ML20052B496
| ML20052B496 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/01/1982 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20052B443 | List: |
| References | |
| NUDOCS 8204300496 | |
| Download: ML20052B496 (10) | |
Text
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,r SAFETY EVALUATION BY THE OFFICE ~0F NUCLEAR REACTOR REGULATION GPU NUCLEAR ~ CORPORATION _
METROPOLITAN EDIS0N COMPANY PENNSYLVANIA ELECTRIC COMPANY JERSEY CENTRAL POWER ~AND LIGHT COMPANY DOCKET NO. 50-320 THREE MILE ISLAND NUCLEAR STATION, UNIT NO. 2 INTRODUCTION By letter dated December 11, 1981, Metropolitan Edison Company proposed changes to Sections 3.7.1, 3.7.2 and 3.8.2.1 of the Recovery Mode Technical Specifications for Three Mile Island Unit 2 (TMI-2) by requesting that the requirements for the operability of the Long Tenn B (LTB) steam generator cooling system and its associated electrical busses 2-31 and 2-41 be delett;'. The requirements of the Recovery Mode Technical Specifications were imposed on the Licensee by Order of the Director, Nuclear Reactor Regulation, dated February 11, 1980 (45 Fed.
Reg.11282). Although this mode of reactor coolant system (RCS) heat removal has been maintained as one of the backup cooling modes available, the presently used " loss to ambient" mode has been successful in removing decay heat since it was fully implemented in January 1981. This change would also remove the operability requirements for LTB associated secondary cooling water and electrical busses from the proposed technical specifications. The Mini-Decay.
Heat Removal System (MDHRS) and Decay Heat Removal System (DHRS) would then become the backup core cooling modes.
MDHRS and DHRS are required to be operable per proposed Technical Specification subsections 3.7.3.3 and 3.7.3.2 respectively.
SUMMARY
The licensee has requested NRC staff approval to delete the operability require-82 04 30 0 Lf %
. ments of Long Term "B" steam generator cooling system as a backup mode for removing decay heat from the reactor coolant system. As discussed in this safety evaluation, the " loss to ambient" cooling mode will centinue to be the primary mode for core cooling with the Mini-Decay Heat Removal System and the Decay Heat Removal System as alternatives. The " loss to ambient" cooling mode has proven itself as an effective way to remove decay heat and its failure is unlikely because it is a passive system. The other Decay Heat Removal Systems are available as approved alternatives. The staff, therefore, has found that the deletion of Long Term "B", its associated secondary cooling water and electrical supply from the proposed technical specifications are acceptable.
EVALUATION By Order of the Director, Office of Nuclear Reactor Regulation, dated February 11, 1980, a new set of formal license requirements was imposed to reflect the post accident condition of the TMI-2 facility. This order incor-porated operability requirements for thn Long Term "B" (LTB) steam generator cooling system. This is a water solid, closed loop, cooling system which is in turn cooled by the Secondary Services Closed Cooling Water System.
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Amendment of Orde, dated November 14, 1980, the Mini-Decay Heat Removal System (MDHRS) was also incorporated into the proposed technical specifications as an alternate cooling mode. MDHRS is also a closed loop water solid system sized such that one pump and one heat exchanger (two of each are installed) could remove up to approximately 1 MW of decay heat.
The MDHRS would be cooled by the Nuclear Services Closed Cycle Cooling System.
l Currently the reactor coolant system (RCS) is generating less than 50 KW of decay heat.
This heat is being removed via the " loss to ambient" cooling mode.
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. Since the approval of this method by the NRC staff in January 1981, it has shown to be an effective and reliable means for core cooling.
In the staff's opinion, since this is a passive mode of heat removal, the chances that an event occurring that would prevent loss of decay heat to be released to ambient is unlikely.
In addition, LTB was originally designed for a decay heat rate corresponding to that existing shortly after the accident with a design heat exchange rate of 12.11.E3 KW (41.35 E6 BTU /hr).
