INTERNATIONAL PEER REVIEWNUMO Pre-siting Site Descriptive Model Based
Safety Case Report for Deep Geological Disposal
IRT chair, Director Jussi Heinonen© 2021 Organisation for Economic Co-operation and Development

International background••

The scientific consensus today is that deep geologicalrepositories (DGR) are a safe and effective approach topermanently dispose of high-level radioactive waste (NEA2020)
Geological disposal is widely accepted as final solution
and a few countries have progressed to licensing,construction and operation of a DGR:– USA: DGR for trans-uranic waste has been inoperation since 1999 (WIPP)– Finland: Operating license application was submitted
at the end of 2021 (ONKALO)– Sweden: Government issued license in 2022
– France: Construction license application wassubmitted January 2023 (Cigeo)
NEA, Management and disposal of high-level radioactive waste: Global
progress and solutions, 2020
© 2021 Organisation for Economic Co-operation and Development

Pictures: Posiva, Andra and NWMO

Step-wise development of a Deep Geological Repository
Pre-operational phase
Safety strategy
NUMO Disposal concept
Site selection
Design finalization
Safety assessments
Excavation and constructionBarrier fabrication
Preparations for operation

Operational phase

Waste packaging
Emplacement in DGR
Periodic safety evaluations…
Closure of DGR© 2021 Organisation for Economic Co-operation and Development

Post-closure phase

Safety is provided bypassively functioning
barriers
Institutional control andmonitoring

NEA International review team main findings© 2021 Organisation for Economic Co-operation and Development

Feasibility of geological disposal and NUMO’s approach (1/2)•NUMO has done significant work to produce the SDM-based generic Safety Case.
– NUMO’s approach for step-wise development of safety case is in line with international
good practices.
– Current safety case is mature and sufficient for this phase.
• Areas potentially suitable for geological disposal in Japan have been identified– With the knowledge already available, NUMO has the capability for detailed site
investigations and safety assessments• The disposal design, conceptual at this phase, appears to be at an adequate stage ofmaturity– The studies and tests show that the technologies are available– Disposal design will be further developed as information of host rock increases© 2021 Organisation for Economic Co-operation and Development

Feasibility of geological disposal and NUMO’s approach (2/2)•NUMO’s approach to conduct safety assessments is consistent with international
recommendations and practices– The numerous studies in support of the safety demonstration, and the resulting models,illustrate NUMO's ability to represent geological disposal, to describe its possible
evolutions, and to analyze their consequences.
– The SDM approach is an adequate, iterative way to describe and integrate geoscientificknowledge• Based on review of NUMO’s safety case, the IRT considers NUMO’s approach to implementa DGR in Japan as feasible– Implementation of DGR still requires many studies and safety evaluations.
– NUMO has demonstrated its ability to fulfill such a mission.

© 2021 Organisation for Economic Co-operation and Development

Overall programme key observations
For successful DGR implementation, the IRT strongly recommends that NUMO initiates orreinforces the dialogue with the major stakeholders. SDM-Based Safety Case forms a basis fordialogue.
Dialogue is suggested with:• the regulator, with the aim to clarify regulatory expectations for coming steps.
• the waste producers, with the aim to have a more realistic understanding of RW inventory,
characteristics and disposability.
• the institutions and teams involved in defining and carrying out R&D for the geologicaldisposal, with the aim of focusing research on the needs expressed by NUMO.
The IRT also notes that international peer review (e.g. IAEA Artemis) focusing on overall
Japanese DGR program and regulatory framework would be useful and would support
successful DGR development.
© 2021 Organisation for Economic Co-operation and Development

Summary of main recommendations to NUMOThe IRT makes the following recommendations to be considered in the development of futuresafety cases:• To continue efforts to further increase understanding of the disposal systems so that
repository performance can be analyzed to an adequate level for each of the future decisionmaking steps.
• To develop a more global understanding of DGR robustness by carrying out sensitivity
analyses that vary waste inventory, site properties, ranges of technical data, etc.
• To develop an R&D proposal based on the current safety case. Such proposal should clearly
define and substantiate key R&D priorities needed in the next phase of siting and safety casedevelopment.
• To continue its investments in international activities, both with the international bodies NEAand IAEA, and with the organizations abroad working with similar geological disposal
projects.

© 2021 Organisation for Economic Co-operation and Development

Summary of specific recommendations to NUMO (1/2)
The IRT makes following detailed recommendations to be considered in the development of future safetycases:
Disposal concept and design• To define performance indicators for safety functions• To consider in more detail the retention of radionuclide transport in the geosphere• To continue design developments, particularly with a view to adapt design as information on sitecharacteristics increases.
• Better integrate monitoring aspects of retrievability concept
Stepwise development and management system• To keep design options open as much as possible in order to keep flexibility in DGR development
phase.
• To implement a configuration management as part of NUMO’s overall management system.
Configuration management’s objective is to record the various technical options studied as well as thesets of calculations associated with each of them.

© 2021 Organisation for Economic Co-operation and Development

Summary of specific recommendations to NUMO (2/2)
Safety assessments• To supplement the operational safety assessment by including additional scenarios and all
potential exposure pathways to workers and the public• To explore phenomena not considered at this stage, since evaluated to be of secondary
importance for repository evolution• To continue developing storyboards and assessing further ways to increase their use• To increase efforts to validate models and computing tools in the near future• To strive for less conservatism, e.g. by developing sensitivity cases with alternative,
reasonably expected, site properties© 2021 Organisation for Economic Co-operation and Development

IRT conclusions
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NUMO’s SDM-based safety case is in line with international standards and fulfils its role wellin the current DGR development phase
NUMO has demonstrated its capability to integrate multiple lines on scientific information andto carry out safety case development
Preliminary results from the siting process and NUMO’s safety case demonstrate thatgeological disposal is feasible in JapanFor successful DGR implementation, it is of key importance that dialogue between mainstakeholders is enhanced
IRT has made observations and recommendations that NUMO should take into account innext steps of site selection and safety case development© 2021 Organisation for Economic Co-operation and Development

Thank You!
© 2021 Organisation for Economic Co-operation and Development