ML19289F599
| ML19289F599 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 06/08/1979 |
| From: | Groce R Maine Yankee |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| WMP-79-61, NUDOCS 7906150162 | |
| Download: ML19289F599 (4) | |
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...s F NelNCE R '.G Of F CE t317 -3U) '8011 DQ _. ; a O B.3.2.1 WMY 79-61 June 8, 1979 United States Nuclear Regulatory Conmission Washington 3 D. C.
20555 Attention: Office of Nuclear Reactor Regulation
References:
(a) License No. DPR-36 (Docket 50-309)
(bT LfAFC Letter to USNRC dated May 14, 1979
Dear Sir:
Subject:
un CSAS Signal We have completed our evaluation of a design change which will isolate component cooling (CCW) to the reactor coolant pumps on a containnent spray actuation signal (CSAS) rather than the present con-tainment isolation signal (CT.3).
This evaluation necessitates equipment modification to assure that in the event of a CCW line rupture inside the containac.nt missile barrier the primary CCW surge tank inventory will not be lost and suf ficient CCW systcm back pressure will be naintained to prevent contain=cnt air back leakage. A sur=ary of the design change is provided below and Draving SK-1 is attached for your inforration:
1.
The isolation signal on valves MOV-3404 (CCW supply line to containment), TV-3414 and TV-3415 (CCW return line from RC punps) will be changed f rom CIS to CSAS.
- 2.
An additional trip valve will be installed between MOV-3404 and the check valve outside containment. The valve will isolate on low CCW surge tank level and be capable of fast closure.
y 3.
Switches will be installed on the MCB to allow remote operation of TV-3414 and TV-3415, as well as the additional trip valve.
4.
Level instrumentation will be installed on the primary CCW curse tank to in;tlate the closure of the new trip valve, TV-3414, and 1V-3415 on low CCW surge tank level.
These design changes were the result of the following evaluations:
2229 097 7906150/M ;(
t United States Nuclear Regulatory Corr 'ssion June 8, 179 Attention: Office of Nuclear Reactor Regulation Page 2 A.
Effects of a ruptured CCW line inside the missile barrier CCW piping located inside the containment missile barrier is exposed to LOCA conditions and therefore susceptible to rupture.
If such a rupture did occur and the broken line was not isolated quickly, the CCW surge tank contents would be lost thereby dis-abling one CCW train.
Motor operated valve MOV-3404, which is a 150 lb. cast steel gate valve with a closure time of 54 seconds, isolates the CCW supply to components uithin the missile barrier.
The addition of a trip valve, capable of fast c1csure, in series with MOV-3404 will minimize less of the surge tank inventory. This valve will isolate on low primary CCW surge tank level.
Our evaluation shows that sufficient head is maintained at the bottom clevation of the prirary CCW surge tank to prevent con-tainment air back leakage through the CCW return line; further-more, isolation of valves TV-3414 and TV-3415 on CSAS and low CCW would also prevent containment air back leakage. Two check valves in series prevent back leakage through the CCW supply line to the RC pumps and motors.
B.
Effects of additional PCCW loads during an accident condition Initial accident flow requirements, prior to a recirculation actuation signal (RAS), are approximately 1000 gpm.
Upon RAS the CCW flow requirements increase to approximately 6000 gpm due to the required flow for the RHR heat exchanger.
The additional flow required to supply all three RC pumps and motors until CSAS is received is approximately 800 gpm.
The total CCW flow requirement of 6800 gpm approaches, but would not exceed the runout capability of the CCW pumps. This situation will occur if an RAS occurs prior to receiving a CSAS (CSAS would tnen isolate the 800 gpm flow to the RCPumps). The additional heat load of the RC pumps (~ 4.0 x 106 BTU /hr. or 4% increase in the accident heat load) can be accomodated by the additional flow.
Additionally, the operator has the option of utilizing an additional CCW heat exchanger, if desired.
Installation of the proposed equipment and changes in isolation signals will not make the plant less safe nor does it create an unrevicued safety issue as defined in 10CFR50.59.
The equipment proposed for this modification will be classified Safety 2229 098
United States Nuclear Regulatory Commission June 8, 1979 Attention: Office of Nuclear Reactor Regulation Page 3 Class 3 and IEEE Class 1E.
We propose to implement this design change during the next scheduled refueling outage.
Icplementation is also dependent on delivery of the IEEE 1cvel instrumentation which could take as long as 26 weeks to procure. 'We will provide a definite schedule for implementation when more inftrmation is available.
We reserve the right to re-evaluate our commitment to this design change, and modify it accordingly; providing additional infornation becomes available, or there is a change in your staff's position.
Very truly yours, MAINE YANKEE ATOMIC POWER COMPANY Kobert H. Groce Licensing Engineer REG /stw 2229 099
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