ML24339A063

Agu Fall 2024 Exhb Poster Presentation-Final

ML24339A063
Person / Time
Issue date:	12/04/2024
From:	Jacqueline Thompson NRC/NRR/DEX/EXHB
To:
References
Download: ML24339A063 (1)

Text

External Hazards Assessments for Nuclear Reactor Siting by the United States Nuclear Regulatory Commission: 50 years of Challenges, Innovative Approaches, and Preparing for What Comes Next Jenise Thompson, Kevin Quinlan, Nebiyu Tiruneh, Mike Lee, Rosalynn Wang, Barbara Hayes, Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Abstract The U.S. Nuclear Regulatory Commission (NRC) ensures safe use of radioactive materials for beneficial civilian purposes while protecting people and the environment. The NRC Engineering and External Hazards staff contributes to this mission by performing technical reviews for nuclear power plants over a wide variety of external hazards, including meteorology, hydrology, seismology, geology, and volcanology. Scientific and engineering methods employed in the assessment of external hazards have evolved substantially since the establishment of the NRC nearly 50 years ago.

By ensuring adequate protection of public health and safety from the civilian use of nuclear power, the NRC ensures the resilience of the domestic nuclear reactor fleet to continue to reliably provide power. The NRC staff performs safety reviews to ensure regulatory compliance with existing regulations and is responsible for guidance in response to emerging needs and legislative requirements. Consistent with the Commissions 1995 Policy Statement on the use of probabilistic methods, the NRC staff promotes the use of advanced analysis tools that include high-speed computer modeling, the adoption of the Senior Seismic Hazard Analysis Committee (SSHAC) process to assess seismic hazards, and the implementation of the hierarchical hazard assessment (HHA) process for the evaluation of hydrologic hazards. The NRC staff develops and updates guidance documents as the state of practice embraces new analysis methods. This includes incorporating lessons learned from national and global operating experience such as the 2011 accident at Fukushima Dai-ichi in Japan and considering new hazard information by implementing NRCs process for the ongoing assessment of hazard information. The development and deployment of an ever-expanding variety of nuclear reactor designs presents regulatory challenges and opportunities.

As a modern regulator, the NRC is enhancing current methods and processes to address the unique facets of these new reactor designs. The NRC staff implements innovative approaches to hazard analysis through risk-informed regulation and a graded approach to site characterization. The NRC continues to evolve and adapt with emerging computational advances that can be used in addition to the technical tools in current use.

The Regulatory Process and Safety Review The regulatory framework is based on laws, regulations and guidance documents. The major laws in use are the Atomic Energy Act of 1954 and the Energy reorganization Act of 1974.

The Code of Federal Regulations (CFR), primarily parts 50, 52, and 100 set the regulatory requirements. The NRC develops several guidance documents which include Standard Review Plan (SRP),

regulatory Guide (RG), and Interim Staff Guidance (ISG).

• 10 CFR Part 50 - Domestic Licensing of Production and Utilization Facilities

• 10 CFR Part 52 - Licenses, Certifications, and Approvals for Nuclear Power Plants

• 10 CFR Part 100 - Reactor Site Criteria

• 10 CFR Part 20 - Standards for Protection Against Radiation The standard review plan provides guidance to NRC staff in performing safety reviews of construction permit (CP) or operating license (OL) applications (including requests for amendments) under 10 CFR Part 50 and early site permit (ESP), design certification (DC), combined license (COL), standard design approval (SDA), or manufacturing license (ML) applications under 10 CFR Part 52 (including requests for amendments). The review of external hazards is based on the guidance provided in the following sections of the SRP.

• SRP 2.3 - Meteorology

• SRP 2.4 - Hydrology

• SRP 2.5 - Geology, Seismology, and Geotechnical Engineering These reviews are performed consistent with NRCs Principles of Good Regulation and the Be riskSMART decision-making framework.

General Design Criterion 2 To ensure the safe operation of nuclear power stations, the Commission established 64 General Design Criteria (GDCs)General Design Criteria for Nuclear Power Plantsat Appendix A to 10 CFR Part 50. The GDCs represent the minimum requirements for the principal design criteria for nuclear power plants similar in design and location to plants for which construction permits have been issued by the Commission. Moreover, the GDCs are intended to amplify the existing Part 50 regulatory requirements. The intent of the GDC 2 requirement was to ensure that natural phenomena, which may be present at the site, do not possess the capability to affect a powerplant operation by disabling important safety systems or, alternatively, undermine or compromise the integrity of those structures containing those safety systems. Similarly, if any of the natural phenomena cited in SRP Chapters 2.3, 2.4, and 2.5 were judged to be present, that the power plant was engineered in such a way that either passive design features and/or operator actions could be implemented in a timely fashion to mitigate any flooding effects.

