ML20106G648
| ML20106G648 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 02/11/1985 |
| From: | Woolever E DUQUESNE LIGHT CO. |
| To: | Knighton G Office of Nuclear Reactor Regulation |
| References | |
| 2NRC-5-019, 2NRC-5-19, NUDOCS 8502150009 | |
| Download: ML20106G648 (7) | |
Text
'
i 5
'Af
%g 2Ngg;,0i9 (412)923-1960 Nuclear Construction Division Telecopy (412) 7s?-2629 Robinson Plaza, Building 2 Suite 210 Pittsburgh, PA 15205 February 11, 1985 United Sta.es Nuclear Regulatory Conunission Washington, DC 20555 ATTENTION:
Mr. George W. Knighton, Chief Licensing Branch 3 Of fice of Nuclear Reactor Regulation
SUBJECT:
Beaver Valley Power Station - Unit No. 2 Docket No. 50-412 Roof Snow Additional Information on outstanding Issue 115 Loadine Centlemen:
Draft Safety Evaluation Report (DSER) Section 2.3.1 identified Out-standing Issue ! D applicable to roof snow loading.
Duquesne Light Company (DLC) responded to this by Reference (a) describing why the DLC design was adequate.
Last December, DLC became aware that the NRC staf f had found this position to be unacceptable.
Discussions with your staff at that time indicated that the FSAR was 'ueing reviewed to an unpublished 1975 position.
DLC then requested that this be reviewed as a backfit (Reference b).
In parallel with this, however, DLC proposed a methodology to calculate a Probable Maximum Winter Precipitation as snowfall.
In a meeting with the NRC staf f on January 15, 1985, DLC presented this methodology and the staf f indi-cated that the approach appeared to be acceptable (pending a full review).
A t t ached to this letter is a detailed description of _ this methodology.
DLC understands that, should this prove to be acceptable, Outstanding issue 115 would be closed, and from the DLC st and point, there would be no need to further pursue the backfit is s ue.
DUQUESNE LIGHT COMPANY By O '
Ep. 7 Woolever Vice President KAT/wjs Attachment
'ec:
Mr. B. K. Singh, Project Manager (w/a)
Mr. G. Walton, NRC Resident Inspector (w/a) 7
References:
a) 2NRC-4-112 dated July 30 1984
[ Ij b) 2NRC-5-008 dated January 16, 1985 N2 A
O E
PDR 3
ADDITIONAL INFORMATION ON OUTSTANDING ISSUE 115 OF BVPS-2 DSER On July 30, 1984 (letter No. 2NRC-4-112), Duquesne Light Company (DLC) responded to outstanding Issue 115 of the Beaver Valley Power Station Unit No.
2 (BVPS-2) Draf t Safety Evaluation Report regarding snow load estimates.
This response justified the use of 72 psf as a design snow load for safety-related structures, based on a 48-hour Probable Maximum Winter Precipitation (PMWP load of 71.2 psf, by demonstrating that it complied with published Nuclear Regula-tory Commission (NRC) guidance. The NRC did not consider this response adequate in light of a Site Analysis Branch Position dated Merch 24, 1975, which states that winter precipitation loads should be based on the addition of the weight of the 100 year snowpack to the weight of the 48-hour PMWP.
Subsequent conver-sations with the NRC staff to clarify the branch position led to the approach of calculating a 48-hour PMWP load as a snowf all rather than a rainf all, to be added to the 100 year snowpack load (30 ps f).
This procedure is discussed in detail in the following paragraphs.
The calculation of the 48-hour PMWP load as a snowf all is based on the principles outlined in Hydrometeorological Repo rt No.
53 (NUREC/CR-1486)l.
These principles include the following:
select major storm of record with near-opt imum precipitation mechanism maximize storm moisture content for time of year adjust storm precipitation for transposition to the location of interest In order to select a controlling s to rm for the BVPS-2 48-hour PMWP 2
snowfall calculation, the 1982 Local Climatological Data Annual Summaries were scanned for record 24-hour snowfalls for the northeast quadrant of the U.S.,
ranging from Maine in the northeast, to Minnesota in the northwest, to Missouri in the southwe s t, and to North Carolina in the southeast.
