ML18170A093
| ML18170A093 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 06/14/2018 |
| From: | Mark D. Sartain Dominion Energy Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 18-.230A | |
| Download: ML18170A093 (18) | |
Text
Dominion Energy Nuclear Connecticut, Inc.
5000 Dominion Boulevard, Glen Allen, VA23060 Dominion Energy.com June. 14, 2018 U.S. Nuclear Regulatory Commission Serial No. 18-.230A Attention: Document Control Desk NRA/WDC RO Washington, DC 20555 Docket No. 50-336 License No. DPR-65 DOMINION NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 2 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING LICENSE AMENDMENT REQUEST TO REVISE INTEGRATED LEAK RATE TEST (TYPE A) AND TYPE C TEST INTERVALS By letter dated October 4, 2017, Dominion Energy Nuclear Connecticut, Inc.
(DENC) requested a license amendment in the form of changes to the Millstone Power Station Unit 2 (MPS2) Technical Specifications (TSs) for facility Operating License DPR-65. This proposed amendment would allow DENC to extend the Type A primary containment integrated leak rate test interval for MPS2 to 15 years and the Type C local leak rate test interval to 75 months, and incorporates the regulatory positions stated in RG 1.163.
In an email dated May 14, 2018, the NRC transmitted a request for additional information (RAI) related to the license amendment request. The RAI contained six questions. DENC responded to RAl-06 in a letter dated May 24, 2018.
- Attachment 1 to this letter provides DENC's response to the remaining RAI que_stions, RAl-01 through RAl-05.
Should you have any questions in regard to this submittal, please contact Wanda Craft at (804) 273-4687.
Sincerely,
~-
Mark D. Sartain Vice President - Nuclear Engineering & Fleet Support COMMONWEALTH OF VIRGINIA COUNTY OF HENRICO The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Mark D.
Sartain, who is Vice President - Nuclear Engineering & Fleet Support of Dominion Energy Nuclear Connecticut, Inc. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that company, and that the statements in the document are true to the best of his knowledge and belief.
Acknowledged before me t h i s ~ day of :f\.l~(..
My Commission Expires: a\A, w).I, 3 l J ZOI ~.
Serial No: 18-230A Docket No. 50-336 Page 2 of2
Attachment:
- 1. Response to Request for Additional Information Regarding License Amendment Request to Revise Integrated Leak Rate Test (Type A) and Type C Test Intervals (RAl-01 through RAl-05)
Commitments made in this letter: None cc: U.S. Nuclear Regulatory Commission Region I .
2100 Renaissance Blvd, Suite 100 King of Prussia, PA 19406-2713 R. V. Guzman Senior Project Manager - Millstone Power Station U.S. N'uclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 08 C2 Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station Director, Radiation Division Department of Energy and Environmental Protection 79 Elm. Street Hartford, CT 06106-5127 L
Serial No. 18-230A Docket No. 50-336 ATTACHMENT-1 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING LICENSE AMENDMENT REQUEST TO REVISE INTEGRATED LEAK RATE TEST (TYPE A) AND TYPE C TEST INTERVALS (RAl-01 through RAl-05)
DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 2
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 1 of 15 By letter dated October 4, 2017, Dominion Energy Nuclear Connecticut, Inc. (DENC) requested a license amendment in the form of changes to the Millstone Power Station Unit 2 (MPS2) Technical Specifications (TSs)"for facility Operating License DPR-65. The proposed amendment revises MPS2 TS 6.19, "Containment Leakage Rate Testing Program," by replacing the reference to Regulatory Guide (RG) 1.163 (September 1995) with a reference to Nuclear Energy Institute (NEI) topical report NEI 94-01, Revision 3-A and the limitations and conditions specified in NEI 94-01, Revision 2-A, as the implementing documents used to develop the MPS2 performance-based leakage testing program in accordance with 10 CFR 50, Appendix J, Option B. This proposed amendment would allow DENC to extend the Type A primary containment integrated leak rate test (ILRT) interval for MPS2 to 15 years and the Type C local leak rate test interval to 75 months, and incorporates the regulatory positions stated in RG 1.163.
In an email dated May 14, 2018, the NRC transmitted a request for additional information (RAI) related to the license amendment request (LAR). The RAI contained six questions.
