[en] Many of the nuclear research and test reactors worldwide operate with high enriched uranium fuel. In response to worries over the potential use of HEU from research reactors in nuclear weapons, the U.S Department of Energy (DOE) initiated a program - the Reduced Enrichment for Research and Test Reactors (RERTR) - in 1978 to develop the technology necessary to reduce the use of HEU fuel by converting research reactors to low enriched uranium (LEU) fuel. The Reactor Conversion program is currently under the DOE's National Nuclear Security Administration's Global Threat Reduction Initiative (GTRI). 55 of the 129 reactors included in the scope have been already converted to LEU fuel or have shutdown prior to conversion. The major technical activities of the Conversion Program include: (1) the development of advanced LEU fuels; (2) conversion analysis and conversion support; and (3) technology development for the production of Molybdenum-99 (Mo⁹⁹) with LEU targets. The paper provides an overview of the status of the program, the technical challenges and accomplishments, and the role of international collaborations in the accomplishment of the Conversion Program objectives. Nuclear research and test reactors worldwide have been in operation for over 60 years. Many of these facilities operate with high enriched uranium fuel. In response to increased worries over the potential use of HEU from research reactors in the manufacturing of nuclear weapons, the U.S Department of Energy (DOE) initiated a program - the Reduced Enrichment for Research and Test Reactors (RERTR) - in 1978 to develop the technology necessary to reduce the use of HEU fuel in research reactors by converting them to low enriched uranium (LEU) fuel. The reactor conversion program was initially focused on U.S.-supplied reactors, but in the early 1990s it expanded and began to collaborate with Russian institutes with the objective of converting Russian supplied reactors to the use of LEU fuel.

[en] Full text: Development of guidelines for severe accident management (SAMG) for Ukrainian NPPs are carried out on the basis of: - An updated national action plan on the results of the ''stress tests''; - ''Comprehensive safety improvement programme of Ukrainian NPPs'' (CSIP) approved by the Cabinet of Ministers of Ukraine; - Working programme for the analysis of severe accidents and development of SAMGs, approved by State Inspectorate for Nuclear Regulation of Ukraine, which establishes general principles, the order and sequence analysis of severe accidents, including design, with the ultimate goal of SAMG development and subsequent SAMG verification and validation for pilot units. At present, SAMGs are developed and implemented only for pilot units, such as: — ZNPP-1 (V-320) - 06.16.2014; SUNPP-1 (B-302) - 28.10.2013; — Rivne NPP-1 (B-213) - 09.04.2014. The SAMGs are applicable to the conditions of intact primary circuit and the Containment. During 2014 and 2013 the State Enterprise ''NAEC'' Energoatom'' performed self-assessment of preparation of NPPs in the areas of Severe Accident Management and Emergency Preparedness. The results of the self-assessment were distributed within WANO-MC members According to the results of SAMG self-assessment, the following conclusions can be made: (a) Several issues were assessed as ''Awaiting Implementation'' as a result of the development of the guidelines for the ''pilot'' Ukrainian NPPs with the subsequent distribution to the ''non-pilot''. According to the CSIP’s schedule for Khmelnitsky NPP, the SAMG are planned to be introduced in 2015 on all power units, that explains why, compared to other nuclear power plants, already having SAMGs, the KNPP has the greatest number of grade ''AI - Awaiting Implementation''. (b) Most issues were assessed as ''Satisfactory progress to date'' received at the South Ukraine NPP, as confirmed by the results of the SUNPP peer review in October 2014. In accordance with the NAEC ''Energoatom'' inspections schedule, similar test was performed at the Rivne nuclear power plant in April 2015. (author)