Presently, the decay heat is Consequently, the LT_ system is oversized for B
less than 50 KW (17.07 E4 BTV/hr).
its potential current usage.
The only transient that would result in a temperature and pressure increase such that " loss to ambient" would no longer be effective would be a recriticality accident. This event was discussed in 'the Final Programmatic Impact Statement (PEIS) for THI-2 issued in March 1981.
Paragraph 4.1 of the PEIS states that "the most probable (although very unlikely) cause of recriticality was found to be boron dilution, which would be a slow enough process that any approach to criticality can be detected and remedied." This statement is still valid.
The staff, therefore, has concluded that this accident does not need to be con-sidered a factor in maintaining the core in its present thermodynamic condition.
All other causes of recriticality are, in the staff's opinion, also very unlikely and need not be considered.
Since the present mode of decay heat removal is effective and dependable, and the MDHRS and Decay Heat Removal System are re. quired per proposed technical specifications to be operable thereby providing adequate backup modes, this proposed change to delete the operability requirements for the LTB system
. is, therefore, acceptable and will not result in a significant increase in the probability or consequences of accidents previously considered nor a significant reduction in a margin of safety and does not therefore involve a significant hazards consideration.
ENVIRONMENTAL C0ASIDERATIONS We have determined that the change does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact. Having made this determination, we have further concluded that the change involves an action which is insignificant from the standpoint of environmental impact and, pursuant to 10 CFR 51.5 (d)(4),
that an environmental impact statement or negative declaration and environmental impact appraisal need not be prepared in connection with the issuances of this change.
CONCLUSION Based upon our review of the effectiveness history of the " loss to ambient" cooling mode, and the availability of approved backup decay heat modes required operable per the proposed technical specifications, the staff finds that the deletion of the Long Term B cooling mode, its associated second-l ary closed cooling water and its electrical busses from the proposed technical specifications is acceptable. The associated bases for the proposed technical specifications have also been modified as requested by the licensee.
_5 We have also concluded, based on the considerations discussed above, that:
4 (1) because the change does not involve a significant increase in the probability or consequences of accidents previously considered and does not involve a significant decrease in a safety margin, it does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the implementation of this change will not be inimical to the common defense and security or to the health and safety of the public.
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FACILITY'0PERATING LICENSE NO. DPR-73 DOCKET NO. 50-320 Replace the following pages of Appendix "A" Proposed Technical Specifications with the enclosed pages as indicated. The revised pages contain vertical lines indicating the area of change.
Pages 3.7-1 3.8-4 B 3/4 4-1 B 3/4 7-1 i
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LIMITING CONDITIONS FOR OPERATION 3.7 PLANT SYSTEMS 3.7.1 FEEDWATER SYSTEM 3.7.2 SECONDARY SERVICES CLOSED COOLING WATER SYSTEM i
3.7.3 CLOSED CYCLE COOLING WATER SYSTEM NUCLEAR SERVICES CLOSED CYCLE COOLING SYSTEM 3.7.3.1 At least two independent nuclear services closed cycle cooling water pumps and heat exchangers and the associated flow path shall be OPERABLE with each pump capable of being powered from separate emergency busses.
APPLICABILITY:
RECCVERY MODE.
ACTION:
With only one nuclear services closed cycle cooling water pump or only one nuclear services heat axchanger OPERABLE, restore the inoperable pump or heat exchanger to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
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THREE MILE ISLAND - UNIT 2 3.7-1 L
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LIMITING CONDITIONS FOR OPERATION 3.8.2 ONSITE POWER DISTRIBUTION SYSTEMS A.C.