DENC responded to RAl-06 in a letter dated May 24, 2018. This attachment provides DENC's response to the remaining RAI questions, RAl-01 through RAl-05.
Background
In the safety evaluation (SE) issued on June 25, 2008 (ADAMS Accession No. ML081140105), the U.S. Nuclear Regulatory Commission (NRG) staff found the methodology in NE/ 94-01, Revision 2, and EPRI Report No. 1009325, Revision 2, acceptable for referencing by licensees proposing to amend their TSs to permanently extend the ILRT interval to 15 years, provided certain conditions are satisfied. Condition 1, set forth in Section 4.2 of the SE for EPRI Report No. 1009325, Revision 2, states that
.the licensee should submit documentation indicating that the technical adequacy of their probabilistic risk assessment (PRA) is consistent with the guidance in Regulatory Guide (RG) 1.200, relevant to the ILRT extension application. Revision 2 of RG 1.200 endorses, with clarifications and qualifications, the American Society of Mechanical Engineers/American Nuclear Society (ASME/ANS) PRA Standard RA-Sa-2009.
The information provided in the LAR is not sufficient for the NRG staff to reasonably determine that the licensee's PRA is consistent with the guidance in RG 1.200, Rev. 2, and therefore, cannot assess the technical acceptability of the licensee's PRA for use in support of this application. The following requests for additional information (RA ls) outline the information needed for the NRG staff to complete its review:
RAl-01 The licensee's LAR does not discuss changes made to the internal events and internal flooding PRA since the 2000 full-scope peer review.
a) Provide an overview of all changes in the internal events and internal flooding PRA since the 2000 full scope peer review that were not subject to the 2012 focused-scope peer review and provide justification as to whether any of these changes fit the definition of a PRA upgrade.
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 2 of 15 b) For each upgrade identified in item a. above, provide the result$ of the focused-scope peer review(s) performed on these upgrades and the disposition of any findings for the application.
DENC Response a) The following table summarizes the changes made to the MPS2 PRA model between the 2000 full scope peer review and the 2018 focused scope peer review that were not subject to either the 2012 or 2018 focused scope peer review. None of these changes meet the definition of a PRA upgrade. ASME/ANS RA-Sa-2009 Non-Mandatory Appendix 1-A was used as guidance for making the determination of PRA maintenance versus upgrade. Specific examples from Section 1-A.3 of the ASME/ANS RA-Sa-2009 have been listed below to provide justification for classification of these items as PRA maintenance.
PRA Maintenance Date/ Model Element Summary of Change Justification**
Updated Loss of Normal Power (LNP)
Update of plant-specific 2000/ Rev 1 IE initiating event frequency with plant data, similar to Example 2 specific data.
Added various equipment unavailability (Test & Maintenance) events to the Correct omission, similar 2001/ Rev 2 DA model to account for scheduled to Example 7 maintenance activities.
LNP logic was subdivided to differentiate Replace initiating events, 2001/ Rev 2 IE between grid-related and weather-similar to Example 1 related LNP events.
Data update including reliability and Data update, similar to 2005/M205A DA unavailability. Examples 2 and 3 Data update, similar to 2005/M205A IE Data update for initiating events.
Examples 2 and 3 Added new common cause failure (CCF) basic events for various components - Correct omission, similar 2005/M205A DA transformers, batteries, and auxiliary to Example 25 feedwater (AFW) pumps.
Corrected the plant specific data for Model error, similar to 2006/M205Aa DA unavailability of an emergency bus. Example 6
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 3 of 15 PRA Maintenance Date/ Model Element Summary of Change Justification**
Applied the generic failure probability distributions and component boundaries Application of generic 2010/M209A DA defined in NUREG/CR-6928 throughout data, similar to Example 3 the model.
Updated the reliability and unavailability Update of plant-specific 2010/M209A DA data with plant-specific data from data, similar to Example 2 January 1, 2000 to December 31, 2009.
Update of plant-specific 2010/M209A IE Recalculated the plant capacity factor.
data, similar to Example 2 Update of initiating event Updated the initiating event frequencies 2010/M209A IE data, similar to Examples in the model based on new data.
