ML20118A609
| ML20118A609 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 09/15/1992 |
| From: | Horn G NEBRASKA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NSD920964, TAC-M68534, NUDOCS 9209240092 | |
| Download: ML20118A609 (7) | |
Text
.
s GENERAL OFFICE
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P O BOX 499. COLUMBUS. NEBR A$KA (S60? 0499 Nebraska Public Power District
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NSD920964 September 15, 1992 U.S. Nuclear Regulatory Connission 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. H68534
Reference:
1)
Letter f rom R.
B.
Bevan, USNRC, to C.
R.
llo rn, NPPD, dated Station June 30, 1992, " Supplemental Safety Evaluation Blackout Rule Cooper Nuclear Station (TAC No. M68534)"
2)
Letter from G.
R.
Horn to USNPC, dated August 11, 1992,
" Followup Response to Rccommendations on Station Blackout" 3)
Simiu, Emil and Michael J.
- Changery, et.al.,
" Extreme Wind Speeds at 129 Stations in the Contiguous United States", NBS Building Science Series 118, U. S. Dept. of Connerce, Issued March 1979.
4)
Letter from G.
R.
Horn, NPPD to the USNRC Document Control
- Desk,
" Followup Response to Recommendations on Station Blackout Cooper Nuclear Station", NSD920243, Attachment 1, (Calculation NEDC 92-023), dated February 27, 1992.
Gentlemen:
By letter dated June 30, 1992 (Reference 1) the Nuclear Regulatory Commission forwarded its Supplemental Safety Evaluation (SSE) on Station 31ackout for the Cooper Nuclear Station (CNS) based on previous submittals from the Nebraska Public Power District (NPPD) regarding 10 CFR 50.63.
NRC concerns in the SSE centered on the CNS plant specific weather data evaluation and the resultant selection of a minimum allowable emergency diesel beneration (EDG) target reliability of 0.95.
In a letter from G. R. Horn to the USNRC dated August 11,1992 (Reference 2), the District responded to the stated concerns in the SSE.
Using the available fastest-minute wind speed values from the CNS weather database, the District re-evaluated the SB0 weather classifications for CNS. The updated evaluation again led to the conclusion that 0.95 is the appropriate minimum target EDC reliability for CNS.
The District's August 11 submittal was discussed in a telephone conversation between NRC staff and NPPD personnel on September 3, 1992.
The NRC concerns l
focused on the CNS fastest minute wind speed data that were used in the submittal. (The latest CNS data, a set of 36 monthly extreme values of wind from 9209240092 920915
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NSD920966 September 15, 1992 Page 2 of 3 1989 through 1991, had been used in the August 11 subtrittal). The NRC staff had questions whether this dataset would be larr,e enough to accurately depict long term extremo wind speeds and capture outlying behavior.
In response to the most recent NRC questions identified in the telephone conferetme, the District has evaluated the NBS 113- (Reference 3) f stert-mile wind speed data for Omaha as applied to CNS.
Extreme wind speeds for a_ number of U.S. weather stations are documented 12 KbS 118. NPfD calculation NEDC 9.?-132 was generated which uses the Omcha data from NBS 118, (a 42 yer.r database), the me6hodology from NBS 118 and standard NU.*AFC 87-00, Revision 1, techniques to deturmine the CNS severe weather (SW) ar.d extremely severe weather (ESW) classifications. A brief description of how the District determined the SW and ESW classifications for CNS are located in the Attachment to this letter.
The Omaha information was derived from a large database and it considered conservative for CNS, Application of the Omaha data to CNS provides further confidence in the determination that CK3. is a
'Pl' plant, and that the appropriate minimum allowable target EDG reliability for the Station is indeed-0.95. The evaluation further supports the conclusions reached in the District's August 11 (Reference 2) submittal, The Omaha fastest mile wind speeds for the period 1936 to 1977 have been extracted from NBS 118,and are included in NEDC 92-132.
Pag.e 162 of NBS 118 (Refere,nce 3) provides the predicted extreme wind values and their corresponding return periods for Omaha. The Extreme Value Type _1 Distribution is appropriate for application to CNS.
