ML20151F495
| ML20151F495 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 07/18/1988 |
| From: | Lentine F COMMONWEALTH EDISON CO. |
| To: | Murley T Office of Nuclear Reactor Regulation |
| References | |
| 4930K, NUDOCS 8807270119 | |
| Download: ML20151F495 (11) | |
Text
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C' Commonwealth Edison
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j one First National Plaza, Chicago, lifinois Address Reply to: Post Office Box 767 e
v Chicago. Illinois 60690 0767 July 18, 1988
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Mr. Thomas E. Murley Director of Nuclear: Reactor Regulation U.S. Nuclear Regulatory Commission
-Mail Station P1-137 Washington, DC.
20555
Subject:
Byron Station Units 1 and 2 Application for Amendment to Facility Operating Licenses NPF-37 and 66, Appendix A, Technical Specifications NRC Docket Nos. 50-454 and 50-455
References:
(a)
June 22, 1988 letter from K.A. Ainger to T.E. Murley (b)
July 14, 1988 letter from F.G. Lentine to T.E. Murley
Dear Mr. Murley:
This letter is in response to the NRC's reguest for additional information regarding the Technical Specification amendment request submitted in reference (a).
The prosed amendment revised the Ultimate Heat Sink Technical Specification Action Requirement 3.7.5.e(2) to add a statement that the provisions of specification 3.0.4 are not applicable, As a result of an inadvertent unit trip and the continued high electric energy demand in the Commonwealth Edison service territory, reference (b) requested that the amendment be processed under the emergency provisions of 10 CFR 50.91a(5).
In a telephone conference on July 14, 1988, the NRC requested additional information on the bases for the Rock River level and flow values in the Technical Specification.
Attachment A to this letter, "Safety Evaluation", provides the information requested.
Attachment B provides Commonwealth Edison's "Environmental Assessment" for the proposed change.
Also provided as Attachment C is Commonwealth Edison's "Evaluation of Significant Hazards Consideration", which had previously been provided in reference (a).
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Please direct any questions _you may have concerning this matter to this office.
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Very truly yours, Y
v7bNG F.
G. Lentine PWR Licensing Supervisor
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Byron Resident Inspector L. N. 01shan Regional Administrator-RIII 4930K J
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ATIACIIMEliT_A Safety Evaluation Commonwealth Edison has previously examined the effect of low water level in the Rock River on the ultimate heat sink capability of Byron Station.
The 670.6 foot Rock River level in Technical Specification is the level at which sufficient river flow is available such that the Oregon dam could fail and river level would remain above 664 feet, thereby ensuring adequate net positive suction head (NPSH) for the essential service water makeup pumps.
Above 670.6 feet river flow does not need to be verified.
Below 670.6 feet, level is not an accurate indication of an adequate water source for the essential service water makeup pumps, so flow must be measured.
Sargent and Lundy modeling and analysis of the Rock River has determined that a minimum flow of 700 cfs is required to maintain an adequate NPSH for the essential service water makeup pumps.
This flow corresponds to a river level of 664.7 feet.
A more detailed explanation of the derivation of these level and flow values follows.
FSAR Table 2.4-15 provides the flows in the Rock River at the intake for various combinations of low Rock River flow duration and recurrence intervals.
On Table 2.4-15, for a 30-day, 100-year recurrence interval, the drought flow at the intake channel is 739 cfs.
As noted in FSAR question 371.13 response, this flow rate corresponds to a surface elevation at the intake with the Oregon Dam intact of 670.6 feet.
As noted in FSAR Section 2.4.11, an extremely low Rock River level could possibly occur through a combination of low river discharge and breaking of the Oregon Dam five miles downstream.
Since the lowest point on the river bottom at the intake is about 10 feet below the dam's crest, removal of the impounding effect of the dam during low flow would lower the water surface at the intake.
Consequently, studies were made to determine that level.
A computer model using a river flow of 400 cfs (FSAR Table 2.4-12), the 1-day lowest flow at the site area, determined the resulting water-surface elevation at the channel intake for the essential service water (SX) makeup pumps would be 664 feet.
As such the design elevation of the pump invert was selected based on the postulated icw water elevation resulting from the breaking of the Oregon Dam during the historic low flow period.
As indicated in FSAR Table 2.4-17, at 664 feet, adequate NPSH would be available for the essential service water make up pumps.
As described in FSAR Section 9.2.5.3 and as shown on FSAR Figure 1.2-16, the top of the basemat ie at elevation 663.5 1
. feet and the screens are recessed within the basemat so that essential service water makeup can be provided.
A sump is provided for each essential service water makeup pump, having a bottom of sump elevation of 660.5 feet, so that the makeup pumps have adequate submergence under all operating conditions.
The NRC staff concurred with Commonwealth Edicon's determination in NUREG-0876 "Safety Evaluation Report related to the operation of Byron Station Units 1 and 2".
