ML18054A538

LER 88-012-01:on 880808 & 1205,unusual Event Declared Due to Plant Chemistry Notifying Shift Supervisor of Secondary Leak Rate at 0.31 Gpm.Caused by Damaged Tube Due to Either Plate Stress,Plate Growth or Tube denting.W/890209 Ltr

ML18054A538
Person / Time
Site:	Palisades
Issue date:	02/09/1989
From:	Johnson B, Kozup C CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-88-012, LER-88-12, NUDOCS 8902170180
Download: ML18054A538 (7)

Text

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AlllA COOi c S Kozup, Technical Engineer, Palisades 6 I 11 6 716 I 41 - I et 91113 CCMP\.ITI Ollll LINI 1'011 IACM CCM'ONINT l'AILUlll DllClllllD IN TMll* lllllOllT 1111 CAUll IYITIM COWONINT x A*1B s 1G I I C 14 I 910 Yes I I I I I I I I I I I I I I I I I I I I I

~lllllNTAI. llll'OllT IXPICTID 1,.1 MONTH DAY YJAll IX,.CTID IUllollalON r1 VII !If,.._, ......- IJf/tfC'rlD JUlll/$11/0N DA TIJ CATI 11111 I I I On August 8, 1988, at 1308, with the Plant operating at 95 percent steady state power, the Shift Supervisor was notified by Plant Chemistry that the calculated primary to secondary leak rate was at 0.31 gpm. An Unusuai Event was declared at 1310. Due to a concern that previous leak rate determinations had been in error and the leak may.have existed for some time, Plant shutdown was commenced at 1315 and entered cold shutdown condition at 0405 on August 10, 1988. Subsequent inspections determined the leaker was in "B" steam generator.

After returning the Plant to service November 29, 1988, on December 5, 1988 the condenser off-gas radiation monitor RIA-0631 [SR;RI] alarmed in the Control Room. At that time the Plant was at approximately 91 percent power and. escalating at one-half of one percent per hour.

Subsequent chemistry s*amples resulted in an estimated primary to secondary leak rate of 0.35 gpm. Plant shutdown was commenced.

Additional chemistry samples determined that the leak was in "B" steam generator [AB;SG]. The Plant entered cold shutdown condition on December 7, 1988.

Technical Specification 3. 1. 5. d indicates that "the primary to secondary leak rate in a steam generator shall not exceed 0.30 gpm for any period of steady state operations greater than 24 consecutive hours".

Subsequent investigations deternined that the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> limiting condition of operation had not been exceeded in either occurrence.

NllCF_ . .

lf.&ll LER 88012-1101 0~50002~)5 F'DC

NRC F0<m 3MA U.I. NUCLEAR REGULATORY COMMIDION 19-'131

• LICENSEE EV REPORT (LER) TEXT CONTINUATIO APPROVED OMll NO. 3150--01~

EXPIRES. 8/31185 fACILITY NAME {11 DOCKET NUMIER 121 LEll NUMelR Ill PAGE \31

'HAiii PALISADES PLANT 05000 255 88-012-01 0 OF 0 6 TEXT / / f - - ii ,.,,,,,;w, - . - . . , . J NltC Fon;. lBil'*I 1171 Description Listed below is the sequence of events leading up to the August 8, 1988 Plant shutdown. The Plant was operating at 95 percent steady state power during this sequence.

August 4, 1988 at 1405: Condenser off-gas radiation monitpr RIA-0631

[SH;RI] alarmed in the Control Room.

Off-gas activity had increased to 1287 cpm from a previous average of 750 cpm.

August 4, 1988 at 1415: The off-gas monitor reading.increased to 15,240 cpm.

August 4, 1988 at 1420: Plant Operations requested.that Chemistry sample the condenser off-gas.

August 4, 1988 at 1445: The off-gas monitor reading had increased to

.176,900 cpm. Operations requested a second

• off-gas sample.

August 4, 1988 at 1508: Operations requested that Chemistry sample I both steam generators rAB;SG]. .

August 4, 1988 at 1515: It was determined that .:'l. steam generator tube leak had occurred which was estimated to be 0.004 gpm based on the first condenser off-gas sample.

August 4, 1988 at 1620: Results of the second off-gas sample indicated a 0.010 gpm primary to secondary leak. Operations requested a.primary coolant system sample.

August 4, 1988 at 1700: The third off-gas sample indicated a 0.022 gpm leak, August 4, 1988 at 1755: A fourth off-gas sample indicated a 0.027.

gpm leak.

August 4, 1988 at 1826: Results from the primary coolant system sample, drawn at 1650, indicated no increase in primary coolant activity.

August 4, 1988 at 1915: Operations requested condenser off-gas and steam generator samples for ra9ioactivity taken every two hours.

August 4, 1988 at 2000: Condenser off-gas radiation monitor RIA-0631 reading 290,200 cpm.

NRC FORM 368.&

19-831 LER 88012-1101

NAC F0r"' ae.a U.I. lllUCLEAll llEQULATOllY COMMllllON 19-831 LICENSEE EV.T REPORT (LERI TEXT CONTINUATIO APPROVED OMI! 1'10. 3150--<1104 EXPIRES: 8/3118!

