ML19266A619
| ML19266A619 | |
| Person / Time | |
|---|---|
| Issue date: | 02/21/2020 |
| From: | NRC/RES/DE |
| To: | |
| SJG1 | |
| Shared Package | |
| ML19266A614 | List: |
| References | |
| RG 1.166 | |
| Download: ML19266A619 (7) | |
Text
Response to Public Comments on Draft Regulatory Guide (DG)-1337 Pre-Earthquake Planning, Shutdown and Restart of a Nuclear Power Plant Following an Earthquake Proposed Combination of Regulatory Guide (RG) 1.166 and RG 1.167 On June 14, 2019 the NRC published a notice in the Federal Register (84 FR 27809) that Draft Regulatory Guide DG-1337, a proposed combination of RG 1.166 and RG 1.167, was available for public comment. The public comment period ended on August 13, 2019. The NRC received comments from the organizations listed below. The NRC has combined the comments and NRC staff responses in the following table.
Comments were received from the following:
Raymond Pace (for) Frances Pimentel (for)
ASME Task Group on Beyond Design Basis Events Nuclear Energy Institute c/o Imperial Engineering Partners 1201 F Street, NW 113 Cedar Street Washington, DC 20004 Milford, MA 01757 raymond.pace@imperiaep.com ADAMS Accession No. ML19198A318 Commenter Section of DG- Specifc Comments NRC Resolution 1337 R. Pace General The ASME Task Group on Beyond Design Basis Events Agree with the comment.
Comment has one comment with respect to the Regulatory Guide.
There is no discussion in Staff Regulatory Guidance A clarification was added to the final RG Section C on use of strain based allowable values for the regarding equipment and structures qualified by directed analytical evaluations of selected components. analysis in ANSI/ANS-2.23-2016. In this The DG limits the results of the analytical evaluation to clarification, the RG now states that strain based Service Level D. allowable values with adequate justification may be used when non-linear analyses are performed.
NEI General The NRCs Draft Guidance takes exception to a key Agree with the comment.
Comment aspect of ANS/ANSI-2.23-2016 in a manner that would involve significant efforts by licensees and is not NRC staff reviewed the ANS/ANSI-2.23-2016 technically warranted or meaningful in the absence of standard with consideration of NEIs comments
significant damage. Further, operational experience for and agree that the standard can be endorsed the 2011 Mineral, Virginia earthquake has demonstrated without exception. Staff finds that the Action that the additional analysis involved by the proposed levels associated with the damage and earthquake exception ultimately provided little or no contribution to levels provide an appropriate risk informed safe plant restart. The regulatory burden associated with response for establishing plant readiness for this earthquake was approximately $25 million and restart.
100,000 man-hours (ML17061A192).
Most recently, the industry effort in response to NRC Fukushima Near-Term Task Force (NTTF)
Recommendations 2.1 (for re-evaluated seismic hazard) and 2.3, which included plant walk-downs, expedited seismic evaluation programs (ESEPs) and seismic probabilistic risk assessments (PRAs), demonstrated that safe-shutdown SSCs have sufficient seismic capacities to withstand accelerations corresponding to SSE and beyond.
The approach provided in ANS/ANSI-2.23-2016 for evaluating plant readiness to restart in the event that the SSE criterion is exceeded in the absence of damage, provides the most balanced, reliable and practical method available. We recommend that DG-1337 be revised to endorse ANS/ANSI-2.23-2016 without exception.
NEI B. Discussion - NEI comment: There is a paragraph that discusses the Agree with the comment.
Background background of why ANSI/ANS-2.23-2016 is being endorsed by the RG; however, there is not a background Text was added to Section B Background to discussion on why ANSI/ANS-2.10-2017 is also endorsed explain that it was added to the RG because the by the RG. standard provides guidance on the retrieval, handling and archiving of recorded data from NEI Recommendation: Include in the background seismic instrumentation in the event of an section a discussion on why ANSI/ANS-2.10-2017 is also earthquake. These are important aspects of endorsed by the RG. responding to strong motion earthquakes.
2
NEI C.1 Exception NEI Comment: As currently drafted, this section takes As noted above, the staff agrees that an exception to Post- exception to Table 1- Action level matrix in Section 7 to the standard is not needed.
Earthquake of ANSI/ANS-2.23-2016 where the licensee is directed to Action Levels follow Action Level 1 (the lowest Action Level) when the Recommended Damage Level is 1 or 0 and the Earthquake Level exceeds in ANS-2.23- the SSE. We recommend that the proposed exception to 2016, Section Section 7.3 of ANSI/ANS-2.23-2016 be deleted based on 7.3 the following:
- 1. There have been numerous seismic industry initiatives that demonstrated that SSCs have sufficient seismic capacities to withstand accelerations associated with the SSE and higher. Those initiatives include:
- The industry effort in response to NRC Fukushima Near- Term Task Force (NTTF) Recommendations 2.1 Seismic and 2.3 Seismic which included plant walk-downs, expedited seismic evaluation programs (ESEPs) and seismic probabilistic risk assessments (PRAs). On July 3, 2019, the NRC issued Treatment of Reevaluated Seismic Hazard Information Provided under Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendation 2.1 of the Near-Term Task Force Review of Insights from the Fukushima Dai-Ichi Accident (ML19140A307). In that letter the NRC states, assessments remain valid based on the demonstrated inherent capacity of SSCs In binning the sites, Category 1 is described as Corresponds to sites where no additional regulatory action is warranted. This category includes sites that where the reevaluated seismic hazard is bounded by the current design basis, or sites where the licensee has demonstrated that existing seismic capacity and plant procedures will address the unbounded reevaluated hazard. This means that both licensees and staff are finished with the 50.54(f) letter seismic reevaluation assessments and backfit decisions for these 3
sites. There are currently 47 sites in this category. Under NTTF 2.1, capacities of SSCs up to at least the ground motion response spectra (GMRS) (and the associated in-structure response spectra (ISRS)) have been determined to be seismically adequate.
