ML19319E245
| ML19319E245 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 09/26/1974 |
| From: | SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | |
| Shared Package | |
| ML19319E242 | List: |
| References | |
| NUDOCS 8003310751 | |
| Download: ML19319E245 (3) | |
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DOCKET No. 50-312-74-4 m'
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Reporting Dato:
September 26, 1974 Occurrence Date:
September-19, 1974 Time:. 0140 Facility:
Rancho Seco Nuc1 car Generating Station
-Unit No. 1-Clay Station, California Identification'oloccurrence:
Imbalance Function Generator setting less conservative thnu the limiting setting established in the Technical Specifications.
Condition Prior to Occurrence:
The~ reactor was at hot shutdown during Zero Power Physics testing; subsequent to initial criticality.
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DescriptionEof'Occurrenec:
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Cach of four reactor protection system channels have eight I
trip'paramotors to limit specific operating transients and protect the reactor system. One;of these parameters is the overpower trip based on flow and itchalance.
To assure that tho. limits establishod 'in the Technical Specifications remain within
. acceptable tolerances;:a, surveillance procedura (SP200.08) is performed monthly te verify tho trip. values.
Figure 2.3-2 of the Technical Specifications shows the envelope'of:allouabic boundaries for the overpouer trip' based on flow and imbalance.
The boundaries shaded and-the points labeled BP1, BP2, EP3 and BP4 are determined byNetting values into a function generator. The surveillance procedure requirce 1BP1 to be 6.739 +'.017' volts and'BP2 to be -3.660 +.010 volts. 'The actual valuas
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for_ Channel "A" measured on September.19, 1974, were 6.939 volts and -3.448 volts respectively. This indicates'BP1 was 0.183 volts high and BP2 was 0.202 voltu too.
. low {as indicated 'on Figure 2.3-2.
The actual loci of points for the boundary
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indicated for thosc~ values is shown dashed on the figure. The dashed line-between-BPI'and-BP2.is in the nonconservative~ direction.
BP3, BP4 and all other boundarv
-limits werc within acceptable limits for the power, imbalcaice, flow Chennel "A".
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- Corrective Action Taken or Which Should be Taken:
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_ Thol function generator for1Chann 1 "A" was not immediatnlv
' readjusted for the purpose of a]Iowing additiona1 monitoring in. hopes of determining 7
Iff.the~ outc of rspecification condition was due to. aisteady rate of calibration drif t.
When ch'ecked later on' September-19 it was concluded;that no drift rate was in fcet-
? occurring..-Channel'"A" was recalibrated.within acceptablo limits on September 2'0,.
- 1974;
'The calibration' values;were 6.737 and;-3.660 volts for BP1 'and EP2.
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Adct ;the function generator only?a single adjustment :of. the #1 deadband
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. potentiometer was:necessary.' The potentiometer was rotated 1/4 turn counter-
' clockwise and. BP1 and BP2 were brought within rolerance. The deadband adjustment chifted the curve.cnclosed;by BPL-and BP2 parallel to the right.
- Checks were performed on Channel "A" BP1 and BP2 oh
.SaptemberL21, 24.and.26.with no detectable drift occurring.
A close surveillance program.is continuingfasl described in " Action Required to Prevent a Reoccurrence".
f-The. function generators for Channels B, C & D were checked'
'and'foundI o be within specifications.
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I Designation of Apparent'Cause: = Unknown.
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Anatysis'of Occurrence:
-The Channel "A" function generator was accurately calibrated l
on September 6, 1974. The reactor remained shut.down until " initial criticality" l
- on September 16 and did not exceed-a-flux level of 2 x 10-7 amps on the intermediate l~
leveliflux channels. 'The power-imbalance boundaries are established in order to prevent reactorzthermal limits from being exceeded. These thermal limits are
. either pcuer peaking kW/f t limits or D53R limits. The reactor-power imbalance
. power inJ the top _ half of core minus pouer in the buttom half of core) reduces the (ipcuet icvel; trip produced by.the power-to-flow ratio so that the boundaries of f*7:re.2.3-2areproduced. ThcLpower-to-flev ratio reduces the power level trip
! associated. reactor--power -imbalance -boundaries by 1.03 percent for a 1 percent 6
" b d reduction.
.Since the power-imbalance; limits are established for operating
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-at power levels much higher than the values encountered during the Zero Power Physics
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. testing,'there was no ccmpromise of the safety margins established for the reactor corn.
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Equipment I.D.:
The' function generator is-located in cabinet 1A-A177 module of the reactor protection system. The generator,is manufactured by Baily Meter Company Jof.Wickliffe, Ohio and:'is' integral to their 880 system, Part No. 6625027A1.
Action Required'to Prevent a Recccurrence:
A surv'cillance: program has been initiated to check the
' Channel "A"l function' generator weekly for.the next three wecks. At this time if the function generator-is within-
,the' acceptable tolerances! the testing will revert to the normal monthly intervals.~
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D Failure Data:
?None.'
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