Based on the analysis of data from contaminated water, the concentration of 137Cs in radioactive waste such as used cesium adsorption vessels and sludge generated from the Cesium Adsorption Device and Second Cesium Adsorption Device and from the Decontamination Device, which were operating or suspended as a part of the contaminated water treatment system at the Fukushima Daiichi nuclear power station was calculated. An estimate is made of the total amount of 137Cs recovered by decontamination from 28 June, 2011 to 12 August, 2014.

An augmented reality-based simulation system for cooperative plant dismantling work has been developed and evaluated. In the system, behaviors of virtual objects such as the dismantling target, chain blocks, and trolleys are physically simulated. Their appearance is superimposed on camera images captured with cameras on users’ tablet devices. The users can manipulate virtual objects cooperatively via touch operation. They can cut the dismantling targets, lift them on the trolleys using chain blocks, and convey them through narrow passages to ascertain whether the dismantling targets can be conducted without colliding with the passages. During the simulation, collisions between the virtual objects and real work environment are detected based on their three-dimensional shape data measured in advance. The collided parts are visualized using augmented reality superimposition. Four evaluators assessed the simulation system. Results show that the simulation system can be useful for prior examination of dismantling works, but some points were also found to need improvement.

The Fukushima Daiichi nuclear plant accident occurred in March 2011 as a result of a major earthquake and tsunami. It is probably the second worst commercial nuclear plant accident in terms of on-site damage and off-site release; Chernobyl was the world’s worst. 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 Expert Group, 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 author is a member of this group.
The paper provides an overall summary of the current status and organization of the Fukushima Decommissioning Project, and identifies several of the key organizations and their roles. The paper discusses 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. Significant progress has been made. The wide range of Japanese and International organizations are energetically and effectively participating in the needed activities. Safety is improving and doses for off-site public and site workers continue to reduce. Damaged buildings and systems are being repaired, spent fuel removal progresses and radwaste cleanup and storage is underway. Successful pursuit and completion of tasks to date has provided important new information, resulted in better performance of many systems on site, and freed up resources to address important additional tasks. Significant R&D is underway, and is helping identify and produce new hardware and techniques to support needed tasks.
The Japanese estimate the Fukushima decontamination and decommissioning task will require 30-40 more years. Based on the data in hand, the author considers that this estimated duration is uncertain, but seems to be a reasonable estimate. The Japanese are strongly committed and dedicated to this effort being safely achieved, despite the high cost and major needed effort, and the author agrees this should be the expected and anticipated result.

Structural materials during a use in a fission reactor are subjected to irradiation by high energy neutrons, and therefore the properties, functions, and performances of materials become gradually degraded. Since keeping material’s integrity is a key to success towards a stable operation of reactors, materials degradation due to irradiation should be taken into account when reactor design and maintenance are considered. One of the issues to be solved for realization of a long term operation is how the integrity of materials in use is ensured for a long time beyond an actually-experienced operation period. To do this, the future ageing behavior of materials should be understood in advance. Usually, an attempt is made to understand the behavior using the existing irradiation facilities with accelerated irradiation environments. In many cases, however, material’s behavior depends much on acceleration coefficients and its dependency is not so simple. To overcome such a difficulty, a numerical simulation study is employed. In the present study, reaction rate analysis is performed to investigate material microstructure changes under various irradiation conditions. Our results have shown that volume swelling due to irradiation is very much different depending on irradiation conditions provided by such irradiation facilities as HFIR, JOYO, KUR, 14MeV fusion neutrons. Based on the results, irradiation correlation methodology is discussed to predict material’s degradation under arbitrary irradiation conditions using the actual existing data obtained with accelerated irradiation conditions.

In Japanese nuclear power plants, surveillance tests are conducted according to the Japan Electric Association Code JEAC4201 in order to monitor the degree of embrittlement of reactor pressure vessel (RPV) material due to neutron irradiation. Through the surveillance tests for Pressurized Water Reactor (PWR) plants, a large number of fracture toughness data have been accumulated for Japanese RPV irradiated materials. New fracture toughness curves have been developed adopting the Master Curve (MC) concept and these curves have been correlated with the Charpy V-notch 30 ft-lb transition temperature, T_r30 for evaluation against Pressurized Thermal Shock (PTS) events. The developed curves are also intended to represent the 5% tolerance lower bound of fracture toughness trend incorporating fracture toughness variation depending on the product form, which consists of plates, forgings and weld metals. In this study, the reliability of the curves is evaluated for predicted T_r30 values in consideration of application to PTS evaluation for Japanese PWR plants and it was demonstrated that the developed lower bound curve has reliability comparable to that for the measured T_r30 by adding a margin of 3 ºC to the predicted T_r30.

This study has investigated multiple-site small cracks in the low cycle fatigue of SUS316L at 873K in air by using the four-point probe DC potential difference method. Small probes with 1-mm spacing between the electrodes were used in order to evaluate small cracks of some hundred micrometers. Morphology of the cracks was evaluated by standard deviation of potential difference σV which detected by the probes and by the crack density by laser microscopy. As a result, it was shown that σV monotonically increased with increasing number of strain cycles and fatigue process was classified into four stages. Furthermore, statistical analysis showed that the cracks initiated at random sites in early stage. However, the randomness was diminished and σV increased significantly with growth and coalescence of the cracks. These results revealed that standard deviation of normalized potential difference could evaluate initiation, growth and coalescence of multiple-site small cracks in each stage.