ML20069N922
| ML20069N922 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 06/17/1994 |
| From: | Cruse C BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9406230268 | |
| Download: ML20069N922 (4) | |
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Curutes Il. CuvsE Baltimore Gas and Electric Company Plant General Manager Calvert Chfs Nuclear Power Plant Calvert Chft Nuclear Power Plant 1650 Calvert Clifs Parkway Lusby, Maryland 20657 410 586-2200 Ext. 4101 Local 4to 260-4101 Baltimore June 17,1994 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
Document Control Desk SUllJECT:
Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 Reply to Request for Additional Information - Senice Water System Operational Psrformange Inspection
REFERENCE:
(a)
Letter from Mr. M. W. Hodges (NRC) to Mr. R. E. Denton (BGE), dated May 19,1994, Calvert Cliffs Units I and 2 Senice Water System Inspection (NRC Combined Inspection Report Nos. 50-317/94-80 and 50-318/94-80)
In Reference (a), you requested that we provide information related to our efforts to increase the margin available to support safety functions at peak bay temperatures. Attachment (1) is provided for your information and details the current status of our efforts. We have approved a revision to the Saltwatej System operating instructions. This revision credits a series of new saltwater differential pressure limits for the Senice Water 11 cat Exchangers that have been calculated to include changes in design basis assumptions and system configurations.
Should you have any further questions regarding this matter, we will be pleased to discuss them with you.
Very truly yours, CllC/JM0/dtm y
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Attachment cc:
D. A. Brune, Esquire J. E. Silberg, Esquire R. A. Capra, NRC D. G. Mcdonald, Jr., NRC T. T. Martin, NRC P. R. Wilson, NRC R.1. McLean, DNR p
J. II. Walter, PSC
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9406230268 940617
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t PDR ADOCK 05000317
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ATTACithfENT Q) '
l REPLY TO NRC REQUEST FOR INFORh1ATION SERVICE WATER SERVICE OPERATIONAL PERFORh!ANCE INSPECTION l
BAY TEMPERATURE LIMIT l
I.
IIACKGROUND As a result of testing performed to verify heat removal capabilities of the Senice Water (SRW) licat Exchangers (liX), we reported the possibility that they may not have been capable of meeting their intended safety function during certain past periods when bay temperature was greater than 78 F. Since the Senice Water System Operational Performance Inspection (SWSOPI) concluded, we have continued to address the low margin issue for SRW llX.
II.
NEW TRANSIENT ANALYSIS A.
Current Status l
The new transient analysis has been completed. The resuhs have been compared to the current bay temperature limit in Operating Instruction (01) 29, " Saltwater (SW) System" and the operability determination made in October 1993 which reduced the maximum bay temperature to 78'F. We have concluded that the results show that our original actions weie sufficiently conservative. A revision to 01-29 that credits the new transient analysis has been approved. This revision will permit plant operation at bay temperatures up to 87'F. We have installed new temporary pressure gauges to indicate SW difTerential pressure for the SRW llXs. This modification improves instrument accuracy and allows manual dampening of the oscillations that were present in the previously installed gauges.
In the near future, we will install new permanent differential pressure gauges. This modification will in prove instrument accuracy and dampen the oscillations that were present in the earlier permanently-installed gauges.
1.
Assumptions and Results of New Transient Analvsis The new SW differential pressure (dP) limits for the SRW IlX are derived in Design Calculation (Calc) M-94-32. The assumptions in Calc M-94-32 are l
essentially identical to those in Calc M-94-13 which you reviewed in detail during l
I the SWSOPl. In Calc M-94-13, we made the following assumptions:
a bay temperature of 87 F; clean Containment Air Coolers (CACs);
2 a 0.0012 F-ft -hr/ BTU fouling factor (microfouling);
I the loss of coolant accident (LOCA) containment temperature profile; and, an initial SRW temperature of 95 F.
Calc M-94-13 had already removed the known non-conservatisms from previous 2
SRW llX calculations and raised the design fouling factor to 0.0012 F-ft.
hr/ BTU. He primary purpose of Calc M-94-13 was to develop the methodology for ar.alyzing transient performance. The calculation used full SRW flow to 1
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1 ATTACIIMENT (1)
R2 PLY TO NRC REQUEST FOR INFORMATION i
SERVICE Wast?R SERVICE OPERATIONAL PERFORMANCE INSPECTION i
BAY TEMPERATURE LIMIT CACs and only evaluated a single bay temperature of 87 F.