2 and 3 New thermal hydraulic Created a new MAAP4 case to update case, similar to Example 2010/M209Aa SC the success criteria for transient 10 but for PWR instead of sequences.
BWR Added detail to the Reactor Coolant Pump (RCP) Thermal Barrier Interfacing Enhancement for System Loss of Coolant Accidents 2011/M209Ab IE completeness, similar to (ISLOCA) model and revised the Example 7 associated success criteria and modeled components.
Generated a new MAAP case for steam New thermal hydraulic generator tube rupture with failed case, similar to Example 2011/M209Ab SC isolation and failed cooldown, but with 10 but for PWR instead of high pressure safety injection throttled. BWR Corrected the modeled emergency diesel Model error, similar to 2012/M209Ac DA generator (EDG) failure rate. Example 6 Updated the RCP Seal Loss of Coolant Update of generic data, Accident (LOCA) probability based on similar to Example 3 /
2017 /M PS2-R05d DA WCAP 15749-P Rl. Credited power Enhancement for recovery during Station Blackout (SBO) completeness,. similar to sequences involving RCP Seal LOCA. Example 7
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 4 of 15 PRA Maintenance Date/ Model Element Summary of Change Justification**
Updated the probability of failure to Update of generic data, 2017/MPS2-R05d DA electrically trip the reactor based on CE similar to Example 3 NPSD-277.
Added Loss of Direct Current initiators to New initiators, similar to 2017 /M PS2-R05d IE SBO accident sequences. Example 1 Added a number of Common Cause Failure {CCF) events to the model for Correct omission, similar 2017 /M PS2-R05e DA components that had previously only to Example 25 been considered for independent failures.
Updated the Steam Generator Tube Application of generic 2017 /MPS2-R05e IE Ruptures (SGTR) event frequency to a data, similar to Example 3 generic industry standard value.
Created explicit Plant Damage State Enhancement for (PDS) logic such that Large Early Release 2017 /M PS2-R05e LE completeness, similar to Frequency (LERF) contribution by PDS Examples 6 and 15 could be determined from the model.
Simplified the containment isolation Enhancement that model by removing credit for all streamlines the model, 2017 /MPS2-R05e LE containment isolation valves that require similar to Examples 6 and an operator action to close. 15 Minor correction to AFW CCF failure probabilities and MPS3 EDG failure Model error, similar to 2018/MPS2-R05f DA probabilities (supporting MPS2 in certain Example 6 sequences).
Update.d initiating event frequencies that Update of generic data, 2018/MPS2-R05f IE utilize generic industry values with the similar to Example 3 latest industry data.
Minor correction made to some support Model error, similar to 2018/MPS2-R05f IE system initiator frequencies. Example 6
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 5 of 15 PRA Maintenance Date/ Model Element Summary of Change Justification**
- Included spurious operation of power-operated relief valves and safety valves Correct omission, similar 2018/MP52-R05g IE as small break LOCA (SBLOCA) initiating to Example 7 events. Merged RCP Seal LOCAs into SBLOCA sequences.
- Refer to ASME/ANS RA-Sa-2009 Non-Mandatory Appendix 1-A.3 for a list of example PRA changes b) No upgrades were identified which have not received a peer review. Refer to the DENC response to RAl-06 for a summary of the most recent peer review results and disposition of findings for this application.
RAl-02 In order to ensure efficiency in its reviews and prevent duplicate reviews of a licensee's PRA technical acceptability, the NRC staff may utilize PRA information from the licensee's previous risk-informed submittals. In the course of its review for this LAR, the staff utilized information from a previous risk-informed LAR submitted by the licensee in October 2014 (ADAMS Accession No. ML14301A112). On page 1 of Attachment 2 of the 2014 LAR, the licensee states that the MPS2 Internal Events PRA (IEPRA) underwent a full-scope peer review in 2000 and that the peer review team used the Combustion Engineering Owner's Group (GEOG) Peer Review Process Guidance as the basis for the review. However, Section 4.6.2 of Attachment 1 to the current LAR states that the MPS2 IEPRA model underwent a peer review by the Combustion Engineering Owners Group (GEOG) in 2000 using the NE/ 00-02 PRA Peer Review Process Guidance. The GEOG peer review guidance is not endorsed by the NRC, and there is no approved correlation available between the compliance levels in GEOG peer review and the RA-Sa-2009 CC levels.
