ML20044E136
| ML20044E136 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 05/17/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20044E135 | List: |
| References | |
| NUDOCS 9305210315 | |
| Download: ML20044E136 (6) | |
Text
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[oan k UrdTED STATES g
NUCLEAR REGULATORY COMMISSION y
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-E WASHINGTON, D. C. 20555 o
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGUL i' RELATED TO AMENDMENT NO. 54 TO FACitlTY OPERATING LICENSE NO. NPF-37, AND AMENDMENT NO. 54 TO FAClllTY OPERATING LICENSE NO. NPF-66 COMMONWEALTH EDISON COMPANY BYRON STATION. UNIT NOS. 1 AND 2 DOCKET NOS. STN 50-454 AND STN 50-455
1.0 INTRODUCTION
By letter dated March 31, 1992, as supplemented May 18, 1992, Commonwealth Edison Company (CECO, the licenset) requested changes to the Technical Specifications (TS) for Byron Station, Ur.its 1 and 2.
These changes resulted from a design basis reconstitution effort completed in 1992. The proposed changes to TS 3/4.7.5 would: decrease the maximum allowed Essential Service Water pump discharge temperature from 98*F to 96*F; require six operable cooling tower fans; apply operability requirements to the basin level switches; and allow mode changes with one makeup pump inoperable. Additional editorial changes and a revision to the TS Bases were also proposed. The May 18, 1992, submittal provided additional clarifying information that did I
not change the initial pro osed no significant hazards consideration r
determination.
i The ultimate heat sink (VHS) for Byron consists of two redundant essential l
service water (ESW) mechanical draft cooling towers and the makeup system to these cooling towers.
Each of the two safety-related cooling towers consi:;ts of a water storage basin, four fans, four riser valves, and two bypass valves.
The basins of the cooling towers are connected. Normal makeup is provided from the circulating water system.
Safety-related makeup pumps automatically start on a low water level signal to pump water from the river.
In the event of the probable maximum flood, there are deep well pumps available to provide
. makeup to the basin.
The mechanical draft cooling towers are used as the heat sink for the ESW system during normal operation, and they are required for safe shutdown. The UHS is capable of providing adequate cooling during a loss of coolant accident (LOCA) coincident with a loss of offsite power (LOOP) in one unit, and a simultaneaus shutdown and cooldown of the other unit from maximum power to Mode 5 using normal shutdown operating procedures.
As part of the 1991 reconstitution of the UHS design basis, several items were identified as being indeterminate or different from those previously assumed in the Updated Final Safety Analysis Report (UFSAR) and design analyses.
The design basis event used in the previous UFSAR included heat input to ESW 9305210315 930517 PDR ADOCK 05000454 P
PDR c
. calculated from the worst case containment analysis of the LOCA unit, which resulted in a peak heat load to ESW of 513 MBTU/hr.
This analysis assumed the maximum heat load in containment, which does not maximite the rate of heat transfer to ESW.
In contrast, the reanalysis maximized the heat transport to the ESW system in order to provide the maximum load to the UHS. The peak heat load was recalculated to be 830.8 MBTU/hr. The large difference in heat loads is attributed to the different single failures analyzed for the reconstitution. The steady state heat loads from the original analysis were also corrected.
Previously, the licensee had assumed a steady-state heat load of 24 MBTU/hr from the non-LOCA unit and 43 MBTU/hr from the LOCA unit based on early design documents that included some inaccurate information. The revised steady state heat loads are 72 MBTU/hr from the non-LOCA unit and 31 MBTU/hr from the LOCA unit based on the actual system configuration and revised calculations. The worst case wet bulb temperature was changed from 78"F to 82*F based on 30 years of meteorological data, which reduced the calculated heat removal capability of the cooling towers under worst case weather conditions.
In addition, the ESW flows previously assumed were different from those used in the reanalysis. The initial analysis assumed 12,000 gallans per minute (gpm) per cell, but the reanalysis used predicted flows ranging from 7,000 to 16,000 gpm per cell.
