ML19257B276
| ML19257B276 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 01/10/1980 |
| From: | Moody D Maine Yankee |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0578, RTR-NUREG-578 NUDOCS 8001150461 | |
| Download: ML19257B276 (4) | |
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' T5'4 B.3.2.1 January 10, 1980 WMY 80-8 United States Nuclear Regulatory Commission Washington, D. C.
20555 Attention:
Office of Nuclear Reactor Regulation Mr. Harold Denton, Director
References:
(a) License No. DPR-36 (Docket No. 50-309)
(b) NUREG-0578 - Lessons Learned Task Force Status Report and Short Term Recommendations dated July, 1979 (c) USNRC Letter to All Operating Nuclear Power Plants dated September 13, 1979 (d) USNRC Letter to All Operating Nuclear Power Plants dated October 30, 1979
Dear Sir:
Subject:
NUREG-0578, Item 2.1.9, Reactor Coolant System Venting References (c) and (d) in accordance with the recoc:mendation made in reference (b) relative to item 2.1.9, requested that information concerning the design and operation of reactor coolant system and reactor vessel head vents be provided.
Accordingly, the following information is submitted:
Maine Yankee will install equipment to vent both the reactor vessel head and the pressurizer by January 1,1981. This equipment will meet the requirements of NUREG-0578 as clarified by your letter of October 30, 1979.
Sketch A, attached provides a flow diagram of the proposed system.
The reactor vessel head vent consists of a motor operated valve installed downstream of an existing manual vent valve. A flow restrictor limits flow rates through the vent path to below the charging system makeup capability. The vessel head vent is piped to the pressurizer quench tank.
The pressurizer vent consists of an existing solenoid operated vent valve, block valve and associated piping which also discharges into the pressurizer quench tank. A rupture disk vents the quench tank to the containment. Maine Yankee is presently reviewing the qualifications of the solenoid operated relief valve and its associated block valve to determine if it meets, or can be upgraded to meet, the required design criteria.
If this criteria cannot be met, a motor operated valve with a suitable restriction orifice will be installed.
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United States Nuclear Regulatory Commission January 1, 1980 Attention:
Mr. Harold Denton, Director Page 2 The vent paths will be safety class I for all portions where a piping failure would result in a LOCA. In the reactor vessel vent portion, the piping downstream of the restriction up to and including the motor operated valve is safety class 2.
The valves meet the single failure criteria when considered together, i.e. two vent valves, one on the reactor vessel head and a redundant vent on the pressurizer. These vents will meet the requirements of IEEE-279 The following section addresses specific NRC design considerations specified in the October 30, 1979 clarification letter:
A.1 Maine Yankee's vent system has been designed to enhance the plants ability to provide core cooling and maintain containment integrity.
A.2 Procedures addressing the use of RCS vents will be provided by January 1,1981 or before the system is placed into operation, whichever is sooner.
C.1 The hot legs are vented thcough the reactor vessel head vent.
A procedure to insure that sufficient decay heat removal is provided in the U tube region will be provided by January 1, 1981. The vent system provides the capability to vent the pressurizer.
C.2 The nominal volume of the reactor coolant system is 11,000 ft3 while the nominal capacity of the single centrifugal charging pump is 120 gpm at operating pressure. It will take approximately 1 he ir to vent 50% of the reactor coolant system volume.
The reactor vessel venting portion of the system is designed such that an inadvertent opening of this valve will not exceed the makeup capacity of a single charging pump. This is accomplished by providing a flow restriction upstream of the motor operated reactor vessel vent valve.
The solenoid operated relief valve is a 21/2" valve rated at 150,000 lb/hr. at 2385 psig. The inadvertent opening of this valve would exceed the makeup capacity of a single charging pump and would result in the venting of 50% of the reactor coolant system in less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.
C.3 A flow restriction is provided at the reactor vessel vent location to limit RCS mass flow through the vent to less than the capacity of the charging system. The pressurizer solenoid operated relief valve is provided with a block valve which can be closed remotely.
C.4 The motor operated vent valve and the motor operated block valve will have direct position indication in the control room. The solenoid operated relief valve has direct indication provided by an acoustic accelerometer.
1749 322
United States Nuclear Regulatory Commission January 1, 1980 I
Attention:
Mr. Harold Denton, Director Page 3 C.5 Each vent will be remotely operated from the control room via operator action. However, power leads must be connected to the vent valves at the Motor Control Center which is located outside the control room and containment.
C.6 The vents will be seismically qualified.
C.7 The system is dasigned to appropriate safety grade requirements. The aotor operator reactor vessel vent valve and the solenoid operated relier valve will be powered from different emergency burses.
C.8 The block valve for the solenoid operated relief valve will have the same qualifications as the solenoid operated relief valve.
C.9 During normal operation, power is removed from the motor operated vent valve.
In addition, the valve will be key locked closed in the control room under administrative control.
The solenoid operated relief valve is normally closed while its block valve is normally open. Both valves are under administrative control.
C.19 Both the reactor vessel and the pressurizer vent discharge into the pressurizer quench tank which provides some cooling of the non-condensable gasses. This tank is equipped with a rupture disc which vents the tank to the containment.
The containment air recirculation fans discharge into a ring duct which directs air into the quench tank area for ventilation and mixing.
C.ll The inadvertent opening of the reactor vessel vent is an unlikely occurrence because of the system design and because of the administrative controls placed on system operation.
The inadvertent opening of this vent does not constitute a LOCA.
Direct position indication is sufficient to identify inadvertent operation.
The inadvertent opening of the pressurizer solanoid relief valve exceeds the makeup capacity of the charging system. An acoustic accelerometer will provide indication of inadvertent operation. The analysis of this type of accident was addressed in YAEC letter WMY 79-113 dated October 18, 1979.
(D. Moody to R. Reid).
We trust that this information is satisfactory; however, if you have additional questions, please contact us.
Very truly yours, MAINE YANKEE ATOMIC POWER COMPANY h
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Moody
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Manager of Operations EWJ/dmp
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