Publicatie Laka-bibliotheek:
The Fukushima Daiichi nuclear power plant accident. OECD/NEA nuclear safety respons and lessons learnt

AuteurOECD, NEA
-
Datum2013
Classificatie 4.21.8.60/10 (JAPAN - FUKUSHIMA (Dai’ichi ongeluk))
Opmerking Online available at OECD website
Voorkant

Uit de publicatie:

                            Executive summary



The Fukushima Daiichi nuclear power plant (NPP) accident that occurred on
11 March 2011 following a massive earthquake and tsunami was one of the most severe
accidents ever experienced at a nuclear power plant and will have to be dealt with for
many years by those in charge of nuclear safety (operators, safety bodies). Following the
accident, nuclear regulatory authorities, governments and international organisations
around the world took immediate actions to support Japan in its response. Under the
control of nuclear regulatory authorities, operators began undertaking a series of
analyses and follow-up measures to ensure the safety of all nuclear facilities. This report
outlines the actions taken by the OECD Nuclear Energy Agency (NEA) and its member
countries. Key messages and their implications for ensuring high levels of nuclear safety
are also summarised.
At the national level, all NEA member countries with
nuclear power plants took early action to ensure and                        Key messages
confirm the continued safety of their operating NPPs and          • NEA member countries implemented
the protection of the public. After these preliminary               focused safety reviews of their
safety reviews, all countries with nuclear facilities               operating reactors and determined
carried out comprehensive safety reviews, often referred            that they were safe to continue
to as “stress tests”. These comprehensive safety reviews            operation. Additional safety
reassessed the safety margins of nuclear facilities with a          enhancements that will help to
primary focus on challenges related to conditions                   better cope with external events
experienced at the Fukushima Daiichi NPP, for example               and severe accidents have been
extreme external events and the loss of safety functions,           identified and are being
or capabilities to cope with severe accidents. The reviews          implemented.
examined the adequacy of design-basis assumptions as
well as provisions for beyond-design-basis events.
NEA member countries with nuclear power plants evaluated, and when warranted,
took actions to improve the safety of the plants. They also undertook to upgrade existing
safety systems or to install additional equipment and instrumentation so as to enhance
the ability of each plant to withstand a natural event that disrupts access to the electrical
power grid and/or ultimate heat sink for an extended period, including events that affect
all the reactors at a single site simultaneously (multi-unit events).
In the weeks following the accident, the NEA already began establishing expert
groups in the nuclear safety and radiological protection areas as well as contributing to
                                                  information exchange with the
                                                  Japanese authorities and other
                                                  international organisations. It
                                                  promptly provided a forum for
                                                  high-level decision makers and
                                                  regulators within the G8-G20
                                                  frameworks.
                                                  Effective implementation is
                                                  being sought of actions aimed at
                                                  making it extremely unlikely that
                                                  an accident similar to that of the
                                                  Fukushima Daiichi NPP accident
                                         could occur in the future. The main focus is on
           Key messages                  enhanced application of the defence-in-depth concept
                                         to ensure robustness against external threats and on
• Nuclear safety professionals have
                                         accident management practices to face loss of safety
  a responsibility to hold each other
                                         functions. In addition, countries are improving their
  accountable to effectively implement
                                         knowledge of the behaviour of spent fuel pools (SFPs)
  nuclear safety practices and concepts.
                                         under accident conditions; gaining better under-
• The primary responsibility for nuclear standing of staff performance under stressful condi-
  safety remains with the operators of   tions through human performance/factors analysis;
  the NPPs, and regulatory authorities   and reviewing and improving crisis communication,
  have the responsibility to ensure that emergency procedures and guidance. Actions are also
  the public and the environment are     being undertaken to improve the effectiveness of
  protected.                             emergency plans, in particular in situations with
                                         severe damage to the local, national or regional
infrastructure that could be caused by an external initiating event. Research and
development programmes related to severe accidents and probabilistic safety
assessments (PSAs) considering natural hazards are being conducted as well.
In addition to revising regulatory requirements to better cope with external hazards
and severe accidents, many countries, and the international radiological protection
community in general, are revisiting approaches to emergency management and recovery
in order to be better prepared nationally for accident situations. This includes reviewing
national preparations for post-accident recovery and for transition from the emergency to
the recovery phase. Improvements in international communications and exchange of
information and expertise among regulatory authorities, their technical crisis centres and
relevant international organisations are also being studied and implemented.
Two years after the accident, the NEA continues to assist the Japanese authorities in
dealing with their recovery efforts, associated challenges and research plans. Current
issues include more comprehensive safety reviews, decontamination, radiological
protection and stakeholder dialogue. The NEA is also supporting research programmes
designed to improve understanding of how the accident progressed as well as to obtain
safety-related information during decommissioning and dismantling.
Based on experience from the Three Mile Island and Chernobyl accidents, a full
analysis of the Fukushima Daiichi NPP accident will take many years. The NEA is working
with the Japanese authorities on the development of the research plans to collect the
information needed to better understand what happened as the accident progressed at
each of the units. Associated activities will continue for several years and new activities
may also be needed in the future.
The key messages and conclusions drawn from the post-accident activities and the
implications they have on ensuring that high levels of nuclear safety are continuously
maintained and improved internationally are
outlined below.                                             Key messages
First among these is that NEA member                      • There is no room for complacency
countries using nuclear power promptly imple-               in the implementation of nuclear
mented focused safety reviews of their operating            safety practices and concepts. 
reactors, considering such impacts as those related       • The Fukushima Daiichi NPP
to extreme external events, and determined that             accident identified significant
they were safe to continue operation while more             human, organisational and cultural
comprehensive safety reviews were conducted.                challenges, which include ensuring
Additional safety enhancements that will help to            the independence, technical
better cope with external events and severe                 capability and transparency of the
accidents have been identified and are being imple-         regulatory authority.
mented in NEA member countries.

