ML20198L197

Informs That Based Upon Conclusion That Current Design & Licensing Basis Does Not Credit Containment Overpressure to Ensure Adequate NPSH to Core Spray & Containment Spray Pumps,Nrc Considers GL 97-04 Closed Per 980807 RAI

ML20198L197
Person / Time
Site:	Nine Mile Point
Issue date:	12/24/1998
From:	Hood D NRC (Affiliation Not Assigned)
To:	Mueller J NIAGARA MOHAWK POWER CORP.
References
GL-97-04, GL-97-4, TAC-MA0013, TAC-MA13, NUDOCS 9901040084
Download: ML20198L197 (7)

Text

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Mr. John H. Mutil:r December 24, 1998 Chilf Nucirr Officer -

• Nirgtrs Mohawk Power Corporation Nine Mile Point Nuclear Station Operations Building, Second Floor P.O. Box 63 Lycoming, NY 13093 l

SUBJECT:

CLOSURE OF GENERIC LETTER 97-04,' " ASSURANCE OF SUFFICIENT NET POS!TIVE SUCTION HEAD (NPSH] FOR EMERGENCY CORE COOLING AND CONTAINMENT HEAT REMOVAL PUMPS," NINE MILE L POINT NUCLEAR STATION, UNIT 1 (TAC NO. MA0013)

Dear Mr. Mueller:

l By letter dated August 7,1998, the NRC staff requested additionalinformation regarding your l written response of January 5,1998, to Generic Letter (GL) 97-04 for Nine Mile Point Nuclear

Station, Unit 1 (NMP1). Specifically, the NRC staff requested hat you provide a response l within 30 days discussing how your response to GL 97-04 related to containment overpressure compares with your current licensing basis.

Niagara Mohawk Power Company (NMPC) responded by letter dated September 8,1998.

Based upon that response and an audit conducted by the NRC staff on September 23 and 24,1998, the NRC staff agrees that NMPC does not take credit for containment overpressure for evaluating NMP1's current design basis loss-of-coolant accident with clean l suction strainers. However, the NRC staff takes exception to NMPC's statement that the l NRC has reviewed and approved the use of containment overprescure. Based upon the i conclusion that the current design and licensing basis does not credit containment overpressure to ensure adequate NPSH to the NMP1 core spray and containment spray l pumps, the NRC staff considers GL 97-04 closed for NMP1. Our evaluation is enclosed.

i Should you have questions, please contact me by phone on (301) 415-3049 or by electronic

! mail at dsh@nrc. gov.

l Sincerely, ORIGINAL SIGNED BY:

Darl S. Hood, Senior Project Manager  !

Project Directorate 1-1 I 9901040084 981224 Division of Reactor Projects - 1/II PDR ADOCK 050002 O Office of Nuclear Reactor Regulation Docket No. 50-220

Enclosure:

As stated cc w/ encl: See next page -

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% ***** / December 24, 1998 Mr. John H. Mueller Chief NuclearOfficer Niagara Mohawk Power Corporation Nine Mile Point Nuclear Station Operations Buil*ng, Seced Floor P.O. Box 63 Lycoming, NY 13093

SUBJECT:

- CLOSURE OF GENERIC LETTER 97-04, " ASSURANCE OF SUFFICIENT NET POSITIVE SUCTION HEAD [NPSH] FOR EMERGENCY CORE COOLING AND ,

CONTAINMENT HEAT REMOVAL PUMPS," NINE MILE POINT NUCLEAR '

STATION, UNIT 1 (TAC NO. MA0013)

Dear Mr. Mueller.

By letter dated August 7,1998, the NRC staff requested additionalinformation regarding your written response of January 5,1998, to Generic Letter (GL) 97-04 for Nine Mile Point Nuclear Station, Unit 1 (NMP1). Specifically, the NRC staff requested that you provide a response within 30 days discussing how your response to GL 97-04 related to containment overpressure compares with your current licensing basis.

Niagara Mohawk Power Company (NMPC) responded by letter dated September 8,1998.

