ML20058D088
| ML20058D088 | |
| Person / Time | |
|---|---|
| Issue date: | 02/26/2020 |
| From: | Margaret Doane NRC/EDO |
| To: | Jeff Baran, Annie Caputo, Kristine Svinicki, David Wright NRC/Chairman, NRC/OCM/AXC, NRC/OCM/DAW, NRC/OCM/JMB |
| Kathleen Blake x1700 | |
| References | |
| Download: ML20058D088 (7) | |
Text
February 26, 2020 MEMORANDUM TO: Chairman Svinicki Commissioner Baran Commissioner Caputo Commissioner Wright FROM: Margaret M. Doane /RA/
Executive Director for Operations
SUBJECT:
CONCERNS PERTAINING TO GAS TRANSMISSION LINES AT THE INDIAN POINT NUCLEAR POWER PLANT:
DETERMINATION NOT TO TAKE IMMEDIATE ACTION This memorandum responds to the Chairmans February 24, 2020, direction to the Executive Director for Operations (EDO) to address matters raised in the Nuclear Regulatory Commission (NRC) Office of the Inspector General (OIG) report, Event Inquiry, Concerns Pertaining to Gas Transmission Lines at the Indian Point Nuclear Power Plant (Case No.16-024). In that memorandum, the Chairman directed the prompt examination to determine if immediate regulatory action is needed based on information in the OIG report and to promptly inform the Commission of the results of that examination and what actions, if any, the staff plans to take. For the following reasons, I have determined that there is no need for immediate regulatory action.
In response to the Chairmans direction, I tasked Dr. Mirela Gavrilas to examine the information in the OIG report (advance copy) and evaluate promptly whether immediate action is warranted.
Dr. Gavrilas was not involved in the matter in question in the OIG report. Dr. Gavrilas received her Ph.D. in nuclear engineering from the Massachusetts Institute of Technology and has decades of experience in nuclear power plant safety.
The determination on whether immediate action is needed was performed in accordance with the agency procedure used to respond to nuclear power plant emergent issues. This procedure is found in section 4.2.1 of LIC-504 Rev. 4 Integrated Risk-Informed Decision-Making Process for Emergent Issues (Agencywide Documents Access and Management System Accession No.: ML14035A143). After reviewing the findings in the OIG report and the technical aspects of the 42-inch gas line that traverses the Indian Point Energy Center property (IPEC),
Dr. Gavrilas has determined that there is no safety issue warranting immediate regulatory action at either Unit 2 or Unit 3.
The Commissioners This conclusion is based on the following summary findings that are explained in more detail in the attached enclosure:
- There is no significant degradation to defense-in-depth at either unit.
- There is no significant loss of safety margin at either unit.
- There is no high-risk impact at either unit from internal or external events, as all risk metrics are under the prescribed thresholds.
I have assigned David Skeen to lead a team of experts to respond to the remaining issues in the Chairmans memorandum, including the direction to provide the Commission with the results of a staff review within 45 days of the date of the memorandum. Mr. Skeen has been a member of the Senior Executive Service for more than a decade, and previously served as the director of the Japan Lessons-Learned Directorate. In that capacity, he had a key role in evaluating the safety of the U.S. nuclear power plant fleet in response to the events at the Fukushima Daiichi nuclear power plant caused by the Great Thoku earthquake and tsunami. Mr. Skeen was not involved in the matters addressed in the OIG report.
As is contemplated under the procedure, LIC-504, during the course of the teams review, the team will be mindful of the need to assess any new emergent issues.
Enclosure:
Evaluation of Emergent Information Pertaining to Gas Transmission Lines at the Indian Point Nuclear Power Plant cc: SECY OGC OIG OPA D. Skeen
The Commissioners
SUBJECT:
CONCERNS PERTAINING TO GAS TRANSMISSION LINES AT THE INDIAN POINT NUCLEAR POWER PLANT: DETERMINATION NOT TO TAKE IMMEDIATE ACTION DATED FEBRUARY 26, 2020.
ADAMS Accession Number: ML20058D088 OFFICE OEDO NRR OGC EDO NAME DJackson MGavrilas MZobler MDoane DATE 2/26/2020 2/26/2020 2/26/2020 2/26/2020 OFFICIAL RECORD COPY
Evaluation of Emergent Information Pertaining to Gas Transmission Lines at the Indian Point Nuclear Power Plant This evaluation is in response to the Chairmans tasking of February 24, 2020, to determine if immediate regulatory action is necessary. This prompt evaluation was performed in accordance with Section 4.21 of Office of Nuclear Reactor Regulation (NRR) office instruction LIC-504 Rev. 4 Integrated Risk-Informed Decision-Making Process for Emergent Issues (Agencywide Documents Access and Management System (ADAMS) Accession No.: ML14035A143) within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of the request.
Defense-in-Depth LIC-504 states that additional regulatory action may be required to place or maintain the plant in a safe condition if defense-in-depth is significantly degraded (e.g., multiple barriers are moderately to significantly degraded, functional redundancy or diversity is significantly compromised, or vulnerability to single failures is significantly increased).
