Following the Fukushima disaster on 11th March 2011, caused by an earthquake and tsunami that resulted in the permanent shutdown of all six units at Tokyo Electric Power’s (Tepco’s) Fukushima Daiichi plant, Japan’s Nuclear Regulator Authority (NRA), introduced a number of new measures to ensure the safety of Japan’s nuclear plants. They included introducing the most recent nuclear reactor simulators, as well as analysis of the safety of instrumentation and control (I&C) systems at Japanese nuclear plants.

The restart of Japan’s nuclear power units has been considerably slower than had been widely expected. The only nuclear plants currently in commercial operation are Sendai 1 and 2 and Shikoku Electric Power Co’s Ikata 3, which resumed commercial operations on 7th September.

Kansai Electric Power Co’s Takahama-3 restarted 1st February, but was ordered to shut by a Japanese court on safety grounds 10th March following a legal challenge to the unit’s restart by local environmental activists.

The slow progress can be attributed to several factors, including legal challenges to the restarts, the relatively slow progress that NRA is making in approving the restarts and a completely new regulatory framework imposed in the country in 2013 in response to the disaster. A UK-based sector analyst said in an interview on 30th September that the “restart of reactors in Japan after the Fukushima accident has certainly been more slow than was widely expected and indeed than the country might have wanted. While it is fair to say that of course Japan would want to take no risks with the restart process and the new regulatory framework that was imposed in 2013, there has been quite a lot of disappointment with the pace of progress so far, both internationally and in Japan.”

The NRA has received and will review applications from operators to restart 21 of the country’s 48 power reactors. These 21 units will remain shut until they undergo technical and regulatory checks undertaken by NRA. The regulator is therefore facing a large workload in reviewing those applications and also undertaking final safety inspections of the units before they are approved for a return to service.

For this task, the regulator has been seeking to add about 30 experienced nuclear engineers. This is the fourth time that the body has launched a recruitment drive in the last year. These engineers will work in several divisions of the regulator, including application reviews prior to reactor restart, safety inspection of existing nuclear units and emergency planning for disaster prevention. This measure has lead to total new hires of about 80 engineers.

According to the NRA, periodic evaluation of safety and a systematic approach to safety, as well as safety improvements through operational experience, have been established as key measures in the agency’s performance.

These measures were adopted by NRA and reported to the 14th International Congress of the International Radiation Protection Association, or IRPA, earlier this year.

Considerable additional reforms have also been undertaken by the Japanese government since Fukushima. Government bodies that deal with the nuclear sector, including the Atomic Energy Commission, the Nuclear Safety Commission, the Ministry of Economy, Trade and Industry, the Agency for Natural Resources and Energy, and the Ministry of Education, Culture, Sports, Science and Technology all now report directly to the NRA. The national regulator in turn operates under the supervision of the Ministry of Environment. This new oversight structure is intended to simplify the legal and regulatory framework under which the nuclear industry in Japan operates.

The Japanese nuclear regulator became a fully independent body after the Fukushima accident. This new structure also gives a clear line of command with respect to safety coordination, which can reduce aspects of human error in nuclear operations.

The NRA hosted a peer review team from the International Atomic Energy Agency (IAEA) in January 2016, the Integrated Regulatory Review Service (IRRS). The 24-member team concluded that NRA had “demonstrated independence and transparency” since it was established in 2012, but said it had to improve technical competence and recruit more expert staff. The NRA must “continue to strengthen the promotion of safety culture, including by fostering a questioning attitude”, said IRRS team leader Philippe Jamet, commissioner at the French Nuclear Safety Authority.

The IRRS mission followed an Operating Safety Assessment Review Team (Osart) mission to Japan in February 2015, at the request of NRA. The Osart mission visited Chubu Electric’s Hamaoka plant, as well as a series of government-run nuclear installations. These included the Fast Critical Assembly and the Plutonium Fuel Production facility both of which are operated by Japan Atomic Energy Agency.

The IAEA has conducted 188 OSART missions, 128 in Europe, 30 in Asia, 18 in North America, eight in South America and four in Africa.

Review areas include leadership and management for safety, training, operation, maintenance, radiation protection, chemistry, emergency preparedness and response, accident management, human technology and organisation interactions, among other areas.

The IAEA mission concluded that the “overall, the nuclear security regime and the implementation of physical protection measures for nuclear facilities and nuclear material in Japan was robust, sustainable, and had been significantly enhanced in recent years.”

Japan’s new simulator

In March 2016 the NRA installed a new simulator at its Human Resource Development Centre in Tokyo, to provide training in situations of potential nuclear disaster.

The simulator is equipped with a touch panel featuring 69 different types of control boards and instruments, replicating the functions of a central control room. It can simulate disaster conditions in both boiling water reactors (BWRs) and pressurised-water reactors (PWRs). Plans are in place to add functions to test the latest-model reactors under disaster conditions.

The new simulator is already serving as a useful tool during study sessions organised by NRA secretariat employees. While these employees will not operate at a nuclear reactor during a disaster, Juichiro Ito, the vice director of NRA’s Human Resource Development Centre, says the simulator “will be effective in terms of conferring the ability to provide guidance during times of emergency.”

The NRA developed training programmes for use in the simulator and implements them in a planned manner. The training programmes cover diversified fields, such as dedicated training on nuclear regulations, qualification of NRA staff for roles such as that of nuclear safety inspectors or nuclear emergency preparedness officers and undertaking practical training to familiarise NRA staff with inspection procedures using full-size equipment.

The simulator is also able to create individual accident sequences and to analyse the role and performance of I&C systems in such sequences.

Following the installation, NRA commissioned CORYS, a French company, through its partners Marubeni and the Mitsubishi Research Institute to upgrade the simulator. The CORYS upgrade will allow for full scope simulation of a three-loop pressurised water reactor, with the functionality of a modern control room, which will enable training during normal, and accident conditions.

As the NRA increases staff numbers and has a more significant role in overseeing the recovery of the Japanese nuclear industry the simulator will have an increasingly important role in the training of these new regulatory employees in a variety of situations.

The UK analyst said: “While of course this simulator is a new and useful tool for Japan, and I hope that it will have particular significance as NRA takes on new inspectors and seeks to generally broaden its staff and mandates, the overall concerns about the pace of the restarts and how this may be increased is still the main challenge facing the Japanese nuclear industry.”

John Large of the Large Associates engineering consultancy in the UK said that “simulation scans only a small part of the risk”.

Large noted that “nuclear disasters are not foreseeable given the experience with Chernobyl and Fukushima, as there is not a way to measure human error, but instead to monitor changes in the manifestation of error”.

Large added: “The biggest challenge today is dealing with errors in computer software, which is used in control systems, as well as fighting terror. Both threats to nuclear power operators cannot be identified in advance, and therefore cannot be simulated”. He was referring to the shift towards the use of digital instrumentation and control (I&C) systems in nuclear plants.

A modern nuclear power plant has 10,000 sensors and detectors and approximately 5000km of cables in its I&C systems. This already highly complex architecture is further complicated by the move from analogue to digital I&C systems.

In the average nuclear power plant, around 40% of the I&C system has some digital components. The use of digital
I&C systems in Japan started in the Kashiwazaki-Kariwa 6 and 7 ABWRs, the first in 1996. The first all-digital I&C systems in Japan are Hamaoka 5 and Tomari 3, which began operations in 2009.

In Russia, Kalinin 3, commissioned in 2004, was the first VVER-1000 equipped with digital I&C safety systems and digital process control systems.