{
a) Clarify whether the 2000 peer review of the IEPRA used the GEOG PRA standard or the standard in NE/ 00-02.
b) If the IEPRA 2000 peer review was performed against the GEOG standard, describe and justify how the licensee concluded that its IEPRA is acceptable for use in supporting this application in accordance with RG 1. 200 Revision 2, given that the IEPRA has not undergone an independent full-scope peer review against an NRC endorsed industry PRA standard.
DENC Response a) The MPS2 PRA model was originally peer reviewed in 2000 using the CEOG peer review process.
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 6 of 15 b) The IEPRA is considered acceptable for use in supporting this application because DENC has performed full-scope self-assessments of the MPS2 PRA model in 2007 and 2011 against the requirements of ASME RA-Sb-2005/RG 1.200, Rev. 1 and ASME/ANS Ra-Sa-2009/RG 1.200, Rev. 2, respectively. The 2007 self-assessment was led by Maracor, a vendor that provided a team of experts with experience in performing NEI PRA certifications and ASME PRA standard reviews, with Dominion providing a review of the *assessment. In 2011, instead of performing a gap assessment to ASME/ANS RA-Sa-2009 requirements as described in NEI 05-04, Section 3.3, DENC performed a full-scope self-assessment of the MPS2 PRA model against the 316 supporting requirements in ASME/ANS Ra-Sa-2009/ RG 1.200 Rev 2.
RAl-03 As referenced in RAl-02 above, the staff utilized information from the October 2014 risk-informed LAR. Table 1 of Attachment 2 of the 2014 LAR only lists one open finding and observation (F&O) from the 2000 IEPRA full-scope peer review. However, Table 7-2 of of the current LAR lists over 80 open F&Os from the 2000 IEPRA peer review. Discuss the discrepancy in the number of open F&Os from the 2000 IEPRA peer review, and clarify the number of open F&Os that are applicable to this application.
DENC Response The 2014 LAR provided disposition of the only F&O from the 2000 peer review that was unresolved at the time. As described in the 2014 LAR, the remainder of the A/B significance-level F&Os were resolved and not listed. Attachment 4 Table 7-2 of the ILRT LAR lists 81 F&Os from the 2000 peer review, all of which are resolved including the one previously unresolved F&O identified in the 2014 LAR (i.e., finding number AS-10).
RAl-04 Section 4.6.2 of Attachment 1 to the LAR states that the MPS2 IEPRA model underwent a self-assessment in 2007 against ASME/ANS PRA Standard RA-Sb-2005 and RG 1.200 Revision1, a gap assessment in 2011 against ASMEIANS PRA Standard RA-Sa-2009 and RG 1.200, Revision 2, and a focused-scope peer review in 2012 against the ASMEIANS PRA Standard RA-Sa-2009 and RG 1.200 Revision 2. However, Notes 1 and 2 to Table 7-1 of Attachment 4 to the LAR reference a 2009 self-assessment.
a) Clarify whether the licensee performed a self-assessment of its IEPRA in 2009.
b) If the licensee did perform a self-assessment of its IEPRA in 2009, provide a discussion describing the purpose of the self-assessment, and any technical issues identified with the PRA that would affect this application.
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 7 of 15 DENC Response a) DENC did not perform a self-assessment in 2009. The discussion provided in Section 4.6.2 is accurate with respect to the self-assessments performed in 2007 and 2011. The intent of Notes 1 and 2 to Table 7-1 of Attachment 4 to the LAR was to reference the 2007 self-assessment.
b) DENC did not perform a self-assessment in 2009.