[en] Full text: Full text: Safe restart of nuclear power plants in Japan is now the primary concern of the Japanese nuclear power operating companies. At the same time, the Nuclear Regulation Authority of Japan (NRA) has stated that “ we will be tireless in our efforts to improve our regulatory measures so that Japan's nuclear regulation standards will be among the world's highest.” The new regulations are a challenge to the operating companies, involving new analyses and, in many cases, costly back-fits. This paper will discuss our direct experience working with several operating companies in Japan to help make the reactors safe for operation under the new regulations. We believe that our work in Japan will be of great interest to the nuclear operating companies of other countries, as well as the methods and techniques we use to ensure nuclear safety. Our main activities are centered on fire protection analysis and safe shutdown; capable fault analysis; probabilistic fault displacement analysis (PFDHA); tornado hazard analysis; plant process computers for emergency control rooms, and probabilistic risk assessments (PRA) to measure the effectiveness of changes to the operating plants. We have performed fire protection analyses at the Sendai NPP and the Genkai NPP for Kyushu Electric Power Company; the Shimane NPP for Hokuriku Electric Power Company; and we are now beginning the same type of analysis for the Tsuruga NPP for the Japan Atomic Power company. The NRA has approved our work at the Sendai NPP and given their approval for the Sendai restart. In several cases we were able to show that costly replacement of cables was not necessary. While tornados in Japan are rare, the new regulations stipulate that tornado hazards must be considered. We have done a tornado hazard assessment at the Genkai NPP. The new NRA regulations for declaring a fault capable are quite stringent: the operating companies must show that there has been no movement on a fault for the last 120,000 – 130,000 years. We have put together international teams with acknowledged experts in geology, seismology, and PRA and done detailed analyses at the Higashidori NPP for Tohoku EPCo and the Tsuruga NPP. While PFDHA is not required under the new regulations, we are now doing a PFDHA at the Tsuruga NPP to consider movements of the Urasoko fault and subsequent sympathetic movement of the D1 crush zone. While not directly related to restart, our plant process computer installed at Fukushima Daiichi Unit 2 survived the earthquake and tsunami on 3.11.11 and is still be used to monitor the reactor in its shutdown state. Because of the proven hardness of our installation, we are now in discussions with operating companies for use in the required emergency control rooms. This paper will review our work with an emphasis on methodology and techniques and their effectiveness in increasing safety. (author)

[en] After the accident at the Fukushima Daichi nuclear power plant, the stability of nuclear power plants against external influences were tested all around the world with stress tests, and it was declared that a high level of operational safety had been reached, in accordance with “international standards.” However, given the experience of two accidents - the Armenian power plant in 1982 and Chernobyl in 1986 (in the aftermath of which the author took part) - we shouldn’t declare such things with confidence because there remain hidden, internal factors that are outside the field of view that don’t lend themselves to being known before a specific situation, and because some documents such as “Probability Safety Analysis” or “Safety Analysis Report” haven’t been taken into account. Many of these hidden factors could be discovered safely if performed at the modular/block level with In-core Monitoring Systems (IcMS), with early forecasting and detection of anomalies in the technical process of the reactor station. For this, it’s necessary to raise its status and quality; above all, it’s in formativeness, the reliability of metrological characteristics, and the stability of its mathematical software. In this sense, as was shown by an analysis, the majority of stationary In-core Monitoring Systems are based on neutron (for example, rhodium Rh-103) detectors that don’t meet today’s requirements for any of these indicators. The root cause of this failure is the need to account for burnout processes, neutron flux depression, and the change in the spectrum of neutrons. Accounting for these requires regular recalibration of integral balance reactor indicators and the existence in stationary In-core Monitoring Systems of interprocess communications with cumbersome computational operations. All of which can result in the failure of a stationary system to provide the information needed to avoid a crisis. In order to achieve the above-mentioned level of control (in-core monitoring), a new concept was introduced by us, and in 1985 an IcMS system project was conducted on the second block of the Armenian nuclear power plant, the physics of which were based on monitoring the gamma-field of the core, and on calorimetric gamma-detectors developed as primary incore sensors. The theoretical and experimental results of this project were presented in a report, including: — The concept and principles for building the system; — The construction of gamma-detectors and measurement channels (probes); — A description of physical processes and control algorithms; — The results of metrological, operational and resource/endurance tests; — The results of system control algorithms and programs in general.