Based upon that response and an audit conducted by the NRC staff on September 23 and 24, l 1998, the NRC staff agross that NMPC does not take credit for containment overpressure for evaluating NMP1's current design basis loss-of coolant accident with clean suction strainers.

l However, the NRC staf' takes exception to NMPC's statement that the NRC has reviewed and '

, approved the use of containment overpressure. Based upon the conclusion that the current i

design and licensing basis does not credit containment overpressure to ensure adequate NPSH to the NMP1 core spray and containment spray pumps, the NRC staff considers GL 97-04 closed for NMP1. Our evaluation is enclosed.

Should you have questions, please contact me by phone on (301) 415-3049 or by electronic mail at dsh@nrc. gov.

Sincerely, Darl S. Hood, Senior Project Manager

Project Directorate I-1 Division of Reactor Projec's - 1/II Office of Nuclear Reactor Regulation

! Docket No. 50-220

Enclosure:

As stated i

cc w/ encl: See next page

Y j John H. Mueller .

Nine Mile Point Nuclear Station Niagara Mohawk Power Corporation Unit No.1 cc:

Regional Administrator, Region i U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 Resident inspector U.S. Nuclear Regulatory Commission P.O. Box 126 Lycoming, NY 13093 Charles Donaldson, Esquire Assistant Attorney General New York Department of Law 120 Broadway New York, NY 10271 '

Mr. Paul D. Eddy State of New York l Department of Public Service Power Division, System Operations 3 Empire State Plaza Albany, NY 12223 Mr. F. William Valentino, President New York State Energy, Research, and Development Authority Corporate Plaza West

- 286 Washington Avenue Extension Albany, NY 12203-6399 Mark J. Wetterhahn, Esquire Winston & Strawn 1400 L Street, NW Washington, DC 20005-3502

. Gary D. 'Nilson, Esquire Niagara Mohawk Power Corporation 300 Erie Boulevard West Syracuse, NY 13202 Supervisor Town of Scriba Route 8, Box 382 Oswego, NY 13126

j ,

4 .

DJ EVALUATION OF RESPONSE TO GENERIC LETTER 97-04 i NINE MILE POINT NUCLEAR STATION. UNIT 1 i

1.'O EVALUATION i

i 1.1 Current NPSH Design Basis Celculation i

By letter dated January 5,1998 (Reference 1), Niagara Mohawk Power Corporation (NMPC and the licensee) responded to Generic Letter 97-04, " Assurance Of Sufficient Net Positive

!- Suction Head for Emergency Core Cooling and Containment Heat Removal Pumos,"

!. (Reference 2). By letter dated August 7,1998 (Reference 3), the NRC staff requested that

] NMPC " provide a response within 30 days discussing how your response to GL 97-04 related l

i to containment overpressure compares with your current licensing basis," for Nine Mile Point '

j Nuclear Station, Unit 1 (NMP1).

4

By letter dated September 8,1998 (Reference 4), NMPC responded to the NRC staff's request l j for additional information (RAl). In its response, NMPC stated it's position that the NMP1 4= design basis NPSH analyses does not credit the containment overpressure that would be I

piesent after a postulated loss-of-coolant accident (LOCA), and that the industry's suggested consideration of 50 percent clogging of suction strainers is not applicable to the NMP1 license basis. Particularly, NMPC's letter stated the following:

L NMP1's originaldesign andlicense basis consists of automaticinitiation of containment

. sprayin both the drywell and torus spray mode. Ourcontainment analysis shows that i i

' the peak bulk torus water temperature in this mode of operation is approximately 158.9 degrees Fahrenheit. With a clean suction grate, NPSH required equals NPSH avellable i at a torus water temperature of approximately 160 degrees Fahrenheit without l containment pressure. Themfore, NPSH requirements are satisfied for the license basis condition.

.i The NRC staff conducted an audit at NMP1 regarding NMPC's NPSH analyses on September l' 23 and 24,1998. Although several different cases are evaluated in the NPSH analyses, the v

NPSH calculations of record-the design basis case-assumed atmospheric pressure and used flow rates of 3820 gpm for the containment spray primary loop,3720 gom for the containment spray secondary loop, and 4825 gpm for one set of core spray pumps which, according to NMPC, are consistent with the flow rates used in NMPC's Appendix K LOCA analysis. The results of the NPSH arsalyses with these conditions are consistent with the values for NPSH available (NPSHA) and NPSH required (NPSHR) reported in NMPC's response to GL 97-04.