RAl-05 EPRI Report No. 1009325, Revision 2-A states that "{w]here possible, the analysis should include a quantitative assessment of the contribution of external events (e.g., fire and seismic) in the risk impact assessment for extended ILRT intervals. For example, where a licensee possesses a quantitative fire analysis, and that analysis is of sufficient quality and detail to assess the impact, the methods used to obtain the impact from internal events should be applied for the external event." EPRI Report No. 1009325, Revision 2-A further states that the "assessment can be taken from existing, previously submitted and approved analyses or another alternate method of assessing an order of magnitude estimate for contribution of the external event to the impact of the changed interval." In Section 5. 7 of Attachment 3 to the LAR, the licensee performed an assessment of external event contribution. The licensee's analysis reflected the contribution from internal fire and seismic events, but did not include a discussion of, or justification for, screening out all other external hazards (high winds, external flooding, transportation events, aircraft, industrial facilities, and other external hazard groups). Provide the following:
a) A discussion of the contribution to risk from high winds, external floods, and other external events, OR b) A justification explaining how the licensee screened out each hazard group consistent with RG 1.200 using the most current information, risk studies and insights.
DENC Response b) External hazards other than seismic and internal fire were screened from applicability to MPS2 per the Individual Plant Examination of External Events (IPEEE) performed in accordance with Generic Letter 88-20 Supplement 4 and affirmed using the progressive screening approach specified in ASME PRA Standard RA-Sa-2009. Table 1 provides a summary of the screening results for the other external hazards and Table 2 provides the definition of the screening criterion codes used in Table 1.
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 8 of 15 Table 1: External Hazard Screening Results Screening Result External Hazard Screening Screened?
Criterion Comment
{Y/N)
{Note a)
Airport hazard meets 1975 standard review plan (SRP) requirements. Airports, military installations and flight corridors around Aircraft Impact y PS2 MPS2 (including Groton Airport) have been considered. Evaluations of aircraft impact associated with these facilities find that it does not pose a significant hazard.
Not applicable to site because of topology.
MPS2 is located on the Long Island Sound Avalanche y C3 with no hilly or mountainous terrain near the site. Avalanches are not a viable external initiator.
Plant design accounts for biological growth.
Slowly developing growth can be detected and mitigated by surveillance. The circulating water system intake structure incorporates several features to control biological fouling including trash racks and Biological Event y Cl,CS traveling screens, a cutoff wall to prevent ecologically rich surface water from entering the system, exit passages for fish are provided, vertical guides allow individual channels to be drained, and a chlorination system for biocide treatments.
Slowly developing event which can be Coastal Erosion y cs detected and mitigated by surveillance.
Plant design eliminates drought as a concern and this event is slowly developing.
The ultimate heat sink (UHS) is the Long Drought y Cl,CS Island Sound which is unaffected by drought since it communicates with the Atlantic Ocean.
The IPEEE documented that most external flooding hazards meet the 1975 SRP requirements or the plant is designed External Flooding y PS2 against the hazards.
As pa rt of the N RC 10 CFR 50.54(f) request
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 9 of 15 Screening Result External Hazard Screening Screened?
Criterion Comment (Y/N)
(Note a) on Reevaluation of External Floods, Dominion Energy is in the process of evaluating the external flooding hazard at Millstone, which includes storm surge, water ponding, local intense precipitation, etc. Currently there are no identified plant modifications or deficiencies that would preclude screening of the external flooding hazard. As part of the reevaluation, any identified discrepancies will be tracked in the corrective action program.
The wind loadings for the structures are based on American Society of Civil Engineers Paper 3269, "Wind Forces on Structures."
The basic design wind velocity for MPS2 Class 1 structures is 115 mph with gusts up to 140 mph.
MPS2 structures are designed for tornados having a maximum rotational velocity of 300 mph and a maximum translational velocity of 60 mph. This design basis tornado has a frequency less than lE-6/yr at MPS2.
Extreme Wind or y Cl, PS4 Failure of a service water pump due to Tornado missile strike is bounded by lE-6/yr. Failure of both EDGs due to missile strike is bounded by lE-6/yr.
Failure of the EDG room ventilation due to tornado is bounded by lE-6/yr. CDF due to tornado-induced failure of the East 480V switchgear room ventilation is bounded by lE-6/yr. Control Room ventilation failure is not a significant contributor to risk because of alternate means of Control Room cooling and the ability to shut down outside the Control Room.
Fog can be a contributor to transportation y accidents. Transportation accidents meet Fog PS2,Cl the criteria of the 1975 SRP.
_J
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 1O of 15 Screening Result External Hazard Screening.
Screened?
