The tenth anniversary of the accident at the Fukushima nuclear power plant (NPP) in Japan on March 11, 2011, caused by a tsunami triggered by an earthquake, provides the occasion to consider the lessons learnt from the disaster for nuclear energy – the only source of low carbon, reliable base load power to satisfy the world’s exponentially growing demand for electricity and heating. The post-Fukushima lessons learnt are of specific relevance for India, given that the country’s first 1,000 MW light water reactors (LWRs) at Kudankulam in Tamil Nadu attained criticality in 2013, but only after local people had laid an eight-month siege to the plant, expressing serious concern over the safety of the reactors in the wake of the Fukushima incident.
Following the accident at the Fukushima, the International Atomic Energy Agency (IAEA) convened a Ministerial Conference on Nuclear Safety in June 2011, which helped develop the IAEA Action Plan on Nuclear Safety that was endorsed by member states of the UN nuclear body in September 2011. The Action Plan detailed a work programme to strengthen the global nuclear safety framework in response to the Fukushima accident.
According to the IAEA, since the adoption of the Action Plan, significant progress has been made in several key areas, including assessments of the safety vulnerabilities of nuclear power plants, the strengthening of the IAEA’s safety peer review services, revision of the IAEA safety standards, improvements in emergency preparedness and response capabilities, capacity building in nuclear and radiation safety, as well as strengthening of safety culture, intensifying of communication and information sharing with and among national authorities, international cooperation, as well as strengthening of relevant international legal frameworks.
As part of their work under the Action Plan, operating countries introduced measures to enhance nuclear safety, including those taken in response to the results from nuclear power plants’ vulnerability assessments. The Action Plan also called on the IAEA, member states and international organizations to review and strengthen the international emergency preparedness and response framework. Countries responded to the accident with immediate measures, which included carrying out ‘stress tests’ to reassess the design of nuclear power plants with respect to site specific natural hazards, installing additional backup sources of electrical power and water supplies, and strengthening the protection of plants against extreme external events.
“Although most of the work under the Action Plan has concluded, there are still some longer-term activities that will be completed in the years to come”, the IAEA said in a recent announcement. As part of the Action Plan, the IAEA has held nine international experts’ meetings that analysed key technical aspects of the Fukushima accident. The agency has also conducted over 15 international experts’ missions to Japan and published reports on these missions reports to create a solid knowledge base for the future and continue strengthening nuclear safety worldwide.
In 2015, the IAEA published The Fukushima Daiichi Accident report which provides an authoritative assessment on the causes and consequences of the accident, as well as lessons learnt. The report is the result of an extensive collaboration that involved some 180 experts from 42 IAEA member states, as well as international organisations.
The report calls for a systemic approach to safety that addresses the entire system by considering the dynamic interactions within and among three types of factors – human or individual, technical, and organisational. The systemic approach to safety works by addressing this complex system of interactions as a whole. According to the report “a better communication strategy is needed to convey the justification for such measures and actions to all stakeholders, including the public.” The report also concluded that in spite of the magnitude of the Fukushima disaster in which three nuclear cores melted, no radiation-induced health effects were observed among workers or members of the public that could be attributed to the accident. This is in line with the conclusions that the independent United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR).
“The report considers human, organizational and technical factors and aims to provide an understanding of what happened, and why, so that the necessary lessons learned can be acted upon by governments, regulators and nuclear power plant operators throughout the world,” IAEA Director General Yukiya Amano said in his foreword to the report.
“There can be no grounds for complacency about nuclear safety in any country. Although nuclear safety remains the responsibility of each individual country, nuclear accidents can transcend national borders. The Fukushima Daiichi accident underlined the vital importance of effective international cooperation. The IAEA is where most of that cooperation takes place. Our Member States adopted the IAEA Action Plan on Nuclear Safety a few months after the accident and have been implementing its far reaching provisions to improve global nuclear safety”, he added.
An expert review of relevant standards following Fukushima, including the IAEA safety standard on design safety, revealed that a higher level of safety could be incorporated into existing nuclear power plants by adhering to more demanding requirements for protection against external natural hazards and by enhancing the independence of safety levels so that, even if one layer fails, another layer is undamaged and stops an accident from occuring. The “defence in depth” concept, which ensures that the various levels of defence in a plant act as independently as possible, was also strengthened. For instance, in the case of a tsunami, back-up safety systems should be located at an elevation sufficiently high to be protected from flooding and ensure their operability when systems designed for normal operation have failed.
Safety assessments, or “stress tests”, implemented in the European Union (EU) following the Fukushima accident focused on the assessment of natural disaters like earthquakes and flooding, and on the behaviour of power plants in such cases. With the objective of strengtheing the robustness of nuclear reactors to extreme natural events the margins of the safety of reactors were analysed and possible improvements were identified. The implementation of those stress tests by member states has resulted in many design and operation enhancements in the EU.
For instance, the French Nuclear Safety Authority (ASN) started an assessment of the country’s 56 nuclear power reactors as well as the 2 EPR reactors under construction. The ASN then prescribed the implementation of both fixed and mobile equipment that could potentially prevent a large release, including high-resistance diesel generators and pumps able to function during events such as major earthquakes or flooding. The availability of alternative sources of water for cooling was also prescribed under the same conditions. In addition, the ASN required a back-up plan including rapid action force groups that can be on site within 24 hours with light equipment, and within three days with heavy equipment.
In a review carried out post-Fukushima, the Indian operator Nuclear Power Corporation of India (NPCIL) identified safety enhancements for the country’s pressurised heavy water reactors (PHWRs). Safety enhancements such as additional emergency power sources, enhanced onsite water inventories, external water injection arrangements, containment venting provision, seismic trip, mobile pumps and on-site emergency support Centre, among others, have been implemented.
At the Russian-aided Kudankulam Nuclear Power Project (KNPP) in India, the first two units of 1,000 MW each have already been commissioned, while 4 more units of similar capacity are being constructed with the assistance of the Russian state atomic energy corporation Rosatom, who have said that all NPPs being developed by Russia, including KNPP, meet all post-Fukushima safety standards and would be able to withstand external events like an earthquake or tsunami.
According to Rosatom, certain technological parameters have been enhanced at the KNPP to increase its safety standards following the Fukushima disaster, and this nuclear plant in the south India is a Generation 3 plus NPP with enhanced safety features, which take into account the Fukushima accident. The VVER-1000 reactors at Kudankulam have been modified with several enhanced safety features, which bring these on par with the IAEA’s Generation 3 category of reactors.
The newly incorporated safety features in KNPP include four safety trains instead of three, passive heat removal system, higher redundancy for safety system, double containment, additional shutdown systems like quick boron and emergency boron injection systems, core catcher in the event of fuel meltdown, passive and hydrogen recombiners inside the containment chamber, among others. The “probabilistic risk assessment” (PRA) study for KNPP conducted by NPCIL has calculated that the probability of serious core damage accident at Kudankulam is one in one million reactor years and it is one of the safest reactors currently operating in the world.