ML18153A057
| ML18153A057 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 08/30/1996 |
| From: | Ohanlon J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 96-441, IEB-96-001, IEB-96-1, NUDOCS 9609100003 | |
| Download: ML18153A057 (7) | |
Text
CATEGORY 1 REGULAT** -:INFOB~TION DISTRIBUTION.lSTEM (IUDS)
~ ACCESSION NBR:9609100003 DOC.DATE: 96/08/30 NOTARIZED: NO "DOCKET#
05000281
- FACIL:50-281 Surry Power Station, Unit 2, Virginia Electric & Powe AUTH.NAM~
AUTHOR AFFILIATION O'HANLON,J.P.
Virginia Power (Virgiriia Electric & Power Co.)
RECIP.NAME RECIPIENT AFFILIATION Document *Control Branch (Document Control Desk)
SUBJECT:
Responds to NRC Bulletin 96-001, "Control Rod Insertion Problems," results of rod drop tests,provided.
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le, TITLE: NRC Bulletin 96 Control Rod Insertion Problems
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1 RECIPIENT ID CODE/NAME PD2-l PD AEOD NRR/DSSA/SRXB NRC PDR NOTE TO ALL "RIDS" RECIPIENTS:
PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM OWFN 5D-5(EXT. 415-2083) TO ELIMINATE YOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!
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VIRGINIA ELECTRIC AND POWER.COMPANY RICHMOND, VIRGINIA 23261 August 30, 1996 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555-0001 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNIT 2 SUBMITTAL OF CONTROL ROD DROP TEST RESULTS IN ACCORDANCE WITH NRC BULLETIN 96-01 Serial No.96-441 NL&OS/GDM RO Docket No.
50-281 License No. DPR-37 NRC Bulletin 96-01, "Control Rod Insertion Problems," dated March 8, 1996, requested licensees to measure and evaluate control rod drop times and rod recoil data for control rods *during 1996 outages of sufficient duration.
On August 3, 1996, Surry Power Station Unit 2 was manually tripped. Following the trip, all rod bottom lights were on, but the individual rod position indication (IRPI) system indicated that four control rods were above ten steps withdrawn. Approximately two minutes after the trip, these IRPls indicated zero. Control Rod drop time tests were performed on the affected rods on August 4, 1996 to ensure that the IRPI indications were due to IRPI instrumentation drift rather than actual incomplete control rod insertion. The results of the rod drop tests are provided in the Attachment to this letter.
Should you have any questions or require additional information, please contact us.
Very truly yours,
~J'-~~6~
James P. O'Hanlon Senior Vice President - Nuclear Attachment
cc:
U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, N. W.
Suite 2900 Atlanta, Georgia Mr. R. A. Musser NRC Senior Resident Inspector Surry Power Station
ATTACHMENT VIRGINIA POWER SURRY UNIT 2 CYCLE 14 CONTROL ROD DROP TEST RESULTS
L e
Evaluation of Surry Unit 2 Cycle 14 Control Rod Drop Time Tests Performed on August 4, 1996 Evaluation - Rod Drop Time Surry Unit 2 was manually tripped on August 3, 1996 due to problems with a leaking fitting on the turbine's electrohydraulic control (EHC) system. All control rods inserted into the core following the trip, but the independent rod position indication (IRPI) system indicated that four control rods were 10 to 12 steps withdrawn immediately following the trip. The core locations for the four control rods are G3, J 13, F12, and F6. Approximately 2 minutes after the trip, the IRPls for these control rods indicated the rods were fully inserted (zero steps withdrawn). The IRPI system is an analog system and it is typical to observe this type of drift in one or more IRPls, particularly following a reactor trip.
There have been recent incidents whereby control rods failed to fully insert that are documented in NRC Bulletin 96-01, "Control Rod Insertion Problems." Virginia Power's response to Bulletin 96-01 indicated that Virginia Power will perform rod drop time tests during a mid-cycle *outage of -sufficient duration when the burn up of the fuel assemblies in rodded core locations exceeds 35,000 MWD/MTU and at least 2500 MWD/MTU have elapsed since the last tests. Virginia Power further committed to perform control rod tests without regard to either of the burnup thresholds if anomalous control rod behavior was observed.
