The IAEA Published a Report on Its February Review Mission of Safety Aspects of Handling of ALPS Treated Water at Fukushima Daiichi Nuclear Power Station

1. Summary

The review mission of safety aspects of handling of ALPS treated water at FDNPS in February was conducted based on the Terms of Reference (TOR) on a comprehensive framework for cooperation on the handling of ALPS treated water, which was signed with the IAEA last July. The IAEA’s review will be conducted by the IAEA Task Force, which consists of IAEA officials and international experts before, during and after the ALPS treated water discharge. This report describes the findings of IAEA’s review, mainly on the Application Documents for Approval to Amend the Implementation Plan, which　was submitted to NRA from TEPCO last December and on the report of assessment of radiological impact on humans and the environment, which was published last November　by TEPCO, in accordance with international safety standards for the safety aspects of handling of ALPS treated water.

Ref) The IAEA Task Force includes international experts, serving in a personal capacity, from Argentina, Australia, Canada, China, France, Republic of Korea, the Marshall Islands, Russia, the United States, the United Kingdom, and Vietnam.

2. Key Points of the Report

*There are quotes from the IAEA report (Including some summaries)
The following eight technical items were assessed regarding the characteristics of the ALPS treated water to be discharged, the safety of the discharge process, and radiological impact on the public and the environment.

1. Crosscutting Requirements and Recommendations
2. Characterization of discharge and source term
3. Safety Related Aspects of Systems and Processes for Controlling Discharges
4. Radiological Environmental Impact Assessment
5. Regulatory Control and Authorization of Discharges
6. Source and Environmental Monitoring Programmes
7. Involvement of Interested Parties
8. Occupational Radiation Protection

The report includes a summary of the discussion points between the IAEA Task Force and the METI/TEPCO and the initial observations for each technical matter. In relation to the safety of related facilities which is the main contents of the implementation plan it was recognized that an enormous amount of analysis was performed by TEPCO for the conduct of the safety assessment, the level of detail, its comprehensive approach, as well as the fact that a large number of potential single failure events were taken into consideration for the development of the design criteria for the discharge of ALPS treated water. On the radiological impact assessment, it was acknowledged that a comprehensive and detailed analysis was conducted and also noted that the radiological impact on the public was expected to be very low and significantly below the level set by the Japanese regulatory body. The IAEA Task Force noted that a significant amount of work and analysis has been performed to discharge the ALPS treated water, but the results need to be clearly described in writing to demonstrate compliance with relevant requirements in the context of IAEA safety standards.

< Main confirmation items>

1. Characterization of discharge and source term

• The Task Force noted that the proposed gross alpha screening methods^*1 for measurements was conservative enough for the REIA and fully acceptable for confirming that discharges are below authorized limits for routine source monitoring.
• The Task Force commented on the importance of defining the source term for the discharge of ALPS treated water in a sufficiently conservative yet realistic manner, as this is fundamental for the conduct of the REIA. Additionally, if the source term is clearly described, it can be more easily understood by interested parties.
• TEPCO stated that they planned to conduct a reassessment^*2 based on this refined assumption. The Task Force agreed with the rationale presented by TEPCO regarding their plan to develop a sufficiently conservative, yet realistic, source term and to revise the REIA.

2. Safety Related Aspects of Systems and Processes for Controlling Discharges

• The IAEA Task Force acknowledged that TEPCO followed a systematic and methodical approach to identify the events that could lead to failure of the system for controlling discharges (single failure events) and their potential consequences. As a result of the assessment, TEPCO successfully incorporated prevention measures in the design of the facility as well as in the associated operating procedures.
• The Task Force noted that TEPCO would be expected to ensure that all aspects considered for the safety assessment, including the methodology and the data used, be sufficiently documented in the safety assessment.
• The Task Force recognized the enormous amount of analysis performed by TEPCO for the conduct of the safety assessment, the level of detail, its comprehensive approach, as well as the fact that a large number of potential single failure events were taken into consideration for the development of the design criteria for the discharge of ALPS treated water.
• The Task Force mentioned the importance of making a comprehensive assessment considering all failure modes and identifying the different initiators that might lead to the discharge of undiluted ALPS treated water. Although some of these aspects are partly presented in the radiological impact assessment, additional documentation of the explanations is needed to justify the design criteria for the system for discharges.

3. Radiological Environmental Impact Assessment

• The Task Force noted that the REIA produced by TEPCO indicates that, using conservative assumptions, the doses to the assumed representative person are expected to be very low and significantly below the dose constraint set by the regulatory body (NRA). The Task Force acknowledged the comprehensive and detailed assessment that was undertaken in the conduct of the REIA.
• The Task Force acknowledged that based on the current REIA, the consideration of organically bound tritium in the estimates of doses was unlikely to impact the overall doses estimated but that it is very important that TEPCO demonstrates that it has considered the different chemical forms of tritium in the environment in the REIA.
• The Task Force mentioned that as part of the safety assessment for facilities and activities, various types of accident are postulated to identify engineered safety features and operational actions to reduce their likelihood. The Task Force discussed with TEPCO that it is important to calculate the doses from all exposure pathways without consideration of protective measures or mitigation measures that could be implemented if such an accident occurred.
• The Task Force emphasized that the REIA needs to be well documented, contain clear explanations of the methodology and data used, and should be translated throughout the process, and when finalized, to enable it to be understood by a broader audience.

4. Regulatory Control and Authorization of Discharges

• The Task force noted that the optimized discharge limits derived from the revision of the REIA might indicate a higher discharge rate for tritium (i.e. the amount of tritium discharged annually that results in a dose to the representative person at or below the dose constraint is greater than 22 TBq per year). This would help TEPCO demonstrate whether the protection of the public is optimized, thus building the confidence of interested parties in the protection of people and the environment and demonstrating that a discharge above 22 TBq/y would still meet the dose constraint, which would be a positive message.

3. Response to the IAEA report

The points raised by the IAEA Task Force have been reflected in the revised application of  the Implementation Plan, which TEPCO submitted to the NRA, and　the report of assessment of radiological impact on humans and the environment. The contents of revised application and revised RIA report are thus further enhanced.
As the discharge plan progresses, and with the findings from the IAEA review, Japan will work to ensure all possible measures are taken to ensure safety and in accordance with international safety standards and all possible measures will be taken to ensure safety.

4. Related Documents

• Press Release of the IAEA
• Report of the IAEA
• Minister's Statements

Division in Charge

Nuclear Accident Response Office, Agency for Natural Resources and Energy