GDC 2 states that Structures, systems, and components important to safety shall be designed to withstand the effects of natural phenomena such as earthquakes, tornadoes, hurricanes, floods, tsunami, and seiches without loss of capability to perform their safety functions. The design bases for these structures, systems and components shall reflect: (1) Appropriate consideration of the most severe of the natural phenomena that have been historically reported for the site and surrounding area, with sufficient margin for the limited accuracy, quantity, and period of time in which the historical data have been accumulated, (2) appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena and (3) the importance of the safety functions to be performed....

Geologic and Volcanic Safety Review The NRC geologists focus the safety review on the geologic conditions at the site that may have the potential to result in hazards to the proposed facility, such as karst, landslides, faults, geologic structures, and volcanic sources.

The geology review focuses on the regions of interest with increasing detail:

Region (320 km), Vicinity (40 km), Area (8 km) and Location (1 km). The time period of interest is the Quaternary. The geology review includes both physical investigations of the site and a literature review. The geology review also has input to the seismic hazards review and the geotechnical review with respect to geologic profiles, geophysical properties of the subsurface units, and other factors.

Volcanic hazards are assessed following the process outlined in Regulatory Guide 4.26, as shown in Figure 1 to the right.

Figure 4: Be RiskSMART steps Figure 3: the New Reactor Licensing Process Seismologic Safety Review Literature Review and Field Investigations Data on Vibratory Ground Motions Tectonic/Non-Tectonic surface deformation Earthquake Recurrence Rates Fault Geometry and Slip Rates Site Foundation Material Seismically induced floods and water waves There should be sufficient information to support evaluations performed to arrive at estimates of the Safe Shutdown Earthquake (SSE) and propose adequate engineering solutions to actual or potential seismic effects.

The seismic safety review focuses on how well a site is evaluated The NRC requires that sites are designed to withstand the effects of natural phenomena such as earthquakes without loss of capability to perform their safety functions.

There are regulatory guidance and NUREGs to help meet NRC regulations for seismic hazard RG 1.208 A Performance-Based Approach to Define the Site-Specific Earthquake Ground Motion update

Include latest data and models

Pacific Earthquake Engineering Center (PEER)

Ground Motion Databases for the WUS and CEUS

NGA East ground motion models

Incorporate lessons learned from Fukushima Near Term Task Force activities.

Provide guidance on selecting appropriate site response approach for a particular site.

Alignment with ANS-2.29 and 2.27.

Senior Seismic Hazard Analysis Committee streamlining process with a SSHAC Level 1 demonstration to provide a guideline for more efficiently performing seismic hazard analyses.

What to look forward to Reg Guides NUREG

• RG 1.208

• RG 1.60

• 0800 SRP Section 2.5

• KM-0017

• 1537, 2115, 2213 Figure 2: the Regulatory Process GC51J-0091 Friday, December 13, 2024, 08:30 am - 12:20 pm

External Hazards Assessments for Nuclear Reactor Siting by the United States Nuclear Regulatory Commission: 50 years of Challenges, Innovative Approaches, and Preparing for What Comes Next Jenise Thompson, Kevin Quinlan, Nebiyu Tiruneh, Mike Lee, Rosalynn Wang, Barbara Hayes Division of Engineering and External Hazards, Office of Nuclear Reactor Regulation, U.S. Nuclear Regulatory Commission GC51J-0091 Friday, December 13, 2024, 08:30 am - 12:20 pm NRC Organization and External Hazards Center of Expertise The NRC is headed by a five-member commission of Presidential appointees who formulate policies and regulations governing nuclear reactor and materials safety, issues orders to licensees, and adjudicates legal matters brought before it. The Executive Director for Operations (EDO) carries out the policies and decisions of the Commission and directs the activities of the program offices. The Office of Nuclear Reactor Regulation (NRR) is responsible for the licensing, oversight, siting, rulemaking, and incident response for operating commercial nuclear power reactors, new commercial nuclear power reactors, advanced reactor technologies, and non-power production and utilization facilities.

Within NRR, the External Hazards Center of Expertise (EHCOE) centralizes the external hazards evaluation functions within multiple business lines across the NRC.

The vision of the EHCOE is to enhance the NRCs ability to shift resources or work assignments to meet the demands of a changing environment, increase organization capacity without an increase in resources, and achieve more effective knowledge management and maintenance of critical skill sets.

