ML13331B185
| ML13331B185 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 06/13/1989 |
| From: | SOUTHERN CALIFORNIA EDISON CO. |
| To: | |
| Shared Package | |
| ML13331B183 | List: |
| References | |
| NUDOCS 8906190033 | |
| Download: ML13331B185 (5) | |
Text
ATTACHMENT 2 PROPOSED TECHNICAL SPECIFICATION P
61:3 pDR ADOCK :O5OD?:
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TABLE 3.5.7-2 AUXILIARY FEEDWATER INSTRUMENTATION SETPOINTS FUNCTIONAL UNIT TRIP SETPOINT ALLOWABLE VALUES
- a. Manual Actuation Not Applicable Not Applicable
- b. Automatic Actuation Logic Not Applicable Not Applicable
- c. Steam Generator Water Level-Low
> 5% of narrow range
> 0% of narrow range instrument span for each instrument span for each steam generator steam generator
- d. AFW Train Interlocks
- i.
Decreasing Flow in Train B/
Start Train A Flow 23 gpm*
> 10 gpm ii. Increasing Flow in Train B/
Stop Train A Flow 37 gpm*
< 48 gpm
- Each flow switch monitoring Train B flow utilizes its set and reset points for permissive signals for starting and stopping Train A.
ATTACHMENT 3 DETAILED DESIGN DESCRIPTION (Conversion of Steam Generator Wide Range Level Transmitters to Narrow Range)
REASON FOR CHANGE The change is being prepared to prevent the recurrence of an unexpected automatic auxiliary feedwater actuation that occurred with the recently upgraded Wide Range (WR) instruments during normal plant power ascension. On May 25, 1989 during an ascension to 25%
power to perform Auxiliary Feedwater (AFW) system tests, Train A WR actuated the AFW system while the steam generator was operating within its normal range, as indicated on the Narrow Range (NR) instrumentation. Subsequent to the actuation, the WR indicators were determined to be reading substantially lower than the NR indicators. At the time of the actuation the steam generator levels were being controlled at approximately 42% of NR as prescribed in the operating procedure. At that time, the Train A Steam Generator level signals (A and B channels from WR transmitters) dropped below 238 inches (equivalent to 5% NR) and actuated the Train A AFW system.
The level transmitters are differential pressure devices which indicate level inferentially from differential pressure readings across sensing points in the steam generator. The measurement from the transmitters is affected by internal circulating flows through the downcomer section of the steam generator (and resultant pressure drops) and density changes of water. The effects of density changes were correctly accounted for in the design calculations and the calibration records for the transmitters. They are hot calibrated for full power operation and read approximately 15 inches lower at low power (as expected).
The effects of internal steam generator circulation flow on the transmitters were not previously considered.
The differential pressure associated with the internal flow circulation is a function of feed flow rate, actual level in the steam generator, and the steam flow rate out of the generator. The decalibration effect on the wide range level instrument resulting from interaction of these variables during a transient will result in erroneous level indications which may result in confusion to the operators. In addition, the steady state indications are lower than actual steam generator levels and will cause false actuation of the AFW system and inhibit high level turbine trips.
The existing (cold calibrated) WR high level alarm and turbine trip/feed isolation signal is also offset by the internal flow in the steam generator and inhibited the trip from actuating at the existing level setpoint.
-2 The purpose of the change is to provide a remote level measurement for AFW actuation which is unaffected by internal flow conditions in the steam generator. The new measurement will be provided from NR transmitters because the NR pressure sensing taps are not affected by the large pressure drops associated with the downcomer flows.
The NR transmitters will provide redundant indication to the operators, a second channel for high level alarming and turbine trip/feed isolation, and automatic actuation of the auxiliary feedwater system.
EXISTING DESCRIPTION Each steam generator is currently provided with three wide range (WR) level channels and one narrow range (NR) level channel in the control room.
