ML19345B142
| ML19345B142 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 11/21/1980 |
| From: | Broehl D PORTLAND GENERAL ELECTRIC CO. |
| To: | Clark R Office of Nuclear Reactor Regulation |
| References | |
| TAC-41023, TAC-49636, NUDOCS 8011260208 | |
| Download: ML19345B142 (8) | |
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?k Ik November 21,[1980 h4 Trojan Nuclear Plant Dockee 50-344 License NPF-1 4
Director of Nuclear Reactor Regulation ATTN:
Mr. Robert A. Clark, Chief Operating Reactors Branch No. 3 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D. C.
20555
Dear Sir:
Attached please find additional information regarding the recent volcanic activity at Mt. St._Helens and.its relation to the Trojan Nuclear Plant.
The attached information is in response to the two questions raised in i
your letter of October 3, 1980.
This submittal and previous responses transmitted on September 15 and October 16, 1980 complete actions required by the NRC regarding the eruptions of Mt.
>t. Helens.
Sincerely,
/
i Attachment c:
Mr. Lynn Frank, Director
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I State.of Oregon Department of Energy 5
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ADDITIONAL INFORMATION IN RESPONSE TO NRC REQUEST (10/3/80)
RECARDING ERUPTION OF Mt. ST. HELENS NRC Question 1:
Since Mt. St..Helens volcanism may continue for an indefinite period of time, issues related to the availability of long-term r.coling supplies should be documented.
In question 361.2 you were requested to discuss the ef fects on Trojan of an eruption occurring on the west-southwest flank of Mt. St. Helens.
Some phenomena potentially impacting the plant i
include tephra, air blast, pyroclastic flows, mud flows, and debris flow.
g.
Coincident with these phenomena, and assuming that the plant is at full operation at the time of the initiating events discussed below, please identify the methods of obtaining coolinf water to shut the plant down and maintain it in a shutdown condition Include both the initial 30-day period, requested by Regulatory Guide 1.27 " Ultimate Heat Sinks for Nuclear Power Plants," and for extended periods of time in excess of j
30 days.
Assume the loss of all water from the Columbia River due a.
to blockage of the intake by sediment disposition.
b.
Loss of use of the cooling tower except for the basin.
c.
A combination of events 1 and 2.
d.
Loss -of 'of fsite power coincident with Items 1, 2, and 3.
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RESPONSE
The response to Question 361.2, submitted in our letter dated September 15, 1980 addressed the potential for loss of plant shutdown capability that could occur from a future Mt. St. Helens eruption similar to that which occurred on May 18, 1980.
Based on the evaluations summarized in our response to Question 361.2, it is unlikely that any future eruption could cause a long-term loss of heat sink function as postulated in this question.
Nevertheless, we have evaluated the implications of the loss-of-function events postulated in the present question on the ability to meet the requirements of Regulatory Guide 1.27, " Ultimate Heat Sinks for Nuclear Plants".
(a) Loss of All Water from the Columbia River Due to Blockage of the Intake Structure by Sediment Deposition.
FSAR Section 9.2.1.3 provides an analysis of the ability to deal with a loss of the Intake Structure.
FSAR Section 9.2.1.2.3.6 describes the method by which the service water system (SWS) is supplied from *he Circulating Water System using the cooling tower as r' altimate heat sink. Without cooling tower makeup water
.e plant can be maintained in a safe shutdown condition..ua t standby) for at least 165 hr to allow time to restore the Intake Structure to service.
Assuming the blockage of the Intake Structure is by sediment deposition, the concentration of solids near the water surface would be far less than at deeper locations.
The re fo re, it is reasonable to assume that cooling tower makeup water (approximately 525 gpm) could be taken from near the water surf ace and supplied to the SWS from the Columbia River through the hose connections provided using fire department equipment or other portabl.: pumping equipeent.
An alternative source of makeup water could be obtained from the Reflecting Lake or Recreational Lake. The combined water volume contained in the Reflecting and Recreational Lakes is approximately 100 million gallons. Assuming no inflow and only 70 percent of the lake volume is available, makeup for approximately 97 days is available.
Hence, the existing plant design is adequate to accommodate the loss of intake structure event.
(b) Loss of Use of The Cooling Tower Except For The Basin For this case, the evaporative cooling capability of the cooling tower is assumed not to be functional. All other plant systems are assumed to be functional, including the intake structure. Therefore, the capability to maintain a safe shutdown is not affected, except that steam would have to be dumped to the atmosphere rather than to the condenser.
The existing plant design is capable of dealing with this event in its present configuration.
9 (c) A Combination of Events a and b In this case it is assumed that both ultimate heat sinks are Inoperable. The analyses appropriate to this combination of events are the same as for the concurrent loss of of fsite power case described below.
(d) Loss of Of fsite Power Coincident With ' Events a and b 1
A loss of both ultimate heat sinks coincident with loss of of fsite power is a more severe combination of failures than was considered in the original Plant design. The FSAR analysis of ultimate heat sink capability, provided in i.
Section 9.2.8, assumes the availability of at least one of
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the two ultimate heat sinks with' of fsite power available.