Hydrologic Safety Review The purpose of the hydrologic safety review is to consider plausible hazards within the natural hydrologic process and determine whether the design basis provides adequate protection and safety margin or if additional mitigative measures need to be taken to ensure the safe operation of the reactor and meet the applicable regulatory requirements. There are seven major areas of the hydrologic safety review:

1. Flooding from various flood causing mechanisms and their combinations

2. Low water considerations

3. Cooling water canals and reservoirs

4. Groundwater level, flow characteristics and potential use at the site

5. Accidental releases of radioactive liquid effluents in ground and surface waters

6. Flooding protection requirements

7. Technical specifications and emergency operation requirements.

Flood Causing Mechanisms There are several flood causing mechanisms, but all may not be relevant at a given site depending on location. The flood causing mechanisms include local intense precipitation, probable maximum precipitation, potential dam breach, probable maximum storm surge, seiche, tsunami, ice accumulation, channel diversion and geomorphological changes.

Flood hazards that could reasonably be combined are analyzed to estimate combined events flood.

Accidental Release of Radionuclides Performed to estimate dose to the public from a postulated failure of a tank from the liquid waste management system with the highest level of radioactive activity.

The analysis considers advective-dispersive transport through surface water and groundwater. Alternate pathways and post-construction site configuration are considered.

The estimated concentration of radionuclides at select public water sources are analyzed to estimate dose to the public.

Meteorologic Safety Review The NRC meteorologist role demands expertise in atmospheric science, focusing on regional climatology, local meteorology, air quality, and atmospheric dispersion modeling, particularly regarding environmental and nuclear safety.

Safety reviews prioritize external hazards, such as tornado and hurricane wind speeds, airborne debris, extreme precipitation, air quality, and climate change impacts.

For assessing potential radioactive releases, local meteorological data and Gaussian dispersion models are used to predict worst-case scenarios and potential exposure locations. This role integrates advanced meteorological analysis with nuclear safety evaluations to manage environmental risks effectively.

Flood Sources Development of Conceptual Site Model PROPOSED FINAL GRADE SOIL AND SAPROLITE AUXILIARY BUILDING AUXILIARY HOLDING POND GROUNDWATER FLOW DIRECTION RADIOACTIVE LIQUID EFFLUENT RELEASED FROM RUPTURED HOLDUP TANK EFFLUENT HOLDING TANK BEDROC K

IN-SITU FILL PARTIALLY WEATHERED ROCK RIVER FILL RC x

C v

x C

D t

C R

=

2 2

Conceptual Site Model of Radioactive Effluent Transport Process for the Ongoing Assessment of Natural Hazard Information (POANHI)

The POANHI framework allows the staff to monitor and assess new and updated natural hazards information to determine the safety significance of the new information. POANHI has three key attributes:

enhances safety, efficiently integrates with existing processes, and provides stability and predictability.

There are three primary components to address new natural hazard information: knowledge base activities, active technical engagement and coordination, and assessment activities. The NRC regularly produces a report of POANHI activities which is available on the POANHI website.

Hazard Guidance for the Future As a modern, risk-informed regulator, the NRC regularly reviews and revises guidance documents providing clarity on regulatory requirements. As new reactor designs emerge, the NRC staff are identifying adaptations to existing guidance to streamline advanced reactor reviews.

This includes learning from successful hazard approaches and adapting those successes to new hazards, as was done in adapting SSHAC for volcanic hazards analysis in RG 4.26 and through the incorporation of engineering judgement from RG 4.26 into DG-1290, the proposed revision to RG 1.59 for flood hazard evaluations of advanced reactor sites. The EHCOE staff are considering other adaptations of successful analyses for use in other hazards.

The staff is also developing guidance on a graded approach to site characterization that would focus the application development on the hazards that the selected design is sensitive to and that are present at the proposed deployment site.

This approach would consider the margin available for the site parameters as well as the dose to determine the appropriate level of grading for each hazard present at the site. This will include how existing site characterization information can be used for future applications.

This Structure

• Enhances ability to shift resources or work assignments to meet the demands of a changing environment

• Increases organizational capacity without an increase in resources

• Promotes more effective knowledge management and maintenance of critical skill sets in external hazards

• Enhances decision making

• Leads to cross-office standardization

• Hydrology

• Meteorology

• Geology/Seismology

• Geotechnical Engineering

• POANHI

• Human Induced External Hazards

• Dam Safety Program Areas of Expertise and Programs within EHCOE For Additional Information see the NRC Public webpage