  A fundamental message from the accident is that there is
no room for complacency in the implementation of nuclear       Key messages
safety practices and concepts.                               • The fundamental concepts of
  The existing national and international requirements         defence-in-depth remain valid and
already in place provide an effective framework for acci-      continue to be shared by those in
dents within the design basis, and efforts are underway to     charge of nuclear safety.
enhance these frameworks to better address accidents
that, although unlikely, could result in catastrophic consequences if unmitigated.
  Nuclear safety professionals have a responsibility to hold each other accountable to
effectively implement nuclear safety practices and concepts. Recognising that the
primary responsibility for nuclear safety remains with the operators of the NPPs,
regulatory authorities have the responsibility to ensure that the public and the
environment are protected from the harmful effects of radiation.
  Although the accident at the Fukushima Daiichi NPP overwhelmed essentially all the
engineering and procedural barriers to the offsite release of radioactive material, the
fundamental concepts of defence-in-depth still remain valid and continue to be shared
by those in charge of nuclear safety. Where there is higher uncertainty, as in the case of
external hazards, effective implementation of the defence-in-depth concept requires
additional measures to address these uncertainties to maintain adequate safety margins.
  There are lessons being learnt, analyses being conducted, and information being
collected to support safety enhancements to cope with events that go beyond the design
basis. This report has shown that there would be benefit from having guidance from
regulatory authorities in each country on the application of DiD in such areas as:
a) prevention and mitigation at each level1 of DiD, b) to ensure that actions taken and
resources relied upon at one level of DiD can be made independent from the other levels,
and c) to minimise the potential for common-cause failures propagating from one level to
another.
  The Fukushima Daiichi NPP accident identified significant human, organisational and
cultural challenges that need to be addressed. Such challenges include ensuring the
independence, technical capability and transparency of the regulatory authority.
  The diversity of national recommendations during emergencies, and in particular the
differences between Japanese protection recommendations and those of foreign
governments for their own citizens in Japan, suggests that mechanisms to share
technical information among governments should be improved.
  It has been recognised that significant improvements are needed in national and
international communications and information exchange among national regulatory
organisations and their crisis response centres. The international information exchange
aspects of nuclear emergencies are also being reviewed internationally in a drive to
improve all communication aspects among countries
that could be directly or indirectly affected by nuclear                Key messages
emergencies.
                                                          • Since an accident can never be
  The NEA International Nuclear Emergency Exercises         completely ruled out, the necessary
(INEX) have focused on this issue, and will continue to     provisions for dealing with and
study national approaches to making related decisions.      managing a radiological emergency
In addition, should a large accident occur, there could be  situation, onsite and offsite, must be
a need for urgent actions in countries adjacent to the      planned, tested and regularly
accident state.                                             reviewed.

