ML18009A658

Submits Addl Info Re Use of Hafnium Control Rods at Facility.All Rods Will Be Removed During Spring 1991 Outage

ML18009A658
Person / Time
Site:	Harris
Issue date:	09/11/1990
From:	Loflin L CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NLS-90-180, NUDOCS 9009180068
Download: ML18009A658 (4)

Text

ACCELERATED DISTRIBUTION DEMONSTRATION SYSTEM

~r REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9009180068 DOC.DATE: 90/09/11 NOTARIZED: NO DOCKET FACIL:50-400 Shearon Harris Nuclear Power Plant, Unit 1, Carolina 05000400 AUTH. NAME AUTHOR AFFXLXATION LOFLIN,L.I. Carolina Power & Light Co.

RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Submits addi info re use of hafnium control rods at facility.All rods will be removed during Spring 1991 outage.

D DISTRIBUTION CODE: AOOID TITLE: OR COPIES RECEIVED:LTR Submittal: General Distribution g ENCL ~ SIZE:

NOTES:Application for permit renewal filed. 05000400 RECIPIENT COPIES RECIPXENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-1 LA PD2-1 PD D BECKER,D D

XNTERNAL: ACRS NRR/DET/ECMB 9H 1 NRR/DOEA/OTSB11 NRR/DST 8E2 1 S NRR/DST/SELB 8D NRR/DST/SICB 7E 1 NRR/DST/SRXB 8E NUDOCS-ABSTRACT 1 OC OGC/HDS 1 1 G E 01 RES/DSIR/EIB 1 EXTERNAL: NRC PDR NSIC D

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NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

TOTAL NUMBER OF COPIES REQUIRED: LTTR 23 ENCL

SNK Carolina Power & Light Company SERIAL: NLS-90-180 SEE' 1 1990 United States Nuclear Regulatory 'Commissi'on ATTENTION: Document Control Desk Washington, DC 20555 SHEARON HARRIS NUCLEAR POWER PLANT DOCKET NO. 50-400/LICENSE NO. NPF-63 HAFNIUM CONTROL RODS Gentlemen:

Carolina Power & Light Company hereby submits additional informat:ion concerning the use of hafnium control rods at the Shearon Harris Nuclear Power Plant (SHNPP). This information is submitted in response to a verbal request from the NRC Staff. The Shearon Harris Nuclear Power Plant utilizes full length hafnium control rod assemblies (RCCAs) and has completed two cycles of operation. Two items of potential concern were identified during the end of fuel cycle two inspection: (1) RCCA R39 contained a rodlet with a severed tip; and (2) during the drag force testing, two RCCAs were reported as having significantly higher than average withdrawal drag forces. These three control rods, plus five additional control rods were replaced with silver-indium-cadmium rods prior to startup of the third cycle in December 1989.

The occurrence of a severed tip is not unique to SHNPP, but is a low frequency event, as shown by industry experience. A total of 592 full length hafnium RCCAs have completed between one and three cycles of operation and only three RCCAs (including RCCA R39 from SHNPP) with damaged or severed rodlet tips have been observed. The severed tip at SHNPP occurred either dur'ing Cycle 1 or Cycle 2. This is not inconsistent with previous experience; the RCCA at Byron 2 had only operated one cycle before the tip severed, while the Maanshan RCCA had operated for three cycles. The occur-ence of severed tips has been evaluated in the Westinghouse Generic Justification for Continued Operation (JCO) and shown to not prevent the affected RCCA from performing its safety function.

The second potential area of concern was the reported high drag forces on two RCCAs (R41 and R49). The drag testing was performed as a screening method (per the Hafnium RCCA examination guidelines issued by Westinghouse) to determine which RCCAs would be visually examined. A spring scale was used for the test which moved the RCCA approximately 3 feet from the fully inserted position. The highest withdrawal load and lowest insertion weights were reported for each RCCA. Since the results of this testing were to be used only as a screening method, the duration of the load/weight was not monitored.

Previous experience, on both silver and Hafnium RCCAs, has shown that pieces of debris or crud in the dashpot or misalignments of the vanes or rodlets could produce the drag increases observed.

411 Fayetteville Street o P. O. Box 1551 o Raleigh, N. C. 27602 90091S0068 900911 PDR ADOCK 05000400 P Fnc

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Document Control Desk NLS-90-180 / Page 2 The highest withdrawal loads on RCCAs R41 and R49 during the 3 foot withdrawal were approximately 150-200 pounds greater than the average withdrawal loads of the remaining RCCAs. However, during the 3 foot reinsertion, the reinsertion weights for these two RCCAs were normal compared to the other RCCAs. Had the RCCAs contained a condition associated with Hafnium hydriding which impeded the upward motion, it would also be expected to impede the reinsertion of the RCCA and be reflected in a lower than average reinsertion weight. Therefore, the reported high withdrawal loads may have been of short duration and not representative of a Hafnium hydride anomaly. In addition, visual examination of the tips of RCCAs R41 and R49 revealed no anomalous conditions. Based on the available data, RCCAs R41 and R49 would not necessarily have been rejected for reuse in Cycle 3, but were replaced anyway. Normally, drag measurements would not have been made at the End-of-Cycle (EOC) and in all likelihood, problem did not occur during change-out to a different fuel assembly if a (videotaping showed all tips to be in good condition), the RCCA would have been reinserted into the core. Since the reinsertion weights appeared to be normal in both RCCAs R41 and R49, it is likely both would have passed the start-up rod drop tests. However, because it was planned to replace eight hafnium control clusters with new silver RCCAs, Carolina Power & Light Company chose to replace both RCCAs R41 and R49 for Cycle 3 along with six other RCCAs. No characteristics, observed or projected, for RCCAs R41 and R49 would place them outside the evaluation envelope of the Westinghouse Generic JCO.

Westinghouse representatives made presentations to the Harris Plant Nuclear Safety Committee (PNSC) prior to plant start-up following Cycle 2 refueling which described the safety basis for concluding that SHNPP is enveloped by the Westinghouse Generic JCO. On this basis, the PNSC concurred that SHNPP falls within the safety basis of the Westinghouse Generic JCO and is safe to operate during Cycle 3 with the remaining hafnium control rods. CPSL has previously committed to remove all remaining hafnium control rods during the next refueling outage, presently scheduled for spring of 1991.

If you have questions or require additional information on this subject, please contact Mr. J. H. Eads at (919) 546-4165.

Yours very truly, L. . Lo in Manag r Nuclear Licensing Section JHE/ecc (642HNP) cc: Mr. R. A. Becker Mr. S. D. Ebneter Mr. J. E. Tedrow