Criterion Comment (Y/N)
(Note a)
Deep draft boats must stay at least 2 miles offshore to avoid running aground on Bartlett Reef. Therefore, a boat that could cause significant damage to the intake structure is highly unlikely to collide with it and would, most likely, run aground first.
Site is cleared preventing fire from Forest or Range Fire y C3 propagating onto the site and is not located in forested or grassland area.
Frost is covered under snow and ice Frost y C4 hazards.
Loss of offsite power (LOOP) events associated with hail are addressed in the Internal Events PRA and the occurrence Hail y C2 frequency is enveloped by the frequency of weather-induced LOOP events. Limited occurrences are bounded by other events for which the plant is designed.
The plant is designed for this hazard.
Ventilation systems provide conditioned air in the plant to cool equipment. Weather-High Summer y induced LOOP events are considered in the Cl, CS Temperature Internal Events PRA. Effects on the UHS are slow to develop if they develop at all because of the size of the Long Island Sound.
y High tide is covered by external flooding High Tide C4 considering storm surge.
y Hurricane is covered by external flooding Hurricane C4 and high winds or tornado.
The plant is designed against freezing temperatures, including procedures to Ice Cover y C1,C4 protect ventilation systems. Ice blockage causing flooding is covered under external flooding.
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 11 of 15 Screening Result External Hazard Screening Screened?
Criterion Comment (Y/N}
(Note a)
Explosive hazard impacts and control room habitability impacts meet 1975 SRP requirements (RG 1.78 and 1.91). Industrial Industrial or Military y facilities are too distant to pose a hazard to PS2 Facility Accident the safe operation of the plant. Nearby military facilities do not conduct operations that could potentially pose a hazard to the safe operation of the plant.
PRAs addressing internal flooding have indicated this hazard typically results in CDFs ~ lE-6/yr. Also, the ASME/ANS PRA Internal Flooding N None Standard requires a detailed PRA for this hazard which is addressed in the MPS2 Internal Flooding PRA.
PRAs addressing internal fire have indicated this hazard typically results in CDFs ~ lE-
.Internal Fire N None 6/yr. The Internal Fire Event contribution was discussed in Section 5.7 of Attachment 3 to the LAR.
y Not applicable to the site because of Landslide C3 topography.
Lightning strikes causing a LOOP or turbine trip are contributors to the initiating event frequencies for these events. However, other causes are included. The impacts are no greater than those already modeled in the internal events PRA.
Lightning y Cl,C4 Additionally, MPS2 does not have a specific vulnerability to lightning and does not have unique features that would create a high likelihood of failing safety-related systems, structures, or components concurrent with a LOOP.
Not applicable to site because of location.
Low Lake Level or River ' M P2 is located on the coast of the Long y C3 Stage Island Sound which is virtually unaffected by
/
lack of precipitation.
Low Winter Temperature y Cl,CS The plant is designed for this hazard.
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 12 of 15 Screening Result External Hazard Screening Screened?
Criterion Comment (Y/N)
(Note a)
Potential pipe freezing is addressed by a requirement for heat tracing operability during cold weather. Impacts on the UHS are slow to develop, if it all, due to the size and salinity of the Long Island Sound.
Event occurrence frequency of meteorites greater than 100 lbs. striking the plant is 7E-9/yr. This frequency is very low in absolute Meteorite or Satellite terms and lower than aircraft impacts.
y C2, PS4 Impact Aircraft impact damage envelops meteorite/satellite impact damage. The site is no more likely to be struck by meteorite/satellite than any other site.
Pipelines are not close enough to Pipeline Accident y C3 significantly impact plant structures.
Plant storage of chemicals meets 1975 SRP requirements {RG 1.78 and 1.91). Control Release of Chemicals in room habitability during postulated y PS2 Onsite Storage chemical releases has been evaluated and it has been determined that habitability is not threatened by this hazard.
Not applicable to the site because of y location. There are no river diversions near River Diversion C3 MPS2. Cooling water is supplied directly from the Long Island Sound.
Not applicable to the site because of Sand or Dust Storm y C3 location. MPS2 is not subject to sand or dust storms.
Not applicable to the site because of location. A seiche in the Long Island Sound or the discharge basin was evaluated and is Seiche y C3 not a hazard for these bodies of water because of their geometry and locations relative to seiche-inducing phenomena.
