Workshop on Developments in Fuel Cycle Facilities (FCFs) after the Fukushima Daiichi Nuclear Power Station (NPS) Accident
The Nuclear Energy Agency (NEA) Committee on the Safety of Nuclear Installations (CSNI) Working Group on Fuel Cycle Safety (WGFCS) held an international workshop on Developments in Fuel Cycle Facilities (FCFs) after the Fukushima Daiichi Nuclear Power Station (NPS) Accident. The workshop was hosted by the Japan Nuclear Regulation Authority.
Working under the mandate of the CSNI, the objective of the WGFCS is to advance the understanding of relevant aspects of nuclear fuel cycle safety for regulators, technical support organisations (TSO) and operators from OECD countries but also from non-OECD countries with FCFs.
The objectives of this workshop were to review and discuss national activities, plans and regulatory approaches by member countries in light of the lessons learnt from the Fukushima Daiichi nuclear power station (NPS) accident, in terms of new safety requirements and operational issues of FCFs.
Within this framework, various characteristics, particularities and a wide range of hazards from FCFs compared to nuclear power plants (NPPs) were be taken into account, considering specific aspects of FCFs such as radiological and chemical risks. The application of a graded approach was also taken into account.
In September 2011, considering the impacts of the March 2011 events at the Fukushima Daiichi NPP on FCFs in general, the working group carried out an exchange of information on the early actions taken, as well as the preliminary lessons learnt thus far. This was done in a special session included in the workshop, Safety Assessment of Fuel Cycle Facilities – Regulatory Approaches and Industry Perspectives, which was held in Toronto, Canada.
Besides nuclear reactors, many NEA member countries have also conducted safety reviews (e.g. comprehensive risk and/or safety assessments, so called "stress tests") of the design and safety of their FCFs with respect to protection of the facilities from extreme natural hazards (earthquakes, floods, tornados). The safety reviews aim to challenge the sites under natural hazardous phenomena, exceeding the levels taken into account by the design basis and current safety requirements applicable to the facilities.
These assessments led, in many cases, to the identification of improvements to maintain and/or strengthen the facilities' capabilities for the prevention and/or mitigation of accidents and consequences under extreme natural hazards. These assessments were performed with consideration of the defence-in-depth concept, fundamental safety functions of the plant and emergency capabilities. Regarding FCFs, it had to take into account the large number and diversity of facilities, among which those with specific features (multiple FCFs sites with "domino effects" risks, FCFs sites with nuclear/chemical hazards).
It is important for member countries with FCFs, existing or planned, to share the lessons learnt from the Fukushima Daiichi NPS accident and the improvement actions used to maintain and enhance the safety level of their facilities.
Within the context of the workshop, the following aspects were presented and discussed by the participating countries:
- feedback of the stress tests or alternative reviews performed, especially regarding the extreme natural hazards considered (such as level of the hazard beyond design basis and combination of events) and, if applicable, the deterministic loss of power supply and cooling functions;
- implementation of post-Fukushima improvements to FCFs, especially front-end facilities, facilities for intermediate storage of spent fuel (SF) and away-from-reactor SF storage pools, reprocessing plants, plutonium facilities, waste management facilities and legacy facilities;
- lessons learnt or issues dealing with the safety assessments of large FCF sites (simultaneous impact on several facilities) with scenarios combining extreme natural hazards, loss of power supply and cooling functions;
- emergency planning (on-site and off-site) and jurisdictional interfaces and decision making process for large site facilities relevant to different regulations/regulators (nuclear / chemical hazards);
- future challenges for new FCFs;
- more work on operational issues related to the safety of FCF (e.g. how cliff-edge effects and threshold effects are taken into account or beyond design basis accidents);
- human and organisational factors (HOF) lessons taken from the Fukushima NPP accident and integration of measures into the implementation of post-Fukushima improvements to FCFs.
The workshop was centered on the following technical focus areas:
Session 1: Feedack of post-Fukushima safety reviews performed for FCFs
This session aimed to present methodologies, scope and feedback of the stress tests or alternative reviews performed for FCFs in terms of:
- events considered (justification of the level beyond the safety limits of the facility, and combination of concurrent extreme events);
consequential events on the facilities and on the facilities sites (including cases of multi-facility sites);
- facility robustness and/or weaknesses/vulnerabilities beyond their design basis (design margins, threshold effects and cliff-edge effects beyond which fundamental safety functions would be lost and consequences would be severe)
- strengths and weaknesses with regards to emergency capabilities on the facilities and on the facilities sites (e.g. chain of command, logistics for measures and communication with external stakeholders);
- analysis of the hazardous effects (fire, explosion, criticality, chemical releases and accessibility of the site).
Session 2: Implementation of post-Fukushima regulatory improvements on FCFs
This session presented the changes and/or enhancements, made or planned, to regulatory framework, in order to address rare initiating events (like natural hazards) that may lead to common-cause failures, "threshold effects" ("cliff-edge effects") and consequential hazards, regarding:
- risks analysis (technical standards for earthquake, flooding, tornado and consequence thresholds used);
demonstration that existing facilities are able to withstand extreme events;
- design basis (new facilities);
- safety requirements (civil engineering and safety support systems);
- methodologies for evaluation of safety margins (beyond the design basis) and cliff-edge effects;
- methodologies to deal with chemical risks, including leakage caused by an earthquake;
- probabilistic versus deterministic methodologies for regulatory decision making;
- methodologies used to define rare initiating events such as frequency and magnitude;
- emergency planning and countermeasures.
Session 3: Implementation of post-Fukushima technical and operational improvements of FCFs
This session addressed technical and operational changes and/or enhancements implemented or planned for FCFs and FCFs sites to withstand severe external hazards:
- safety support systems (electrical supply, cooling and heat sink, containment);
- instrumentation, control and monitoring systems;
- human and organisational measures (procedures, training, exercises, communication and maintenance);
- emergency organisation (design of new crisis management centres, deployment of a national task force);
- emergency equipment and measures.
Session 4: Future challenges for new FCFs
This session presented future developments for FCFs in the context of long-term planning on post-Fukushima feedback actions:
- further studies to address uncertainties (e.g. level of extreme natural hazards to be considered);
- utilisation of probabilistic risk assessment (PRA) for extreme situations;
- projects aiming at a better understanding of phenomena involved in accidents on SF storage pools;
- existing or further R&D (e.g. concerning equipment and decision making in case of an emergency).
Participation was open to experts from FCF operating organisations, regulatory authorities and their technical support organisations, FCF designers and vendors, and industry associations and observers from NEA member countries.
WGFCS FCFs members' area (password protected | reminder)
18 November 2016
Aomori City, Japan