ML20125D977
| ML20125D977 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 12/09/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20125D970 | List: |
| References | |
| NUDOCS 9212160120 | |
| Download: ML20125D977 (8) | |
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4 UNITED STATES NUCLEAR REGULATORY COMMISSION n
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WASHING TON, D. C. 20555 a
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SAFETY EVALVATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 72 TO FACILITY OPERATING LICENSE N0. NPF-49 NORTHEAST NVCLEAR ENERGY COMPANY. ET AL.
MILLSTONE NVCLEAR POWER STATION. UNIT N0. 3 DOCKET NO. 50-421
1.0 INTRODUCTION
By letter dated November 2, 1992, with supporting information provided by letters dated November 12 and 18, 1992, the Northeast Nuclear Energy Company (the licensee), submitted a request for changes to the Millstone Nuclear Power Station, Unit No. 3 Technical Specifications (TS).
The requested changes would change the technical specification definition of operability of the charging pump. The revised definition provides that, for Cycle 4 operation only, with the outside air temperature below 17 F, the operability of the charging pump includes credit for a temporary heating source in order to maintain at least 32 F The outside air temperature dropped below 17 F at 5:50 a.m. on December 9 and in order to avoid plant shutdown the licensee verbally requested NRC approval for plant operation to continue under the provisions of the revised definition of charging pump operability.
The licensee documented the request, describing the circumstances requiring the waiver and supporting the waiver, by letter dated December 9, 1992.
2.0 BACKGROUND
The Auxiliary Building Ventilation and Filter System (ABVS) is designed to control the release of radioactive material from the area of the charging pump and plant component cooling water pumps and heat exchangers in the auxiliary building during an accident by directing releases through a filtered path to assist the Supplementary Leak Collection and Release System (SLCRS) in maintaining a negative pressure around containment.
In addition to the engineered safety feature function of ABVS, it also cools certain safety related equipment in the auxiliary building during normal plant operation as well as after an accident.
During normal plant operation, the ABVS draws air from the outside atmosphere and distributes air to the charging pump cubicles, component cooling water heat exchanger area, and the motor control center / rod control booster pump t
area, and exhausts the warm air to the auxiliary building vent stack.
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, Temperature indicating controllers maintain temperatures by modulating supply and recirculation dampers.
The licensee recently discovered that the temperature control function of the ABVS system must be disabled in order to assure that Technical Specification surveillance testing requirements can be met.
The licensee pinned the variable vanes for the ABVS, which modulated to regulate auxiliary building temperatures to a fixed position in order to assure proper operation of the engineered safety feature of ABVS. Therefore, the ABVS dampers can no longer regulate auxiliary system temperatures as outside temperatures change, in order to avoid possible boron precipitation problems in the charging pumps during extreme cold weather.
With the outside temperatures that existed at the time of reactor startup in early November no problem existed in meeting the Auxiliary Building 65'F ambient air temperature which is mentioned in the FSAR. The licensee expected that a problem would arise in early December, however, in meeting auxiliary building temperature requirements without supplementary heating.
For this reason, the licensee provided additional heaters and necessary power supplies to cope with colder weather until the next refueling outage (this summer) when a permanent safety-grade design change will be made.
The licensee regards the temporary modification, which will be needed soon, but is not presently needed, as an unreviewed safety question (USQ), and consequently submitted a proposed license amendment as called for by 10 CFR 50.59(c) before the modification is placed in service.
Because the need for the temporary heating equipment depended on the time at which the outside temperature reached 17'F, which cannot be predicted precisely, the proposed amendment was requested on an exigency basis.
The licensee determined that the modification constituted a USQ because:
1.
The space heaters being added are not QA Category I.
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- 2. - With loss of one train of heaters during a Loss of Power (LOP), if l
outside temperatures are between 17'F and -10.7'F, the Auxiliary Building temperature could drop below the 65"F mentioned in the FSAR, down to as low as 32*F.
Operation with outside air temperature below -10.7 F is precluded by Technical Specifications 3.5.2 and 3.0.3.
This is because operation with outside air temperature below -10.7*F is not addressed by this analysis supporting charging pump operation so the pumps must be l
considered' inoperative.
Reactor shutdown is called for by Technical i-Specification 3.0.3 if charging pump operability requirements are not met.
3.0 EVALUATION The licensee's two letters dated November 12, 1992 describe the changes in plant design.
The staff specifically reviewed:
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. 1.
Temporary Heating System Design.
Millstone 3 has proposed to add two 'crains of non-safety (non-Class-lE) heating units in certain safety-related Auxiliary building areas to provide assurance that adequate room operating temperatures will be maintained. This change will require eight heating units, four on each train, to be powered from the emergency diesel generator (EDGs) which are available during a LOP event.
The EDGs were analyzed to ensure there is sufficient capacity available to power the eight heating units.
Some nonessential equipment loads which have a greater Kw rating than the heating loads being added will be disconnected from the EDGs. The same block signals that were sent by the EDG load sequencer to the disconnected loads will now be sent to the new heating loads so that these loads cannot be energized prior to 40 seconds after the EDG is supplying power.
