ML19317F218
| ML19317F218 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 08/25/1970 |
| From: | Morris P US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Price H US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8001080930 | |
| Download: ML19317F218 (4) | |
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AUG 2 51970 Harold L. Price, Director of Regulation MODIFICATION OF THE OCONEE CORE FLOODING LINE MOTOR-OPERATED VALVES, DOCKET 3 50-26)., 50-270, AND 50-287 We plan to require modification of the B&W core flooding tank system design starting with Oconee Unit 1.
Based on discussions with Duke Power Company, the Oconee units can be modified to confom with this position. The proposed modification and the basis for the change are discussed in the attached memorandum.
Since this modification represents a change to the design that was reviewed at the construction permit stage, it would repre-i sent backfit, and therefore you may wish to discuss this require-ment with the Commission.
Original Signed by Peter A. Morris Peter A. Morris, Director Division of Reactor Licensing
Enclosure:
Eecommendation Distribution:
Docket (3)
DRL Reading PWR-2' Reading FSchroeder TRWilson RCDeYoung RSBeyd RWKlecker Attorney, OGC DRL/PWR Branch Chiefs ASchwencer CKBeck MMHann CLHenderson SHanauer
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Form AEC-Sls (Rev.9-33) ABCM 0240 m.s. novenement, esse..e er,ma, eee e-ase-so 8001088f30 g
RECOMMENDED MODIFICATION TO THE MOTOR-OPERATcD VALVES IN B&W SYSTEM CORE FLOODING LINES
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Background===
To date all B&W system core flooding lines have one motor-operated valve and two check valves in series between the core flooding tank and the reactor pressure vessel. Figure 1 shows the Duke Oconee system which is typical. This arrangement has been approved without exception to date.
F cent examination, however, has raised the question of the possibility of inadvertent closure of this motor-operated valve during normal plant operation. This valve is required to be full open during normal opera-tion to permit emergency cooling immediately, if required.
It also is required to be. closed to isolate the core flooding tank from the reactor coolant system both during startup and shutdown to prevent unwanted and undesirable changes in boron concentration in the reactor coolant. The normal procedure would be for the operator to close the valve at some point slightly above 600 psig on the system cooldown and open the valve i:
above 600 psig on system startup. Thus, it can be seen that it is im-possible to eliminate the valve from the design or to lock this valve
.open prior to operation.
The ACRS recently considered this problem in connection with their review '
of the VEPCO, North Anna Power Station Units 1 and 2.
The Committee stated in their letter to the Chairman that: "... the lines connecting each accumulator to the remainder of its piping system contain a normally open motor-operated valve.
Since inadvertent closing of these valves would seriously degrade emergency core cooling capability, the Committee believes that more positive assurance of proper valve function should be provided."
Discussion We have explored several possible ways te assure that this valve will remain open whenever the reactor pressure is abcve 600 psig:
1)
Position indication is very important. There should be two inde-Since pendent means of detecting and displaying valve position.
rate of flow is important, these means of detecting valve position should provide for control room alarm annunciations whenever the valve is not fully _open.
2)
To provide further assurance that the valve cannot be inadvertently closed by operator action or system failure, the electrical power required to close the valve should be positively locked out at the motor control center. Care must be taken that this action does not eliminate either ons~of ~the two independent valve position indica-tion means discussed above. It is probable that the power to one i
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set of.the position indicators presently is derived from the same motor control center circuit breaker that operates the valve motor.
'Where this is be provided to the position indicators.the case, a separate source of p 3)
We have considered adding an automatic valve opening signal to command the valve to open (if inadvertently in the closed position) upon receipt 6f an engineered safeguard signal.
this for two reasons.
We decided against (1)
It necessitates keeping the valve motor connected to its source of power at all times, thereby increasing the possi-bility that some active electrical control or protection circuit failure could close the valve.
(2)
The nature of motor operated valve is such that significant time would be required to fully open a fully closed valve i
Some loss-of-coolant accidents require core ficoding tanks to start injection within 5 seconds (double ended hot break) whereas emergency power to start opening the valve leg (if closed) would not be available that soon (for Duke Oconee emergency power can be established withir 2' seconds following a LOCA).
4)
We have not considered the use of redundant valves and line the reactor pressure vessel because the need to close these val during startup and shutdown would still exist, ves impossible to eliminate a-common mode failure (operator error) thus making it that could still cause both valves to be inadvertently closed long as power is available to operate the valves.
so Recommendation Based on the above, we recommend that for B&W plants the followin closed during reactor operation:a reasonable and practical modification to a g is 1)
The power supply to the valve operator shall be locked out whenever the reactor coolant pressure is above 600 psig.
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2)
There shall be two independent means of determining valve position each of which shall utilize separate detectors and separate power supplies.
3)
In addition to the above, at any time the valve is not in the fully open position, this fact shall be alarmed to the operator in the ciated to the operator. control room in the same manner that protective alarm
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