ML20024B599
| ML20024B599 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 07/01/1983 |
| From: | Broehl D PORTLAND GENERAL ELECTRIC CO. |
| To: | Clark R Office of Nuclear Reactor Regulation |
| References | |
| TAC-49636, NUDOCS 8307110003 | |
| Download: ML20024B599 (13) | |
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Pbetiswxih BectricCoirpaior g
Donald J. Broehl Assstant Vice President July 1, 1983 Trojan Nuclear Plant Docket 50-344 License NPF-1 Director of Nuclear Reactor Regulations Atta:
Mr. Robert A. Clark, Chief Operator, Reactor Branch No. 3 Division of Licensing U. S. Nuclear Regulatory Commission Washington DC 20555
Dear Mr. Clark:
Potential Mudflows from the Hypothetical Failure of Spirit Lake Blockaae Your letter of May 27, 1983 requested additional information relating to potential mudflows from a postulated failure of the Spirit Lake blockage.
Following receipt of your request, we contracted with the consulting firm of Simons, Li and Associates to perform an evaluation of Columbia River flooding i
levels due to postulated sediment influx from the Cowlitz River. The results I
of this evaluation, together with assumptions, are given in the Attachment.
Based on the results in the Attachment, it is concluded that maximum Columbia i'
River flood levels at Trojan (Columbia River Mile 72.5) will be below l
Elevation 39 ft MSL.
This includes flood levels computed for nine conser-vative scenarios for preexisting Columbia River flows and Cowlitz River mud hydrographs. Our evaluation considered physical transport phenomena that affect sediment transport in the Toutle, Cowlitz, and Columbia Rivers, in addition to the results of USGS Report WRI 82-4125.
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8307110003 830701 PDR ADOCK 05000344 P
PDR l
121 S W Sa: mon Street, Pocrx1 Oregon 97204
Pbritand General BedricCompany Mr. Robert A. Clark July 1, 1983 Page two It is not considered credible that water levels could exceed flood design Elevation 45 ft MSL at Trojan. Therefore, the safety of the Plant would not be affected. Refer to our previous letter of April 12, 1983 for a discussion of Plant response to loss of intake structure and loss of offsite power.
Sincerely, g;?
Attachment c:
Mr. Lynn Frank Director State of Oregon Department of Energy l
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Trajes Nicloce Plent-Rabart A. C1crk Docket 50-344 July 1, 1983 License NPF-1 Attachment Page 1 of 5 NRC REOUEST FOR ADDITIONAL INFORMATION In referring to USGS' Report 82-4125, you state that the Trojan Plant is pro -
tected against conditions that might be expected from a failure of the Spirit Lake debris blockage. You apparentit base this statement on the fact that the design basis flood for Trojan,. 4,400,000 cfs, is substantially more than the 1,090,000 cfs postulated by the USGS in their report. We would agree with this reasoning if the Spirit Lake breakout flood was a clear-water flood.
However, since it would be a mudflow, the forces considered in analyzing fluid flow (particularly pressure, inertia, and viscosity) would be significantly different. We would expect that the more viscous mudflow would result in reduced channel efficiency and higher flood levels for a given flow.
In addi-tion, the mudflow would be capable of depositing a tremendous amount of sedi-j.
ment in the Columbia River, thus resulting in even higher flood levels.
The staff position is that you.have not provided sufficient information to show that a breakout of Spirit Lake and the ensuing mudflow would not affect the safety of the Trojan Plant. You should therefore provide the following information for staff review.
1.
Taking the scenario in the USGS report as a "given", discuss the likeli-hood of water levels exceeding plant grade elevation of 45 feet MSL at Trojan.
2.
Discuss the effect of water levels higher than elevation 45 feet MSL on the safety of the Trojan Plant assuming various dcrations and levels of flooding.
PGE RESPONSE TO INFORMATION REQUEST 1 Pursuant to NRC Information Request 1, PGE retained the consulting firm of Simons, Li & Associates, Inc. (SLA)1 to provide an evaluation of USGS Report WRI 82-4125 with regard to potential effects of the hypothesized Spirit Lake debris plug breach mudflow on the Columbia River reach in the vicinity of the Trojan Plant.