FACILITY lllAME 111 DOCKET lllUM9Ell 121 Liii N~lll 111 l'AQI 131 PALISADES PL.ANT o 1s I o I a Io I 2 I 51 5 818 - O Il I 2 - o I 1 o 1 3 OF o I 6 TEXT,,,,_._;.,......,. - - N M : -.-..*111171 August 5, 1988 at 0300: RIA-0631 reading 318,400 cpm.

August 5, 1988 at 1135: Results from an 0805 condenser off-gas sample calculated the prirnRry to secondary leak rate at 0.06 gpm. This increase was attributed to an increase in the off-gas flow. rate since there had been no increase in the stack gas radiation monitor RIA-2326 fVL;RI],

August 6, 1988 at 0000 to August 7, 1988 at 1800: Calculations of condenser off-gas samples indicated essentially no primary to secondary leakage even though the condenser off-gas radiation monitor RIA-0631 increased to as high as 481,432 cpm. An investigation of this anomaly disclosed that there was considerable air inleakage at the condenser off-gas sample point which was diluting the samples and leading to a low estimate of the primary to secondary leakage. Correction of this problem resulted in a valid leak rate of 0.31 gpm o,n August 8, 1988.

Listed below is the sequence of events regarding the December 5, 1988 steam generator leak.

December 5, 1988 at 2109: Condenser off-gas radiation monitor RIA-0631 alarms in Cbntrol Room. Control Room requests that Plant Chemistry sample condenser off-gas.

December 5, 1988 at 2150: Control Room requests Chemistry to sample the steam generators for activity to determine the affected steam generator.

December 5, 1988 at 2258: Chemistry estimates the primary to secondary leak rate ~t 0.35 gpm.

December 5, 1988 at 2307: Commenced Plant shutdown at 12 perce*nt per hour.

December 5, 1988 at 2318: Control Room completed notifications on the Plant shutdown to the NRC Senior Resident, Duty & Call Superintendent, Plant Manager and Operations Superintendent.

• December 6, 1988 at 0005: Chemistry reports to the Control Room that sampling indicates the leak to be in 11 B11 steam generator. Control Room isolates "B" steam generator blowdowns and the ai~ to 1 'B 11

""'RC FORM Je&A 19-l!JI LER 88012-LIOl

NAC F0tm lMA U.I. NUCLEA .. IUQULATO .. Y COMMllllQ!lj 19-l!JI LICENSEE EVENT REPORT (LERI TEXT CONTINUATION APPROVED OMll NO. 3150--0104 EXPIRES: 8/3118!

FACILITY NAME C11 LE .. N!Mel .. Ill 'AGE 131 PALISADES PLANT TEXT !If,,,,,,. - * ,.,,,,._, - - NftC Fomt MM'*I 1171 0 1s I 0 I 0 I 0 12 I 5 15 s, 8 - 01112 - 0 11 0I 4 OF 0 I6 steam generator atmospheric steam dumps to prevent an inadvertent release to the environment.

December 6, 1988 at 0115: Additional samples by Chemistry estimates the primary to secondary leak rate at 0.18 gpm. The decrease in the leak rate is attributable to the power reduction.

December 6, 1988 at 0648: Reactor is sub-critical.

December 6, 1988 at 0800: Reactor in hot standby condition.

December 6, 1988 at 0919: All control rods inserted and reactor manually tripped.

December 7, 1988 at 1849: Plant -in cold shutdown condition.

Cause Of The Event The steam generator tube leak in August 1988 was identified on September 9, 1988 by pressurizing the secondary side of "B" steam generator with nitrogen to approximately 55 psi. Subsequent e_ddy current testing of the steam generator tubes with a 4C4F probe and the Motorized Rotating Absolute Pancake Coil (MRPC) identified a circumferential crack in a tube at the lower edge of support plate 13.

The leaking tube is in the same quandrant as a 1987 "leaker" and was tested with a 4C4F technique in December 1987. At that time, there was no detectable indication present. The damage mechanism is not known, but is believed to have resulted from a combination of several factors including support plate stresses, plate growth, tube denting, existing intergranular attack and U-bend "bending" stresses in conjunction with normal operating stresses.

The cause of the December 5, 1988 shutdown was first thought to be a steam generator tube leak. Hydrostatic testing and eddy current testing, however, determined that the source of leakage was a welded plug which had been installed during the August 1988 steam generator inspection. The plug was a manually installed interference fit plug.

