Regulatory standard value
Based on international recommendations, the amount of radioactive materials discharged into the environment from nuclear power stations and other sources is defined as the regulatory standard value for the amount that does not cause any effects on the human body.
The regulatory standard values of radioactive materials are defined not based on whether they exist or not, or on the number of types they contain, but on the principle that “additional radiation exposure to the public (effect on a human body) should be less than 1 mSy per year”.
This is based on the recommendation of an international organization called ICRP (International Commission on Radiological Protection).
The standard for liquid is defined as “the concentration at which the average dose rate would reach 1 mSv per year if a person continued to drink approximately 2 liters of water at that concentration every day from birth until the age of 70”
The regulatory standard values are applied uniformly to all nuclear facilities.
When ALPS treated water is discharged into the sea, in addition to the purification process of radioactive materials by ALPS and other facilities, the water will be diluted (100 time or higher with seawater) to reduce the tritium concentration that cannot be removed by ALPS. This procedure also leads to further reduce the concentration of “Nuclides other than tritium” which is already below the regulatory standard value prior to the dilution.
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Regulatory concentrations limits, Sum of ratios to regulatory concentrations
The concentration limit of radioactive materials that can be discharged into the environment is defined for each nuclide by the related law (Public Notice)*, which is called a regulatory concentrations limits. If the radioactive material contains multiple nuclides, evaluation will be conducted by adding up the ratios of activity concentration for each nuclide to the regulatory concentration limit. This added value is called the sum of ratios to regulatory concentrations.
*：“Notification Establishing Dose Limits, etc. Based on the Provisions of the Regulations, etc. Concerning the Refining Business of Nuclear Source Material or Nuclear Fuel Material”, Notice by the Nuclear Regulation Authority (August 31, 2015)
Japanese regulatory standards, which are based on international recommendation, the concentration limits of radioactive materials in liquid/gaseous wastes discharged from nuclear facilities into the environment is defined for each nuclide.
When specific nuclides are contained in water or air, the permissible concentration level is established by the relevant law (Public Notice), and is called the “regulatory concentration”.
When discharged water or air contains multiple nuclides like ALPS treated water, the regulatory standard values are determined by comprehensively considering the effects of contained multiple radioactive materials. This means that discharged water or air is managed not only by the existence or the amount of each specific nuclide. Instead, it is managed that the radioactive material a whole satisfy the regulatory standard value. In such case, a concept called “sum of the ratios to regulatory concentrations limits” is used.
“sum of the ratios to regulatory concentrations limits” is the sum of values where respective concentration of nuclides in liquid/gaseous waste is divided by the regulatory concentration limit (ratio to regulatory concentration). If this value is 1 or less, the waste is regarded to satisfy the discharge standard of radioactive materials.
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The Series of Environmental Radioactivity Measuring Methods
The Series of Environmental Radioactivity Measuring Methods is a manual* established by the government as methods to separate and quantify radioactive materials such as tritium in environment efficiently and accurately.
*“Tritium Analysis”, Ministry of Education, Culture, Sports, Science and Technology (revised in 2002)
The Series of Environmental Radioactivity Measuring Methods is a standard manual for analysis and measurement methods for radiation of environmental samples and others, as a means of methods to separate and quantify radioactive materials in environment efficiently and accurately. At present, 36 kind manuals are prepared including the analytical methods for tritium.
In order to reflect the knowledge from the accident of Fukushima Daiichi Nuclear Power Station and latest technology, the contents are being revised by the Nuclear Regulation Authority.
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uncertainty
In the analysis of ALPS treated water, the analysis results contain variation within certain range (uncertainty). Such variation is basically caused by each factor in the analysis process, such as the methods for sample fractionation, calibration and the usage environment of analysis tools and instruments, and the pretreatment methods. In addition to these factors, the variation is also caused by multiple factors such as human factors like proficiency of the technicians. Therefore, it is required to evaluate the extent of such variation. For the analysis of low concentration samples, since slight differences in factors tend to affect the analysis results, the uncertainty becomes larger. There is no uniform method for identifying factors that should be taken into consideration in evaluating uncertainty. Instead, uncertainty factors will be set based on the analysis method, facility, and analysis skill level by the person conducting the analysis.
In the analysis of ALPS treated water, the analysis results contain variation within certain range (uncertainty). Such variation is basically caused by each factor in the analysis process, such as the methods for sample fractionation, calibration and the usage environment of analysis tools and instruments, and the pretreatment methods. In addition to these factors, the variation is also caused by multiple factors such as human factors like proficiency of the technicians. Therefore, it is required to evaluate the extent of such variation. For the analysis of samples with low activity concentration, since slight differences in factors tend to affect the analysis results, the uncertainty becomes larger. There is no uniform method for extracting factors that should be taken into consideration in evaluating uncertainty. Instead, an analysis technician sets the uncertainty factors according to the analysis method, facility, and analysis skill level.
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Accreditation to ISO/IEC 17025
The ISO/IEC 17025 accreditation indicates that the company has established a quality control system based on international standard and that the reliability of the analysis results has been internationally recognized.
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〇ISO/IEC 17025 is a standard that accredits testing and calibration laboratories on their ability to produce accurate measurement/calibration results by an authoritative third-party accreditation body.
〇ISO/IEC 17025 is called “Laboratory Accreditation”, and it defines requirements for testing laboratories that perform product testing, analysis, and measurement, and calibration laboratories that perform calibration services for measuring instruments.
○The accreditation is granted to testing and calibration laboratories and calibration laboratories when they are judged to be appropriate to obtain accreditation after an assessment in accordance with the requirements of the standard, including management capabilities in conducting product control and quality control and technical capabilities in producing reliable test/calibration results.
Description by PJLA
https://www.pjlabs.com/accreditation-programs/isoiec-17025
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