Viewpoint: Japan must avoid over-conservatism in clearance of material

23 July 2019

The Nuclear Regulation Authority of Japan (NRA) is considering changes that would make the clearance of radioactive material about ten times stricter than international standards, creating unnecessary confusion and cost, writes Dr Charlotta Sanders, senior project manager at World Nuclear Association.

Charlotta Sanders (Image: World Nuclear Association)

The clearance of radioactive material is a regulatory process that provides for material used at a reactor site of very low activity to be recycled, reused or disposed of as non-radioactive material. NRA is currently considering a change to the regulatory standard on the methods of applying uncertainties for evaluated radioactivities included in cleared material, which - if implemented - would be a considerable parting from current national, and international, standards and practices with regard to clearance of radioactive material.

Current procedure in Japan, for the clearance of material, is for a licensee to attain a confirmation from the NRA that the concentrations of radioactive contaminants do not exceed a criterion established through NRA ordinance. NRA confirms the methods used for measuring and evaluating the radioactive concentrations of clearance-target material is in compliance with established regulatory principles. Next, NRA verifies that the licensee implements the approved methods through reviewing written records or sampling. Once such a confirmation of clearance is received by a licensee from the NRA, the licensee is able to exclude this material from being classified as radioactive contaminants, requiring no further restrictions.

A 2016 application to the NRA by The Japan Atomic Power Company (JAPC) for clearance of material from Tsuruga Nuclear Power Plant took into account the uncertainties of measurement and nuclide vector - i.e. ratio of difficult-to-measure nuclides, such as beta and alpha emitters (e.g., Sr-90 and Pu-239), to easy-to-measure nuclides, such as gamma emitters (e.g., Co-60 and Cs-137) - that are permissible for up to ten times the clearance level. The application followed the current accepted NRA methodology also described in Atomic Energy Society of Japan (AESJ) Standard, Monitoring for Compliance with Clearance Level, as well as similarly described in the International Atomic Energy Agency (IAEA) Safety Report No.67, Monitoring for Compliance with Exemption and Clearance Levels.

The JAPC application for clearance of material used this internationally recognised methodology. As shown in Safety Report No.67, the treatment of the uncertainty of measurement of a key nuclide is closely related to the concept of detection limits. In other words, the current conservative practice for uncertainty in clearance already requires an applicant to use detection limits for radiation measurements (e.g. applying three times the standard deviation of the measurement results in Japan). This practice is well justified because what one is attempting to measure is usually beyond detection limits. Applying a relative error of measurement to the results that is always less than about 30% provides significant safety margins because “established activity concentration values … are generally based on trivial potential doses to the public”, as highlighted in the IAEA report.

Even so, in reviewing the JAPC application, NRA is considering regulatory changes that would require applicants to follow a new guide for measurement and evaluation for clearance, with an updated investigation of uncertainties in measurement and nuclide vector that would be about ten times stricter than the concept described in the AESJ standards and the IAEA Safety Report No.67.

The proposed NRA change would lead to additional conservatism in the clearance of material for an already conservative practice. The proposed regulatory modification would bring about an increase in cost to Japan’s nuclear industry, as material which could previously have been cleared, would now require disposal in near-surface facilities.

This potential development of a divergent path in Japan, with regard to clearance of material from globally recognised standards and practices, could have a number of unintended consequences. These include increased complexity and therefore risk of error such as: measurement errors; incorrect accounting of material; and inappropriate material being cleared or material being consigned unnecessarily as radioactive waste. There is also the risk of regulatory instability due to unconscious infringements, and a convolution of existing safety cultures.

World Nuclear Association recommends the NRA maintain regulations for the clearance of material on the basis of established scientifically-based standards, founded on technical knowledge. It further suggests the NRA, and other national regulatory bodies, consistently take into consideration internationally recognised standards and practices as they formulate policy.

It is the Association’s position that a cohesive global framework of standards and practices better informs a nuclear safety culture, facilitates a reduction of uncertainty and risk, and generates long-term regulatory stability, while ensuring the ability of the nuclear industry to continue to provide a low-carbon means of energy security for the global community.

In early July, World Nuclear Association, based on consultation from its Radiological Protection Working Group, made up of leading nuclear industry experts in the practical application of the radiological protection system, submitted its opinion regarding the proposed change to the regulatory standard on uncertainties for clearance of material by the NRA in accordance with Japan’s Administrative Procedure Act.

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