The tube was removed from service because both MRPC and 4C4F probes detected a crack-like indication at the 13th support plate on the hot leg side. At the time of the plugging, the indication was not thought to be thru-wall because no leakage was detected during secondary side pressurization. A dye-penetrant examination of the tube plug did not identify any abnormalities in the plug and it is assumed that the defect was located in the weld metal rather than the plug. Subsequent eddy current testing of the tube after plug removal indicated that the crack-like indication at support plate 13. had increased. The mechanism causing the degradation to progress in this previously plugged tube is not known, but may result from a combination of support plate growth, Nl::IC ~ORM :ieeA 19-831 LER 88012-LIOl

"IAC Form*-.. U.I. "IUCLEAll llEOULATORY COMMIDION (11-331 LICENSEE EVE T REPORT (LERI TEXT CONTINUATIO APPROVED OMll NO. 3150-0104 EXPIRES: 8/311115 FACILITY "I.AME 111 DOCKET pjUMHll 121 Liil ... ~IR 111 f'AOl 131 PALISADES PLANT 0 1s i0 I 0 I 0 I 2, 5 I 5 s, s - 0 11 I 2 - ~ 1 0 I 5 OF 0 TEXT 1 1 ' - - i l - - . - - - N f t C Fotrrt.-..'111171 tube denting, U-bend "bending" stresses, hot-to-cold lock-up stresses in addition to normal operating stresses.

Analysis Of The Event The report is being made for information purposes. Investigations of both events, August 8, 1988 and December 5, 1988, determined that the Plant did not exceed Technical Specifications regarding primary to secondary leak rate. Because the Technical Specification limit was not exceeded, it is concluded that no safety consequences resulted from *I either event.

Further, the FSAR safety analysis (Section 14.15) for a steam generator tube rupture assumes a double-ended rupture, therefore, both_ events were bounded by this accident analysis.

Corrective Action Licensee Event Report 50-255/88012 referred to an air inleakage problem at the condenser off-gas sample point. Evaluation of this problem, using data available since June 1988, determined that between June 1988 and August 7, 1988 th.e primary to secondary leak rate had been

~nderestimated.

A number of corrective actions were taken to ensure an accurate primary to secondary leak rate. These included revising the condenser off-gas sampling procedure to add two tests for ~ystem integrity and .

operability. These tests will be performed each time the sampling system .is used. A backup method for determining primary to secondary leak rate was developed. Verification of this method will be performed when a tube leak is present. After recalibrating the condenser off-gas radiation monitor, a graph was developed for estimating the leak rate at various condenser off-gas flow rates. This will be used as a Control Room operator aid.

Following the identification of the "leaker" which resulted in the August 1988 shutdown, approximately 50 percent of the tubes in both steam generators were eddy current tested. The testing resulted in plugging of 34 tubes, 10 in "A" steam generator and 24 in."B" steam generator. In addition, 11 plugs were removed and reinstalled as a corrective measure after they were observed to be damp or dripping during the hydrostatic test of 11 B11 steam generator. Full details of this steam generator inservice inspection is included in our correspondence docketed November 15, 1988.

The December 1988 shutdown resulted in eddy current testing of 134 tubes in the cold leg and 160 tubes in the hot leg at the 13th support plate.

One of these tubes was found to contain a crack-like indication and it was plugged. In addition, three tubes which contained somewhat PlilRC FOR'-' 388A 19-l!ll LER 88012-1101

NlllCFut"'~ U.I. NUCLEAlll lllEQULATOlllY COMMIDIOH IMJI LICENSEE EVE T REPORT (LERI TEXT CONTINUATIO ,t.PPROVEO OMll NO. 3150~1.04 EXPIRES: B/31185 fACILITY NAiii (11 DOCKET NUM9Elll 121 LElll N~llll 111 PAQI 131 PALISADES PLANT TEXT llf - . . . . ia .........,, - l1dtlldotW NltC Foml .-..*11 1171 ambiguous signals at support plate 13 were electively plugged. A total of nine tubes were plugged in "B" steam generator in addition to replugging five deplugged tubes. All of the plugs were manually

.installed interference fit welded tube plugs.

Our correspondence dated January 31, 1989_, "Steam Generator Tube Stabilization Evaluation", details additional long term corrective actions. Briefly, these actions include the following:

1. Perform crack size/vibration analysis

2. Reinspect all "B" steam generator hot leg tubes pluggeq for cracking at the 13th support* plate.

3. Review all tubes plugged for cracking in "A" and "B" steam

• generators against tube stabilization analysis and to stabilize tubes as needed.

4. Revise this evaluation to factor in results of the January 1989 tube leak investigation.

Additional Information Similar events are documented *in Licensee Event Reports82-012 and 88-012.

NRC FO,illM 368A

!9-831 .

LER 8801.2-LIO 1

consumers Power l'DWERINli MICHlliAN'S l'RDliRESS General Offices: 1945 West Parnell Road, Jackson, Ml 49201 * (517) 788-0550 February 9, 1989 Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 DOCKET 50-255 - LICENSE DPR PALISADES PLANT -

LICENSEE EVENT REPORT 88-012 STEAM GENERATOR TUBE LEAKAGE Licensee Event Report (LER) 88-012-01 (Steam Generator Tube Leakage) is attached. This event is being reported to the NRC as an informational LER.

Brian D Johnson Staff Licensing Engineer CC Administrator, Region III, USNRC NRC Resident Inspector - Palisades Attachment OC0289-0043-NL02