Plenary Lectures
The Great Eastern Japan Earthquake and Tsunami occurred in March 11, 2011, and as a result, the accident of Fukushima Daiichi Nuclear Power Plant occurred. Utilization of remote-controlled machine technology including robot technology (RT) was essential for the response against the accident to accomplish various tasks in the high-radiation environment. In this presentation, it is introduced how the technology has been utilized in the emergent situation of the accident, and what kind of technology is still demanded for decommissioning. It is also analyzed why the robot technology developed in the past projects in Japan could not be introduced smoothly in the emergent situation, and issues are discussed how we should prepare for the future possible disasters and accidents, including not only technological development but also maintenance of technology, training of operators, establishment of mockups and test fields, and political strategy.
Many lessons can be learned from the Fukushima Daiichi Nuclear Power Plant accident. First, if an isolation condenser (IC) continues to operate, the accident would be terminated soon. A reactor core isolation cooling (RCIC) steam turbine also stopped due to loss of battery power in Unit #2 and #3. suppression pool (S/P) temperature and pressure were so high that the accident management water injection took took too long time. After the loss of ECCS and IC core cooling, Containment Vessel pressure increased. Hydrogen explosion occurred after venting. The analysis results show that the depressurization of the reactor pressure vessel (RPV) started before RPV bottom failure. It is hoped that the lessons learned from this accident will help to establish resilience technology for nuclear power plants, based on the defense in depth philosophy.
The progress of the nuclear industry within the United States (US) in responding to regulatory changes following the events at Fukushima Dai-Ichi is significant and rapidly evolving. The US Nuclear Regulatory Commission (USNRC) has issued questions related to submitted utility approaches in satisfying order EA-12-049. In addition to responding to these questions, the US nuclear industry has continued to perform plant modifications, procure equipment, establish national response centers, establish new plant procedures, and address other Regulatory orders and directives. In addition to these required activities, the US nuclear industry has also identified means to utilize these new capabilities to provide other benefits.
Panel Discussion
In this paper, a new discipline called resilience engineering is
discussed from the perspective of nuclear safety engineering as well as
maintenance science& technology.
Invited Lectures
The application of the software PVrisk is discussed, which in 2008 was compiled to solve probabilistic fracture mechanical problems in case of pressure vessels and pipes by utilizing approaches based on the (FAD) Failure Assessment Diagram. The probabilistic feature is embedded due to Monte Carlo simulation. Compared with other tools available the advantage of PVrisk is to take into account the combination with NDT results based on (POD) Probability of Detection data. These data can be the result of an experimental POD trial using a representative set of test specimens with crack-like defects and describing as a whole statistically sufficiently enough the NDT inspections task or are computed POD-curves due to numerical modeling of the inspection process. The here presented contribution uses POD curves by evaluating experimental data obtained in a project in the German nuclear safety research program. The NDT task was the inspection of welds in austenitic stainless steel plates by using ultrasonic testing (UT) and the application of phased array transducers (PAUT - Phased Array UT) as inspection technique. Taking into account a realistic statistical population of half-elliptical, axial oriented, inside and surface breaking cracks in a larger diameter austenitic pipe as well as the material properties elastic limit Rp0.2, tensile strength Rm, and fracture toughness KIC, numerical statistical modeling is used to calculate the probability of failure (POF). The advantage to use NDT with optimized POD is documented.
The Fukushima Daiichi nuclear plant accident occurred in March 2011 as result of a major earthquake and tsunami. It is probably the second worst nuclear plant accident in terms of on-site damage and off-site release; Chernobyl was worse. Japan has begun a huge, complex and expensive effort to recover from the accident at the site, prevent and reduce further off-site damage and health effects, and decommission all the plants on the Fukushima Daiichi site. A major plan and roadmap has been developed and is being pursued. The plan and roadmap are also continually reviewed, and are changed and modified as the actual accident conditions are discovered, and the detailed technical efforts and equipment to achieve success must be dealt with. An overall project organization has been set up in Japan for the decommissioning. It involves several portions of the Japanese government such as METI and NRA. It also includes TEPCO, IRID and many other Japanese and International companies, R&D organizations, universities, laboratories, local governments etc. The Japanese have also sought out and set up work with a small international group of experts, the IEG. These six individuals have extensive knowledge and experience in dealing with the sort of problems and issues that must be faced at Fukushima. Much of this experience comes from dealing with nuclear plant accidents and problems, including severe core damage, at locations outside Japan. The lecturer is a member of this group.