The purpose of this block signal is to ensure that these heaters are added to the last load step to ensure the existing EDG loading envelopes the proposed change.
The change was further analyzed to ensure that the Class-lE power supply system is not degraded.
The Class-lE busses and non-Class-lE heaters will be isolated by two Class-1E breakers in series, i.e., each train of four heaters will be connected through two series breakers to an emergency 480 volt load center bus.
The system is coordinated such that faults on any part of the feeder circuit including the individual heating units will not result in the loss of the emergency load center.
The Class-lE cabling from the emergency load center to the first Class-lE breaker, between the two series breakers, and between the second series breaker and the local distribution panel will be installed and color coded as safety related cabling. The cabling from the local distribution panels to the individual heaters will be installed as non-safety related cabling but separation between the redundant train heater cabling will be maintained.
The staff has reviewed the licensee's proposed change and concludes that the addition of these non-safety related loads will not degrade the Class-lE power supply. Therefore, the staff concludes that the design of the temporary heating system is acceptable.
2.
Auxiliary Building Post-Accident Design Basis Below 65*F.
The FSAR refers to a temperature of 65'F maintained in the Auxiliary Building by the ABVS. The licensee has proposed lowering this temperature to 32*F under conditions of low outside air temperature and LOP. The concern is that boron in the boric acid tank (BAT) path, which is a; very high concentration, would at lower temperatures precipitate clogging the boration path, and potentially damaging the charging pump (s).
The licensee identified temperature alarms and procedures which would align two baration paths taking suction from the refueling water storage tank (RWST) and isolate the BAT path. The RWST path boron concentration (2900 ppm) is lower than that of the BAT path and would not be expected to encounter boron precipitation at temperatures above 32 F (corresponding to -10.7'F outside
. temperature). The licensee stated that all Millstone 3 licensing and other regulatory bases are met by the safety grade RWST path down to -10.7'F outside temperature.
The proposed TS change is temporary and would be effective only until the next refueling outage (currently planned for summer 1993).
Based on the facts that Millstone 3 can meet all its licensing and other regulatory bases with the proposed low temperature RWST path, that administrative alarms and procedures are in place to implement that path when dictated by plant temperatures, and that the change is temporary, the staff finds the proposed lowering of the Auxiliary Building temperature under the above conditions acceptable.
3.
Charging Pump Operation.
The proposed use of the charging pumps differs from the. licensed design because the charging pumps are called upon to function at lower temperature conditions than before and reliance is placed on operator action.
By letter dated November 18, 1992, the licensee provided the results of analysis from Westinghouse Electric Corporation which evaluated the operation of the charging / safety injection pumps for an ambient temperature of 30'F for 30 days during safety injection and recirculation operation, if the pumps are first started from an ambient temperature of at least 55'F. The analysis concluded:
i The evaluation addressed the critical areas of the pump including the mechanical seals, couplings, shaft alignment, motor bearings, i
gear box bearings / oil and pump bearings / oil.
The evaluation demonstrated that the charging pump assemblies will operate successfully during these conditions with no effect on the pump t
performance. No special maintenance activities are necessary to support this operation for up to 30 days.
l Because the Westinghouse analysis assumes the pumps are first started the staff considered the operator actions required. The licensee described the
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alarms and procedural requirements which determine operator action by letter dated November 18, 1992. Temperature alarms in the control room call for operator action when auxiliary building ventilation duct temperature goes below 69'F.
- If~the temperature in the charging pump cubicle cannot be restored above 65 F within 30 minutes of alarm receipt the operator starts a second charging pump. The operator would also isolate the high-concentration BAT path to avoid boron precipitation problems.
Becausethecharginggump(s) will be started within 30 minutes of the temperature dropping below 65 F, the l
charging pump (s) would continue to remain operable even if the temperature in the auxiliary building dropped to 32*F.
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4 1 Based on the staff's review of the licensee's support for the continued operation of the charging pump (s) and the description of provision for operator action to assure pump operation, the staff concludes that the proposed reliance on charging pump operation under the new conditions is acceptable.
4.0 EXIGENT CIRCUMSTANCES
The licensee's November 12, 1992 letter requested that expeditious approval of the proposed amendment was required to avoid unnecessary shutdown of the plant, which would be required if the outside ambient temperature dropped to 17 F.
The licensee's best estimate as to when ambient temperatures would drop to 17*F was December 1.
The staff finds that this request should be processed on an exigent basis.
Shutting the plant down if the outside ambient temperature reaches 17*F would subject the plant to unnecessary transients that would be detrimental to safety. Although an outside ambient air temperature of 17 F was not reached on December 1,1992, it will likely be reached before expiration of the normal 30-day comment period. Therefore, the Commission finds, pursuant to 10 CFR 50.91(a)(6), that exigent circumstances-exist warranting prompt action on this request.