In Section~2.4.8 the staff stated that the 1-day, 10-year drought low of 714 cfs (FSAR Table 2.4.15) would have a water surface elevation at the river screenhouse of about 665.0 ft.
The staff considered this to be the lowest level, during winter months when icing is possible, for which there was reasonable assurance that water would reach the service j
water pump sumps.
I On September 27, 1984, a meeting was held Bethesda to review a revised backwater analyses based upon more realistic assumptions for the failure of the Oregon dam.
The attendees included Messr. Staley and Jachowski of the NRC, Mr. K. Briezo of CECO and Messrs. Komanduri and Netzel of S&L.
The assumptions used in the analysis were as follows:
1.
The cross-sections from the River Screen House to a section downstream of the Oregon dam location were modified.
A 1 ft. wide channel with two horizontal to one vertical side slopes below the bottom of the river channel was provided such that the longitudinal bottom slope downstream of the River Screen House is 0.00015.
2.
A Manning's coefficient 'n' of.027 was used.
3.
Oregon dam was completely removed.
The results of this analysis gave a water level elevation at the River Screen House of 664.7 ft. for a low flow of 700 cfs in the Rock River without the Oregon dam.
The meeting concluded with NRC agreement with the analysis.
The NRC indicated that the flow of 700 cfs and the corresponding water level of 664.7 ft in the river Screen House with the Oregon Dam in place should be used in the Technical Specification.
. The 700 cfs Rock River flow rate is the ultimate criterion that must be met to ensure adequate NPSH for the essential service water makeup pumps in the event of a' failure of the Oregon dam.
With a level of 670.6 feet we are assured of having a flow greater than 700 cfs.
(This is substantiated by the flow data currently being accumulated at Byron during the existing drought conditions, which was provided in reference (b).)
However, below 670.6 feet, level is no longer a highly accurate indication of the river flow rate.
Therefore, Technical Specification 3.7.5 was wr'itten to require that river flow be monitored every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> when level decreased below 670.6 feet.
Only if the flow rate decreased below 700 cfs or level decreased below 664.7 feet would a unit shutdown be required.
It should be noted that the above scenario which formed the basis for the technical specification is based on a combination of occurrences of very low probability.
First, a LOCA or other event that requires the essential service water system to provide cooling capacity must occur.
Coincident with that event, a seismic event must occur which totally disables the deep well pumps and causes the Oregon Dam to be completely removed.
This must occur during drought conditions when the Rock River level and flow are at minimum values.
FSAR Question 371.13 response evaluated the probability of a 500 year seismic event of.05g concurrent with the 30-day, 100-year drought.
From data presented in a recent study for Dames and Moore (Reference 3 of FSAR Question 371.13) it was estimated that the probability of an earthquake having a mqximum acceleration equal to or greater than 0.lg is about 3.0 x 10-4 per year.
This combined with the 100 year drought conditions results in a probability of 3.0 x 10-6 per year.
The essential service water cooling towers and their makeup lines and pumps supplying water from the Rock River are Safety Category I, Quality Group C.
The makeup pumps are located in the river screen house and they take their suction from behind the bar grilles and traveling screens located therein.
The screen house structure is Safety Category I; the traveling screens and bar grilles are.saismically qualified.
In the event the dam failure is due to a seismic event, the essential service water makeup system would still be operational.
. Essential Service water makeup can be provided by two redundant systems, the essential service water makeup pumps and the deep wells.
In the event that both of these redundant systems are
. unavailable there are several contingency actions available to provide the cooling capability.
These include:
1.
Using the crosstie between the fire protection system and the essential service water system.
2.
Using water from the fire hydrants.
3.
Using non-essential service water to fire protection to essential service water crosstie.
4.
Using fire hoses from non-essential service water connections in the circulating water pump house or turbine building.
5.
Using portable pumps to transfer water from the circulating water flows to the essential service water tower basins.
6.
Using portable pumps to transfer water from the Rock River to the essential service water makeup pump suction sump.
7.
Using portable pumps to transfer water from the Turbine Building basemat to the essential service water tower bacins.
In summary, the 670.6 foot level is a level that assures a 700 cfs flow rate and is essentially an alarm setpoint that requires l
the station to verify Rock River flow on a 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> cycle.
The 664.7 foot level and 700 cfs flow limit are minimum values to ensure l
adequate water level following the postulated failure of the Oregon l
dam.
Operation above these values endures an acceptable level of safety for continued operation without time limit under the present technical specifications.
Therefore, the proposed change of adding a statement that the provisions of Specification 3.04 are not applicable is justified i
on the following basis.
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(1)
Verification of flow and level will continue to be l
performed on the frequency specified in the Technical l
Specifications.
If the minimum limits are nnt met i
Action Requirements 3.7.5e(1) and (3) require the unit to shutdown.
Action Requirements 3.7.5e(1) and (3) are not being revised by this proposed amendment.
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(2)
The minimum limits have been established on a conservative basis for a combination of events of low probability.