(An additional WR channel provides level indication at the remote shutdown panel.) Two WR channels (LT-2400 A, B, & C and LT-3400 A, B, & C) are safety related (SR), environmentally qualified, and provide low level input signals to the two trains of Auxiliary Feedwater Auto Initiation Circuitry. Theses two WR channels also provided post-accident monitoring information to meet TMI and Regulatory Guide 1.97 requirements. The third WR channel (LT-450, LT-451, LT-452) provides a high level signal to the main feedwater control system for high level alarm and turbine trip/feedwater isolation function. The NR channel (LT-453, LT-454, LT-455) provides a signal to the main feedwater control system and also provides a redundant signal for the high level alarm and turbine trip/feedwater isolation function.
DESIGN DESCRIPTION The modification consists of converting the existing Safety Related (SR) WR level transmitters (LT-2400 A, B, & C and LT-3400 A, B, & C) to NR transmitters to provide automatic actuation of the AFW system.
The WR channels (LT-3400 A, B, & C) will be modified to provide a redundant channel for the high level alarm and turbine trip/feedwater isolation on each steam generator. This will replace the function of the existing WR level transmitter (LT-450 LT-451 LT 452) for the high level alarm and turbine trip/feedwater isolation functions.
In addition, this modification adds a new qualified Train A SR wide range level loop (LT-465 A, B, & C) for post accident monitoring information to meet TMI requirements for backup AFW flow indication to the steam generators and Regulatory Guide 1.97 requirements.
DESIGN DETAILS This proposed change consists of reconverting Steam Generator level loops LT-2400 A, B, C and LT-3400 A, B, C from wide range back to narrow range, adding new Train A safety related and environmentally qualified wide range level loops LT-465 A, B, C and replacing the existing wide range level trips from LT-450, 451, 452 with isolated trips/alarms from Train B narrow range loops LT-3400 A, B, & C.
These changes are discussed below:
-3
- 1.
The existing wide range SG level loops LT-2400 A, B, & C and LT-3400 A, B, & C will be converted back to narrow range.
Six new narrow range transmitters will be installed and tagged LT 2400 A, B, & C and LT-3400 A, B, & C at the required instrument location with new instrument tubing installed to tie into the narrow range taps. A new conduit will be installed from the existing junction boxes to these transmitters to reconnect the cabling. A qualified field splice will be made in the junction boxes. The loops and indicators will be rescaled to narrow range. The existing WR level transmitters which were LT-3400 A, B, & C will be removed and their tubing and conduit capped.
- 2.
The existing WR level transmitters which were LT-2400 A, B, & C will be retagged new WR level loops LT-465 A, B, & C using existing tubing and conduit. New environmentally qualified instrument cables will be installed from control room panel C69 to electrical penetration EI-4 to the transmitters. New Train A conduit will be installed from C69 to EI-4 for all three cables. Inside of containment existing Train A raceways will be used. New Foxboro I/V cards will be installed in C69 which is powered from vital bus 3A. New instrument cables will be routed in conduit which was installed in PFC 1-89-017 from C69 to C71.
The existing Train A Sigma level indicators for LI 2400 A, B, & C will be replaced with dual Sigma indicators which will have both WR and NR LI-465 A, B, & C and LI-2400 A, B, & C.
- 3.
After level loops LT-3400 A, B, & C are reconverted to narrow range, these Train B loops will be used as part of the 2/2 high Steam Generator level turbine trip initiation logic.
The existing wide range level loops LT-450, 451 and 452 will be taken out of their high SG level trip and alarm functions. New Foxboro contact isolation cards will be installed in panel C70 to provide electrically isolated contacts to the high Steam Generator level trip circuitry in panel C37.
Two new conduits (one Train A and one Train B installed by PFC 1-89-017 will be used to route the trip and alarm circuits. Spare dual alarm cards in C70 will provide the high Steam Generator level setpoint to operate the contact isolation cards.
The existing bistables and relays (LC-450C, LC-451C, LC-452C, LC-450CX, LC 451CX and LC-452CX) will be disconnected from panel C24 and spared in panel C37. Wide Range loops LT-450, 451, 452 will be used for Indication only (cold calibrated).