This was demonstrated-in ;he District's submittal of February 27,1992 (Reference 4) and has been accepted by the NRC, as documented in the SSE. The technical methodology used in this submi' w similar to the approach employed by the Omaha Public Power District (OPPE
.ts SB0 evaluation for the Ft. Calhoun plant.
OPPD used Omaha weather data i establish an EDG reliability of 0.95 for Ft. Calhoun, using an approach which has been accepted by the NRC.
The Omaha fastest-mile data from NBS 118, a 42-year database, confirm - the District's earlier conclusion, which was based on 36 monthly extreme wind values from the CNS plant-specific meteorological database. While the Omaha data yield a more conservative ESW category result, the CNS plant-specific data and the Omaha data lead to the same conclusion insofar as the EDG target reliability is concerned.
Previous evalrat ans using the CNS plant-specific weather data have indicated that there is ample conservatism in the EDG target reliability determination for CNS.
Application of the 47-year Omaha database to CNS confirms previous statements by the. District to this effect and provides further evidence regarding the appropriateness of the 0.95.EDG target reliability value.
Based on the abnve discussienn, and results of the NPPD calculation (NEDC 92-132)
CNS falls ia weather classificz.tions ESW2 and 5V2, While the newest calculation using Omaha data determines a more conservative ESW classification for CNS (ESW2), CNS still remains a. P1 plant using NRC accepted guidance of NUMARC 87-00,
-Revision 1.
For an SB0 coping duration of 4-hours, and a P1 weather plant, it follows that the target EDC reliability is 0.95.
4
NSD920964 September 15, 1992 Page 3 of 3 With the resolution of these additional concerns, and in conjunction with previous District submittals and-commitments, the District satisfies the SB0 rule, and concludes that 0.95 is the appropriate target EDG reliability for CNS under 10 CFR 50.63.
If there are any additional questions, or concerns, plesse call.
Sine rely, c~
Horn -
Nuc ear Power Groap Manager GRH/tj a: sbo-fol Attachment cc:
NRC Regional Administrator Region IV Arlington, TX NRC Resident i. -
.or Offica Cooper Nuclear St.ation
_____.___.____,__._.___._______.m
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r Attachment to NSD920964 September 15, 1992
^
SupMARY OF WEATHER CLASSIFICATION CALCULATIONS USING NBS 118 ESW CATEGORY 1
4
> Usine the oower law techniaue. Ean. 2.4.2 of NBS 118.
(1)
U (10) 1 U (z)
(z/10)"
where = - 1/7 and z - 30 meters, the transmission line height. Conservatively, 4
the NUMARC 87-00, Revision 1, cutoff criteria are assumed to apply at _ the transmission *1ine height. It is-necessary to transpose these criteria to the 10- -
1 meter elevation, the common recording height for the Omaha data in NBS 118.
Substitution into Equation (1) gives the sustained wind transposition factor i
between the 30 meter and 10-meter elevations:
1 U (10) 0.85475 U (z) i-i-
Equation 2,4.6 of NBS 118 is next used calculate the appropriate transposition factor when using the fastest.-mile _ data:
l (2)
U,, (10)
U(10)
(z 10)
- (1 +-
- 0.02)
U,, (z)
U(z) 10 0-85475 (1 + 2
- 0.02) g 0.88894 4
Consistent with NUMARC 87-00, Revision 1,_ _ we use U,g-125 aph @ z' - 30 meters.
_This yields 4,-
1 (2a)
U,, (10) - 0.88894
- 125 - 111.1.mxh
[
as the appropriate ESW evaluation criterion at the 10-meter elevation. From the Omaha data,-_page 162 of-NBS 118 (Reference 3), interpolation gives the return' period:
1652 years.
4 4
, +-+,, -
e e
nn e-
,me-e e
s e
em
Attachment to NSD920964 September 15, 1992 The expected frequency of occurrence of the 125 mph wind at 30-meters rollows directly, i.e.
1 0.00061 < 0.001 e
N 1
> Alternatively. use the lorarithic law of NBS ~18 (Ean. 2. 4.1 Y.
(3)
U (10)
In (10/z,)
'l where U (z)
In (z/z,)
- 0.05. = consistent with past work for z - 30 meters and the relative roughness z$ the CNS and Ft.
