ML19257C291
| ML19257C291 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 01/14/1980 |
| From: | TENNESSEE VALLEY AUTHORITY |
| To: | |
| Shared Package | |
| ML19257C287 | List: |
| References | |
| NUDOCS 8001250524 | |
| Download: ML19257C291 (7) | |
Text
e ENCLOSURE 1
'1809 323 8 0012 5 0 S a. y
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LPCI loop selection logic and trips the recirculation pumps.
The low p
reactor water level inntrumentation that is set to trip when reactor r*K water level is 17.7" (378" above vessel zero) above the top of the active fuel (Table 3.2.8) initiates the LPC1, Core Spray Pumps, contributes to ADS initiation and starts the diesel generators. These trip netting levels were chosen to be high enough to prevent spurious actuation but lov enough to initiate CSCS operation so that post accident cooling can be accomplished and the guidelineo of 10 CFR 100 vill not be violated.
For large breaks up to the complete circumferential break of a 28-inch recirculation line and with the trip setting given above, CSCS initiation is initiated in time to meet the above criteria.
The high drywell pressure instrumentation is a diverse signal to the water level instrumentation and in addition to initiating CSCS, it causes isolation of Groups 2 and 8 isolation valves. For the breaks discussed above, this instrumentation vill initiate CSCS operation at about the same time as the lov water level instrumentation; thus the results given above are applicable here also.
Venturis are provided in the main steam lines os a menno of measuring steam flov and also limiting the loss of mass inventory from the vesoel during a steam line treak accident. The primary function of the instru-nentation-is to detect a break in the main secan line.
For the vorst case accident. main stean line break outside the dryvell, a trip setting of 140% of rated steam flow in conjunction with the flow limiters and nain steam line valvo closure. limits the mass inventory loss such that fuel is not uncovered. fuel cladding temperatures remain below 1000*F and release of radioactivity to the environs is well belov 10 CFR 100 guidelines. Reference Section 14.6.5 FSAR.
Teoiperature mon!toring instrumentation in provided in the rain stean lir.c tunnel to detect traks in these arcon.
Trips are prnvided on this instru-mentation and when exceeded, cause closure of isointion valves. The octting of 200*F for the main steam line tunnel detcetor is lov enough to detect leaka of the crd.er of 15 gpm; thus, it is capable of covering the entire spectrum of breaks.
For large breaks, the high steam flov instru-mentation is a backup to the temperature instrumentation.
High radiation monitors in the main steam line tunnel h;ve been provided to detect r.ross fuel failure as in the control rod drop accident. With the established set ting of 6 times nornal background, and main steam line isolntion valve closure, finnion product relcase is limited so that
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10 CFR 100 guidelines are not exceeded for this accident. Reference ts proviced aknal sot point of 3 1/ 6 A n 115 C9, with a. noa X
f ul'1 p. 2 FS Af. k ground, Secti norna[n so.
ower v2c Pressure instrumentation is provided to close the main steam isolation valves in Run Mode when the main steam line pressure drops belov 825 pois.
1809 324 112 P-
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Revisul 11-30-79 an1 1t Pc t,
-s and tr ips the re:ltculation pumps.
The low reactor water level instrumentation that is set to trip *(aen reactor water level is 17.7" ( M8".ibove vessel zero) above *:he top of the active fuel (Table 3. 2. D) initiates the LPCI, Core Spray Pumps, contributes to ADS initiation and starts the diesel generators.
These trip sott ing leveis were chosen to be high enough to prevent spurious actuation but low enough to initiate CSCS operation so that post accident cooling can be accomplished and the guidelines of 10 CFR 100 will not be violated.
For large breaks up to the complete circumferential break of a 28-inch recirculation line and with the trip setting given above, CSCS initiation is initiated in time to meet the above criteria.
The high drywell pressure instrumentation is a diverse signal to the water level instrumentation and in addition to inf'iating CSC S, it causes isolation of Groups 2 and 8 isolation valves.
For the breaks discussed above, this instrumentation will initiate CSCS operation at about the same time as the low water level inst.rumcntation ; thus the results given above are applicalbe here also.
Vonturin are provided in the t'viin steam lines as a means of mea no ri ng steam flow and also limiting the loss of mass inventory t ro.n the vessel during a steam line break accident.
The primary function of the instrumentation is to detect a break in the main steam line.
For the worst case accidenL, main steam line break outside the drywell, a trip setting of 140% of rated steam flow in conjunction with the flow limiters and main steam line valve closure, limits the mass inventory loss such that fuel is not uncovered, tuel clodding temperatures remain below 10000F and release 01 radioactivity to the environs is well below 10 CFR 100 quidelines.
