ML20077S502
| ML20077S502 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 01/05/1995 |
| From: | Hill W NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-88-20, NUDOCS 9501240119 | |
| Download: ML20077S502 (5) | |
Text
.
s o
Northem States Power Company Monticello Nuclear Generating Plant 2807 West Hwy 75 Monticello, Minnesota 55362-9637 l
January 5,1995 US Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Supplemental Response to Generic Letter 88-20, Supplement No. 4 Individual Plant Examination of Extemal Events for Severe Accident Vulnerabilities The purpose of this letter is to revise Monticello's commitments related to the Individual Plant Examination of Extemal Events (IPEEE) effort. Generic Letter 88-20, Supplement No. 4, requested licensees to describe their proposed programs for completing the IPEEE. By letter dated December 20,1991, Monticello committed to conduct a Level 1 seismic Probabilistic Risk Assessment (with a containment performance analysis as discussed in Appendix 2 of the Generic Letter) to address the seismic portion of the IPEEE. Monticello committed to submit the IPEEE report en or before March 1,1995.
By this letter Monticello is providing notification that a reduced scope Seismic Margins Assessment is to be performed in lieu of a Level 1 seismic Probabilistic Risk Assessment to satisfy the NRC objectives for the seismic portion of the IPEEE and that the submittal due date for this portion of our IPEEE report will be extended to November 20,1995. The method of examination will be in accordance with NUREG-1407 for seismic margins methodology.
The technical basis for Monticello's revised commitment is the draft of NUREG-1488, " Revised Livermore Seismic Hazard Estimates for 69 Nuclear Power Plant sites East of the Rocky Mountains", which provides significant new inforr,1ation relative to large reductions in the seismic hazard at Eastem U.S. sites. Specifically, these revised Lawrence Livermore National Laboratory (LLNL) results show that the mean seismic hazard at Monticello is low, lower in fact than the 1989 Livermore mean seismic hazard estimates for the group of plants which were originally designated for the reduced scope level of effort to address the seismic IPEEE.
l The Nuclear Energy institute (NEI) has developed a White Paper, entitled " Justification for Reduction in IPEEE Program Based on Revised LLNL Seismic Hazard Results", which provides a detailed evaluation of the impact of the new LLNL results. This paper provides the t3chnical basis for applicability of the reduced scope margins methodology for all but a handful of plants. Monticello believes that this paper provides the necessary justification for reclassification of the Montice'lo Nuclear Generating Plant as a reduced scope plant.
nnn.
{
9501240119 950105 PDR ADOCK 05000263
/
P PDR 1
9
USNRC NORTHERN STATES FOWER COMPANY January 5,1995 Page 2 i
i As discussed in the White Paper, the reduction in the level of effort for a reduced scope program is in no way associated with a reduction in the level of safety. There is a consensus among the industry seismic experts that the most important aspect of any seismic review is the plant welkdown performed ly a competent review team consisting of seismic and systems 1
engineers guided by plant operations personnel. The walkdown requirements for a reduced scope program are the same rigorous requirements applied to a Level 1 seismic Probabilistic Risk Assessment (PRA). A competent review team will identify the same potentially weak elements independent of the type of seismic review that is conducted. Industry experience of the past 15 years shows that seismic review teams have successfully identified the weak elements at the time of the walkdowns (which are subsequently modified or repaired), and in no cases were weak components determined to require modification based solely on the analyses which are mandated under the full, focused scope, or PRA programs.
The White Paper also discusses the inherent margins beyond the Safe Shutdown EarthquMe (SSE) level which exists in nuclear power plants. Typically, the median capacity for core i
damage from seismic events is in the range of 3 to 6 times the SSE lev 6l for plants in the eastem United States. Both Seismic Probabilistic Risk Assessments and Seismic Margin Assessments have shown that the vast majority of safety-related equipment and structures have high seismic capacity.
Finally, the revised LLNL results confirm that the mean seismic hazard at Monticello is much lower than originally estimated. The NEl White Paper showed that for Monticello, the seismic hazard probability (probability of exceeding the 5 and 10 Hz spectral velocity) using the revised LLNL data is lower than the probability calculated (based on the %89 LLNL data) for the plants originally designated for the reduced scope level of effort to address the seismic IPEEE.