CNS. (Based on the 12/11/91 CPPD submitta Calhoun terrains are similar, and the use of z, - 0.05, the' preferred SAIC approach, is conservative for both plants).
Substitution into Equation (3) yields U (10) 0.82826 U (z)
Using Eqn. (2) as before for the fastest-mile data, U,,(10)
_0.82826
- 1.04 0.86139 U,, (z) 4 With U,, (z)- - 125 inph @ 30 meters, this gives (3a)
U,, (10) - 0.86139
- 125 - 107.67 mph.
Interpolation from page 162 of NBS 118 (deference 3) for a Type 1 distribution gives the return period:
l
- 1052 years.
P
1
--Attachasnt to J
NSD920964 September 15, 1992 l
l-It follows that; i
1 0.00095 < 0.001
{-
e i:
N i
. Using NUMARC 87-00, Revision _1,_ Table 3-1, for either case CNS is in Categorv j
j ESW2 based on the Omahe (fastest mileF data, i
d i
Table 3-l*
i EXTREMELY SEVERE WEATHER CROUPS (ESW).
i
.. +,.
j.
. ESW Group J Annual Windspeed Expectation -;t 125 mph'.
f 1
e < 3.3 x 10-4
~
~
'2-3.3 x 10-4 5
e < 1 x 10-3 f
3 1 x 10-3 5
e < 3.3 x 10-3 4
3.3 x 10-3 s
e < 1 x 10-2 S
1 x 10-2 s-e i
l
- Extracted from NUMARC 87-00, Revision 1
?
g_
Thus, in either case-(i.e. using the power law or the lo~garithmic law of NBS-118 with a conservative _ value of z,); the_ result.'is the same:
Use of.the l
Omaha fastest-mile. data places CNS in Si,0 weather group ESW2.
i
)..
l-i.
- SW CATEGORY
?
p.
Using, Part 1.C ' of NUMARC 87-00, - Revision 1, with c -- 0 ;(i.e., no '. salt spray-vulnerability.at CNS),
1.3E-4 * 'h
=+- 12.-5
- -- h '~+- 0.012, *^Ih.
(4)
'f 3
2 3
From.calculatilon NEDC 92-023, which wasiincluded with a previous NPPD submittal
. j (Reference 4):-
i p
h, -' 30" per year (the annual. snowfall for CNS, from NUMARC 87-00, Ravision_1) j i
1 d
l' h - 2.357E-4 yr L(NSSFCtornadofrequencyforCNSatBrownville, Nebraska)'
2 We must determine h, ~ the expected frequency of storms;with winds 2: 75 mph at the-transmissionlineefevation.
4
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._,.~.r__..
,,.. -. _....,,,,. - ~,...
,-....-u
~
. -... ~..
Attachment to
- j --
NSD920964 September 15, 1992' j-4 The Omaha 'fastost-mile' results from page 162 of NBS 118 (Reference _3), are again l
used.
Using Equations (1) and (2) with U(z) - 73 mph at z - 30 meters above:the ground, Ug (10) - 66.7 mph at 10 meters above the ground. From page 162 of NBS 118 (Reference 3), the return period:
i a
7.75 years, and 4
0.1291 (for a Type 1 distribution).
1/
h a-3 1
i Substitution of h and the other values above into -Equation _ (4) yicids 7
3 1
f 0.0084 i
L 2 with Since f < 0.01, Table 3-4 of NUIMRC 87-00,. Revision 1, places CEi in SV Group the Omaha data, i
Table 3-4*
I SEVERE WEATHER GROUPS (SW)
,i t
l l'
. Estimated Frequency of Loss of Offsite Powern l
?: SW GROUP _
L
'1 i < 0.0033 i:
2-0.0033 5
f < 0.0100
-3
' O.0100 5
f < 0.0330 l
-4
'O.0330 5
'f
< 0.100 i
5-
' i=
5 0.10~
p
'
- Extracted from NUMARC 87-00. Revision 1 I:
.u.-.
...a.
.. - -,,. _.. _...... _... _.. _. _...... _ -. _ _. _....,., _ _.