ML20099G910
| ML20099G910 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 08/11/1992 |
| From: | Horn G NEBRASKA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NSD920817, TAC-M68534, NUDOCS 9208180014 | |
| Download: ML20099G910 (6) | |
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'L' u -. w..hl id2 NSD920817 August 11, 1992 U.S. Nuclear Regula. tory Conunission Attention:
Document Control Desk Washington, DC 20555
Subject:
Followup Response to Recommendations on Station Blackout,10CFR50.63 Cooper Nuclear Station NRC Docket 50-298, DPR-46 TAC No. M68534 Reference 1) 1.etter from R.
B.
Bevan, USNRC, to G.
R.
llo rn, NPPD, dated June 30, 1992, " Supplemental Safety Evaluation - Station Blackout Rula Cooper Nuclear Station (TAC No. M68534)"
2)
Letter from G.
R.
Horn to USNRC, dated February 27, 1992,
" Followup Response to Recommendations on Station Blackout" 3)
- Simiu, Emil and Robert H.
- Scanian,
" Wind Efft. cts o-Structures", Second edition, Chapter 3, Section 3.2.3, Jola Wiley 6 Sons, Nev Wrk, 1986.
Gentlemen:
The District submitted in Reference 2 a plant specific weather data calculation (NEDC 92-023) for review by the staff, in this calculation the CNS
'.d speed database was used to determine the Station Blackout. ESW and SW classifications for CNS. The calculation utilized the available published data for 1975 to 1590 f rom the CNS meteorological towers. The data consisted of 192 samples (16 years) of monthly extreme, hourly average wind speed values.
Appilcation of extreme valae statistical techniques to this database placed CNS in the weather classifications ESW1 and SW2 with substantial margin, which in turn resulted in a calculated minimum target EDC reliability of 0.95.
There was sssumed to be considerable conservatism in this determination.
By letter dated June 30, 1992, (Reference 1), the Nuclear Regulatory Commission forwarded its Supplemental Safety Evaluation (SSE) on Station Blackout (SBO) for the Cooper Nuclear Station (CNS) based on previous District submittals.
'he Supplemental Sa fe ty Evaluation chronicled staff acceptance of all District responses concerning SB0.,ith the exception of site-specific weather analysis that determine the extreme severe weather (ESW) and severe weather (SW) classifications, which are used in establishing the emergency diesel generator (EDC) target reliability for CNc.
Tha Staff conchded in Reference 1 that it was improper for the District to use average buurly wind speeds (in lieu of fastest mile, or fastest minute wind speeds) in determining the probability of extreme wind speeds at CNS, and questioned whether the use of monthly maximum wind speds (rather than yearly i
maximums) resulted in a conservative analysis.
This submittal provicies a followvn response that will resolve both NRC. concerns dealing with the CNS site-Sh,/ { ;
specific weather analysis as identified in Reference 1.
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i i e, NSD920817 August 11, 1992 Page 2 of 3 As discuaned earlier the stafi took exception to the submitted CNS site specific weather data (Reference 1), in particular, the staff raised two concerns.
The District wishes to address each concern separately; 1)
Regarding the monthly ext:reme values of wind, the NRC stated in the SSE
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that:
"The staff questions whether the use of nannthly marimum nind speeds (rather than party matimums) results in a conservative analysis...a sensitiw*ty analysis shondd be made to detennine whether the monthly cruemes or the annual cetremes results in the most conservative anaysis."
To address the above concern, the District has recalculated the CNS weather classifications using the yearly extremes of hourly data.
The results, which are stunmar! zed in Table 1 (Attachment), show that use of CNS monthly maxima, as was used in Calculation 92 023 (submitted in Reference 2), yields more conservative results rompared to using the CPS yearly maxima.-
This addresses the above itRC concern and indicates that the procedure in NEDC 92-023 is appropriate.
2)
Regarding the use of hourly average wind speed data, the NRC provided the Eollowing guidance in the SSE: "1he staffbelieers that thefastest mile, or the fastest minute, annual wind speeds should nonnally be used for the ESWand SW calculations."
In response to the staff's directicin in the SSE, the District has reviewed the CNS wind speed database and the fastest-minute values we.re extracted-from the hour that had the highest average value.
In general, these fastest mitiute samples proved to be roughly 35% greater than the corresponding previously reported hourly average values. Accordingly, the ESW and SW calculations have been re-evaluated (NPPD calculation NEDC 92-105 "CNS site specific wind speed correlation).
Using the approach similar to that presented in calculation NEDC 92-023,
-- submi tted-. In Reference 1,
and following the procedure recommended by Simiu in Reference 3, the latest data at CNS (a set of 36 monthly extremes from 1989 throua,h 1991) have been used for the determination of the ESW and SW classifications.
Use of monthly extremes, which are listed in Table 2 (Attachment), is considered both appropriate and conservative based on the findings discussed in section 1 above.
The results of the new calculation (NEDC 92-105) are listed in Table 3, (Attachment).
Cooper Nuclear Station falls into weathier classifications ESW1 and SW2 when using the fastest-minute data, again with margin. This coincides with previously determined weather classifications.
In summary, the District previously submitted calculation NEDC 92-023 in Referonae 2.
This calculation utilized extreme value statistical analysis techniques to' determine the expected frequency of occurrence of 75 sph and 125-mph. winds at Cooper Nuclear Station.
The plant specific hourly average wind speed data-indicated that CNS is in SB0 weather classifications ESW1 and SW2 with considerable margin.
