The IAEA has reviewed the Tepco short- and medium-term plan to decommission the Fukushima Daiichi nuclear power plant. It concluded that although a relatively stable cooling of the fuel (and fuel debris) in the reactors and spent fuel pools has been established and is adequately removing decay heat, there are several challenges to achieve a sustainable situation.
It concluded that the accumulation of enormous amounts of liquids due to the continuous intrusion of underground water into the reactor and turbine buildings is influencing the stability of the situation and requires additional countermeasures in the short term. For ensuring the long term stability of the fuel (and fuel debris) cooling, it will be necessary to continue the efforts to improve the reliability of essential systems, to assess the structural integrity of the site facilities and to enhance the protection against external hazards.
The report, IAEA's international peer review mission on the mid-and-long-term roadmap towards the decommissioning of Tepco's Fukushima Daiichi nuclear power station units 1-4, highlights 9 areas of signigicant progress to date and offers advice on 17 points where the team felt that current practices could be improved.
For example, it praises the roadmap: "The IAEA team acknowledges that the Roadmap was developed early after the accident. It indicates that solid engineering studies of alternatives have been performed to provide a basis for further implementation of activities towards the decommissioning of Fukushima Daiichi NPS."
The review has been organised in two steps, and the IAEA conducted the first part in Japan from 15 to 22 April 2013. The objective of the first mission was to undertake an initial review of the Roadmap, including assessments of decommissioning strategy, planning and timing of decommissioning phases and a review of several specific short-term issues and recent challenges.
The mission was conducted through the assessment of the information provided to the team from the government of Japan and Tepco, professional and open discussions with the relevant institutions in Japan, and a visit to Tepco's Fukushima Daiichi NPS, which provided an opportunity to observe how the roadmap items were progressing and to discuss the generic and specific site issues with the plant operator.
In strategy and planning - The IAEA team encouraged all stakeholders to continue discussions on appropriate end-points for the radioactive waste.
In termaof stakeholder involvement & communication - Tepco and the government of Japan are encouraged to co-operate and collaborate to promote stakeholder involvement and communication in a more transparent and systematic manner.
The IAEA team encouraged Tepco to conduct a comprehensive assessment of its current procedures for reporting to concerned parties and for communicating with the public, both in normal and abnormal situations.
In preparation for licencing - The review team considered that Tepco should take a more proactive approach for licensing for decommissioning of the Fukushima Daiichi NPS in order to ensure the decommissioning process would be prepared and implemented in a timely way.
On recent challenges - single-point vulnerabilities should be systematically and continuously evaluated, especially for the essential structures, systems and components (SSCs)
Tepco should consider inclusion of transition plans from mobile and temporary SSCs, including monitoring equipment, to reasonably permanent ones in a timely manner to increase reliability against ageing, external hazards, and human induced failures.
Tepco should consider ensuring the separation of the reactive (rapid fix of problems) scope and responsibility of Emergency (Immediate) Response Headquarters from the proactive scope and responsibilities, that is, to anticipate, identify and prevent 'potential' issues.
Fuel debris removal
Considering the complexity of the implementation of fuel debris removal, the IAEA team encouraged Tepco to ensure that adequate contingencies are in place to address the huge uncertainties that are likely to be faced during project execution.
On waste management
The IAEA team encourages TEPCO to start preparing its strategy and long-term waste management plan by estimating volumes, types and characteristics of different waste streams and by identifying optimized waste management scenarios for all phases.
The IAEA team encourages TEPCO to review its strategy for accumulated water management and to work out a comprehensive plan taking into account the constraints and associated risks in the current approach in consultation with all relevant stakeholders, including the NRA and the public.
Dose management - the IAEA team suggested that the government of Japan and Tepco should establish a frank and informed discussion with the relevant authorities and stakeholders, including the NRA and local authorities, to assess the balance of risks and benefits of the dose limit to the public and its practical implementation, particularly from the direct exposures at the site-boundary arising from contaminated solids and accumulated liquids on the site and for the possibility of controlled discharges of liquid from the site.
The IAEA team suggests further improvement and enhancement of the operational radiation protection system for reducing radioactive exposure of the workers. It may include following measures: application of passive dosimeters; increasing the number of online monitoring stations; clarification of high radiation dose areas; application of ventilated masks in special situations; application of dose optimization software when possible and increasing the whole body counting possibilities by gamma spectrometry.
On decontamination - the IAEA team wanted Tepco to define an adequate end state of debris removal and then consider a simplification of the floor decontamination techniques.
On structural integrity - seismic and structural integrity analysis could be enhanced. Additional peer review and/or independent confirmatory analyses by experts in the areas of dynamic seismic analysis, finite element modelling, progressive collapse, thermal effects on structures, and reinforced concrete inelastic behaviour are advised to improve the confidence of the results and conclusions.
On management of ageing - the ageing management programme could be enhanced by the following items:
-Develop or expand upon current structural and materials aging management programmes for the reactor buildings and other critical structures to provide for the long-term decommissioning efforts;
-Consult with experts in the international community in the areas of materials degradation including corrosion and corrosive environments, steel embrittlement due to the high radiation levels, and reinforced concrete degradation
-Prepare methods and procedures to mitigate and repair additional damage that may occur due to future aging-related degradation to the critical structures required to function for the long term decommissioning.
On external hazards - the Re-evaluation of External Hazards programme could be enhanced by the following items:
-To complete the external hazard re-evaluations for the Fukushima-Daiichi NPS site as early as possible with broad involvement from the scientific community and to share the results with the public; and
-To continue assessing the tsunami protection to ensure consistency with the hazard.
Install accelerometers with recording capability on the building structures (e.g. reactor buildings) at characteristic locations to allow for the proper establishment of the level of shaking being experienced during possible future earthquakes.
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