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January 06, 2022

CNL continues to represent Canada in study of Fukushima Daiichi nuclear event

It’s been about seven years since CNL received a call from a representative at the Organization for Economic Development (OECD) asking us to contribute to international efforts supporting the Fukushima Daiichi nuclear disaster in Japan in 2011. We had the knowledge, skills and capabilities with severe accident phenomena and also were very focused on international project collaboration, enabled by AECL’s Federal Nuclear Science & Technology Work Plan (FNST). It was not only an opportunity for us to learn and contribute, but it gave CNL the opportunity to represent the Canadian nuclear industry and showcase why we hold the reputation for attracting the best and brightest.

In our early project work, CNL’s Advanced Reactors Directorate developed a computer simulation of the incident to better understand how it happened and its progression using an advanced severe accident modelling code. The result was the first boiling water reactor severe accident analysis performed by CNL, and the first analysis using the MELCOR integrated severe accident analysis code (a US-NRC tool, developed by Sandia National Laboratories). CNL then went on to identify challenges in getting the fuel debris out of the reactors at Fukushima, so that analysis of this debris can be used to assist in the refined severe accident analysis of the Unit 2 reactor and upcoming analysis of the Unit 3 reactor.

More recently, CNL has helped with final efforts for a joint task force (JTF) initiative with international partners. This work involved a study of some initial debris samples taken from the Fukushima Daiichi containments, provided to JTF participants to understand the debris forms found.

“For our part, CNL subject matter experts performed a thorough review of the data and were able to provide significant contributions and insight on what the debris structure and composition may mean with respect to how the accident progressed, including the potential temperatures reached during the accident, oxidation of the debris, and the presence of materials indicating molten core concrete interaction,” says Andrew Morreale, research scientist with CNL’s Advanced Reactors Directorate.

Additionally, through CNL’s participation in the OECD Fukushima projects, areas of improvement in original simulation efforts have been implemented in a refined analysis that better reflect the postulated accident progression.

And the international collaboration will continue. CNL is looking forward to work that will further support both understanding of the severe accident and the generation of valuable insight and information for decommissioning of the Fukushima Daiichi units. Part of this work is a proposed round-robin debris analysis initiative that CNL has been spearheading, which will take well characterized samples from a severe accident experiment and provide them to various international laboratories for analysis and comparison of techniques, procedures and results – work that will help to increase the body of knowledge on the analysis of fuel debris, exchange information to help build analysis programs and develop debris analysis capabilities, and provide improved understanding of accident phenomena and information for both severe accident knowledge and decommissioning.

“Being connected with the international community, being able to present CNL research and share our knowledge on a high visibility stage, and give a Canadian perspective means a lot,” says Morreale. “CNL is the representative of Canada in many such international projects related to nuclear science as we are the national lab and hold the expertise in the country thanks to CNL research priorities and our work under the AECL-FNST program. We’re happy to have this federal support for our participation and the opportunity to bring information back to our federal stakeholders. Participation in the OECD-NEA Fukushima Daiichi projects has improved understanding of severe accident management of the current CANDU fleet, and provided insight on the current status of the Fukushima units and the decommissioning effort. What’s more, this work as well as our participation in international working groups, is contributing to our capabilities in future advanced designs and small modular reactors.”

Continued success in these international efforts are thanks to the hard work of CNL staff and support of management and AECL. The efforts of staff of the Thermalhydraulics and Safety Analysis Branch are recognized in particular, along with the support of the Advanced Reactors and Reactor Fleet Sustainability teams.

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