Spent Fuel Storage and Transportation Sub-Arena

Objective

Utilize risk information on a case-by-case basis to prioritize and address regulatory initiatives in spent fuel storage and radioactive materials transportation.

Basis

SECY-99-100 and SECY-04-0182, as well as the related staff requirements memorandum (SRM), provide the conceptual framework for risk-informing the NRC's waste activities. Guidance on how to apply this framework is provided in "Risk-Informed Decision-Making for Material and Waste Applications". In particular, individual risk-informed applications must meet the established screening criteria.

In this subarena, the NRC staff is limited in its ability to risk-inform the agency's regulatory activities because it is not cost-beneficial to perform risk-assessment of each of the numerous storage or transport designs. As a result, the agency has conducted (or sponsored) risk assessments for a few selected designs. In addition, the staff may apply risk assessments to specific activities on a case-by-case basis, provided that the screening criteria are met. For example, the staff has completed and documented a pilot study PRA of a dry cask storage facility, and determined that the risk from that facility was negligibly small.

The goal described below meets the screening criterion for cost/benefit by assessing risk impacts by judgment.

Goals

The staff has established the following goal for risk-informed and performance-based activities in this subarena:

• Produce updated versions of NUREG-1536, "Standard Review Plan for Dry Cask Storage Systems," and NUREG-1567, "Standard Review Plan for Spent Fuel Dry Storage Facilities."

Summary Description

Most dry storage systems utilize a welded austenitic stainless-steel canister emplaced in a sheltered environment created by a reinforced concrete or steel and concrete structure. Although there are many advantages to using austenitic stainless-steel canisters including general corrosion resistance and high material toughness, these materials are susceptible to chloride induced stress corrosion cracking (CISCC). The objective of this research is to perform an independent probabilistic risk assessment on the likelihood and timing of the occurrence of CISCC.

Previous Fiscal Years

FY 2022

This year, the first draft of a report titled “Literature Review & Identification of System Performance Failure Modes Pertinent to CISCC Evolution and Risk Sequence” was submitted to the NRC documenting the results of a preliminary scoping study on CISCC. The study identified and compiled the current state of knowledge on the susceptibility, crack initiation and growth, and consequences of CISCC. Furthermore, the study identified performance failure modes pertinent to the potential evolution and risk sequence of CISCC in dry storage of spent nuclear fuel.  Next year we will evaluate previously performed risk assessments and consequence analyses, and identify critical parameters for the CISCC probabilistic assessment. Subsequently we will complete the probabilistic assessment.

FY 2023

The NRC staff has evaluated previous risk assessments and identified the critical parameters for a CISCC consequence analysis. Initial assessments of the consequences of CISCC were shown to be low. In addition, the NRC staff has evaluated models for CISCC that utilize material and environmental inputs to identify parameters that are significant for a probabilistic assessment of CISCC as based on site conditions and time in service. Next year, we will conduct a risk assessment that considers the probability of CISCC occurrence and the consequences for dry storage systems.

Summary Description

As shown in existing probabilistic risk assessment studies, the risk associated with dry cask storage under 10 CFR Part 72 is very low. The NRC is engaged in multiple activities with the goal being to enhance the framework for spent fuel storage.  The results would be to enable the staff to perform more risk-informed regulatory reviews, improve guidance, streamline casework activities, help assess 10 CFR 72.48 changes, and evaluate requests for exemptions to the regulation while maintaining appropriate margins of safety and security.  One of these activities is the development of what is called the graded approach for determining the content and format of certificates of compliance (including their appendices).

The graded approach takes into consideration quantitative and qualitative risk insights, as well as key regulatory requirements to ensure dry storage system certificates of compliance contain the necessary storage system design information and requirements for maintaining safety and security and ensuring that the associated regulatory requirements are met.

Previous Fiscal Years

FY 2020

In FY 2020, the staff continued work on the graded approach for spent fuel certificates of compliance. The goal of this approach is to streamline the certification and oversight of spent fuel dry storage designs following the principles of risk-informed regulations. The graded approach provides the framework and criteria for establishing an appropriate level of information in spent fuel storage systems’ certificates of compliance and their appendices as well as a uniform format for the certificates and their appendices. The graded approach provides criteria to determine the information and requirements that are of sufficient safety or risk significance that they should be included in the certificate of compliance and its appendices and that information and those requirements which may remain in the other licensing basis documents for a dry storage system design (e.g., final safety analysis reports) to which regulatory processes such as 10 CFR 72.48 may be applied. In a January 8, 2020, letter to the Nuclear Energy Institute, the NRC endorsed the use of the graded approach program (ADAMS Accession No. ML19353D373). In FY 2021, the staff plans to explore additional activities that will incentivize the use of the graded approach.

FY 2021

In FY 2021, the staff began exploring the potential need for guidance to facilitate implementation of the graded approach and review of applications using it. The staff plans to continue that exploration in FY 2022, considering the lessons learned and experience gained from review of applications with the graded approach, including the pilot amendment and recent applications seeking to use the graded approach.

FY 2022

No update

FY 2023

The NRC staff continues to explore the lessons learned and experience gained from review of applications with the graded approach, including the pilot amendment and recent submittals applying the graded approach.

Summary Description

The NRC staff is developing a guidance document to include risk information in the review of dry cask license applications and license amendments. The tool is based on risk studies, past safety evaluation reports, and staff expert knowledge. This dry cask Risk Tool would be used to rate specific licensing actions in four different color coordinated results which correspond to high (red), medium (yellow), or low (green) risk, and outside the scope of the tool (blue). This preliminary risk rating can then be used alongside other information and staff experience to determine the level of review required for a specific requested licensing action.

Previous Fiscal Years

FY 2020

The development of the dry cask Risk Tool began in September 2019.  Major activities have included the construction of the draft tool by Idaho National Laboratory followed by review and contributions from a working group of senior NRC technical reviewers.  Work on this project is now transitioning from development of the Risk Tool to creating a guidance document for implementation and developing training materials for educating staff in its application.  A public meeting to communicate the tool to industry stakeholders took place on September 9th (ADAMS Accession No. ML20248H381).

The level of effort required for evaluating a requested licensing action will also depend on the quality of the application, uniqueness of the design, and the methodology used for demonstrating compliance.  The inclusion of the dry cask Risk Tool in the planning of reviews will support allocating more time to difficult/high risk items to further ensure adequate safety, while making lower risk reviews more efficient.

FY 2021

FY 2022

The NRC staff continues its ongoing efforts related to the implementation of risk insights in the licensing process and operations of dry cask spent fuel storage. The Risk Tool was presented during a technical session at the NRC’s Regulatory Information Conference held March 8-10, 2022, which focused on the impacts of using comprehensive risk tools and risk management for optimizing the resources in the regulatory process.

FY 2023

The NRC staff continues to pilot the Risk Tool for all new dry cask storage licensing reviews. The pilot will run through August 2024. Staff will collect data during the pilot period to facilitate improvements to the Risk Tool.