Good agreement is shown between the results of the revised LLNL cata and the 1989 EPRI seismic hazard analyces provided in EPRI-NP-6395-D, "Probabilistic Seismic Hazard Evaluations at Nuclear Plant Sites in the Central and Eastem United States: Resolution of the Charleston Earthquake issue", which further reinforces the low risk associated with the seismic hazard for the Monticello plant.
In light of the significant new information, we believe that the current understanding of seismic hazards no longer justifies the previously committed level of effort at Monticello to satisfy the seismic IPEEE. The extension of tne Monticello submittal schedule to November 20,1995 coincides with our submittal schedule for information to address USI A-46. We recognizu that this submittal date is beyond the goais established for closure of the severe accident issues.
However, inis change to our IPEEE commitment will ensure the requisite evaluation is perfumed to provide an enhancement to plant safety while providing a significant savings in Licensee and NRC Staff resources. In order to support progress towards the closure of the severe accident issues for Monticello we will submit the fire Probabilistic Risk Assessment and a'1 evaluation (utilizing the screening approach) of the impact of other extemal events (high winds, extemal floods, and transportation / nearby facility accidents) as originally committed to by March 1,1995.
1 s
l 4
4 USNRC NORTHERN STATES POWER COMPANY January 5,1995
. Page 3 Please contact Mary Engen, Sr Licensing Engineer, at (612) 295-1291 if you require further information.
/)f/bdr~
f I' W J Hill Plant Manager Monticello Nuclear Generating Plant I
c:
Regional Administratc/-lit, NRC NRR Project Manager, NRC Sr Resident inspector, NRC State of Minnesota Attn: Kris Sanda J Silberg
Attachment:
Affidavit to the US Nuclear Regulatory Commission i
e I
t a
UNITED STATES NUCLEAR REGULATORY COMMISSION
~
NORTHERN STATES POWER COMPANY MONTICELLO NUCLEAR GENERATING PLANT DOCKET NO. 50-263 Supplemental Response to Generic Letter 88-20, Supplement No. 4 Individual Plant Examination of Extemal Events for Severe Accident Vulnerabilities Northem States Power Company, a Minnesota co@ oration, hereby provides supplemental information conceming NRC Generic Letter 88-20, Supplement No. 4, Individual Plant Examination of Extemal Events for Severe Accident Vulnerabilities, dated June 28,1991.
This letter contains no restricted or other defense information.
NORTHERN STATES POWER COMPANY By h tlN w l
4 W J Hill d I
Plant Manager Montir.?llo Nuclect Generating Plant i
On this __$_ day of diew
/996 before me a notary public in and for said County, personally 45peared W J Hill, Plant Manager, Monticello Nuclear Generating Plant, and being first duly swom acknowledged that he is authorized to execute this document on behalf of Northem States Power Company, that he knows the contents thereof, and that to the 4
best of his knowledge, information, and belief the statements made in it are true and that it is not:;,terposed for delay.
d.t
]r
~
Qn:yy i
TRANSMITTAL MANIFEST NORTHERN STATES POWER COMPANY NUCLEAR LICENSING DEPARTMENT MONTICELLO NUCLEAR GENERATING PLANT Supplemental Response to Generic Letter 88-20. Supplement No. 4 Individual Plant Examination of Extemal Events For Severe Accident Vulnerabilities Correspondence Date: January 5,1995 Monticello intemal Site Distribution Special Instructions Kcleen Hilsenhoff......USAR File..............Yes No_x_
Steve Ludders........NRC Commitment....Yes_x_ No Lila Imholt..............Monti OC Sec........Yes No_x_ - 10, No dist to OC members below if YES Mel Opstad.............Monti SAC Sec.........Yes No_x_ - 6
- Mail Room Mont' Posting Yes No_x_ 7 Monticello Intemal Site Distribution:
~
- Monti Document Control File Monti Site Lic File W J Hill, Plant MGR Steve Ray, SR Res insp, NRC Craig Nierode NSP Intemal Distribution E L Watzl, VP Nuc Gen R O Anderson, Dir LMI, SAC Communication Dept Yes No_x_
Extemal NSP Distribution
- Doc Control Desk, NRC Kris Sanda, State of Minn R giona! Admin-lli,NRC J. Silberg Beth Wetzel, NRR-PM, NRC Wes Brinsfield, TENERA
- Advance Distribution made by Site Licensing Manifest Date: Janurry 9,1995 i
i l