5.0 FINAL NO SIGNIFICANT HAZARDS CONSIDERATION
DETERMINATION The Commission's regulations in 10 CFR 50.92 state that the Commission may make a final determination that the license amendment involves 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.
l Changes made to the ABVS cannot increase the probability of an accident i
because the ABVS system functions to mitigate accident consequences. An accident cannot be initiated by the ABVS, and no adverse interaction between ABVS and the rest of the plant has been identified that could cause an accident. Therefore, changes to ABVS cannot increase the probability of an accident.
Although the proposed change relies on non-QA heaters in the aux *.liary building, this reliance does not change the performance characteristics of any safety-related equipment contained in the auxiliary building (i.e.,
charging system). Thus, the accident analysis results are unaffected and the doses will not be increased. The installation of the heaters along with the previous changes to the system will improve the capability of ABVS in assisting SLCRS to draw a negative pressure and thus the design basis analysis offsite dose calculations are not affected. Therefore, the proposed changes have no effect on the consequences of the previously evaluated accidents.
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The proposed change has no adverse impact on the electrical' distribution system or emergency diesel generator-(EDG) loading.
Since one EDG load (the fuel building ventilation system) is being replaced with a smaller EDG load (the auxiliary building heaters) and-the Class lE busses and non-i Class lE heaters will be isolated by two Class IE breakers in series, i
there is no increase in loads on the electrical systems such that they 1
would be operated outside of their design or tested limits.
Therefore, the probability of occurrence of those accidents initiated by the electrical distribution system and the consequences-resulting from such an i
accident, remain unchanged.
The fuel building ventilation system is required to support fuel handling i
and spent fuel cask drop accidents. However, there will be no movement of new or spent fuel or heavy loads over the storage pool during the time-the i
fuel building exhaust filter system is disconnected. Therefore, these-previously evaluated accidents cannot occur during this time period and i
their dose consequences will not be increased.
2.
Create the possibility of a new or different kind of accident from any accident previously evaluated.
The proposed change and its associated failure modes do'not increase the possibility of an accident of a different type. ' Although multiple i
failures associated with'the change can result in the initiation of an-accident, they are similar-to failure modes that exist with the current system. The possibility of a failure of all the heaters which causes a loss of component cooling water pump and charging injection without an LOP is negligibly low.
The reasons for this being negligibly low are because there are two redundant trains of heaters, and even if both trains. failed, the outdoor temperature would; seldom be low enough to reduce the auxiliary l
building temperature below 32*F.
There 'are also two temperature alarms that would alert the operators of-a low temperature and there _is sufficient time available for operators to take actions.
3.
Involve a significant reduction in a margin of safety, r
l The proposed changes do not-impact the physical. protective boundaries -nor t
do they affect the performance of the charging or ABV' systems. Therefore, there is no impact on the margin'of safety.
Further, the changes will improve the overall reliability of the ABVS when compared to the as found system _and thus provides added assurance that_the I
offsite dose calculations in the FSAR remain valid.
With the addition of credit.for non-QA equipment, the impact on charging system reliability is judged to be negligible.
Accordingly, the NRC staff concludes that the proposed amendment involves no significant hazards consideration.
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6.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Connecticut State official was notified of the proposed issuance of the amendment.
The State official had no comments.
7.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released 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 amendment involves no significant hazards consideration, and there has been no public comment on such finding (57 FR 55288, corrected 57 FR 57081).
Accordingly, the amendment meets 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 amendment.
8.0 TEMPORARY WAIVER OF COMPLIANCE The outside air temperature dropped below 17'F at 5:50 a.m. on December 9 and in order to avoid plant shutdown the licensee verbally requested NRC approval for plant operation to continue under the provisions of the revised definition of charging pump operability. The licensee documented the request by letter dated December 9, 1992, describing the circumstances requiring the waiver and supporting the waiver.
The waiver was needed because operation with outside air temperatures is precluded by Technical Specifications 3.5.2 and 3.0.3.
This is because operation with air temperatures below 17 F is not addressed with approved analysis until the amendment is issued, so the pumps must be considered inoperable.
Reactor shutdown is called for if charging pump operability requirements are not met. The licensee's Plant Operations Review Committee (PORC) has reviewed and approved the requested temporary waiver of compliance.
The discussions in this Safety Evaluation dealing with background, evaluation, exigent circumstances, final no significant hazards determination, state consultation, and environmental consideration are valid for the temporary waiver of compliance, as well as for the proposed amendment.
Therefore, based on our review of the licensee's request, we find that operation of the Millstone 3 plant in conformance with the revised definition of charging pump operability provides an acceptable level of safety and does not represent any undue ris.: to the health and safety of the public.
Therefore a temporary waiver of compliance with the existing technical specification requirements is appropriate from 8:15 a.m. December 9, when the requested waiver was verbally approved, until the requested amendment is issued.
9.0 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 wil)l not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment and temporary waiver of compliance will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributors:
V. Rooney, C. Thomas, F. Orr Date:
December 9,1992 l
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