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Configuration of Nuclear Safety Goals

Published on Jun. 16, 2015 : The Denki Shimbun (The Electric Daily News)
Shojiro Matsuura
Chairman of JANSI

As one of the strong reflection points following the Fukushima Daiichi Nuclear Power Station accident, discussions aimed at the reconstruction of nuclear safety goals are internationally and domestically being moved forward. It is said that internationally, the discussions of the IAEA INSAG (International Safety Group) are approaching the final confirmation stages as a document.

On the other hand, since the time of the inauguration of the Nuclear Regulation Authority (NRA) domestically, this has been cited as one of the important issues to be handled. NRA has already set a requirement of 100 terabecquerel for cesium-137 or below as indication for safety goals for the maximum limit of radioactive material release from reactors at the time of a severe accident. This value is approximately 1/100 of the cesium-137 released during the Fukushima Daiichi accident, and is thought to be a practical criterion for the purpose of preventing disturbances to the surrounding environment. However, as for safety goals which include all the characteristics of reactor facilities and surrounding conditions, reconstruction is once again necessary through discussions including experts from various fields.

Additionally, at the Nuclear Risk Research Center (NRRC) newly established at the Central Research Institute of Electric Power Industry (CRIEPI), in order to challenge "Construction of a the Integrated Risk Informed Decision Making System " as the most important issue, activities are being moved forward with cooperation from nuclear power generation business officials. Safety target settings are believed to be critical in exerting the true value of this system.

As a response to the question of "How safe is safe enough for nuclear power usage?" there is a record that the said settings were proposed in the United States in 1976 taking into consideration mitigating severe accident risks which go beyond the design basis. Immediately following this the TMI-2 accident occurred in 1979, causing severe accident risks to be strictly re-examined, and discussions of safety targets increased.

These discussions continued mainly within the U.S. Nuclear Regulatory Commission, aiming to set safety targets as regulatory standards. Although many examination results were published, they did not reach the establishment as regulatory standards, and were temporarily ceased in 1993. While the philosophy of qualitative safety goals as "risks from nuclear power usage should be lowered sufficiently below the risks in general social life" was established, it is believed that the recognition of many practical difficulties in setting quantitative safety goals as regulatory standards hampered the progress of the discussion.

However, this thorough discussion serves as proof of just how deeply the TMI-2 accident was reflected on by the United States. In addition, up to the present day it has provided us with a solid foundation in helping to think about "How to practically and realistically reduce risks associated with nuclear energy usage" from both the regulator and the nuclear operator.

From reflections of the 1986 Chernobyl accident, debates were held internationally by professionals regarding safety goals at INSAG, and those results were reflected in the INSAG Text -3 (Basic Safety Principles for Nuclear Power Plants, 1988). This document lists not only qualitative safety goals, but also quantitative safety goals as core damage probabilities and large scale release probabilities of radioactive materials according to the technological levels at that time.

Looking back on the discussions surrounding safety goal settings up until now shows the extreme difficulty in the setting of quantitative safety goals. This is to say, no matter how small the risk in nuclear energy usage is, the significance of it would not be perceived by society. It is not an issue of gaining an understanding simply through rationality.

I wish to recommend that the safety goals are set not for gaining an understanding from society, but for the self-improvement of operators as a merkmal for their pursuit of safety excellence. Ideally operators configure those goals to be automatically raised in a stepwise manner once they are achieved. Technical capabilities, facility and equipment functions, organizational strength, and management power shall be fully leveraged in order to realistically and practically further reduce risks, and by showing society a figure which continues to put forward such sincere efforts, confidence and trust in nuclear power would surely gradually recover.




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