ML13331B159
| ML13331B159 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 04/01/1989 |
| From: | Nandy F SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 8904050347 | |
| Download: ML13331B159 (3) | |
Text
0g Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD, CALIFORNIA 91770 F. R. NANDY TELEPHONE MANAGER OF NUCLEAR LICENSING April 1, 1989 18181 302-189 U. S. Nuclear Regulatory Commission Attention:
Document Control Desk Washington, D.C.
20555 Gentlemen:
Subject:
Docket No. 50-206 Additional Information Regarding Amendment Application No. 164 Design Details of Reactor Coolant Pump Undercurrent and Overcurrent Trips San Onofre Nuclear Generating Station Unit 1 Supplement 2 and Supplement 3 to Amendment Application No. 164 were submitted to the NRC on March 4 and March 11, 1989, respectively. Those supplements added, among other things, Technical Specifications regarding the overcurrent and undercurrent Reactor Coolant Pump (RCP) trips which were being installed as an input to the RCP breaker open reactor trip.
These new inputs are designed to provide backup protection to the low flow reactor trip to protect against RCP locked rotor and sheared shaft events.
This letter provides additional design details for those trips and specifies a revision of the settings as they appear in the technical specifications.
An undercurrent relay (A phase only), a supplemental overcurrent relay (C phase only), a time delay relay and an auxiliary relay are being added in each RCP breaker control circuit to provide RCP breaker trips in the event of an RCP failure. These relays are being installed in 4160V Switchgear #lA and #lB cubicles 11AO1, 11A03, and 11803 for RCPs G-2C, G-2A and G-2B, respectively.
In addition, an indicating light will be installed in the front panel of each RCP switchgear cubicle to provide positive indication of undercurrent or overcurrent relay operation.
The addition of the undercurrent, supplemental overcurrent, time delay and auxiliary relays will ensure that an RCP breaker trip and a consequent reactor trip occur within 6 seconds following a reactor coolant pump sheared shaft or seized rotor failure.
On a sheared shaft event, the undercurrent relay will trip the RCP breaker when the motor current falls below the undercurrent setpoint value.
The limit for the setting established by the proposed technical specification is the no load current of 110 amps at 4160V. Since the time delay associated with this setpoint does not depend on bus voltage, the indication in the previously proposed technical specification should be changed to remove any reference to the bus voltage. This change is reflected in the enclosed revised table. The actual setting will be above this value and will be based on this value, the 8904050347.890401
,qc PDR ADOCK 05000206 P
Document Control Desk
-2 rated full load current of 506 amps at rated voltage, the 362 amps running current measured during a load monitoring program, system voltage fluctuations and current transformer and relay accuracy factors. A one second time delay in the undercurrent trip relay eliminates potential lockout of the circuit breaker and spurious indication of undercurrent relay operation that could result due to possible race between the time delay relay and the undercurrent relay on breaker normal trip.
For the rotor seizure event, the maximum setting established by the proposed technical specification change assures that the supplemental overcurrent relay will trip the RCP breaker when motor current exceeds the setpoint value.
However, the value proposed in our March 4, 1989 letter for the overcurrent setting (i.e., 2900 amps at 4160 volts) may be misleading and should be changed to "2400 amps."
The 2900 amp at 4160 volts value indicates the equivalent amperage at 4160 volts of a much lower actual trip setting at an assumed lower bus voltage. A revised page change for this proposed technical specification change is enclosed. This overcurrent safety limit of 2400 amps is based on worst expected degraded grid voltage conditions. The actual setpoint will be below this value to account for current transformer and relay accuracy factors. A constant (i.e., not inversely dependent on current) three second time delay for the supplemental overcurrent relay is provided to allow it to ride through momentary voltage dips.
The time delay relay will prevent spurious trips by disarming the undercurrent and overcurrent trip circuit during the motor starting period. The undercurrent relay contact, initially closed on a tripped breaker condition, would remain closed until the current setpoint value is exceeded, and the supplemental overcurrent relay contact would close on starting current. Both relay contacts fail open upon loss of control power to their respective solid state relays, thus minimizing spurious reactor coolant pump trips.
If you need additional information, please contact me.
Very truly yours, Enclosure cc:
- 3. B. Martin, Regional Administrator, NRC Region V F. R. Huey, NRC Senior Resident Inspector, San Onofre Units 1, 2 and 3 J. H. Hickman, California Department of Health Services
Enclosure TABLE 2.1 MAXIMUM SAFETY SYSTEM SETTINGS Three Reactor Coolant Pumps Operating
- 1. Pressurizer
< 20.8 ft. above bottom of pressurizer High Level when steam/feedflow mismatch trip is not credited, or
< 27.3 ft. above bottom of pressurizer when steam/feedflow mismatch trip is credited
- 2. Pressurizer
< 2220 psig Pressure: High
- 3. Nuclear Overpower
- a. High Setting**
< 109% of indicated full power
- b. Low Setting
< 25% of indicated full power
- 4. Variable Low Pressure
> 26.15 (0.894 AT+T avg.) - 14341
- 5. Coolant Flow
> 85% of indicated full loop flow
- 6. Reactor Coolant Pump Breaker Open
- a. Overcurrent
< 2400 amps
- b. Undercurrent
> 110 amps
- c. Undervoltage
> 60% of rated bus voltage Credit can be taken for the steam/feedflow mismatch trip when this system is modified such that a single failure will not prevent the system from performing its safety function.
The nuclear overpower trip is based upon a symmetrical power distribution.
If an asymmetric power distribution greater than 5% should occur, the nuclear overpower trip on all channels shall be reduced one percent for each percent above 5%.
May be bypassed at power levels below 10% of full power.
SAN ONOFRE -
UNIT 1 AMENDMENT NO.