ML20206E744
| ML20206E744 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 04/08/1987 |
| From: | Goldberg J HOUSTON LIGHTING & POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| REF-PT21-87-104-000 PT21-87-104, PT21-87-104-000, NUDOCS 8704130715 | |
| Download: ML20206E744 (4) | |
Text
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The Light NE f Ifouston I.ighting & Power P.O. Ikix 1700 Ilouston, Texas 77001 (713) 228-9211
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April 8, 1987 ST-HL-AE-2026 File No.: G12.370, C2.2 10CFR50.55(e)
U. S. Nuclear Regulatory Commission Attention:
Document Control Desk Washington, DC 20555 South Texas Project Units 1 and 2 Docket Nos. STN 50-498, STN 50-499 Final Report Concerning RTD Time Response On March 9, 1987 Houston Lighting & Power Company notified your office pursuant to 10CFR50.55(e), of an item concerning reactor coolant system resistance temperature detector (RTD) time response.
Enclosed is the Final Report on this item. We have determined that this item is reportable pursuant to 10CFR50.55(e) and 10CFR21.
If you should have any questions on this matter, please contact Mr.
C. A. Ayala at (512) 972-8628.
J. H. Goldberg Group Vice Pres dent, Nuclear LRC/hg
Attachment:
Final Report Concerning RTD Time Response l
87041307Y5 870408 PDR ADOCK 05000498 A
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W ST-HL-AE-2026 File No.: G12.370, G2.2 Houston Lighting & Power Company Page 2 cc:
Regional Administrator, Region IV M.B. Lee /J.E.'Malaski Nuclear Regulatory Commission City of Austin 611 Ryan Plaza Drive,-Suite-1000 P.O. Box 1088 Arlington, TX 76011 Austin, TX 78767-8814 N. Prasad Kadambi, Project Manager A. von Rosenberg/M.T. Hardt U.S. Nuclear Regulatory Commission City Public Service Board 7920 Norfolk Avenue P.O. Box 1771 Be thesda,,)U) 20814 San Antonio, TX 78296 Robert-L. Perch, Project Manager Advisory Committee on Reactor' Safeguards.
U.S. Nuclear Regulatory Commission U.S. Nuclear Regulatory Commission 7920 Norfolk Avenue 1717 H Street Bethesda, MD 20814' Washington, DC 20555 Dan R. Carpenter Senior Resident Inspector / Operations c/o U.S. Nuclear Regulatory Commission P.O. Box 910 Bay City, TX 77414 Claude E. Johnson Senior Resident Inspector /STP c/o U.S. Nuclear Regulatory Commission P.O. Box 910 Bay City, TX 77414 M.D. Schwarz, Jr... Esquire Baker & Botts One Shell Plaza Houston, TX 77002 J.R. Newman, Esquire Newman & Holtzinger, P.C.
1615 L Street, N.W.
l Washington, DC 20036 i
T.V. Shockley/R.L. Range i
Central Power & Light Company P. O. Box 2121 Corpus Christi, TX 78403 l
l-L4/NRC/rd/hg-0 Revised 2/3/87 l
Attachment ST-HL-AE-2026 File No.: G12.370, G2.2 Page 1 of 2 South Texas Project Units 1 and 2 Docket Nos. STN 50-498, STN 50-499 Final Report Concerning RTD Time Response I. Summarv On March 9, 1987, Houston Lighting & Power Company (HL&P) notified your office, pursuant to 10CFR50.55(e), of an item concerning reactor coolant system (RCS) resistance temperature detector (RTD) response time, i
Test results at STP indicated that RTD response times were longer than those required by the FSAR and Technical Specifications. The unsatis-factory response will be corrected by silver-plating the end of the RTDs which will improve the radial fit and consequently improve the thermal conductivity between the RTDs anu the thermowells.
We have determined that, had this deficiency been left uncorrected it could have resulted in delayed reactor trips. As such, this item is reportable pursuant to 10CFR50.55(e).
II. Description of Deficiency The RTDs provide reactor coolant temperature signals for use in reactor control and protection. Two reactor trips, overtemperature delta-T and overpower delta-T (see STP FSAR section 7.2.1.1.2) utilize the outputs from these RTDs.
These reactor trips mitigate the consequences of certair. postulated accident conditions. Additionally, the RTDs provide inputs to certain Engineered Safety Feature (ESF) trips.
The RTDs were response time tested using the loop current step response method during hot functional testing at STP.
The results of these tests l
indicated that the response times for twenty-three of the twenty-five RTDs tested did not meet the FSAR or Technical Specification requirements.
RTD response times measured were in the range of five (5) l to eleven (11) seconds whereas, FSAR Table 15.0-4 assumes 6.5 seconds for the protection circuit (RTD and electronic reaction time) for accident analyses.
The RTDs and thermowells were specified and supplied to STP by Westinghouse. The RTDs were manufactured by RdF Corporation (23 Elm Ave., Hudson, NH 03051) while the thermowells were supplied by RdF j
Corporation and Penn State Tool & Die Corporation, 7590 Route 30, North Huntingdon, PA 15642.
Exact physical measurements were taken of the installed RTD thermowells.
i Testing of spare RTDs in thermowells was performed to determine the cause of the slow response times.
Several of the thermowells measured have too l
wide an angle at the end, precluding a good radial fit between the RTD and thermowell resulting in inadequate heat transfer characteristics for L4/NRC/rd/hg-0
Attachment ST-HL-AE-2026 File No.: G12.370, G2.2 Page 2 of 2 acceptable response times. Additionally, some of the tharmowells incurred installation damage such as bending, scratches, burrs or contamination which further affected the poo*: heat transfer characteristics.
III. Corrective Action Approximately two inches of the end of several RTDs were silver-plated.
These were then tested in thermowells by both plunge bath and loop current step response methods. The test results indicated that the silver-plating significantly improved the heat transfer from the RTD
- thermowell to the RTD by compensating for the lack of a good radial fit between the RTD end and the thermowell.
The bent thermowells will be straightened, and the scratches and burrs removed. The Unit 1 RTDs will be silver-plated and installed prior to fuel load. Retesting of the RTDs will be performed after fuel load when the RCS is at operating temperature and flow conditions. Retesting and response time verification will be completed prior to initial criticality. The RTDs for Unit 2 will also be silver-plated.
IV. Recurrence Control The description and drawings for the RTDs are being revised by Westinghouse to show the silver-plated portion of the RTD. Accordingly, replacement RTD's will be silver-plcted to assure adequate mechanical fit between the RTD and its thermowell.
V. Safety Analysis Several FSAR Chapter 15 accident analyses assume mitigation by the overtemperature delta-T or overpower delta-T reactor trips. Had this deficiency remained uncorrected, the unsatisfactory response of the RTDs could have resulted in an unanalyzed condition.
Therefore, HL&P has determined that this item is reportable pursuant to 10CFR50.55(e) and 10CFR21.
L4/NRC/rd/hg-0