1 Based on recommendations solicited by PGE from representatives of the Corps of Engineers, Portland District, USGS Water Resources Division, Tacoma, Oregon State University Water Resources Department, and others, with regard to firms especially qualified in the field of mud flow hydrology, SLA wss selected by PGE based on their qualifications and experience in this field and their specific experience background as participants on the board of consultants to the Corps of Engineers, Portland District relative to mudflow and sedimentation problems in the Toutle-Cowlitz River systems resulting from the 5/18/80 Mt. St. Helens eruption.
I
Trojan Nucloce Pirnt Esbirt A. Cicek Dockst 50-344 July 1, 1983 License NPF Attachment Page 2 of 5 A summary of the SLA evaluation and conclusions is provided below.
1.0 Assumptions for Inflow Hydroaraohs 1.1 The volume of clear water _from failure of the Spirit' Lake blockage
.is 310,000 ac-ft.
1.2 The shape of the inflow hydrograph from the Cowlitz River at the confluence with the Columbia is from the USGS WRI 82-4125 with a time to peak of four hours and a total base time of 35.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. No attenuation was considered.
1.3 A range of sediment volumes was assuuad to be entrained in the inflow hydrograph from the Toutle River at Spirit Lake. The sediment concentrations by volume considered are 39, 52, and-65 percent. The resulting sediment. concentrations by volume'at the confluence of the Columbia and Cowlitz were 20, 30, and 45 percent (Table 1).
1.4 Assuming the voids of the sediment available for entrainment contain 30 percent moisture, this would represent an additional two to four percent of total water volume. This was neglected since the volume of water used is greater than would realistically be expected to be released from Spirit Lake.
1.5 Three peak flows on the Columbia River were considered. The flows were 125,000, 400,000, and 800,000 cfs. The tidal level was assumed to be 7.5 MSL.
1.6. Sediment hydrographs for the flows on the Columbia River were developed assuming a preexisting Columbia River sediment concentra-tion of 500 ppe.
2.0 Assumptions for Sediment Routing Model 2.1' Based on sediment size distributicas in Figure 1, incipient motion analysis, and USGS data, the wash load (<0.0625 mm) for the Cowlitz River was assumed to be 50 percent of the sediment inflow by volume, and the preexisting wash load for the Columbia River was assumed to be 80 percent by volume.
2.2 The wash load was not deposited downstream of the confluence of the Cowlitz and Columbia Rivers, as evidenced by measured bed-g material-size distribution in the last three years along the Columbia River.
2.3 Sediment transport relations (bed-material load) were based on the l
Meyer-Peter, Muller method with the Einstein suspended sediment method.
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Trajcn Nucloce Plent R:bert A.' Clark Dockst 50-344 July 1, 1983 License.NPF-1 Attachment Page 3 of 5 1
2.4 Correction ~ factors for the bed-material load transport were adjusted for wash-load concentrations, and the factors were calculated from the Colby method.
2.5 A bulking factor of 1.4 was used for sediment that deposited.
2.6 The shape of the mudflow sediment deposit at the confluence of the Cowlitz and Columbia Rivers was ratioed from the configuration mes-suced due to the mudflow developed after the Mount St. Helens 5/18/80 eruption. In actuality, for high flow conditions the chan-nel velocities may limit the extent of the upstream migration of the sediment.
3.0 conclusions 3.1 Time to peak for the water and sediment hydrograph to arrive at the Trojan Nuclear Plant was calculated to be about 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />.
3.2 The maximum bulked sediment volume available for transport from the debris avalanche could be on.the order of 1 bcy (1.28 bcy per Table 1).
3.3 Conditions evaluated considered initial mudflow sediment concentra-tions by volume of 65, 52, and 39 percent from the debris avalanche area along the upper North Fork of the Toutle River.