- Individual Plant Examination of External Events (IPEEE) and Unresolved Safety Issue (USI) A-46, "Verification of Seismic Adequacy of Mechanical and Electrical Equipment in Operating Reactors,"
results demonstrated that safe shutdown Structures, Systems, and Components (SSCs) are capable of withstanding accelerations in excess of SSE loading.
- Seismic margin assessments such as documented in A Methodology for Assessment of Nuclear Power Plant Seismic Margin, EPRI NP-6041-SL.
- 2. Evaluation of the focused visual inspections and tests of the accessible areas performed by engineering prior to restart, by its definition, determines the significance of the results, including comparison with acceptance criteria and any previous results (trending), and would be applicable to any inaccessible areas within a reasonable proximity.
There is no apparent technical basis for concluding that an additional evaluation program following restart would provide a meaningful increment in safety assurance.
Therefore, no formal technical evaluations or involved technical justifications for inaccessible areas are justified after restart since the evaluation of the accessible areas would not have identified these areas as being susceptible to damage.
- 3. The approach in ANS/ANSI 2.23-2016 is consistent with the observations from a number of nuclear plants that experienced significant beyond-design basis earthquakes 4
that the plant itself is the best indicator of potential damage, not instrument recordings or analyses alone. For the Mineral, Virginia M5.8 earthquake of August 23, 2011, which exceeded the North Anna plant's SSE spectra in certain frequency bands, the licensee was requested by the NRC to perform sample analyses of SSCs prior to restart. These analyses were performed based on the recorded motions; however, in- structure response spectra (ISRS) could not be calculated in the short timeframe prior to re-start. Therefore, approximations were made in some cases. No issues were identified, and no safety benefits resulted from these sample analyses. The thorough walk-downs of plant areas and SSCs that showed no significant damage (consistent with the Cumulative Absolute Velocity (CAV) for this event) and the detailed functional and surveillance tests that were performed led to the conclusion that North Anna plant was safe for restart. Accordingly, we do not believe that analytical evaluation of a sample of SSCs is technically warranted or particularly meaningful in the absence of significant damage. This is supported by the experience-based conclusion that the types of SSCs that are amenable to analytical evaluation are typically the least seismically vulnerable SSCs in a nuclear plant. Extensive evaluations and functional testing of equipment performed at North Anna following the 2011 Mineral, Virginia earthquake (even though thorough inspections did not reveal any damage) demonstrated that SSCs were capable of performing their required design basis functions. This is further evidenced by the fact that North Anna continues to operate well eight years after the Mineral event.
- 4. DG-1337 refers to potential unobserved latent damage and its safety impact on continued operation of SSCs. The potential latent damage issue has been thoroughly reviewed at nuclear plants in 5
several past earthquakes, such as the Niigata- Chuetsu-Oki earthquake of 2007 for the Kashiwazaki-Kariwa plant and the Mineral, Virginia earthquake of 2011 for the North Anna plant, where the damage levels (DLs) were 0 or 1. No evidence of latent damage was found at these plants. (Refer to Dominion letter dated October 18, 2011, Serial No.11-577 A, for a discussion of the North Anna review for latent/hidden damage. [ADAMS ACCESSION No. ML11292A151]).
- 5. The CAV threshold of 0.16 g-sec recommended in ANS/ANSI 2.23-2016 for a Safe Shutdown Earthquake (SSE) is the same as that for an Operating Basis Earthquake (OBE), which is highly conservative. For earthquakes that have small strong- motion durations, the CAV is expected to be small. If the CAV is above the threshold, the SSE spectra can be easily exceeded, as was the case for the Mineral, Virginia earthquake of 2011; however, the DL can still be 0 or 1 and Action Level 1 is considered appropriate.
- 6. New technology plants that are required to meet this version of the Reg Guide are generally of a Passive (or Fail Safe) design. Requiring this additional analysis following restart is unwarranted based on margins included in those designs.
- 7. The sentence in this section that states, "Because plant configurations do not rapidly change,licensees should consider developing a list of these SSCs in advance of an event," should be deleted since this requirement is met in Section 5.4 of ANS/ANSI 2.23- 2016.
In summary, ANS/ANSI 2.23-2016, "Nuclear Power Plant Response to an Earthquake," provides adequate justification for performing focused visual inspections and 6
tests only for Damage Level (DL) 0 and DL 1 - Action Level (AL) 1. Additionally, Table 1 of ANSI/ANS- 2.23-2016 provides adequate guidance for all Action/Earthquake/Damage Levels.
NEI Recommendation: The proposed exception to Section 7.3 should be deleted based on the points discussed under comment / basis. Additionally, this exception would impose significant burden on licensees without adequate justification.
NEI References NEI Comment: Reference 13 is not the latest version of Agree with the comment.
the EPRI guidance document and is no longer available from EPRI. It has been superseded by EPRI 3002005284. The RG was updated to reference the latest version of the EPRI guidance.
NEI Recommendation: Replace with EPRI report 3002005284, dated 2015 7