ML17262A920
| ML17262A920 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 07/02/1992 |
| From: | Mecredy R ROCHESTER GAS & ELECTRIC CORP. |
| To: | Andrea Johnson Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9207090160 | |
| Download: ML17262A920 (9) | |
Text
ACCELERATED DISTRIBUTION DEMONSTE&TION SYSTEM REGULATO INFORMATION DISTRIBUTION STEM (RIDS)
ACCESSION NQR:9207090160 DOC.DATE: 92/07/02 NOTARIZED: NO DOCKET CIL:56-244, Robert Emmet Ginna Nuclear Plant, Unit 1, Rochester G
05000244 UTH.NAME AUTHOR AFFILIATION CREDY,R.C.
Rochester Gas 6 Electric Corp.
RECIP.NAME RECIPIENT AFFILIATION JOHNSONPA.R.
Project Directorate I-3
SUBJECT:
Provides update of progress re evaluation
& enhancement of hydraulic flow balancing of service water sys for util in response to NRCs SWSOPI team rept 50-244/91-201 dtd 920130.
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Ilute ROCHESTER GAS AND ELECTRIC CORPORATION o
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rite 89 EAST AVENUE, ROCHESTER N.Y. 14649-0001 ROBERT C MECREDY Vice President Clnne Nudeer Production Ji ly 2, 1992 TELEPHOkE AREACODE 718 546 2700 U.S. Nuclear Regulatory Commission Document Control Desk Attn:
Allen R. Johnson Project Directorate I-3 Washington, D.C.
20555
Subject:
Service Water System Operational Performance Inspection (SWSOPI)
Re-balancing of Flow to Safety-Related Coolers R. E. Ginna Nuclear Power Plant Docket No. 50-244 Ref.(a):
Letter from R.
E. Smith, RG&E, to A.
R. Johnson,
- NRC,
Subject:
Re-Balancing of Flow to Safety-Related
- Coolers, dated 1/31/92 (b)-
Letter from Robert E. Smith, RG&E, to James C. Linville, NRC Region I,
Subject:
Response to Notice of Violations, NRC Inspection Report 92-02, dated May 4, 1992
Dear Mr. Johnson:
This letter provides an update of our progress regarding the evaluation and enhancement of the hydraulic flow balancing of the service water system for the R.E.Ginna Nuclear Power Plant.
This activity is in response to concerns raised by NRC's SWSOPI Team Inspection (50-244/91-201 dated January 30, 1992).
RG&E has assessed the existing flow balance for service water system flow to the Emergency Diesel Generator (D/G) coolers and determined that the existing flow balance is satisfactory and that no change to these service water system flows is warranted at this time.
RG&E is still evaluating the overall service water system hydraulic flow balance and is planning to confirm the overall hydraulic balancing of the service water system as part of our 1993 refueling outage as previously stated.
in Reference (a) and reiterated in Reference (b).
Our evaluation to date indicates:
1.
Hydraulic Performance of the Diesel Generator Service Water System Coolers Hydraulic testing and flow measurements of these coolers indicate that for normal operation as well as the accident condition (safety injection concurrent with an undervoltage condition) flow to the Diesel Generator coolers is I'DR 9>O~Oa '-".-;
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approximately 550 gpm.
This is well in excess of the design flow for these coolers of 320 gpm and assures that service water flow to the Diesel Generators will exceed the minimum required design flow.
No Apparent Adverse Effects to Service Water System Diesel Generator Coolers Review of maintenance and eddy current inspections of the service water system Diesel Generator coolers indicate that the actual flow to the coolers, which exceeds the design flow by 230 gpm (item 1), has had no apparent adverse effects upon the coolers.
Specifically, visual examinations have shown no excessive wear of shell, tubesheet, or baffle components and eddy current testing has resulted in plugging of only one tube to date.
Plugging was the result of general/pitting type corrosion; not erosion due to high flow velocities or eddying.
Hydraulic Performance. of Diesel Generator Service Water System Coolers at time of plant licensing The NRC SWSOPI team was concerned during their inspection that the current hydraulic lineup of the Diesel Generator service water coolers is significantly different than originally established by the service water system startup test program in 1968.
Closer review of the original startup test reports indicates that, during the original hydraulic flow balancing of the service water system, the hydraulic balancing and flows for the Diesel Generator coolers were essentially the same as the present time.