This data scan revealed that the la rges t 24-hour snowfall within this region was 30.4 inches at Albany, New York in March,1888. A more detailed investigation of the Albany snowfall revealed that it was caused by the " Blizzard of 88" which is well 3
documented in the Bulletin of the American Meteorological Society. This storm dumped a total of 46.7 inches of snow in Albany and 55 inches in Troy, New York over a period of about 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br />.
Based on its severity and notoriety, this blizzard was chosen as the - controlling snowstorm fo r the 48-hour PMWP analysis.
In order to convert the 24-hour snowf all of 30.4 inches to a 48-hour 4 were examined period, the depth-area-duration curves of Hydromet Report No. 33 for the month of March. The largest correction factor in Zone i for this month is 1.60 to conve rt a 200 square mile, 24-hour value to a 10-square mile, 48-hour PMWP.
When applied to the record 24-hour snowf all of 30.4 inches at A lbany, a 48-hour PMWP snowfall of 48.6 inches was obtained.
Although the depth-area-duration curves were developed for rainf alls over drainage basins of varying size, they are applied in a very conservative manner to the water
. equivalent of the record snowf all. A 48-hour snowfall of 50 inches was conser-vatively chosen considering the value of the 24-hour snowfall adjusted to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> at Albany (48.6 inches) and 60-hour snowfall of 55 inches at Troy.
. The adjustment to this 48-hour snowfall to maximize the moisture content of the storm and to account for the transposition of this storm from the northeast ceastal waters with its large supply of moisture to western Pennsylvania was chosen in a very conservative manner from Hydromet Report No. 53.
Table 2 of this report indicates that the highest total storm adj us tment factor for any storm and for any time of the year is 1.5.
The re fo re, a conservative total storm adjustment factor of 1.5 was chosen for this analysis, giving a 48-hour PMWP snowf all of 75 inches when applied to the 48-hour snowf all of 50 inches taken from the " Blizzard 88."
The conservat ism of this 48-hour PMWP snowfall is further support ed by data presented in Ludlum's " Weather Record Book"5 Single storm record snowf alls are reported for each state including 50 inches in Morgantown, Pennsylvania, for a 3-day storm; 69 inches in Watertown, New York for a 5-day snowf all; 60 inches in Middletown, Connect icut for a 4-day storm; 47 inches in Peru, Massa-chusetts fo r a 4-day storm; and 50 inches in Readsboro, Vermont for a 5-day snowfall.
The highest single storm snowf all within the northeast quad rant of the U.S. was 77 inches in Pinkham Notch in the White Mountains of New Hampshire for a 5-day snowfall.
In order to conve rt the conse rvat ively chosen 48-hour T MWP snowfall of 75 inches to a building roof load, a separate analysis was performed to estimate the snow depth to water equivalent ratio expected to occur at the BVPS-2 site.
This was done by examining daily precipitation records for Greater Pittsburgh Airport for 98 " snowy days" during the pe riod 1945-1953, 1963-1965, and 1978-1980.
A snowy day was defined as one in which at Isast 0.10 inch of water equivalent fell in the form of snow, sle e t, or ice pe41ets as indicated by the daily observations.
A list of the snow depths and water equivalent s for the 98 " snowy days" is shown in Table 1.
This table indicates that the average snow-depth to water equiv11ent ratio observed at Pittsburgh for 98 " snowy days" is 10 to 1.
This comparea with a 14 to I ratio calculated from measurements at Central Park in New York City for the " Blizzard of 88".
Therefore, the conservative 48-hour PMWP snowf all corre-s ponds to approximately 7.5 inches of water.
This amount of water produces a load of 39 psf.