While a pipe rupture could impact certain structures on the site (e.g., gas turbine fuel oil tanks, the switchyard, emergency operations facility, FLEX equipment storage building), the pipeline is located approximately 1500 ft (rev 2) from the nearest safety related structure and barriers to radioactive release (i.e., the fuel cladding, reactor coolant system pressure boundary, and containment) would be maintained. Impacts to nearby structures could affect the plant response measures or the probability of additional initiators. However, there are still multiple diverse barriers and mitigation measures in place to minimize the challenges to the plant, preventing events from progressing to core damage, containing the radioactive source term, and ensuring emergency preparedness capabilities. Impacts on structures in the proximity of the explosion do not significantly degrade defense in depth.
Safety Margins LIC-504 states that additional regulatory action may be required to place or maintain the plant in a safe condition if there is significant loss of safety margin (e.g., the calculated ASME code structural factors for a component are equal to or less than 1). Regulatory Guide 1.174 also indicates that safety margins are adequate if (1) the codes and standards or their alternatives approved for use by the NRC are met and (2) licensing basis safety analysis acceptance criteria are met.
A pipe rupture does not affect the plants compliance with codes and standards. Compliance with the plants technical specifications ensures adequate margin is maintained against design basis accidents.
Enclosure
Risk Assessment Assumptions and Inputs:
Appendix F in the Federal Emergency Management Agency (FEMA) Handbook of Chemical Hazard Analysis Procedures 1989-626-095-10575, 1989 (ref 1) identifies accident rates for pipelines with a diameter greater than 20 inches at 5E-4 accidents per year per pipeline mile.
The FEMA Handbook also states that only 20% of events constitute large pipe ruptures.
Based on this probability, the frequency of pipeline rupture is calculated assuming 3935 ft of pipeline are near the site. This is equal to (3935 ft / (5280 ft / mi ) ) = 0.745 mi of pipeline (ref 2).
The frequency of pipeline ruptures is therefore:
Frequency of pipeline rupture = Failure rate rupture percentage of failures pipeline length Frequency of pipeline rupture
= (5 10 failures/year/pipeline mile)(0.2 complete ruptures/failure )(0.745 pipeline miles)
Frequency of pipeline rupture = 7.45 10 The values of risk to be compared against the risk action thresholds provided in LIC-504 are calculated by making three conservative assumptions:
- All complete ruptures lead directly to core damage.
- The as-is condition exists for 45 days (the duration of the Chairmans tasking memo).
- Large early release probability is 0.1 of the core damage probability.
Under these assumptions:
- The conditional core damage frequency (CCDF) can be calculated as the frequency of a pipeline ruptures times the probability that a pipeline rupture leads to core damage, or:
(7.45 10 ) (1) = 7.45 10
- The conditional large early release frequency (CLERF) is calculated as 0.1 of the conditional core damage probability or:
(7.45 10 ) (0.1) = 7.45 10
- The incremental conditional core damage probability (ICCDP) in the 45-day window can be calculated by multiplying the conditional core damage probability, the initiating event frequency, and the duration of the condition, or:
(1) (7.45 10 events/year) (45 days365 days/year) = 9.18 10
- The incremental large early release probability (ICLERP) can be calculated as 0.1 of the incremental conditional core damage probability, or:
(9.18 10 ) (0.1) = 9.18 10 These values can be compared against the risk action thresholds in LIC-504:
Parameter LIC-504 Risk Action Threshold Calculated Value CCDF 1E-3 7.45E-5*
CLERF 1E-4 7.45E-6 ICCDP 5E-5 9.18E-6 ICLERP 5E-6 9.18E-7 Discussion:
The numbers provided above represent median estimates of the conditional core damage probability and large early release probability. However, they were calculated assuming various conservatisms, some of which are enumerated in the table below.
Source of Conservatism Effect Large pipe ruptures lead to deflagrations or detonations. The FEMA 1 order of magnitude Handbook notes that in the event that there is a failure in a pipeline, most often the outcome is a small leak.
Assumptions on pipeline failure rates were structured around studies 1 order of magnitude (or performed in the 1980s. Since then, codes and standards have improved greater) and probabilities of failure would be less than those assumed. The probability of failure for this specific section of pipeline is reduced since it was constructed to specifications that exceed current code requirements and was covered with concrete planks to prevent inadvertent damage from digging.
The analysis assumes that pipeline failures lead directly to core damage. In 3 orders of magnitude reality, a pipeline explosion would not directly cause damage to the reactor (or greater) core, though it could damage safety-related equipment that may be needed to prevent core damage if another initiating event were to occur at the same time.
Thus, the calculated values for CCDF of 7.45E-5, CLERF of 7.45E-6, ICCDP of 9.18E-6, and ICLERP of 9.18E-7 represent upper bound estimates, and there are several orders of magnitude of conservatism separating these values from more realistic estimates.
Conclusions No significant degradation of defense in depth nor loss of safety margins were identified. The evaluation above shows that the CCDF, CLERF, ICCDP, and ICLERP values associated with pipeline explosions at IPEC are smaller than the LIC-504 risk action thresholds. Therefore, no immediate regulatory action is required to maintain the plant in a safe condition.
Note that this is a conservatively bounding value for a station blackout initiated by a pipeline explosion because it does not account for various factors, such as the limited line of sight between the explosion and the diesel generator buildings.
References
- 1. Safety Evaluation Performed by Entergy Under 10 CFR 50.59 (ADAMS Accession No. ML14253A339), August 21, 2014
- 2. FEMA Handbook of Chemical Hazard Analysis Procedures, Appendix F, 1989-626-095-10575, 1989