. 3.4 Based on average slopes along the Cowlitz River, the maximum sedi-ment volume by percent that would move through the Cowlitz River to the Columbia River is 45 percent (Table 2),
Based on reasonable estimates of concentration and available data, the maximum reason-able sediment volume by percent that would move through the Cowlitz River to the Columbia River is 30 percent.
3.5 Based on minimum slopes within the Cowlitz River, the maximum particle size to be transported to the Columbia River is between 18 and 9 mm (0.71 and 0.35 in.)'.
This is shown in Table 2.
3.6 Based on minimum slopes within the Cowlitz River, the maximum sedi-ment volume by percent to move from the Cowlitz River into the Columbia River is 15 percent (Table 2).
3.7 Sediment concentratirn by volume at the confluence of the Cowlitz end Columbia Rivers was determined to be in the range of 45, 30, and 4
20 percent (Table 1).
j 3.8 Considering the return period of the flows used in the Columbia River, the most reasonable Columbia River flow to evaluate is 400,000 cfs (approximate annual flood).
' ' Trajcn tueleer Pltnt Rsbirt A. Clark Dock:t 50-344 July 1, 1983 License NPF-1 Attachment Page 4 of 5 Sediment transport analyses have been performed for three different mudflow sediment concentrations and three different Columbia River flows (9 separate cases). Results are summarized in Table 3.
In summary, two final hypothetical hazted scenarios can be presented. One is considered to be a maximum reasonable scenario with conservative assumptions contained in the analysis. The second is a worst-case scenario. The most reasonable scenario is with a flow of 400,000 cfs in the Columbia River and 30 percent sediment by volume in the inflow hydrograph from the Cowlitz River. The channel profile and water-surface elevation for this case are shown in Figure 2.
l The worst case is based on a flow of 800,000 cfs (>100 yr. recurrence interval flood) in the Columbia River and a sediment volume of 45 percent for the inflow hydrograph from the Cowlitz River. The channel profile and water-surface elevation for the worst-case scenario are shown in Figure 3.
Conser-vative assumptions for both cases include the volume of sediment entrained, no attenuation for the inflow hydrograph along the Cowlitz River, high tidal con-ditions, and the level of flow in the Columbia River as compared to the annual average (230,000 cfs).
The water surface elevation at Columbia River Mile 72.5 (Trojan Plant) for all cases evaluated is below the Plant power block grade elevation of 45 ft MSL.
For the two scenarios the freeboard at the Trojan Plant is 21 and 6 feet, respectively.
PGE RESPONSE TO INFORMATION REOUEST 2 i
The maximum water level at Trojan does not exceed flood design Eleva-tion 45 ft MSL.
Therefore, evaluation of Plant flooding need not be considered.
TB/Aeh 5130N.683
Trajcn Nuclocr Plcnt R:bset A. Clerk Dockst 50-344 July 1, 1983 License NPF-1 Attachment Page 5 of 5 RELATED INFORMATION Extensive data analysis and literature is available on the Mount St. Helens eruption and a potential failure of the Spirit Lake blockage. This information was used as a basis for the subsequent analysis and is listed below.
Cummans, J.
Mudflows Resulting from the May 18. 1980 Eruption of Mount St. Helens. Washington. Geological Survey Circular 850-B.
1980.
Federal Emergency Management Agency. Flood and Sedimentation Hazards in the Toutle and Cowlitz River System as a Result of the Mount St. Helens Eruption.
January, 1981.
Hubell, D. W., J. M. Laenen, and S. W. McKenzie. Characteristics of Columbia River Sediment Following the Eruption of Mount St. Helens on May 18, 1980.
Geological Sur'.sy Circular 850-J.
1983.
Lombard, R.
E., M. B. Miles, L. M. Nelso, D. L. Kresch, and P. J. Carpenter.
Channel Conditions in the Lower Toutle and Cowlitz Rivers Resulting from the Mudflows of May 18, 1980. Geological Survey circular 850-c.
1981.
State of Washington Water Research Center, Washington State University, ar.d the University of Washington. Proceeding from the Conference Mt. St. Helens:
Effects on Water Resources.
1982.
U.S. Army Corps of Engineers, Portland District. Mount St. Helens Eruption.
