ML19256G364
| ML19256G364 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 12/19/1979 |
| From: | Swart F PUBLIC SERVICE CO. OF COLORADO |
| To: | Vassallo D Office of Nuclear Reactor Regulation |
| References | |
| P-79264, NUDOCS 7912310175 | |
| Download: ML19256G364 (4) | |
Text
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public service company ou' cdonde December 19, 1979 Fort St. Vrain Unit No. 1 P-79264 fir. Domenic B. Vassallo, Acting Director Division of Project Management Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission liashington, D.C.
20555 Docket #50-267
Reference:
Letter Fuller /Denise 1/13/78 Letter Spies / Fuller 5/4/79 Meeting:
Bethesada 8/20/79
Dear Mr. Vassallo:
In the references, a number of items were discussed which require a response by PSC.
This memo addresses those items, and PSC now considers them closed.
1.
PCRV Relief Valve Vent Line and Filter.
These were discussed as to their availability to perform their function after a seismic event.
The Vent Line and Filter at Fort St. Vrain are not classified as Class I Seismic.
To determine their ability to remain operational in the event of a seismic event, we analyzed them using the same criteria for Class I equipment within the plant.
The analysis indicates that the relief line and filter are mounted so that they meet the criteria required for Class I seismic equipment.
2.
Moisture Monitors.
In the past, we have experienced false trips and indications that moisture within the PCRV was above a desirable range or above the allowable limit.
False trips were also caused during surveillance testing when the test signal was applied to only one of the three channel monitors.
Line noise and internal module generated noise has also been a source of trouble.
During maintenance or other times when a monitor had to be removed from service, the reenergization of the monitor for service has also caused false tripping.
Extensive review of the monitor's operation, the internal physical configuration and the circuit design was performed during which several problems were identified.
The individual problems and the corrective actions taken are as follows:
1661 344 7912310 1
5
Mr. Domenic B. Vassallo December 19, 1979 Page 2 A drawing is attached for reference.
a)
Replacement of C-17 with R-24 (5.6k Resistor)
Purpose - The dual monostable multivibrator (Single-Shot) A4 requires a high going logic level to initiate a change of state.
With C-17 between pin 5 and pin 9, the low signal was inverted, resulting in a positive going logic level being applied to pin 9.
This results in both " single shots" being triggered within a few nano seconds of each other.
By replacing C-17 with R-24, a desirable time delay sequence was obtained.
The time delay provides an immunity of noise (72 miliseconds).
b)
The RC fietwork was altered for each single shot.
Purpose - The " delay" one shot time was increased to 168 ms to exclude any 60 cycle components and loading transients. The " window" one shot was shortened to 72 ms to decrease the probability of tripping from noise.
c)
Physical separation of the " delay" one shot RC network from the " window" one shot output.
Purpose - This modification prevented unwanted cross-coupling between output pin 14 and the RC network for the delay single shot.
d)
Addition of " Power Up Trip Inhibit" circuitry.
Purpose - To allow stabilization of the trip module circuitry after a power up. (energization) e)
Addition of filtering capacitors to the 15 volt on the circuit card.
Purpose - To minimize induced noise on the DC input lines.
3.
Steam / Water Two Loop Dump.
The PSC letter dated January 13, 1978 propcsed modifications to the steam / water dump system. These modifications were a result of the November 23, 1976 power failure on an uninterruptible DC power bus which resulted in a reactor scram and a steam / water dump in both steam generator loops.
The flRC letter of May 4, 1979 stated your position that all requirements had been satisfied with the exception of two. Those two are as follows:
1661 345
Mr. Domenic 8. Vassallo December 19, 1979 Page 3 a)
Qualification test information on the K-1 relay and the S-5 switch.
Qualification test information for the K-1 relay and the S-1 switch are now on file in our Quality Assurance Record System.
b)
Remove the R-58 and R-59 1X ohm resistors.
The two resistors (R-58, R-59) were removed.
Documentation is on file as a portion of FCti-3822C.
Another item which PSC had proposed in the January 13, 1978 letter was the removal of a temporary time delay relay.
This temporary relay was installed as an interim measure to prevent a steam water two loop dump until an in-depth review could be made of the circuitry involved and a permanent fix determined. Our engineering review has determined and the results of this review were discussed with you at the August '79 meeting in Bethesada, that the concept of the time delay relays is the best way to prevent a two loop dump.
The two loop dump can occur when a moisture monitor in each loop is out for maintenance, calibration or test, and a manual trip is installed which by-passes the first in with lockout inhibit. When the plant is in the " manual trip mode", a transient can occur which will create a trip signal to both loops simultaneously.
The time delay relay, with a one second delay, was made permanent to prevent the two loop trip from occurring under the conditions described.
Sincerely,
/
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