A summary of the conservatism that entered into the calcula-tion of this value is given below:
- Record New England /New York blizzard with Atlantic moisture source transposed to wastern Pennsylvania Largest pos sible correction from 24-to 48-hour snowf all used from Hydromet Peport No. 33
- 48-hour snowf all of 50 inches chosen compared to highest snowfall of 55 inches in 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> Highest po ssible total storm adju stment factor used from Hydromet Report No. 53 for any storm, any time of year Snow depth to water ratio of 10 to I used compared to 14 to I ratio observed in New York City from " Blizzard of 88"
By adding the weight on. the ground of the 100 year recurrence interval snow-6 load of 30 psf from ANSI-A58.1,1982, without correction for roof load, to the weight of the conser'eative 48-hour PMWP snowfall of 39 psf, a total design snow-load on the ground of 69 psf was obtained.
Therefore, the BVPS-2 design snow-load of 72 paf for Category I structures is adequate to sup port this weight.
References 1.
Ho, F. P. and Riedel, J. T.
" Seasonal Variation of 10-Square-Mile Probable Maximum Precipitation Estimates--United States East of the 105th Meridian,"
Hydrometeorological Report No. 53.
National Weather Service, U.S. National Oceanic and Atmospheric Administration, June 1980.
2.
Local Climatological Data, Annual Sununaries for 1982. National Oceanic and Atmospheric Administration, National Climatic Data Center, Asheville, NC, 1982.
3..
Kocin', P. J.
"An Analysis of the Blizzard of 88". Bulletin of the American Meteorological Society, Vol. 64, No. 11, November 1983.
4.
Riedel, J. T., J. F. Appleby, and R. N. Schloeme r.
" Seasonal Variation of the Probable Maximum Precipitation East of the 105th Meridian for Areas from 10 to.1000 Square Miles and Durations of 6, 12, 24, and 48 Hours:
Hydrometeorological Report No. 33.
U.S.
Department of Commerce, Weather Bureau, April 1956.
5.
Ludium, D. M.
" Weather Record Book, United States and Canada.". Published by Weatherwise, Inc. Princeton, NJ, 1971.
6.
American National S t andard Minimum Design Loads for Buildings and Other Structures, ANSI A58.1, American National Standards Institute, Inc., March 10, 1982.
m p
-.n.
i TABLE 1 p;
SNOW DEPTR TO WATER EQUIVALENT RATIOS AT GREATER PITTSBURGH AIRPORT r-Day / Year.
Snow Depth Water Equivalent Snow / Water Ratio (inches)
(inches)
January 1, 1945 3.8 0.71 5.4
-Janua ry _7, 1945 1.6 0.17 9.4 January 15 1945 2.4 0.24 10.0
. January 22-23, 1945 2.7 0.44 6.1 January 28-30, 1945 4.3 0.54 8.0 February ~ 20, 1945 2.0 0.19 10.5 December 13-15, 1945 6.0 0.70 3.6 December 19-20, 1945 4.8 0.45 10.7
- December 22,-1945~
1.9 0.10 19.0
' December 31, 1945 1.5 0.19 7.9 January 20-21, 1945 3.7 0.37 10.0 February 19-20, 1946-3.0 0.50-6.0 February 24, 1946 1.0 0.10 10.0 December, 20, 1946.
3.6 0.69 5.2-January >1[1947-1.0 0.13 7.7
--- J anuary 5-6, 1947 1.9 0.19 10.0-
-March 1, 1947.
1.6
~0.21 7.6 March 2, 1947 1.0 0.10-10.0
-December 26, 1947' 1.3 0.11 11.8 March 11-12,1948
'1.4
.0.23 6.1 December.19, 1948 4.7 0.23 20.4.
. January 31, 1949 2.5 0.33 7.6
.5xvember 17, 1949 2.8 0.30 9.3 February 16,.1950 1.9 0.17 11.2 February 19,' 1950 1.2
- 0.15 8.0 March 11,~1950 1.9 0.37 5.1
'c March 23,:1950 5.2.