Reference Section 14.6.5 FSAR.
Temperature monitoring instrumentation is provided in the main steam line tunnel to detect leaks in these areas.
Trips are provided on this instrumentation and when exceeded, cause closure of isolation valves.
The setting of 200CF for the main steam line tunnel detector is low enough ta detect leaks of the order of 15 qpm; thou, it is capable of covering the entire spectrum of breiks.
For larue breaks, the high steam flow instrumentation is a backup to the temperature instrumentation.
liigh radiation monitors in the main steam line tunnel have been provided t o detect grous fuel f ailure as in the control rod drop accident.
With tho established setting of 6 times normal backqround, and main uteam line isolation valve closure, fission product roloase in li.ni ted :f a that 19 CFR 100 quidelines are not exceeded tor this accident.
Reference Section 14.6.2 FSAR.
An l alarm, wit h a nominal uet point of 3 x normal full power background, is provided also.
L809 325~
o 109 kmbent No. 23
6 ENCLOSURE 2 1809 326'
JUSTIFICATION The recomnended setpoint in GEK 779, Volume IV is 3X background for alarm and 6X background for isolation trip.
The accuracy of the MSLRM is
+ 25 percent for the 100 - 1000 MR/HR range with a + 3 percent per week drift (Reference GEK 32426A).
The current setpoint of 1.5X and 3X background is very hard to maintain without exceeding technical specifications when the instrument drifts down or having high alarms when the instrument drifts up.
The MSLRM is installed to detect and respond to increases in main steam line radiation that might indicate gross fuel cladding ruptures (NEDO-10174, October 1977). Neither precision nor accuracy is required to measure gross failures as 1.ndicated by GE specifications.
Therefore, raising the setpoints will not degrade instrument response to gross failure but will allow instrument accuracy to be taken into effect when setpoints are calculated.
As requested by the letter dated October 25, 1979, from T. A. Ippolito to H. G. Parris, we have researched our maintenance records for the main steam line radiation monitor (MSLRM) over the past two years.
Spurious alarms and trips are not a problem area with the MSLRM.
Because there appears to be some confusinn concerning the need for the proposed change an explanation of the problem is detailed below.
A routine NRC audit of the radiation monitoring system found the setpoints cn unit 2 MSLRM too high with respect to the current background. The set-points were revised, an LER submitted, and an investigation was initiated 4
to determine why the background had actually decreased.
1809 327
. The investigation revealed an instrument drift problem, in this instance down, which resulted in the f; 1.5X and $; 3X background setpoints being high. The MSLRM drawers (log rad monitor G3 #194X629G9) have an elec-trometer tube which is very sensitive to light, touch, or temperature changes. The majority of the drift problems occur following a log rad monitor calibration, which necessitates the drawer being out of the panel and the cover off the electrometer tube. The calibration procedure has been revised and maintenance personnel informed of the potential problem areas. The drift problem has made a drastic improvement.
The accuracy of the MSLRM as furnished by GE is + 25 percent on the 100-1000 mr/hr decade. A typical background at BFNP is 300 mr/hr.
The standard approach for setpoint determination is to allow for instrument inaccuracy org(337foralarm$;((300-(300x.25)]X1.5)and$;675forisolation 3; ( 300-(300 X.25) X 3).
The difference between 300 and 337 on a log scale is not much more than the width of a pointer, plus the alarm is common to two MSLRM's.
Since no two read exactly the same, it is conceivable to have the alarm in all the time.
Another approach is to calculate setpoints based solely on the current background, j[ 450 for alarm and dh900 for isolation. This approach allows more operating margin in that the difference between two channels or a little drif t upward does no harm. However, any downward drif t results in a LER and a setpoint revision.
1809 32[f
i
. Obviously, a middle-of-the-road approach has been taken for setpoint determination, but instrument inaccuracy cannot be taken into consideration and future LER's are a possibility.
Setpointchangestojf3Xforalarmand
$;6Xforisolationwouldallowustotakeinstrumentinaccuracyintosetpoint determination and maintain enough margin so drif t would not be a problem.
Using300asbackground,setpointswouldbe$5675foralarmandff1350for isolation.
The MSLRM's are installed to detect and respond to increases in main steam line radiation that might indicate gross fuel cladding ruptures (NED0-10174, October 1977). Neither precision nor accuracy le required to measure gross failures as indicated by GE specifications.
Therefore, raising the setpoints will not degrade instrument response to gross failure.
1809 329
.