[en] Full text: First we present EDF Group nuclear safety policy. Then, after an overview of the EDF SA nuclear fleet and of its Management of safety, we present the verification line: an in-house independent nuclear safety assessment function put in place at power station level, Company level, and Group level. Lastly, after a short presentation of human resources management and corporate communication on safety, we develop EDF policy about international peer reviews. (author)

[en] Full text: In Switzerland operating licences for nuclear power plants are time-unlimited. A nuclear power plant can be operated as long as the safety requirements are met. The condition of the plant is reviewed continuously as part of normal supervision, and additionally by means of a comprehensive Periodic Safety Review (PSR) which must be conducted every 10 years. After 40 years of operation, the operators must submit a safety analysis for long-term operation in addition to the usual PSR documents. This safety analysis shall demonstrate that the design limits of the safety-relevant plant components are not reached in case of an extended period of operation. The safety analysis for long-term operation has to cover the following four key areas: — Ageing management: Programmes and measures for maintenance and monitoring of ageing, taking account of internal and external operational experience and the latest state of science and technology; — Time-limited ageing analysis (TLAA): Renewal of the TLAAs, covering aspects such as embrittlement of the reactor pressure vessel, the fatigue resistance of the reactor cooling system and break preclusion (''leak-before-break'') for the main coolant piping; — Accident analyses: Updating of the deterministic and probabilistic safety analyses; — Backfitting: Review of the plant design on the basis of the state of science and technology. The safety analyses for long-term operation of the Beznau and Mühleberg nuclear power plant have been reviewed by ENSI. In both plants the ageing management corresponds to the state of science and technology, and provides a good basis for assessing the effects of long-term operation. The TLAAs of both plants show that all material criteria were met. ENSI required additional investigation on the corrosion at inaccessible parts of the primary steel containments of both plants. Due to the continuous plant improvements implemented over the years, the safety concept for the Beznau and Mühleberg nuclear power plants guarantees effective and reliable control of design-basis accidents. The deterministic and probabilistic accident analyses are up to date and conform to the statutory requirements. It should be noted however, that investigations in connection with the PEGASOS project indicate that the earthquake hazard in Switzerland was underestimated in the past. The safety analyses must therefore be revised as soon as the newly determined earthquake hazard assumptions are available in definitive form. Despite the upgrading and replacement measures implemented to compensate for the original design weaknesses, a 40-year-old nuclear power plant does not have all the design features of a latest-generation nuclear power plant. An important part of the safety analysis for long-term operation lies therefore in the assessment of technological obsolescence. As a result of its review ENSI required from the Mühleberg nuclear power plant to backfit a diverse heat sink and an additional possibility to feed coolant into the reactor in order to overcome deficits in the spatial separation of the safety systems. The backfitting programme for the Beznau nuclear power plant includes four earthquake-resistant diesel generators and an additional seal water pump for every unit. The positive impact of the backfitting campaigns has also been confirmed by a further reduction in core damage frequency. The updated PSAs show that all Swiss nuclear power plants have core damage frequencies (covering internal and external events) below 10^-5 per reactor year. (author)

[en] It has been exactly 5 years since we held our last conference on this topic. This was another era, before the Fukushima Daiichi accident in March 2011. Today, at this event, we are focussing more closely on Operational Safety at (NPPs). Indeed, NPPs are extremely high on our focus four years after the accident. We have today a better knowledge and understanding of the events in March 2011. A milestone was reached two weeks ago, when we presented to the Board of Governors the IAEA Summary Report on the accident. This summary report will be followed by the release in September of the detailed five technical volumes, drafted by some 180 experts from more than 40 Member States. We all know how important it is that we respond to that event. Of course we, collectively, have made great progress, and I will address this in a few moments. But we should not ignore the hard issues we still face. Now we all know that statistics do not tell the whole story: in round terms there are — or soon will be — about 450 nuclear power reactors on the planet. Accept for a moment a core damage frequency for each of these reactors of once in a million years (ten to the minus 6) and it can be argued that such an event might occur every couple of thousand years. But if we look back only to, say, 1970, there were five major core-damaging events including the three at Fukushima Daiichi. On average one every 9 years. And of course the world is changing in so many other ways. At the time of the Three Mile Island accident in 1979, 6 months after I started working in the nuclear field, we mostly read reports in the newspapers. In 1986 the information about the Chernobyl accident reached me first in Moscow where I was living, as a confidential rumour coming from Scandinavia, and I had to negotiate with the TASS Agency to buy one picture of the damaged reactor. In March 2011, just 6 months after I joined the Agency, we watched the accident develop live on our screens, and heard about it almost instantly through social media. Soon after the Fukushima Daiichi accident a number of papers appeared with titles such as ‘Never Again’ or the equivalent. This goes to the core of public acceptance, and also to the challenge that States need to address when making economic and technical choices regarding their energy mix. This is why conferences such as this are important and can truly make a difference.