The combined effect of these changes increased the calculated heat loads and decreased the predicted cooling capability of the UHS.
The revised assumptions resulting from the design basis reconstitution decreased the margin to the ESW design maximum temperature for the worst case accident. Therefore, the licensee has proposed changes to the TS that will compensate for the previous non-conservative assumptions and ensure that the UHS is capable of providing adequate cooling during the design basis accident.
l 2.0 EVALUATION 2.1 ESW Temperature Limitina Condition for Operation (LCO)
The current TS requirements are based on the original cooling tower analyses which determined that the pump discharge water temperature should be limited in 98*F.
The TS limit is below the 100*F design maximum temperature of the l
water inventory within the UHS basin. The temperature limit is specified to j
assure that the maximum reactor containment fan cooler inlet temperature assumed for the containment heat removal safety function is maintained, and the inlet temperature assumed for equipment coolers serviced by the ESW system is not exceeded.
The licensee performed extensive testing of the ESW cooling towers in 1987 to characterize their performance.
The tests verified that the cooling towers were capable of removing the peak accident heat load of f
580 MBTU/hr at design conditions (78*F wet bulb temperature) with four of eight fans running.
However, using the revised assumptions from the design basis reconstitution, the licensee calculated the peak temperature when initial basin temperature was 98*F, as allowed by current TS. The resulting peak temperature was 100.5*F.
Basin temperature remained above 100*F for less than 10 minutes.
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l The licensee has proposed reducing the ESW pump discharge temperature limit in i
Limiting Condition For. Operation (LCO) 3.7.5.d from 98'F to 96*F.
For all analyzed scenarios, the peak basin temperature remained below 100*F when the initial basin temperature was less than or equal to 96*F.
l The staff has reviewed the change and finds that reducing the temperature.
limit to 96*F ensures that the basin temperatute will not exceed the ESW design maximum temperature during normal operation or the design basis event.
Therefore, the staff finds that this change is acceptable.
t 2.2 ESW Fan LCO The current TS requires specific fans to be operable, depending on which unit is operating. The licensee has proposed a revision to TS LCO 3.7.5.b that i
will require six fans to be operable in the high speed mode with either one or both units in Mode 1 - 4.
The revision would also remove all unit-specific fan requirements..When the ESW pump discharge temperature is between 80*F and 96*F, the fans would be required to be running in high speed.
The unit-specific fan requirements are being eliminated because the UHS functions as one common system for the station, not as two independent heat sinks. The two discharges from each unit run into separate return lines to the cooling towers, and each return line is fed from one discharge from each unit.
The cooling towers are arranged so that any cell can receive water from either or both units.
The proposed fan requirements are expressed as a minimum number of fans required to support either single or dual unit operation. The reconstitution analyses indicated no need to restrict fan operability requirements to a given unit.
The licensee's calculations showed that five fans are the minimum number of fans needed to dissipate the heat load during a design basis a
accident.
Four fans are sufficient when the failure of an emergency diesel
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generator (EDG) eliminates approximately one-half of the containment heat removal systems (two reactor containment fan coolers and one containment spray pump unavailable). The combinatien of LCO 3.8.1.1 and the EDG requirement of proposed action statement 3.7.5.b assures that the minimum number of fans with engineered safety features-supplied power are available to safely shut down the plant during the postulated LOCA with concurrent shutdown of the other unit.
The staff has reviewed the proposed change and finds that it is acceptable because eliminating the unit-specific fan requirements will not affect the i
safety function of the UHS.
2.3 ESW Fan Action Reouirements i
The current TS 3.7.5 action statement b requires that if only five of the eight fans are operable then a sixth ran must be restored within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or i
the unit must be shut down. The licensee has proposed a revision to this y
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action statement, requiring that the five operable fans are capable of being powered from their respective diesel generator.
It is important that at least 5 fans are powered from their respective emergency diesel generators since the analysis for one-half containment heat input assumed 4 fans are running in high speed.
The additional requirement of an EDG being operable for each fan relied upon assures that the minimum number of fans are available to safely shut down the plant assuming a design basis LOCA/ LOOP on one unit and a concurrent safe shutdown of the opposite unit.
