ML20077G109

Forwards Revised LERs 77-043/03X-1,80-007/03X-2, 80-020/03X-2,81-024/03X-2 & 83-022/03X-1

ML20077G109
Person / Time
Site:	Fort Saint Vrain
Issue date:	07/21/1983
From:	Warembourg D PUBLIC SERVICE CO. OF COLORADO
To:	Jay Collins NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20077G111	List: ML20077G109
References
P-83251, NUDOCS 8308030372
Download: ML20077G109 (5)

Text

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." *' ' 16805 Road 19 1/2, Platteville, Colorado 80651-9298 July 21, 1983 Fort St. Vrain Unit No. 1 P-83251 Mr. John T. Collins, Regional Administrator @ f Region IV t Nuclear Regulatory Commission 611 Ryan Plaza Drive 41.251983 Suite 1000 Arlington, Texas 76011

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Reference:

Facility Operating License No. DPR-34 Docket No. 50-267

Dear Mr. Collins:

Enclosed please find a copy of Reportable Occurrence Reports No. 50-267/77-043, 50-267/80-007, 50-267/80-020, 50-267/81-024, and 50-267/83-022, Revised Fi nal s , submitted per the requirements of Technical Specification AC 7.5.2(b)2.

Also, please find enclosed one copy of the Licensee Event Report for Reportable Occurrence Reports No.50-267/77-043, 50-267/80-007, 50-267/80-020, 50-267/81-024, and 50-267/83-022.

Very truly yours, Do, W em b s.9 M2?rlcs3J Don Warembourg Manager, Nuclear Production DW/djm Enclosures -

cc: Director, MIPC D

8308030372 830721 PDR ADOCK 05000267 S PDR DI l)k

, REPORT DATE: July 21.1983 '

' REPORTABLE OCCURRENCE 77-43 ISSUE 1 OCCURRENCE DATE: November 26, 1977 Page 1 of 4 Y

FORT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO 16805 WELD COUNTY ROAD 19 1/2 PLATTEVILLE, COLORADO 80651-9298 l REPORT NO. 50-267/77-43/03-X-1 l Final IDENTIFICATION OF OCCURRENCE:

During rise-to power testing, while at approximately 63% thermal power, the reactor was operated with an individual region outlet temperature greater than the limit of LCO 4.1.7(a) for continuous operation. This constitutes operation in a degraded mode permitted by LC0 4.1.7(a) and is reportable per Fort St. Vrain Technical Specification AC 7.5.2(b)2.

EVENT DESCRIPTION:

l During power ascension testing, it was discovered that at reactor power levels in excess of about 53%, the power output of some core l regions began to oscillate. Although individual core regions l appeared to be oscillating in power, the average core power remained l essentially constant. One result of the oscillations was observed to be an apparent corresponding variation in region gas outlet temperature. Prior to the event described in this report, no LCO limit had been exceeded during the region power oscillations.

Region power oscillations had been seen and documented for later analysis on three previous occasions at 53%, 55%, and 59% thermal power. At the time of this event, reactor power level was increased l from 53% at 1248 hours0.0144 days <br />0.347 hours <br />0.00206 weeks <br />4.74864e-4 months <br /> to 68% at 1510 hours0.0175 days <br />0.419 hours <br />0.0025 weeks <br />5.74555e-4 months <br />. The reactor operated at 68% power until 1550 hours0.0179 days <br />0.431 hours <br />0.00256 weeks <br />5.89775e-4 months <br /> when oscillations began. At approximately l 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br />, the operator initiated a reduction in reactor power to 63% which was reached at 1610 hours0.0186 days <br />0.447 hours <br />0.00266 weeks <br />6.12605e-4 months <br />. Reactor power level was held at 63% until 1650 hours0.0191 days <br />0.458 hours <br />0.00273 weeks <br />6.27825e-4 months <br /> while primary coolant flow through the entire

,' core and then through a single region was increased to record the effect of this change on the oscillations. When the observations of the effect of the flow changes were completed, a reactor power reduction to 53% power was initiated, and 53% power was reached at i 1843 hours0.0213 days <br />0.512 hours <br />0.00305 weeks <br />7.012615e-4 months <br />. Oscillations stopped at 1930 hours0.0223 days <br />0.536 hours <br />0.00319 weeks <br />7.34365e-4 months <br />.

l During operation between 1610 hours0.0186 days <br />0.447 hours <br />0.00266 weeks <br />6.12605e-4 months <br /> and 1715 hours0.0198 days <br />0.476 hours <br />0.00284 weeks <br />6.525575e-4 months <br />, the Region 28 l outlet temperature exceeded the region outlet temperature limit of LCO 4.1.7(a) on several occasions (see Table 1). For a region whose control rod is inserted more than two feet (applicable to Region 28 l

at this time), LCO 4.1.7(a) limits the outlet temperature of the

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• REPORTABLE OCCURRENCE 77-43 ISSUE 1 Page 2 of 4 region to core average outlet temperature plus 50 degrees fahrenheit.