The calculation provided a methodology and verified that lowering the bay temperature limit by 1I F was conservative.
Calc M-94-32 ha 5cen completed and approved since the SWSOPL It combines the transiev. analys methodology developed in Calc M-94-13 with the general approach used in Calc M-91-16 (reviewed during the SWSOPI) to develop SW dP limits for the SRW HXs. The only difference between the assumptions of the new transient analysis (Calc M-94 32) and Calc M-94-13 is the reduced SRW flow to i
the CACs during the initial stages of a LOCA. The modification that reduces SRW flow is derc6cd in II.A.2 below.
i The approach u:~i in Calc M-94-32 was to assume a fouling factor of 0.0012 F-f12.hr/ BTU (microfouling) and select a given bay temperature. Then the number of tubes available was reduced (macrofouling) until the SRW HX outlet temperature peaked at 115 F.
The emergency diesel-generator (EDG) manufacturer has reviewed this transient and concluded that EDG performance is not impacted. All SRW temperature transients were verified to return to 105'F within 25 minutes. The number of blocked tubes was then used to compute a set of dPs across the heat exchanger for a number of different flow rates during normal operation. This set of dPs established a new dP limit for the heat exchanger at the selected bay temperature. The calculation was repeated for a range of bay temperatures in 1*F increments to provide a series of new dP limits for 01-29.
Calc M-94-32 indicates that safe plant operation is possibic at a bay temperature up to 87 F. The uncertainties of the installed instrumentation scheme are included in the revised 01-29 dP limits.
t 2.
Modeling of Reduced SRW flow rates to Containment Air Coolers l
Since the SWSOP1 concluded, Units 1 and 2 have been modified per Facility Change Request (FCR)93-207 as follows:
SRW flow to the Containment Air Coolers (CACs) is automatically reduced during a Loss of Coolant Accident (LOCA) prior to the recirculation actuation signal (RAS).
After the RAS, full SRW flow to the CACs is automatically restored.
The FCR design package was reviewed during the SWSOPl. The reduced flows are analyzed in M-94-30 and M-94-31 using the hydraulic models which you reviewed during the SWSOPl.
Post modification testing verified the flow
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n A'ITACIIMENT (1)
REPLY TO NRC REQUFSF FOR INFORMATION SERVICE WATER SERVICE OPERATIONAL PERFORMANCE INSPECTION.
BAY TEMPERATURE LIMIT calculations. Calc M-94-32 uses these SRW flows to analyze the worst case accident heat loads of a LOCA.
B.
Use of Additional Marcin from New Transient Analysis Any additional margin has been applied to an increase in macrofoui:ng allowance, i.e., higher dP limits. In Calc M-94-32, the microfouling factor is astumed to be 2
0.0012 F-fl -hr/ BTU. The additional margin gained by both the modificatior, and the new transient analysis has been used to raise the dP limit and reduce the frequency of CRW HX tubesheet cleaning. The result is SW header availability will be increased.
III.
VERIFICATION OF FOULING FACTOR ASSUMPTION 2
The design SRW IIX fouling factor of 0.0012 F-ft.hr/ BTU was developed through extensive analyses and thermal performance testing. It includes adequate allowance for microfouling uncertainties and test result inaccuracies. It is consistent with Tubular Exchanger Manufacturers Association (TEMA) recommended practices.
We do not expect to be able to verify the fouling factor with thermal performance testing. Our conclusion is based on the inability to mathematically separate the effects of microfouling (fouling factor) and the area reduction effect of macrofouling. Additionally, thermal performance testing reduces SW header availability. Therefore, we are maintaining the current periodicity of 90 days for ilX bulleting pursuing other evaluation techniques.
We are evaluating other techniques for verifying the microfouling factor. One example of an evaluation technique that shows promise is a side-stream monitor. This device is essentially a single tube heat exchanger that is precisely modeled and operated to reflect a system's thennal hydraulic conditions. Its advantage is that it should allow us to continuously monitor fouling factors and microfouling rates without affecting SW header availability. Such information could be used to further revise SRW HX operating limits.
Additionally, in the near future, we anticipate that the State of Maryland will approve our use of Clamtrol, a chemical biocide. We expect Clamtrol to slow fouling build-up. A maximum fouling 2
factor of 0.0012 F-ft -hr/ BTU will remain in the design calculations until firm empirical data is available to substantiate different values.
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