The staff has reviewed the proposed requirement for operable EDGs and finds it to be acceptable because it provides additional assurance that the minimum number of fans will function during a design basis event.
2.4 UHS Coolino Tower Basin level Switches
.1 The current TS have no operability requirements for the UHS cooling tower basin level switches. These level switches provide an automatic start signal to the makeup pumps on low basin level.
The proposed TS 3.7.5.e would require two operable UHS cooling tower basin level switches. The action statement would require that with one inoperable level switch, the switch must be restored within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or both basin levels must be verified to be greater than 82% every two hours. This new basin level switch action statement allows credit for manual action to maintain the required basin level when a level switch is inoperable.
v The proposed change is consistent with existing TS actions that replace automatic makeup capability with manual makeup capability. Based on the i
licensee's design calculations, the proposed actions provide adequate assurance that basin inventory is available to support ESW operation during l
normal operation and accident conditions. Therefore, the staff finds that the-operability requirement and action statement for the basin level switches are acceptable.
r 2.5 ESW Makeup pump The current TS 3.0.4 does not allow a mode change with one ESW makeup pump inoperable. The proposed revision to TS action statement 3.7.5.c.2 would permit a modo change while one ESW makeup pump is inoperable.
The corresponding action statement would require the same-train deep well pump to be operable and the basin level to be greater than 82%.
This change does not affect the capability of the UHS to perform its safety function. The deep well makeup pumps are seismically qualified and powered from an engineered safety features bus.
The requirements for an operable backup deep well train and increased basin level provide assurance that I
adequate makeup flow will be available.
The staff has reviewed the proposed TS change and finds it to be acceptable.
The allowance for a unit to enter another operational mode with gne train of i
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l ESW makeup inoperable will not affect the ESW system function when the i
compensatory actions (increasing the basin level and verifying the corresponding deep well train is operable) are implemented.
2.6 Editorial Chanaes l
The licensee has proposed a number of editorial changes to TS 3/4.7.5.
These changes correct and clarify the TS and do not change any requirements.
i Therefore, the staff finds that they are acceptable.
2.7 Summary t
The design basis reconstitution of the UHS resulted in revised assumptions that decreased the margin to the ESW design maximum temperature for the worst case accident.
Consequently, the licensee proposed changes to the TS to ensure that the VHS is capable cf providing adequate cooling during the design basis accident. Reducing the cooling tower basin temperature limit to 96*F-i ensures that basin ~ temperature will not exceed the 100*F ESW design maximum temperature during normal operation or the design basis event.
Eliminating the unit-specific fan requirements does not affect the safety function of the UHS. The added requirement for operable EDGs provides further assurance that the minimum number of fans will function during a design basis event. The operability requirement and action statement for the basin level switches ensure that basin inventory is available to support ESW operation during i
normal operation and accident conditions.
Implementation of compensatory l
actions provides assurance that changing operational mode with one train of ESW makeup inoperable will not affect the ESW system function. The editorial l
changes correct and clarify the TS and do not change any' requirements.
i The staff reviewed these changes ar,d found that the licensee meets the ~
requirements of General Design Criterion 44 with respect to cooling _ water by providing a system to transfer heat from structures, systems, and components i
important to safety to an ultimate heat sink. These changes do not reduce the capability of the ESW system to transfer heat loads to the UHS under both normal operating and accident conditions. Therefore, the staff finds that these changes are acceptable.
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3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Illinois State official' was notified of the proposed issuance of the amendments. The State official I
had no comments.
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4.0 ENVIRONMENTAL CONSIDERATION
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The amendments change a requirement.with respect to the installation or use of l
a facility component located within the restricted area as defined in 10 CFR
-l Part 20 and change surveillance requirements. The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released l
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offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (57 FR 24664). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
5.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health.and safety of the public will not be endangered by operation'in the proposed manner, (2) such activities will be conduc.ted in compliance with the Commission's. regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: Ann Dummer, NRR Date: May 17,1993 i
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