ML20138H899
| ML20138H899 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 12/10/1985 |
| From: | Whittier G Maine Yankee |
| To: | Heltemes C NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| References | |
| 6723L-FWS, GDW-85-309, MN-85-207, NUDOCS 8512170366 | |
| Download: ML20138H899 (4) | |
Text
MAIRE HARHEE ATOMICPOWERCOMPARUe avausrl 0*S"a 5 (207) 623-3521 December 10, 1985 R4-85-207 GDW-85-309 United States Nuclear Regulatory Commission Office of Analysis and Evaluation of Operational Data Washington, D. C.
20555 Attention:
Mr. Clemens J. Heltemes, Jr., Director
References:
(a) License No. OPR-36 (Docket No. 50-309)
(b) MYAPCo Letter to USNRC dated July 26, 1985 - Maine Yankee Licensee Event Report 85-006 Emergency Diesel Generator Cooling System Deficiencies
Subject:
Additional Information on Resolution of Diesel Generator Cooling Water Event Gentlemen:
During a recent visit to Maine Yankee, Messers E. Leeds, and S. Ruben of your staff requested that we provide a summary of our action and evaluation concerning cooling water for our emergency diesel generators. Their visit was a follow-up-to a Maine Yankee LER, Reference. (b).
Attached for your information is the summary based upon a report from our associated company, Yankee Atomic Electric, Nuclear Services Division.
We hope that you find it useful.
Very truly yours, MAltE YANKEE ATOMIC POWER C0t43ANY 8512170366 05 09 ADOCK 05 PDR G. D. Whittier, Manager PDR S
Nuclear Engineering & Licensing GDW/bjp
Enclosure:
(3 Pages)
[(
cc: Mr. Ashok Thadani Dr. Thomas E. MJrley Mr. Cornelius F. Holden b DD'.
l 6723L-FWS
. MAINE YANKEE ATOMIC POWER COMPANV ATTACHMENT
SUMMARY
- This report concerns a deficiency in the design of the component cooling water control scheme for the emergency diesel engines and supplements information provided in LER 85-006-00.
BACKGROUto - Status Prior to Corrective Action The diesel engines are cooled by separate CCW trains; PCCW cools Diesel A and SCCW cools Diesel.B.
Temperature Control Valves TCV-1730A and TCV-1730B modulate the CCW flow when the diesels are operating to maintain a 25of delta T across the heat exchangers. The operating mode of the control valves is air-to-open and fail closed on loss of air. The safety-grade air supply to both TCVs and controllers is provided from the diesel starting air _ tanks through a common air line having a single
. pressure reducing valve, DG-P-61 (PCV-2701). Failure of this reducing valve could cause both temperature control valves to travel closed resulting in loss of cooling water to both diesels (existing service air hackup is NNS and nonseismic).
An additional problem exists with the CCW to fire water cooling transfer-
' control circuit. An engine jacket water temperature of 190oF will-automatically open the associated Fire System inlet / outlet valves and -
close the CCW control valve. This causes a loss of cooling water to the'-
associated diesel since the Fire System is maintained isolated. The control circuit for the CCW cannot be reset until the jacket water
' temperature is at or below 180oF.
ACTION The. component cooling water TCVs at each diesel cooler outlet have been blocked open to allow continuous full flow to the heat exchangers.
Continuous full flow has been reviewed for-impact on overchilling of lube oil and jacket water, maximum flow velocity causing erosion of heat exchanger tubes, and increased flow demand on the CCW Systems. A summary of our evaluation follows.
1.
Chilling of Lube Oil and Jacket Water General Motors, Electro Wtive Division, representatives agreed via telecon that full CCW flow to the heat exchangers (tube side) will not adversely impact jacket water and lube oil temperature. The' self-contained AMOT thermostatic mixer valve located in the diesel jacket-water system regulates' the temperature of the jacket water, not the CCW temperature control scheme. When the diesels are in standby, the mixer valve is in the full bypass position around the heat exchanger and the jacket water circulation pumps are off. When a diesel is running, the mixer valve regulates the amount of jacket water flow to the heat exchanger (shell side) to maintain about 180oF. This is done independent of CCW flow and temperature.
6723L-FNS
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MAINE YANKEE ATOMIC POWER COMPANY 2.
Maximum Heat Exchanger Velocity The maximum obtainable flow rate with the CCW TCVs fully open will not exceed the design flow rate of the heat exchangers. A calculation was performed to determine the maximum flow rate which could be delivered by the diesel cooling water piping. The calculation conservatively assumed an available pressure head equal to the shutoff head of the CCW pumps (approximately 238. feet). This achieved a maximum flow rate of approximately 700 gpm total. Each
. diesel has two heat exchangers connected in parallel, therefore, approximately 350 gpm would flow through each heat exchanger. This is below the manufacturer's maximum permissible flow rate, therefore, tube erosion should not be a concern.
3.
Flow Demand on CCW Systems-An assessment of the increased CCW flow demand was conducted to estimate the potential for starving other loads with full flow to the diesels. The estimated minimum flow to the diesels is. aproximately 520 gpm. This occurs when the CCW pumps are supplying normal plant loads or safeguard loads estimated at 6,500 gpm total flow. The total swing in diesel flow across the entire pump curve is, therefore, approximately 180 gpm (700 at shutof f, ~520 at runout).
100 gpm on the pump curve results in only a 4 feet to 5 feet change in TDH. Therefore, full CCW flow to the diesels should not significantly affect flow distribution to other cooling loads. The CCW estimated flow rates are documented in Calculation MYC-681.
SAFETY EVALUATION The PCCW System is classified SC-3.
The portion of the SCCW System which provides safeguards cooling ~1s also SC-3.
Cooling water flow to the diesel heat exchangers, E-82A,.and B, is essential to ensure proper operation of the emergency diesel generators.
Blocking open the TCVs to allow continuous full flow will improve the reliability of the diesels. Cooling water flow control will not be subject to a single active common mode failure. Also, a hot jacket water temperature will not isolate the associated TCV, causing loss of heat sink to a single diesel. Continuous flow to the diesel heat exchangers is acceptable with regard to its impact on lube oil and jacket water temperature, tube erosion due to the increased velocity and added CCW flow demand as discussed above.
Accordingly, this action does not constitute unreviewed safety questions as defined in 10 CFR 50.59(a)(2) as defined below:
a.
The modification does not increase the probability of occurrence or
- the consequences of an accident.
b.
The modification does not create the possibility of an accident or malfunction of a different type than previosuly evaluated in the Safety Analysis Report.
6723L-FWS
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MAINE YANKEE ATOMIC POWER COMPANY
..The modifica' tion 'does not decrease the margin of safety as defined in c.
the Technical Specifications.
'This' change ' doe's not create an unreviewed safety question as defined -in
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