The NRC staff notes that for the Emergency Operating Procedure (EOP) case for which containment spray is manually inhibited (e.g., pulled to lock), the calculated peak bulk torus water temperature is 163 degrees Fahrenheit. This EOP case is beyond the design basis and therefore, not considered the design basis calculation of record. Based upon the audit results and NMPC's response to the NRC staff 4 RAI, the NRC staff agrees that, for the design basis case with the flow rates discussed above, clean suction strainers, and a maximum suppression pool temperature equal to or less than 160 degreet Fahrenheit, NMPC does not credit containment overpressure in the NMP1 NPSH analyses and is within the current licensing basis.

Enclosure

g, 4 .

2-

[ 1.2 Credit for Containment Overpressure in Licensing Basis NMPC's response also stated that "the use of containment overpressure for NPSH evaluation 4

was approved by the NRC in Region I Combined Inspection Report Nos. 50-220/90-04 and 50-

410/90-04 dated June 20,1990," and in Amendment No.133. The NRC staff disagrees with NMPC's statement that the use of containment overpressure has been reviewed and approved by the NRC staff.

t i NRC Region l Combined Inspection Report Nos. 50-220/90-04 and 50-410/90-04 dated i June 21,1990 (Reference 5), included a safety evaluation (SE) in the attachment from NRC's Office of Nuclear Reactor Regulation (NRR) that evaluated the unresolved items identified in 4 the NRC staff's Safety System Function Inspection Report 50-220/88-201. The unresolved i

items identified were 1) the NPSH for the core spray pumps may not be adequate to support the flow expected during large-break LOCAs, and 2) the design of the core spray " keep filr system did not appear to prevent water hammer throughout the system and existing testing did not ensure that water hammer would not occur under certain LOCA conditions. The NPSH case in question used a different set of assumptions than the current design basis calculation.

These assumptions included a lower peak suppression pool temperature, higher core spray flow rates for one pump set operation and 40 percent strainer blockage. The NRC staff's SE i stated:

+ .

During one pump set operation at a reactorpressure of 0 psig, the calculated flow through the core spraypumps is about 5000 gpm. From the pump performance curves, the required NPSH at this flow is 39 feet. At the maximum water temperature during a LOCA of 140 *F and a torus airpressure of 0 psig (Regulatory Guide 1.1 Conditions), the available NPS4is calculated to be 41 feet with a clean (unblocked)

! pump suction strainer. However with the strainer 40 percent blocked, the available l NPSH is calculated to be 35 feet, i.e., 3 feet less than the required NPSH. This NPSH 1

deficiency may result in pump cavitation.

The NRC staff's SE continues to state, as reiterated in NMPC's response, that "the initial

]

conditions given in Regulatory Guide 1.1 are conservative. For design basis accident condition the containment pressure will be greater than 0 psig and suppression pool i temperature will be less than 140 *F during a LOCA. The operators will start suppression pool

, cooling sufficiently early to keep the pool temperature below 140 *F and the containment will i be pressurized during a LOCA." As noted is Section 1.1 above, the current design basis condition is calculated with a maximum pool temperature of 158.9 degrees Fahrenheit with a core spray flow rate of 4825 gpm for one set of pumps and clean suction strainers. The NRC staff's SE evaluated a different set of values that assumed the operators would maintain the suppression pool temperature to less than 140 degrees Fahrenheit. The NRC staff's SE did not approve the use of containment overpressure at NMP1, but evaluated an NPSH case for which the suction strainers were assumed to be 40 percent blocked. The NRC staff considered this case to be acceptable based upon operator action to start suppression pool cooling early and availability of attemate water systems which could be aligned to keep the core covered in the unlikely event the core spray pumps become inoperaole due to cavitation.