In order to assess the capability to maintain the plant in the safe shutdown mode in the event neither the cooling tower evaporative cooling function, nor the Intake Structure nor of fsite power is available, analyses have been completed to determine heat loads and required cooling flow rates under this set of conditions. The following assumptions have been made:
i 1.
The plant would be immediately shut down and maintained in hot standby (>350*F) by j
steaming. with all nonessential equipment secured to minimize water depletion, until either of fsite power or the intake structure is restored. No attempt would be made to cool down via the Residual Heat Removal System.
2.
Offsite power would be restored to Trojan within less than 12 hr.
Considerable data I
were accumulated by PGE and the Bonneville Power Administration during the previous Mt.
St. Helens eruptions regarding the potential for loss of of fsite power due to ' ash-induced insulator shorting. The experience has been that large scale disruptions of the 230-kV grid supplying Trojan did not occur and are not expected to occur during future eruptions due to the inherent design of the 230-kV, insulators. Methods have been developed for cleaning insulators of ash under both wet and dry conditions.
Af ter the loss of the Intake Structure and of fsite power, only the cooling tower basin water inventory was assumed to be available for cooling by once-through gravity' drain from the Circulating Water System to theLSWS to the Dilution Structure as shown in Figure 1.
i The Condensate Storage Tank inventory is suf ficient for removal of decay heat by steaming the steam generators ' for approximately 48 hr.
A flow rate of about 4,000 gps is required to the S*4S from the cooling tower basin to maintain hot standby. The basin inventory is suf ficient to supply this flow rate for about 21 hr.
Once of fsite power is restored, the cooling tower evaporative cooling function would become available.
In this case, the plant could be maintained in hot standby as described in FSAR Section 9.2.1.2.3.6 using the cooling tower basin as the ultimate heat sink. Makeup would be required at a rate of about 525 gpm to account for drift and evaporation losses in the tower.
If this water is drawn only from the Recreational and Reflecting Lakes, makeup for up to 97 days is available.
Once the Intake Structure is restored, the plant could be maintained in hot standby indefinitely by steaming and venting to the atmosphere.
The plant could also be brought to a cold shutdown condition using the Intake Structure and maintained indefinitely, even assuming the cooling tower could not be restored to operation for an extended period.
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7 NRC Question 2:
Describe the actions being taken, or that have been taken, subsequent to the May 18, 1980 Mt. St. Helens eruption to protect safety-related
. equipment, systems,- and components from suspended sediment in the Columbia j-River water withdrawn for Plant use.
Include discussions of maintenance i
schedules for equipment which can be, or has. been, adversely af fected by suspended sediment in the~ water from the Columbia River.
4
Response
k On May 20, 1980, subsequent to the May 18, 1980 Mt. St. Helens eruption, j
an' underwater inspection was performed by two divers in and around the l
Intake Structure for silt accumulation. The river area in front of l
the intake was -inspected first, and it was noticed that the diffuser pipe between the outermost pipe support and the end gate was covered by silt.
4 The inspection of the area between the intake grill and traveling screens 1
and the interior basin also indicated an accumulation of approximately j
4-6 inches of silt 'since the previous underwater inspection on April 28, l-1980. This silt-accumulation is believed to be due to the high river i
turbidity condition this past summer. On June 1, 1980, the silt accumulation over the discharge pipe and in the Intake Structure was cleaned by use of a large suction pump and the fire pumps. The underwater mechanisms of the 4
traveling screens were reported to be in good condition with no indication j
of severe erosion, corrosion, or wear.
3 On Septemb'er 24, 1980, an underwater inspection was again conducted in i
the area of the discharge pipe' and the intake structure.
It was indicated during this inspection that the area around the discharge pipe was clear,
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and no additional silt was observed in the Intake Structure.
Subsequent to the May underwater inspection, selected Service Water System components were inspected under the scheduled maintenance program.
j The service water pump-A, four service water booster pumps, and one component cooling water heat exchanger were inspected for any silting r
j effect. The result of the inspection disclosed no noticeable damage in equipment due to sitting, and no extra wear was detected in mechancial seals, packings, and bearings.
It is believed that the low intake j
velocity, which allows silt to settle, together with the strainers in the Service Water System have prevented additional wear due to silt being 1
- pumped through the Service Water System.
In addition, the cooling tower j
basin, spray nozzles, and selected heat exchangers in the Turbine Building 1
-cooling water system were also inspected. No damage due to river silta-I tion was identified, and the sediment deposition in the cooling tower 4
basin and Circulating Water System pipings was no greater than that noted during inspections prior to the Mt. St. Helens eruptions.
i It is presently planned to conduct an underwater inspection of the j
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- Intake Structure at least :once a year. The frequency of the inspection
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may be increased depending on the activity levels at Mt. St. Helens and j
' the river channel conditions in the Columbia River upstream of the Trojan Nuclear Plant.
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The present schedule for the maintenance program calls for an inspection
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of the Service Water System, cooling tower basin, Turbine Building cooling water system, and Circulating Water System at every refueling I
outage. Equipment in this inspection will include a selected service l
water pump, a service water booster pump, and a heat exchanger in the l
Component Cocling Water System and Circulating Water System. Each piece of equipment till be inspected on a rotational basis at every refueling outage, or more frequently as the situation warrants.
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