US Efforts in Support of Examinations at Fukushima Daiichi – 2016 Evaluations

Abstract

Much is still not known about the end-state of core materials in each unit that was operating on March 11, 2011 at the Fukushima Daiichi Nuclear Power Station (Daiichi). Information obtained from Daiichi is required to inform Decontamination and Decommissioning (D&D) activities, improving the ability of the Tokyo Electric Power Company Holdings, Incorporated (TEPCO Holdings) to characterize potential hazards and to ensure the safety of workers involved with cleanup activities. This document, which has been updated to include Fiscal Year 2019 (FY2019) information, summarizes results from a U.S. effort to review Daiichi information and extract insights to enhance the safety of existing and future nuclear power plant designs. This U.S. effort, which was initiated in 2014 by the Department of Energy Office of Nuclear Energy (DOE-NE), is completed by a group of experts in reactor safety and plant operations that identify examination needs and evaluate recent Daiichi examination data to address these needs. Each year, annual reports are issued that document significant safety insights being obtained in areas of special emphasis. For FY2019, the areas emphasized by the expert panel include component performance, radionuclide surveys and sampling, debris end-state location, combustible gas effects, and plant operations and maintenance. In addition to reducing uncertainties related to severe accident modeling progression, these insights have and continue to be used to update guidance for severe accident prevention, mitigation, and emergency planning. Reduced uncertainties in modeling the events at Daiichi improve the realism of reactor safety evaluations that inform future D&D activities. In addition, the process established by this U.S. effort provides an example that Japan may wish to implement in future international efforts to support D&D.

U.S. Efforts in Support of Examinations at Fukushima Daiichi- November 2020 Meeting Notes with Updated Information Requests

“…To facilitate exchange of this information, the U.S. DOE collaborated with the U.S. NRC to host a U.S.-Japan TMI-2 Knowledge Transfer and Relevance to Fukushima meeting in FY2017 to promote exchange of relevant information to cognizant organizations within Japan. [5] Unique U.S. expertise provides Japanese organizations an independent assessment of their progress reports, the adequacy of severe accident analysis code models for evaluations to support their D&D plans, and the adequacy of available examination information and proposed plans for additional examinations. In the latter case, U.S. input focuses on the desired amount of information, the resolution of data required from sampling, and the cost versus the benefit of obtaining such information.…”

Light Water Reactor Sustainability Program, U.S. Efforts in Support of Examinations at Fukushima Daiichi-2017 Evaluations

“…As indicated above, there are several potential safety benefits from this U.S. effort. In fact, as discussed in [2,3,4,5] and within this document, the U.S. has already gained significant safety benefit from information obtained from the affected reactors at Daiichi.…”

“…Experts from the U.S. NRC, the U.S. DOE, and TEPCO Holdings also attended and informed participants during these meetings. This effort resulted in a report [5] with a prioritized initial list of information of interest to U.S. stakeholders. In this report, special attention was devoted to identifying why such information is important and how it will be used to benefit the U.S. nuclear enterprise.…”

“…b Although details varied, U.S. experts generally identified needs required to answer fundamental questions related to how the accident progressed in each unit, understand equipment and component survivability, and benchmark severe accident progression and dose assessment codes. These needs are organized in Reference [5] tables per location [e.g., the reactor building (RB), the primary containment vessel (PCV), and the reactor pressure vessel (RPV)]. These tables also identify the b Because of the hydrogen explosion damage observed at Unit 4 (1F4), this unit is also of interest.…”

“…Prioritization of possible examination activities[5] Activities used to complete the second objective are shown in Figure1. As shown in this figure, activities and products completed by U.S. organizations are shown in purple and focus on Phase 2 Activities associated with the Mid-and-Long-Term Roadmap for D&D (the blue box; see Section 2.3).…”