Specifically, the original startup test report indicates that the discharge throttle valves for the Diesel Generator coolers were left wide open and the cooler inlet pressures and
'IPs were about 43 psig and 21 psid.
respectively.
(No flow measurements were available at that time).
Currently these are the same conditions under which flows of 550 gpm are measured for the coolers.
Preferential Tendency to Biofouling RGGE's experience with biofouling due to introduction of Zebra Mussels into the Great Lakes has indicated that the Diesel Generator coolers tend to be the first affected by biofouling because of their relatively small tube diameter as compared to other service water system heat exchangers.
The Diesel Generator coolers have been the only safety related service water system heat exchangers significantly affected to date by Zebra Mussel fouling.
The additional flow to these coolers above that required by design provides a margin for assured operability during periods of heavy biofouling'(due to heavy mortality at the start of a biocide injection period),
to allow increased time for plant remedial actions such as
5 Na
the coolers. It also provides added assurance that biofouling will not pose a potential problem during a loss-of-offsite power event.
Critical Nature of the Demand for Service Water, System Cooling A review of the cooling demands for service water system cooling during Design-Basis accident conditions indicates that the Diesel Generators are limiting in terms of degradation or loss of service water flow.
Specifically, during a plant transient following a safety injection signal concurrent with an undervoltage condition, there are a number of service water loads which continue 'to be supplied with service water and are not interrupted by the initiation of the transient.
The loads that are safety-related.
are:
the Diesel Generator coolers; the Containment Air coolers; the Pump Area coolers; and equipment cooling for the safety injection
- pumps and the motor-driven and turbine-driven auxiliary feedwater pumps.
The Diesel Generators produce an immediate cooling demand as soon as they are energized and loaded.
Loss or degradation of cooling flow could result in the loss of emergency power 'to critical core cooling components.
The time for restoration of service water cooling to the Diesel Generators without adverse consequences is limited.
Sensitivity analyses of containment heat removal indicate that for the three heat sinks available to the containment (Containment Air coolers, Containment Sprays, and Structures) the Containment Air coolers provide the least benefit early in the transient and have little effect on peak containment
'pressure.
- Hence, a degradation of service water system flow to the Containment Air coolers, although not desirable, can be tolerated while operator corrective actions are taken.
Equipment cooling for the safety injection pumps is not required for the injection phase of the accident, since the pumped fluid, supplied by the Refueling Water Storage
- Tank, provides the necessary cooling for the pump internals and limits bearing heatup.
The Pump Area coolers have also been shown by analysis not to be essential during the injection or recirculation phases post accident.
The amount of service water flow to the motor-driven and turbine-driven auxiliary feedwater pumps is small.
Fluctuations in the flow balance to the more significant service water loads will not greatly affect the auxiliary feedwater pump
- demands, since these supply lines are small.
6.
No Adverse Effect on Associated Service Water System Equipment Evaluations conducted in conjunction with RG&E's review and confirmation of the basis for our service water system Technical Specifications also indicate that the excess flow to the Diesel Generator coolers does not adversely divert flow from other service water system cooling demands during the injection phase of the postulated accident.
Specifically, the evaluations show that there is still adequate cooling capability to limit containment pressure via a combination of containment spray and Containment Air coolers.
Therefore, since initial plant startup, there has been a surplus of service water flow to the Diesel Generator coolers.
That surplus flow provides added cooling margin beyond the design flow against biofouling and other potential causes of flow degradation to the Diesel Generator coolers.
These safety related coolers are not only critical to the safe shutdown of the unit, but also limited in their capability to withstand an interruption of.service water flow.
Furthermore, the surplus flow has produced no evidence of having adversely affected the performance of the Diesel Generator coolers or the associated service water system cooling demands which might receive an increase in service water flow if flow to the Diesel Generator coolers were to be throttled.
Based on the
- above, RG&E believes that optimal performance and safety margins result from maintaining the hydraulic flow balance for the Diesel Generator coolers as is presently balanced.
Very truly yours, GAH/235 Robert C. Mecredy xc Mr. Allen R. Johnson (Mail Stop 14D1)
Project Directorate I-3 Washington, D.C.
20555 U.S. Nuclear Regulatory Commiss'ion Region I 475 Allendale Road King of Prussia; PA 19406 US NRC Ginna Senior Resident Inspector
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