(3)
Redundant sources of water and multiple contingency actions are available in the event that the minimum limits are violated (which would require a unit shutdown).
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ATTACHMENT B Environmental Assessment IdentilisAtion of the Proposed Action:
The Rock River is one of two makeup sources for the ultimate heat sink at Byron Station.
This proposed amendment revises a technical specification action requirement concerning Rock River water level and flow.
The action requirement is being revised to state that the provisions of technical specification 3.0.4 are not applicable.
This will have the effect of permitting changes in operational nodes while relying on the action requirement.
The_ Reed for the Propnsed Action:
The ongoing drought in the mid-western part of the nation h,as caused the level in the Rock River to drop below the limit specified in the limiting condition for operation of the ultimate heat sink technical specification.
That limit is 670.6 feet mean sea level (MSL).
As a result, Byron Station has entered technical specification action requirement 3.7.5.e.
This action requirement permits reactor operation to continue for an unlimited period of time as long as river flow remains greater than 700 cubic feet per second (cfs) and river, level remains above 664.7 feet MSL.
River flow must be verified every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> under these conditions until the level exceeds 670.6 feet MSL.
General technical specification 3.0.4 applies to technical specification 3.7.3.
According to specification 3.0.4, entry into an operational mode or other specified condition cannot be made unless the conditions of the limiting condition for operation are met without reliance on provisions contained in the action requirements.
As a result, if Byron Unit 1 or 2 shut down, the unit cannot be restarted because the limiting condition for operation would not be satisfied without feliance on an action requirement, even though the action requirement would permit continued operation.
In other words, a shut down unit would be prevented from startup until the Rock River level exceeded 670.6 feet MSL.
This would represent an unwarranted burden on Commonwealth Edison and its customers and is not necessary to achieve the underlying purposes of the technical specification.
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. s Environmental _ Impact of the Proposed Action:
Commonwealth Edison has concluded that, following the proposed change, the level of safety with respect to ultimate heat sink capability will be equivalent to that achieve by compliance with the existing technical specifications.
Radiological releases will not differ from those determined previously and the proposed action does not otherwise affect facility radiological effluent or occupational exposure.
With regard to potential nonra'diological impacts, the proposed action does not affect plant nonradiological effluents and has no other environmental impact.
Therefore, Commonwealth Edison concludes there are no measurable radiological or nonradiological environmental impacts associated with the proposed action.
4 Alternatives to the Proposed Action:
Since Commonwealth Edison concluded there is no measurable environmental impact associated with the proposed action, any alternatives with equal or greater environmental impact need not be evaluated.
The principal alternative to the exemption would be to prevent a shutdown unit from startup until the Rock River level exceeded 670.6 feet MSL.
Such action would not enhance the.
protection of the environment and would result in unjustified costs for Commonwealth Edison and its customers.
Alternative Use of Resources:
This action does not involve the use of resources not considered previously in the Final Environmental Statement for Byron Nuclear Power Station, Units 1 and 2.
Einding_of No Significant Impact Based upon the environmental assessment, Commonwealth Edison concludes that the proposed action will not have a significant effect on the quality of the human environment.
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ATTACHMENT C 1
! EVALUATION OF'SIGNIFICANT HAZARDS CONSIDERATIQll Cdmmonwealth Edison has evaluated this proposed amendment and determined that:it involves no significant hazards consideration.
Accordint; to 10 CFR 50.92(c), a proposed amendment to an operating license..nvolves no significant hazards consideration if operation of the facility in accordance with the amendment would not:
1)
Involve a significant increase in the probability or consequences of an accident previously evaluated; or 2)
Create the; possibility of a new or different kind of accident from any accident previously evaluated; or 3)
Involve a significant reduction in a margin of safety.
The Rock River is one of two makeup sources for the ultimate heat sink at Byron Station.
This proposed amendment revises a technical specification action requirement concerning Rock River water level and flow.
The action requirement is being revised to state that the provisions of technical specification 3.0.4 are not applicable.
This will have the effect of permitting changes in operational modes while relying on the action requirement.
Water level and flow in the Rock River have no effect on the probability of previously evaluated accidents.
Therefore, the probability of previously evaluated r4ccidents will not be increased.
The affected action requirement permits reactor operation to continue as long as river flow and level stay above minimum requirements.
The minimum flow and level limits that assure adequate suction for the essential service water makeup pumps are not being changed by this amendment.
As a result, the consequences of previously evaluated accidents will not be increased.
This proposed amendment does not allow any new mode of operation beyond what is already permitted by the action requirement, In addition, this amendment does not allow any modification to the plant.
Therefore, operation of the facility in accordance with the proposed amendment will not create the possibility of a new or different kind of accident from any accident previously evaluated.
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Since the technical specification minimum flow and level limits for the Rock River are not being changed, this ameadment does not involve'a significant reduction in a margin of safety.
For the reasons stated above, Commonwealth Edison believes this proposed amendment involves no significant hazards consideration.
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