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The LCO, however, also specifies that if the limit is exceeded at less than 50 degrees fahrenheit, the violation must be corrected or the reactor shutdown within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

CAUSE DESCRIPTION:

The cause of the operation in a degraded mode of LCO 4.1.7(a) was the region power oscillations which resulted in Region 28 exceeding the LCO limit by a few degrees for short periods of time.

l The temperature fluctuations affected the nuclear channels, region l outlet temperatures, and steam generator module temperatures. During l fluctuations, however, the total core coolant flow and core thermal l power remained essentially constant.

lA comprehensive program to evaluate and resolve the power I oscillations and temperature fluctuations was begun in late 1977.

l The program revealed that small (approximately 0.10 inch) lateral l movements of fuel columns caused changes in gap distribution, helium l crossflow, and.(for the seven northwest boundary regions, Regions 20 l and 32 through 37) changes in the amount of cool transverse helium l flow along the sleeves surrounding the region outlet temperature l thermocouples.

CORRECTIVE ACTION:

The corrective action for the excess region outlet temperature of region 28 was to reduce reactor power, which in turn reduced the magnitude of the region power oscillations and brought Region 28 into compliance with LCO 4.1.7(a).

l Core region constraint devices (RCDs) were installed in November, l 1979. These mechanical links limit the small lateral movements of l fuel columns to which the fluctuations were attributed. Fluctuation l testing up to 100% power with the RCDs installed was completed in l November, 1981, and clearly demonstrated that the RCDs were l successful in inhibiting the oscillations or fluctuations. The i results of these tests were formally submitted to the Nuclear i Regulatory Commission in July,1982.

l On October 5, 1982, the Nuclear Regulatory Commission issued l Amendment No. 28 to the Fort St. Vrain Operating License. In this l amendment, the Nuclear Regulatory Commission concluded, based upon a l review of the test data submitted in July, 1982, that the fluctuation l issue is resolved.

l No further corrective action is anticipated or required.

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REPORTA8LE OCCtlRRENCE 77 43 ISSUE.1 Page 3 of 4 TABLE 1 Maximus Region Outlet Core Average Temperature Allowed By Region 28 Time Outlet Tewerature LCO 4.1.7(a) Outlet Temperature 1503 1281 1331 1312 1508 1283 1333 1314

. 1514 1285 1335 1314 1519 1287 133' 1317 1524 1*a8 -

1338 1316 1530 1289 1339 1319 1535 1289 1339 1317 1541 1287 1337 1317 i

! 1546 1287 1332 1317 1550 1282 1332 1306 1552 1282 1332 1306 e 1555 1280 1330 1296 1557 1280 1330 1294 1558 1280 1330 1301 1601 1273 1323 1309 1318 1317 I

1606 1268 1607 1268 1318 1318 1610 1262 1312 1315*

I 1615

• 1261 1311 1312*

l 1616 1261 1311 1312*

1619 1261 1311 1309 1621 1261 1311 1313*

1626 1261 1311 1297 1627 1261 1311 1300'

! 1630 1261 1311 1297 l

1635 1250 1300 1294 l 1641 1259 -

1309 1306 1642 1265 1315 1311 1644 1265 1315 1315 1646 1265 1315 1310 1651 1247 1307 1310*

1657 1267 1317 13l9*

1658 1267 1317 1320*

1702 1259 1309 1313*

1705 1259 1309 1312*

1710 1262 1312 1314*

l 1715 1257 1307 1314*

i 1720 1258 1308 1307 1722 1258 1308 1307 1748 1254 1304 1294

• 1adicates region outlet temperature in excess of applicable limit of LCD 4.1.7(a).

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REPORTABLE OCCURRENCE 77-43 ISSUE 1

-- . Page 4 of 4 Prepared By: i .MAmy . A Duane L. Frye c7 Senior Technical Services Technician 0 [

Reviewed By: h h _,

Frank \,/.Novachek Technical Services Engineering Supervisor Reviewed By: / Y,

k. Miltdh"McBride' '

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Station Manager Approved By: [~ 7M,u d %

Don Warembourg g Manager, Nuclear ProductMn a

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