hard core.

Deployment for other nuclear facilities

The CEA research reactors.
The findings of the review conducted by IRSN led ASN to require operators to define a hardened safety core for four reactors: Phenix (currently being dismantled), Osiris (shutdown since late 2015), Orphée (operating) and RJH (under construction).
The ILL High Flux Reactor (HFR).
The operator has proposed significant changes to the facility aimed at strengthening its capacity to withstand extreme aggressions. The HFR hardened safet core will be fully operational in the first half of 2016.
The fuel cycle facilities.
This activity is characterised by a wide variety of facilities and of materials and processes used. In addition, Areva has defined, on a case by case basis, the hard core measures. This has been analysed in detail by IRSN. Moreover, Areva has initiated actions to strengthen the crisis management means.

 

Download "Lessons learned from the Fukushima accident for the safety of French facilities"  (PDF, 285 Ko)

Modelling radioactive fallout in a crisis situation

The Fukushima accident has shown the need to improve prognostic tools designed to assist governments in their decision making in crisis situations. In Japan, the simulation had difficulty in reproducing several radioactive release dispersion episodes and discrepancies were found between the modelling results and the radiological measurements in the environment.

Download "Modelling of atmospheric transport and release fallout emitted during the Fukushima accident" (PDF, 618 KB)

  

The main input data for the atmospheric dispersion models of entry comprise weather conditions and the characterisation of the releases:

The weather conditions determine the radioactive plume transport in the atmosphere. However, the difficulty of properly taking into account the orography (description of the topographic relief) in the weather forecasts was raised by the IRSN. Thus, precipitation forecasts, which are responsible for soil contamination due to the leaching of the plume, do not always reflect reality.The source term, that is to say the change over time of the rate of each radionuclide released into the atmosphere, is an essential input for atmospheric dispersion models. However, there is no clear consensus to identify a source term that is more realistic than another. The differences can be attributed to weather conditions and to the types of measurements used (volume activity, dose rate or total deposition).

Since 2011, simulations have become more realistic and the model /measurement differences have now been significantly reduced. Decisive progress has been made through the use of various weather forecasting sources and of more realistic source terms, as well as through a better understanding of environmental contamination episodes.

This work is currently still underway. And for good reason: all studies still indicate weaknesses and often face the same difficulties in modelling some contamination events in Fukushima.

Download "Main contamination events subsequent to the Fukushima accident" (PDF, 375 Ko)

  

For IRSN, the purpose of improving the operational assessment tools is to enhance the adequacy of the Institute's response to nuclear accidents, particularly regarding the exposure of populations:

The dispersion models used in an operational context generally have very simplified deposition models. Also, the challenge is knowing whether complex models taking into account the physics of aerosols, particle size or even precipitation would better simulate depositions.A complex deposition model does not solve the difficulty in reproducing some episodes. These difficulties seem mainly due to remaining uncertainties about the input data and to the modelling of plume behaviour within the context of a complex orography.

 

Coupling environmental measurements with the atmospheric dispersion model 

Since 2011, IRSN has been working to improve the understanding of the Fukushima accident and its environmental consequences, by coupling the analysis of environmental measurements with atmospheric dispersion modelling.

This work is largely being carried out as part of international collaborations. This analysis has enabled the path of the plumes in the atmosphere and the periods of leaching by rain leading to the main soil contamination episodes to be specified.

It also revealed areas that were subjected to significant atmospheric contamination with caesium 137, although the depositions measured in these are low and the dose rates showed no significant increase.

Download "Updating of the knowledge relating to the dispersion and deposition of atmospheric releases from the Fukushima Daiichi nuclear accident in March 2011" (PDF, 884 Ko)

 

​View of the 4 cooling towers and reactor buildings of the Cattenom nuclear power plant. © Arnaud Bouissou/MEDDE/IRSN

Modelling radioactive fallout in a crisis situation

Modelling radioactive fallout in a crisis situation

​View of the 4 cooling towers and reactor buildings of the Cattenom nuclear power plant. © Arnaud Bouissou/MEDDE/IRSN

The Fukushima accident has shown the need to improve prognostic tools designed to assist governments in their decision making in crisis situations. In Japan, the simulation had difficulty in reproducing several radioactive release dispersion episodes and discrepancies were found between the modelling results and the radiological measurements in the environment.

Download "Modelling of atmospheric transport and release fallout emitted during the Fukushima accident" (PDF, 618 KB)

  

The main input data for the atmospheric dispersion models of entry comprise weather conditions and the characterisation of the releases:

The weather conditions determine the radioactive plume transport in the atmosphere. However, the difficulty of properly taking into account the orography (description of the topographic relief) in the weather forecasts was raised by the IRSN. Thus, precipitation forecasts, which are responsible for soil contamination due to the leaching of the plume, do not always reflect reality.The source term, that is to say the change over time of the rate of each radionuclide released into the atmosphere, is an essential input for atmospheric dispersion models. However, there is no clear consensus to identify a source term that is more realistic than another. The differences can be attributed to weather conditions and to the types of measurements used (volume activity, dose rate or total deposition).

Since 2011, simulations have become more realistic and the model /measurement differences have now been significantly reduced. Decisive progress has been made through the use of various weather forecasting sources and of more realistic source terms, as well as through a better understanding of environmental contamination episodes.

This work is currently still underway. And for good reason: all studies still indicate weaknesses and often face the same difficulties in modelling some contamination events in Fukushima.

Download "Main contamination events subsequent to the Fukushima accident" (PDF, 375 Ko)

  

For IRSN, the purpose of improving the operational assessment tools is to enhance the adequacy of the Institute's response to nuclear accidents, particularly regarding the exposure of populations:

The dispersion models used in an operational context generally have very simplified deposition models. Also, the challenge is knowing whether complex models taking into account the physics of aerosols, particle size or even precipitation would better simulate depositions.A complex deposition model does not solve the difficulty in reproducing some episodes. These difficulties seem mainly due to remaining uncertainties about the input data and to the modelling of plume behaviour within the context of a complex orography.

 

Coupling environmental measurements with the atmospheric dispersion model 

Since 2011, IRSN has been working to improve the understanding of the Fukushima accident and its environmental consequences, by coupling the analysis of environmental measurements with atmospheric dispersion modelling.

This work is largely being carried out as part of international collaborations. This analysis has enabled the path of the plumes in the atmosphere and the periods of leaching by rain leading to the main soil contamination episodes to be specified.

It also revealed areas that were subjected to significant atmospheric contamination with caesium 137, although the depositions measured in these are low and the dose rates showed no significant increase.

Download "Updating of the knowledge relating to the dispersion and deposition of atmospheric releases from the Fukushima Daiichi nuclear accident in March 2011" (PDF, 884 Ko)