,ij NMP1 License Amendment No.133 (Reference 6) revised TS 3/4.1.4 (core spray system), TS 3/4.3.2 (pressure suppression syttom and suppression chamber water temperature and level),  ;

. TS 3/4.3.7 (containment spray system), and associated Bases to authorize an increase in the I

maximum allowable water temperature limit of Lake Ontario (ultimate heat sink) from 77 degrees Fahrenheit to 81 degrees Fahrenheit. Additionally, the amendment approved 4 the revision of the minimum downcomer submergence from 3.0 feet to 3.5 feet, to increase the 1 maximum allowable torus water operating temperature from 77 degrees Fahrenheit to 85 degrees Fahrenheit, and the change of initiation of suppression pool cooling from 30 minutes to 15 minutes.

In it's response, NMPC stated that the NRC staff again approved the use, of containment overpressure in the SE for Amendment No.133 when the NRC staff evaluated the effects of delaying initiation of suppression pool cooling from 15 minutes to 30 minutes. This assumed l

that the operators did not initiate suppression pool cooling within 15 minutes with the increased maximum water temperature of Lake Ontario. In this case, the NRC staff's SE stated:

For the design basis spray mode of operation, the maximum pool temperature is expected to increase from 159.5 *F to 162.4 *F at 0 psig containment pressure and remain bounded by the maximum analyzed temperature of 165 'F a ssociated with the core spray NPSH requirement. In tha EOP mode of operation, the maximum pool l temperature is expected to increase from 163 *F to 166.S *F. This slight increase in pool temperature will not affect the core spray NPSH requirements due to positive ,

pressure of about 4 psig in the containment expected at the time of maximum pool '

temperature.

Again, the NRC staff did not approve the use of containment overpressure for the design basis NPSH case at NMP1 but evaluated the acceptability of the EOP case, which is beyond the design basis and not considered the calculation of record. The NRC staff considered this case to be acceptable because the EOPs instruct the operators to tum off the containment sprays when containment pressure is equal to 3.5 psig. This conclusion is reaffirmed in conclusion in the NRC staff's SE which states that " based on the above evaluation, the NRC staff concludes that the proposed changes to TS 3.1.4/4.1.4, TS 3.3.2/4.3.2, TS 3.3.7i4.3.7, and associated Bases for minimum and maximum submergence levels, maximum torus and lake water temperatures, and initiation time for raw water system are acceptable."

2.0 CONCLUSION

Based on the NRC's audit results and NMPC's response to the NRC staff RAl, the NRC staff agrees that, for the design basis case with the flow rates discussed above, clean suction strainers, and a maximum suppression pool temperature equal to or less than 160 degrees Fahretiheit, NMPC does not credit containment overpressure in the NMP1 NPSH analyses and ,

is within NMP1's current licensing basis. However, the NRC staff does not conclude that '

containment overpressure credit has been approved for use at NMP1.

d Based upon the conclusion that the current design and licensing basis does not credit containment overpressure to ensure adequate NPSH to the NMP1 core spray and containment spray pumps, the NRC staff considers GL 97-04 closed for NMP1.

REFERENCES

1. Conway, J.T., NMPC, to USNRC, "90 Day Response to Generic Letter 97-04,

' Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps,'" January 5,1998.

2. USNRC Generic Letter 97-04, " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps," October 7,1997,

3. Hood, D.S., USNRC, to J.H. Mueller, NMPC, " Request for Additional Information Reflated to Generic Letter 97-04, Nine Mile Point Nuclear Station, Unit No.1 (TAC No.

MA0013)," August 7,1998.

4. Abbott, R.B., NMPC, to USNRC, " Request for Additional Information Related to Generic Letter 97-04, Nine Mile Point Nuclear Station, Unit No.1 (TAC No. MA0013),"

September 8,1998.

5. Linville, J.C., USNRC, to L. Burkhardt, Ill, NMPC, "NRC Region I Combined Inspection Report Nos. 50-220/90-04 and 50-410/90-04," June 21,1990.

6. Brinkman, D.S., USNRC, to B.R. Sylvia, NMPC, " Issuance of Amendment for Nine Mile Point Nuclear Station Unit No.1 (TAC No. M81731)," October 14,1992.

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