For an SB0 coping duration oi 4-hours, and a P1 weather plant, it follows that the target EDG reliability is 0.95.
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NSD920817 August 11. 1992 Page 't of 3 In response te stated concerns in tbo NRC's Supplemental Safety Evaluaticn (Reference 1), the District has determined that it is more conservative for CNS to use the monthly extremos of data, as was in fact done in calculation NEDC 92-023, as opposed to yearly extremos. Therefore, the previously submitted analysis was conservative in this respect. The District has further determined that the use of the CNS fastest-minuto data discussed above increases the calculated frequency of occurrence of the 75 nph and 125-aph extreme winds but that this j
data does not alter the SB0 weather classification determinations.
CNS still remains in weather classifications ESW1 and SW2 with margin when using this wind spee l data.
With the resolution of these concerns, and in conjunction with previous District submittals and cominitments, the District satisfles the SB0 rule, and concludes that 0.95 is tne appropriate target EDG reliability for CNS under 10CFR50.63.
If there are any additional questions, or concerns, please call.
Sinc re y, h
lorn e
Nu ar Power Group Manager GRll/tj a:sbo A*.tachment cc:
NRC Regional Administrator Fegion IV Arlington, TX NRC Resident Inspector Office Cooper Nuclear Station l
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Attachment to NSD920817 Anst 11,1992 Page 1 of 3 TABLE 1
CNS STATION BLACKOUT WEATHER GROUP FREQUENCY COMPARISON USING MONTHLY AND YEARLY HOURLY AVERAGE WIND EXTREMES t
CALCULATED FREOUENCIf4 MH H
Monthly Maxima
g, g g.)
f=0.0069 c
-1 Yearly Maxima e=3.76E-12 yr
f=0.0068 MCULATED RFJ_ URN PERIODS E8W E'*
ID3 Mont. 9 Maxima N=3.06E7 years #
1/h =1,409 years #
3
- 71) Maxima N=2.66E11 years 1/h =93,268 years 3
+
(a)
From NPPD Calculation NEDC 92-023 and Chapter 3 of NUMARC 87-00, Rev.1.
(b)
Since the monthly maxima yield higher calculated frequencies (i.e. shorter return periods) it is more conservative to use the monthly maxima to determine the CNS weather classifications for 10CFR50.63. Howeu r, both the monthly and the yearly datasets yield the satro station blackout weather classifications.
(c). Return period for 123 mph wind at 30 meter elevation.
(d)
Return period ior 75 mph wind at 30-meter elevation.
Auzclment to NSD920817
+
/tyyt 11,1972 Page 2 of 3 TABLE 2
COOPER FUCLEAR STATION WIND DPEED DATA 10-METER 10-METER HOURLY FASTEST MONTH AVERAGE MINUTE JAN 89 23.9 29.2 FEB 'd9 24.5 31.3 MAR 89 33.6 42.2 i
APR 89 24.8 33.9 MAY 89 28.3 35.3 JUN 89 19.2 35.5 JUL 89 15.6 23.6 AUG 89-15.1 42.6 S2P 89 23.8 30.2 OCT 89 21.1 28.5 NOV 89 26.2 32.8 DEC 89 24.9 31.4 JAN 90 27.2 33.3 FEB 90 23.4 30.3 MAR 90 21.6 28.0 APR 90 24.7 29.0 MAY 90 22.8 29.5 JUN 90 27.9 38.4 JUL 90 18.1 22.8 AUG 90 16.2 21.4 SEP 90 19.5 25.9 OCT 90 30.0 41.0 NOV 90 24.6 31.2 DEC 90 23.1 26.9 JAN 91 14.5 18.2
-FEB 91 27.8 134.2 MAR 91 33.6 40.9 APR 91 30.2 40.7 MAY 91 23.9 31.5 JUN 91 18.3 32.0 JUL 91 17.2 29.3 AUG 91 13.1 17.6 CEP 91 20.3 27.6 OCT 91 21.2 22.8 NOV 91 24.2 29.7 DEC 91 23.3 30.7 l-l f
Attachrunt to NSD920817 Aptst 11,1972 Page 3 of 3 TABLE 3
WEATHER CATEGORY RESULTS FOR COOPER NUCLEAR STATION USING HOURLY AVERAGE AND FASTEST-MINUTE DATA CALCULATED FREOUENCIER Hour 1v Averare Eqstest Minute RESULTANT CATEGORY ESW Group e-3.26E-8(*) y:
- e-1.98E-6 yr-2 ESW1 SW Group f-0.0069(*) yr f-0.0070 yr-1 SU2
-1 (a)
See Calculation NEDC 92 023 (Reference 2)
TABLE 3-1 EXTREMELY BEVERE WEATHER GROUPS (EBW)
-ESW Croup Annual Wind Speed Expectation 2125 inph, 1
e < 3. 3 x 10-'
2
- 3. 3 x 10-'
s e < 1 x 10'8 3
1 x 10-5 6
e < 3.3 x 10-3 4
3.3 x 10-8 f
e < 1 x 10-2 5
1 x 10-2 g
TABLE 3-4 BEVERE WEATHER GROUPS (SW)
SW Group Estiinated Frequency of Loss of Offsite Power
-1 f < O'.0033 2
0.0033 f < 0.0100 3
0.0100 f < 0.0330 4
0.0330 f < 0.100 5
0.100 5
f
- Extracted from NUMARC 87-00, Rev. 1
,