The lecture will provide an overall summary of the current status and organization of the Fukushima Decommissioning Project and identify several of the key organizations and their roles. The lecture will also discuss a few technical issues and problems currently being pursued on the site, e.g., spent fuel removal, fuel debris removal, monitoring and controlling radiation dose on the site, and collecting, processing, storing and releasing water from the site.
The Nuclear Regulatory Agency of Japan mandates compliance to the design basis accident as well as severe accident requirements. It is well recognized that the defense-in-depth conception is the basis of ensuring reactor safety. The effectiveness and importance of the additional provisions for the severe accident are to be evaluated in view of defense-in-depth to assess the achievement level of the reactor safety goal. At the same time, the achievement level of reactor maintenance goal needs to be assessed as well. The assessment depends on the definition of the maintenance goal and the implementation of the defense-in-depth conception for the maintenance. The author discusses how the conception is effective for ensuring reactor maintenance and quantifying the achievement level of the maintenance goal.
After the onset of the Fukushima Daiichi accident, Taiwan Power Company had implemented Comprehensive Safety Assessments to all NPPs. Proactive plans had been made to enhance the resistance of extreme disasters and countermeasures been made based on the condition of Station Blackout & Loss of Ultimate Heat Sink.
Three and half years have passed since the accident, and the decontamination and decommissioning activities of Fukushima-Daiichi have progressed steadily. The fuel debris is cooled through continuous reactor water injection at unit 1, 2 and 3. And fuel removal has commeneed from the unit 4 spent fuel pool.
On August 1, 2013, the International Research Institute for Nuclear Decommissioning (IRID), was founded under a charter granted by the Minister of Economy, Trade and Industry. In collaboration with 18 Japanese organizations, IRID has conducted the above research and development in an effective and efficient manner, while maintaining the long-term view to reinforce the foundation of the decommissioning technology for the future.
In this research, a new index "The Resilience Index" was proposed to evaluate the reliability of system safety of nuclear power plant under severe accident plant by considering the resilience capability from the loss of function of system safety.
Cement based materials may be very durable. Examples, 2000-3000 years old, have arrived until present days showing still good performance and therefore, they are suitable candidates to play an important role in the long term immobilization of radioactive wastes. The record of modern concrete is however no longer than about 100 years. During this time, it has been noticed that the material presents a good performance in many environments, however several chemical aggressive species in the water, soil or the atmosphere may react with the cement mineralogical phases and affect its integrity. The challenge of the concrete as engineering barrier is therefore its long term stability. In Spain, Enresa has selected the place of El Cabril (Cordoba) for the placement of a repository of low and medium radioactive wastes and cementitious materials have been identified for being an important part of the engineering barrier. The aim of present paper to is to summarize some of the requirements defined for the cement based materials (CBM) in order to achieve a target service life of 300-500 years and to illustrate the basis of models that will be used to try to make a reliable prediction of their durability. It is described as well the monitoring of corrosion parameters in a container which has been buried to reproduce real conditions.
This paper will cover two topics pertaining to statistical analysis of data from nondestructive inspections: 1) The proper interpretation of the a90/95 value commonly used as a measure of inspection reliability, and 2) the elicitation of expert user input for develop and proper use of software for probability of detection (POD) studies. A statistical concept known as the "probability of coverage" will be used to illustrate how POD confidence bounds should be interpreted. The development of a new software package that will help the analyst avoid pitfalls in POD analysis will also be discussed.
The conventional approaches have not considered sufficiently how to manage residual risks that spill out of the design basis of a complex socio-technical system. Resilience, which means the ability of a system to absorb changes and disturbances in the environment and to maintain system functionality, is a key concept for resolving the above situation. In this talk, some relevant topics in resilience engineering will be discussed: the prehistory of resilience engineering, how system resilience can be evaluated and implemented.
Japan Nuclear Safety Institute (JANSI) was established on November 15, 2012. The establishment of JANSI, as a new entity that can serve as a powerful industry driver, was decided by the nuclear industry, reflecting upon the Fukushima Daiichi accident caused on March 11, 2011 and in a bid to further reinforce nuclear plants' safety assurance measures, including severe accident countermeasures. The project, Maintenance Technology Basis Activities, is a program to technically support the improvement of the safety of NPPs from the view of maintenance activities. And all the nuclear operators in Japan and JANSI have continuously promoted cooperatively this project so far. JANSI supported and promoted Maintenance Technology Basis Activities as one of technical supports to improve the safety of NPPs, and is making efforts for further development and fulfillment at present.
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