                                              The implementation of protective measures remains
  Key messages                            problematic, in particular as the situation transitions to
• Ensuring safety is a national           longer-term recovery, and those evacuated wish to return
  responsibility but poses a global       to their normal lives. This transition requires significant
  concern due to potentially far-         resources and efforts to effectively engage with stake-
  reaching accident consequences.         holders so as to understand and appropriately address
                                          their concerns. This is particularly complex in a post-
• Complete experience feedback from       accident situation where public trust may often be low.
  the Fukushima Daiichi nuclear power
  plant accident will take many years.       To date, a considerable amount of work has been
• A questioning and learning attitude    completed  to gather in-depth experience and feedback
  is essential to continue improving     from  the Fukushima    accident, but much more remains
  the high level of safety standards     to be  done  by the   whole  nuclear community. As the
  and their effective implementation.    accident-recovery    process  continues to evolve and
                                         reach specific conclusions, the latter could have an
effect on the long-term recommendations for research and development. Such work
could be included in NEA ongoing research, with the goal of developing enhanced
analysis methods for those areas that were found to require increased scrutiny following
the preliminary safety assessments and technical evaluations carried out after the
accident (i.e. severe accidents, external hazards assessments). These and other activities,
some to be identified, will continue for several years to come.
   For medium- and longer-term actions to address lessons learnt, international
co-operation provides a forum for collecting, sharing and analysing data to develop
consistent approaches that can be applied within the national regulatory framework.
This international co-operation also provides a forum in which peer regulators can
actively encourage each other to remain vigilant in ensuring the safety of their nuclear
power plants and help avoid the complacency that contributed to the accident at the
Fukushima Daiichi NPP.
  Since an accident can never be completely ruled out, the necessary provisions for
dealing with and managing a radiological emergency situation, onsite and offsite, must be
planned, tested and regularly reviewed in order to integrate experience feedback from drills
and from the management of real-life situations. As a complement to these safety
provisions, the NEA will continue working on appropriate communication of nuclear risks.
  Following the large societal, economic and psychological impacts of the accident, the
nuclear safety organisations considered that provisions should be identified to prevent
and mitigate the potential for severe accidents with long-term, offsite consequences.
   To conclude, it is the collective responsibility of nuclear safety professionals to ensure
that there is no complacency in the effective implementation of the practices and
approaches that have been developed over decades of use of nuclear power to protect the
public and the environment from the harmful effects of radiation. A questioning and
learning attitude is essential to continue improving the high level of safety standards and
their effective implementation.
   Ensuring safety is a national responsibility but poses a global concern due to
potentially far-reaching accident consequences. Within this context, international
co-operation is important for identifying commendable practices to ensure that nuclear
safety is effectively addressed within the national regulatory framework of countries with
nuclear power programmes. The NEA provides an effective forum for this international
co-operation.
  Working together through international co-operation, regulatory authorities can
identify commendable practices that will support national programmes as they develop
and implement the medium- and longer-term actions in response to the lessons learnt
from the accident.

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