ML20113G388
| ML20113G388 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 09/23/1996 |
| From: | Ohanlon J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 96-442, IEB-96-001, IEB-96-1, NUDOCS 9609270183 | |
| Download: ML20113G388 (6) | |
Text
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VIRGINIA ELucTHIC AND POWER COMPANY HICHMOND,Y1HOINIA 20261 September 23, 1996 United States Nuclear Regulatory Commission Serial No.96-442 Attention: Document Control Desk NL&OS/ETS R1 Washington, D. C. 20555-0001 Docket No. 50-338 License No. NPF-4 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY FORTH ANNA POWER STATION UNIT 1 fJJBMITTAL OF CONTROL ROD DROP TEST RESULTS IN ACCORDANCE WITH NRC B_l)LLETIN 96-01 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 all control rods during 1996 outages of sufficient duration. North Anna Unit 1 experienced an automatic reactor trip on August 27,1996. The commitments made in our response to NRC Bulletin 96-01 did not require control rod drop testing be perfromed because there were no anomalous control rod insertion indications by examination of the individual rod position indicators (IRPIs) following the reactor trip, and no fuel in any rodded assembly had yet exceeded bumup of 35,000 MWD /MTU. However, the decision was made to test the drop times of all 48 control rods to provide assurance that no control rod insertion problem exists in the North Anna Unit 1 Cycle 12 core.
Attached is an evaluation of the rod drop time tests that were performed on August 28, 1996.
Should you have any questions or require additional information, please contact us.
Very truly yours, W
James P. O'Hanlon Senior Vice President - Nuclear Attachment
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T 9609270183 960923 PDR ADOCK 05000338 G
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U. S. Nuclear Regulatory Commission Region 11 101 Marietta Street, N. W.
Suite 2900 Atlanta, Georgia 1
Mr. R. D. McWhorter NRC Senior Resident Inspector 1
North Anna Power Station i
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ATTACHMENT I
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VIRGINIA POWER NORTH ANNA UNIT 1 CYCLE 12 CONTROL ROD DROP TIME TEST RESULTS
Evaluation of North Anna Unit 1 Cycle 12 Control Rod Drop Time Tests Performed on August 28.1996 Evaluation - Rod Drop Time North Anna Unit 1 experienced an automatic reactor trip on August 27,1996. All control rods inserted into the core following the trip (i.e., the rod bottom lights illuminated), and no anomalous control rod insertion behavior was observed on the independent rod position indication (IRPI) system.
There have been recent incidents whereby control rods failed to fully insert that are documented in NRC Bulletin 96-01, " Control Rod Insertion Problems." The Virginia Electric and Power Company response to Bulletin 96-01 indicated that rod drop time tests would be performed during a mid-cycle outage of sufficient duration when the bumup 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. The response further committed to perform control rod tests without regard to either of the bumup thresholds if anomalous control rod behavior was observed.
North Anna Unit 1 Cycle 12 achieved initial criticality on March 10,1996. At the time of j
the reactor trip on August 27, 1996, no rodded fuel assembly had yet achieved a cumulative bumup of 35,000 MWD /MTU. All rod-bottom lights were illuminated following the trip, and there was no anomalous control rod insertion behavior as indicated on the individual rod position indicators (IRPIs).
Therefore, per Virginia Electric and Power Company response to NRC Bulletin 96-01, control rod drop time testing was not required.
However, the decision was made to test the drop times of all 48 control rods to provide assurance that no control rod insertion problem exists in the North Anna Unit 1 Cycle 12 core. The tests were completed on August 28,1996 and were performed under hot, full flow RCS conditions.
Figure 1 compares the drop time test results from the August 28,1996 tests to the drop time test results that were obtained at the beginning of Cycle (BOC) 12. 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 en August 28,1996. On average, the drop times measured on August 28 are approximately 0.03 seconds less per rod than the drop times measured at BOC. The rod drop times were within the specified limit of 2.13 seconds. Therefore, by examination of the rod drop time test results, there is no significant change in the drop time behavior of the control rods.
Evaluation - Rod Recoil l
Recoil was observed for all rod drop tests and was recorded on Periodic Test l
Procedure 1-PT-17.2, Rod Drop Time Measurement. Recoilis 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 l
inserted.
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'Conciusion Based on the control rod drop time measurements that were performed following the reactor trip and the fact that recoil was observed on the timing traces for all 48 control rods in the North Anna Unit 1 core, it is concluded that all 48 control rods promptly, fully inserted during the reactor trip.
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Figure 1 North Anns Unit 1 Cycle 12 BOC Contr:1 Rod Dr:p Time Mexurements Compared to August 28,1996 Control Rod Drop Times (Drop times are measured to the dashpot and are represented in seconds)
A B
C D
E F
G H
J K
L M
N P
R 1
A D
A 2
1,73 1.60 1.73 1.62 1.60 1.70 SA SA 3
1.74 1.71 1.66 1.66 C
B B
C 4
1.75 1.71 1.65 1,73 1.67 1.69 1.64 1.72 SB SB 5
1.70 1.75 1.66 1.73 A
B D
C D
B A
6 2.03 1.75 1.72 1.77 1.69 1.73 1.64 2.04 1.74 1.70 1.78 1.69 1.74 1.60 SA SB SB SA 7
1.74 1.66 1.65 1.73 1.70 1.62 1.68 1.68 D
C C
D 8
1.82 1.69 1.72 1.78 1.83 1.64 1.69 1.75 SA SB SB SA 9
1.58 1.71 1.63 1.78 1.56 1.70 1.62 1.68 A
B D
C D
B A
10 1.84 1.71 1.73 1.70 1.64 1,73 1.79 1.81 1.70 1.70 1.70 1.61 1.74 1.72 SB SB 11 1.69 1.80 1.66 1.81 C
B B
C 12 1.75 1.67 1.79 1.69 1.72 1.63 1.75 1.66 SA SA 13 1.72 1.71 1.66 1.69 A
D A
14 1.79 1.73 1.97 1.72 1.72
_1.94 15 Legend k
BankID BOC Test 8,"28/96 Test l
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