[en] Full text: The accident at Fukushima Daiichi NPP in japan which occurred on March 11, 2011 was one of the most catastrophic events in the history of NPP operation which spans over half a century. The event resulted in core meltdown in multiple-units accompanied by significant radiological and environmental consequences. The aftermath somewhat hampered the prospects of otherwise rapidly growing nuclear industry necessitated by rising energy demand and depletion of fossil fuel reserves. Initiated by WENRA stress tests, the event led to a worldwide quest by the nuclear industry to re-assess safety of operating nuclear power plants on the basis of lessons learnt from Fukushima accident so as to recuperate public perception. In Pakistan, there are three nuclear power plants in operation with a total installed capacity of around 800 MWe. Among these, Karachi Nuclear Power Plant (KAN UPP) is a pressurized heavy water CANDU type reactor which completed its design life in 2002 and has been re-licensed after implementing various safety upgrades to operate till December, 2016.C- 1 and C-2 are two loop(325 and 330 MWe gross electrical output each) pressurized water reactors which started commercial operation in 2000 and 2011 respectively. Two more similar units C-3 and C-4 are under construction and are expected to start commercial operation in 2016 and 2017 respectively. Following Fukushima accident, Pakistan Nuclear Regulatory Authority {PNRA}, an independent regulatory body authorized to supervise and oversee safety of nuclear installations issued directives to its licensees to conduct targeted reassessment of existing safety margins in order to identify and rectify vulnerabilities in the areas of extreme natural hazards, extended loss of electrical power, emergency preparedness and response, severe accident management and safety culture. Post Fukushima assessments of each nuclear installation were conducted under the Fukushima Response Action Plan {FRAP)and the issues identified during the assessments were addressed in the form of activities to be undertaken as short term, medium term and long term actions. This paper describes the post Fukushima upgrades identified and so far implemented to improve the operational safety of NPPs in Pakistan, the challenges being faced from the view point of regulator. (author)

[en] Full text: WANO international Peer Reviews aim to help members compare their operational performance against their standards of excellence through in-depth, objective operational reviews by an independent team from outside their utility. These reviews are important because as we all know, peer judgment is an excellent and perhaps unique means of improving ourselves both as single plants and utilities but also collectively. Since the Fukushima severe accident in 2011, international peer reviews have become even more important. At the WANO board level we have revisited the Peer Review framework and the way we use them with our members and also outside our own organization. I believe this session will enable the audience to understand what we have tried to achieve and what we have accomplished so far. (author)

[en] The civil nuclear power industry changed forever on 11 March 2011. As the people of Japan came to terms with the devastating effects of a large undersea earthquake and a destructive tsunami, the world watched the evolution of a nuclear accident at the Fukushima-Daiichi Nuclear Power Plant. The effects of that accident are still evident, over four years later, well beyond the areas immediately affected. Public and investor confidence has been eroded. Several existing and proposed nuclear power programmes were stopped or curtailed. However the industry has set out on a rigorous path to ensure the lessons from the event are learned and defences strengthened to make operational safety more robust. The IAEA and its member states unanimously agreed to a Nuclear Safety Action Plan with a comprehensive set of improvements across a wide range of activities. Regulators, utilities and designers of nuclear plants came together to demand, find and implement improvements to nuclear plants and their safe management. And now, in 2015 more than 70 new nuclear units are under construction and several countries have announced their intention to embark on new or expanded nuclear power programmes. This diverse situation poses a number of operational safety challenges to governments, regulators and operators involved in the nuclear industry. It was in this context that the IAEA’s 2015 international conference on operational safety was conceived. The purpose of the conference was to review the progress of operational safety improvements being introduced in the light of the Fukushima Daiichi accident and to foster the exchange of information on operational safety performance and operating experience at nuclear power plants.