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 13 of 15 Screening Result External Hazard Screening Screened?
Criterion Comment (Y/N)
(Note a)
PRAs addressing seismic activity have indicated this hazard typically results in Seismic Activity
- N None CDFs ~ lE-6/yr. The seismic event contribution was discussed in Section 5.7 of Attachment 3 to the LAR.
Event damage potential is less than other events for which the plant is designed.
Snow y Cl,C4 Potential flooding impacts are covered under external flooding.
Plant is designed for this hazard. The MPS2 FSAR Chapter 2.7 describes the characteristics of the area geology, soil Soil Shrink-Swell conditions, testing, foundations and backfill.
y Cl Consolidation Allowable bearing pressures for soil-supported structures are greater than contact pressures as determined by backfill testing. The potential for this hazard is low.
Storm Surge y C4 Storm surge is covered by external flooding.
Toxic gas is addressed by the industrial or military facility accident, the release of chemicals in on-site storage, and the transportation accident. Control room Toxic Gas y C4 habitability during postulated chemical releases has been evaluated and determined that habitability is not threatened by this hazard.
Potential hazards meet the 1975 SRP requirements. The hazards resulting from
' potential transportation accidents (i.e.,
highway, waterway, railroad, and air) do not contribute significantly to plant risk.
Transportation Accident y PS2,C4 Highway-The distance to the nearest highway exceeds the RG 1.91 safe distance criterion.
Waterway- Most ships passing MPS2 are
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 14 of 15 Screening Result External Hazard Screening Screened?
Criterion Comment (Y/N)
' (Note a) deep draft and must remain at least 2 miles offshore to avoid running aground.
Railroad - Hazardous materials are transported about 0.25 miles from the protected area. Most of the transported hazardous materials (chlorine, anhydrous ammonia, carbon dioxide and carbon disulfide) meet the RG 1.78 screening criterion for low transport frequency. The remaining transported hazardous material (propane) presents negligible potential for damage due to explosion and is not a threat to control room habitability due to toxic gas plume.
Air- Covered under aircraft impact.
Tsunami y C4 Covered under external flooding.
Bounding analysis is used to show core Turbine-Generated y PS4 damage frequency (CDF) for turbine Missiles generated missiles is less than lE-6/yr.
Not applicable to the site because of Volcanic Activity y C3
- location. There are no volcanos within the vicinity of MPS2.
Waves y C4 Waves are covered under external flooding.
Note a - See Table 2 below for descriptions of the screening criteria.
Serial No. 18-230A Docket No. 50-336 Attachment 1, Page 15 of 15 Table 2: Progressive Screening Approach for Addressing External Hazards Event Analysis Criterion Source Comments NUREG/CR-2300 and Initial Preliminary Cl. Event damage potential is<
ASME/ANS Standard Screening events for which plant is designed.
RA-Sa-2009 C2. Event has lower mean NUREG/CR-2300 and frequency and no worse ASME/ANS Standard consequences than other events RA-Sa-2009 analyzed.
NUREG/CR-2300 and C3. Event cannot occur close ASME/ANS Standard enough to the plant to affect it.
RA-Sa-2009 NUREG/CR-2300 and Not used to screen.
C4. Event is included in the ASME/ANS Standard Used only to include definition of another event.
RA-Sa-2009 within another event.
CS. Event develops slowly, allowing adequate time to eliminate or ASME/ANS Standard mitigate the threat.
Progressive PS1. Design basis hazard cannot ASME/ANS Standard Screening cause a core damage accident. RA-Sa-2009 PS2. Design basis for the event NUREG-1407 and meets the criteria in the NRC 1975 ASME/ANS Standard Standard Review Plan (SRP). RA-Sa-2009 PS3. Design basis event mean NUREG-1407 as frequency is< lE-5/y and the mean modified in ASME/ANS conditional core damage Standard RA-Sa-2009 probability is< 0.1.
NUREG-1407 and PS4. Bounding mean CDF is< 1E-ASME/ANS Standard 6/y.
RA-Sa-2009 Screening not successful. PRA NUREG-1407 and Detailed PRA needs to meet requirements in the ASME/ANS Standard ASME/ANS PRA Standard. RA-Sa-2009