0.82 6.'3 November 24-25, 1950.
- 24.1 2.64 9.1 November 26-29, 1950 7.2 0.69
-10.4 January 7, 1951 8.0,
0.88 9.1 March.15, 1951 3.0 0.30 10.0 I'
March 16, 1951 1.3 0.13 10.0
,i.
p.
Day / Year Snow Depth Water Equivalent Snow / Water Ratio (inches)
(inches)
March 21, 1951 1.5 0.15 10.0 April 3-4,1951 4.2 0.53 7.9 November 2, 1951 2.5 0.30 8.3 November-17, 1951' 1.5 0.15 10.0 December 12, 1951 1.1 0.11 10.0 December 14, 1951 5.3 0.69 7.7 December 15, 1951 1.0 0.10 10.0 December 18, 1951 4.0 0.28 14.3 January 10, 1952 1.4 0.14 10.0 January 24, 1952 1.1 0.11 10.0 February 6, 1952 1.1 0.11 10.0 February 11, 1952 2.2 0.27 8.1 March 1, 1952 5.9 0.59 10.0
~ March 15,1952 1.0 0.11 9.1-March 29, 1952 1.4 0.14 10.0 April 6-7,1952 4.7 0.47 10.0 November'29,.1952 1.5 0.12 12.5 December 2,1952 3.0 0.29 10.3 December 31, 1952 1.8 0.25 7.2 April 18, 1953 3.9 0.54 7.2 November 7, 1953 1.9 0.19.
10.0 November 27, 1953 1.1 0.11 10.0 December 15-16, 1953 1.5 0.13 11.5 November 2,1963 1.4 0.14 10.0 November 29-30, 1963 4.4 0.46 9.6 December 9-10, 1963 2.3 0.29 7.9 December 11, 1963 2.5 0.14 17.9 December 18-19, 1963 3.6 0.19 18.9 December 23-24, 1963 4.1 0.31 13.2 January 1,1964 3.5 0.39 9.0 January 12-13, 1964 15.6 1.19 13.1
~ February 18-19, 1964
- 6. 7.
0.70 9.6 February 26, 1964 1.5 0.10 15.0 March 12, 1964 2.2 0.20 11.0 March 31, 1964 1.7 0.13 13.1 November 30, 1964 1.2 0.11 10.9
Day / Year Snow Depth Water Equivalent Snow / Water Ratio (inches)
(inches)
December 2, 1964 2.6 0.27 9.6 January 1, 1965 1.3 0.17 7.6 January 10, 1965 1.7 0.17 10.0 January 13, 1965 1.0 0.11 9.1 January 16, 1965 2.0 0.14 14.3 February 1, 1965 1.9 0.14 13.6
' February 18-19, 1965 2.8 0.16 17.5 February 21, 1965 0.7 0.15 4.7 February 25-26, 1965 4.2 0.42 10.0 March 5-6, 1965 6.0 0.51 11.8 March 20, 1965 2.2 n.21 10.5 November 26-27, 1978 2.2 0.32 6.9 December 9, 1978 1.6 0.13 12.3 January 2, 1979 1.5 0.20 7.5
-January. 25, 1979 3.8 0.39 9.7 January 28,-1979 3.5 0.33 10.6 January 29, 1979 1.1 0.10 11.0 February 7, 1979 3.0 0.27 11.1 February 12, 1979 3.5 0.39 9.0 February 18-19, 1979 6.1 0.50 12.2 February 26, 1979 1.1 -
0.10 11.0 January 4,1980 1.8 0.20 9.0 January 5, 1980 1.1 0.20 10.5 January 23, 1980 1.2 0.11 10.9 January 24, 1980 1.5 0.10 15.0 January 31, 1980 0.8 0.11 7.3-February 27, 1930 1.2 0.10 12.0 L
March 13, 1980 2.3 0.35 6.6 March 14, 1980 2.5 0.22 11.4 Average 2.8 0.31 10.1 l
L