Surry Unit 2 Cycle 14 achieved initial criticality on June 5, 1996, and on August 3, 1996, 2500 MWD/MTU of cycle energy had not yet been expended since the control rod drop times were last measured at the beginning of the cycle (BOC). Therefore, the Unit had not yet entered the test window. However, even though it is not uncommon to observe drift in analog IRPls, it was decided to test the drop times of the four control rods whose IRPls indicated incomplete insertion and treat the observed drift in the IRPls as anomalous behavior.
Rod drop times are measured at Surry by concurrently dropping all the rods in a single bank. Thus drop time data from all the rods in a single bank are obtained at one time.
.. Three banks of control rods had to be dropped in order to obtain the drop times from the four control rods. The drop time tests were performed on August 4, 1996. The banks that were tested were control B-Bank and D-Bank to obtain drop time data from rods F12 and F6, respectively, and shutdown SA-Bank to obtain drop time data from rods G3 and J13. The tests were performed under hot, full flow RCS conditions.
Figure 1 compares the drop time test results from the August 4, 1996 tests to the drop time test results that were obtained at the beginning of Cycle 14. The shaded locations on Figure 1 represent the locations of the control rods whose IRPls indicated incomplete insertion. As can be seen on Figure 1, there is very little variation in the drop times that
were measured at BOC compared to the drop times that were measured on August 4, 1996. The average change in measured drop times for the twenty three control rods is less than zero (BOC time less 8/4/96 time). This indicates that the drop times measured for the twenty three control rods on 8/4/96 are overall less than the same drop times measured at BOC. In fact, three of the four control rods in question had measured drop times that were reported to be less than the corresponding drop times at BOC. All rod drop times for the tested control rods were within the limit of 2.4 seconds as specified in Section 3.12.C.2 of the Surry Technical Specifications. Therefore, by examination of the rod drop time test results, there is no significant change in the drop time behavior of the control rods.
Note that the control rod location H2 was tested with the other rods in control D-Bank, but the results of the test are not included on Figure 1. There was a malfunction with the recorder for that rod trace. The recorder "stuck" giving a false, rapid rod drop time. A retest was not performed since the IRPI for this rod indicated that the rod fully inserted normally after the trip.
Evaluation - Rod Recoil Recoil was observed for all rod drop tests and was recorded on Procedure 2-NPT-RX-014. Recoil is the control rod bounce that occurs when the spring pack on the control rod impacts the top nozzle of the fuel assembly. The existence of recoil is positive indication that the control rod has fully inserted.
Conclusion Based on the measured drop times following the reactor trip, and the fact that recoil was observed on the timing traces for the control rods in question, it is concluded that control rods in locations G3, F6, F12, and J13 promptly and fully inserted during the trip, and that instrumentation drift associated with the IRPls was responsible for the indication that these four control rods were above ten steps following the reactor trip. The drop time test data from the remaining control rods in the three banks that were tested indicate that there has been no significant change in the control rod drop behavior since the control rods were last tested at startup of Cycle 14.
,(
A 2
3 4
5 6
7 8
9 10 11 12 13 14 15 Surry 2 Cyc. 4 BOC Control Rod Drop Time.surements Compared to August 4, 1996 Measurements (Drop times are measured to the dashpot and are represented in seconds)
B C
D C
A B
1.29 1.28 SA 1.29 1.30 D
1.30 1.31 SA 1.26 1.30 A
B 1.27 1.25 C
E SB SB F
A B
1.28 1.30 II C
D 1.33 1.32 A
D C
C D
1.26 1.29 J-SA 1.28 1.30 SB SB K
A B
1.29 1.26 D
1.30 1.30 C
D 1.30 1.30 B
1.28 1.26 A
L SB SB M
C B
1.25 1.25 B
1.31 1.27 C
R A
D 1.27 1.27 A
Legend Bank ID BOC Test 8/4/96 Test