Long Term Program for Cowlitz and Toutle River Basins. July, 1981.
U.S. Army Corps of Engineers, Portland District. Mount St. Helens Eruption.
The Challenge to Restore and Protect. October, 1981.
U.S. Army Corps of Engineers, Portland District.
Mt. St. Helens. Cowlitz and Toutle Rivers Sedimetnation Study /1980-1982. Decembor, 1982.
U.S. Geological Survey. The 1980 Eruptions of Mount St. Helens. Washington.
l Geological Survey Professional Paper 1250. 1981.
l l
U.S. Geological Survey. Mudflow Hazards Along the Toutle and Cowlitz Rivers l
from a Hypothetical Failure of Spirit Lake Blockage. WRI 82-4125.
1983.
I Other Related Information Channel cross sections from Portland General Electric (River Miles 59 through
- 78) based on hydrographic surveys from Army Corps of Engineers between May 1982 and March 1983.
Stage Capacity Curves from Portland General Electric (River Miles 59 through 78).
TB/Aeh 5130N.683
TABLE 1 Estimation of Sediment Volumes Transported into the Columbia River Based on an Estimated Volume Transported from the Debris Avalanche.
l Bulked Volume Estimated Bulked of Silt Bulked Volume Bulked and Clay Bulked Bulked Volume of Volume of of Sand, Volume into and volume Volume Material Material Silt and of Sand Through of Sand of Sand Moved Transported Clay into into the the Cowlitz Deposited Through Percent Through Percent from Debris the Cowlitz Cowlitz River Along the the Cowlitz Sand by the Cowlitz Sediment Avalanche (0.6 of 1)
(0.67 of 2)
(0.33 of 2)
Cowlitz (3-5)
Volume (6+4/1.4) by volume (bey)
(bey)
(bey)
(bey)
(bey)
(bcy)
(bey) at Columbia 1.28 0.77 0.51 0.26 0.20 0.31 54 0.40 45 0.75 0.45 0.30 0.15 0.15 0.15 50 0.21 30 0.45 0.27 0.18 0.09 0.10 0.08 47 0.12 20 i
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TABLE 2 Date Used for Evaluating Mobility of Water and sediment Hydrograph.
3 Incipient Percent Peek 01scharoe (cfs) 2 Sediment Minimus Motion, Maximum of Mad 1
Depth Concentration Slope for Particle size (by Volume)
Water Sediment Total (ft)
(ppe)
Motion (mm) 10 530,000 58,300 588,300 23.4 225,700 0.000031 8.9 20 530,000 132,500 662,500 25.1 398,500 0.0001 10.2 30 530,000 227,100 757,100 27.1 531,700 0.0002 13.2 40 530,000 355,100 885,100 29.7 639,700 0.0003 16.0 50 530,000 530,000 1,060,000 33.0 726,000 0.0005 19.7 Assumes no attenuation
- Depth, y,
is from Manning's for n = 0.06, side slopes = 20/1, base width = 6,000 ft and slope for river
' Average slope along Cowlitz River 0.0004, reach along Cowlitz River has minimum slope of 0.00006.
Base on Shields' criteria e and slope of 0.00006 for river mile 17 to 20.
C = Vs (2.65)
_ X 106 s
Vw + V (2.65)
C - sediment concentration (ppm) s Vs - volume of sediment V - volume of water w
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TABLE'3 Results of Sediment Transport Analysis.
g Approximate Maximum Water-surface Inflow from Accumulated Elevation at Columbia River Cowlitz River Sediment Trojan Nuclear Discharge
% Sediment Volume Plant (cfs) by volume (bef/ bey)
(ft MSL) 125,000 45 7.54/0.28 31 125,000 30 4.01/0.15 18 125,000 20 2.33/0.09 11 400,000 45 7.48/0.28 35 400,000 30 3.96/0.15 24 400,000 20 2.30/0.09 17 800,000 45 7.37/0.27 39 800,000 30 3.79/0.14 27 800,000 20 2.22/0.08 22 sediment volume includes bulking factor of 1.4.
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