DISTRIBUTION 3.8.2.1 The following A.C. electrical busses shall be OPERABLE and energized with tie breakers open (unless closed in accordance with procedures approved pursuant to Specification 6.8.2) between redundant busses:
4160 volt Emergency Bus # 2-1E and 2-3E 4160 volt Emergency Bus # 2-2E and 2-4E 4160 vo.lt Busses # 2-3 and 2-4 480 volt Emergency Bus # 2-11E, 2-12E and 2-31E 480 volt Emergency Bus # 2-21E, 2-22E and 2-41E 480 volt Busses # 2-32, 2-42, 2-35, 2-36, 2-45, and 2-46 120 volt A.C. Vital Bus # 2-1V 120 volt A.C. Vital Bus # 2-2V 120 volt A.C. Vital Bus # 2-3V 120 volt A.C. Vital Bus # 2-4V APPLICABILITY:
RECOVERY MODE.
ACTION:
l With less than the above complement of A.C. busses OPERABLE, restore the inoperable bus to OPERABLE status within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.
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THREE MILE ISLAND - UNIT 2 3.8-4
3/4.4 REACTOR COOLANT SYSTEM BASES 3/4.4.1 REACTOR COOLANT LOOPS Several alternative methods are available for removal of reactor decay heat.
These methods include use of the Mini Decay Heat Removal System, the
" Loss to Ambient" cooling mode.
Either of these cooling methods provides ade-quate cooling of the reactor and each method is available for decay heat removal.
Procedures have been prepared and approved for use of these cooling methods.
3/4.4.3 SAFETY VALVES The pressurizer code safety valves operate to prevent the RCS from being pressurized above its Safety Limit of 2750 psig.
Each safety valve is designed to relieve 348,072 lbs per hour of saturated s, team at the valve's setpoint.
3/4.4.9 PRESSURE / TEMPERATURE LIMIT The RCS pressure and temperature will be controlled in accordance with approved procedures to prevent a nonductile failure of the RCS while at the same time permitting the RCS pressure to be maintained at a sufficiently high value to permit operation of the reactor coolant pumps.
Reactor coolant chemistry surveillance requirements are included in the Recovery Operations Plan.
These req'uirements provide assurance that localized corrosion or pitting in crevice areas, which could tend to promote stress corrosion cracking in heat affected zones of welds in stainless steel piping or components, will not occur.
This assurance is provided by maintaining the reactor coolant dissolved oxygen concentration and pH to within the specified limits.
The oxygen concentration must be limited since the chloride concen-l tration is relatively high and cannot be reduced due to the unavailability of the purification demineralizers.
Hydrazine is used to control the oxygen i
concentration in the presence of metallic impurities in the reactor coolant.
i THREE MILE ISLAND - UNIT 2 B 3/4 4-1
4 3/4.7 PLANT SYSTEMS BASES 3/4.7.1 FEEDWATER SYSTEM 3/4.7.2 SECONDARY SERVICES CLOSED COOLING WATER SYSTEM 3/4.7.3 CLOSED CYCLE COOLING WATER SYSTEM 3/4.7.3.1 NUCLEAR SERVICES CLOSED CYCLE COOLING SYSTEM OPERABILITY of the nuclear services closed cycle cooling system is required during operation of the MDHRS since this system provides the heat sink for the MDHRS.
3/4.7.3.2 DECAY HEAT CLOSED COOLING WATER SYSTEM The decay heat closed cooling water system is required to be maintained in an OPERABLE status since it is provided to remove heat from the DHR system which is being maintained OPERABLE in a backup status for possible core cooling.
3/4.7.3.3 MINI DECAY HEAT REMOVAL SYSTEM (MDHRS)
OPERABILITY of the MDHRS is required since it is an alternative method for removing decay heat from the reactor.
The MDHRS is provided with two pumps and two heat exchangers; one pump and one heat exchanger have adequate capacity l
for removing the present level of decay heat from the core.
l 3/4.7.4 NUCLEAR SERVICE RIVER WATER SYSTEM The nuclear service river water system uses river water to cool the nuclear services closed cycle cooling system, the secondary services closed cooling water system, and decay heat closed cooling water system; therefore, it must be OPERABLE too.
This system rejects its heat to the river as the l
l THREE MILE ISLAND - UNIT 2 8 3/4 7-1