ML20129A544
| ML20129A544 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 10/15/1996 |
| From: | Ohanlon J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 96-529, IEB-96-001, IEB-96-1, NUDOCS 9610220177 | |
| Download: ML20129A544 (8) | |
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VIRGINIA ELECTHIC AND Pownn COMPANY llICIIMOND,VIHGINIA 20061 October 15, 1996 United States Nuclear Regulatory Commission Serial No.96-529 Attention: Document Control Desk NL&OS/ETS R1 Washington, D. C. 20555-0001 Docket No.
50-339 License No.
NPF-7 Gentlemen:
ylBGINIA ELECTRIC AND POWER COMPANY N_ ORTH ANNA POWER STATION UNIT 2 CONTROL ROD DROP TIMFJD DRAG TEST RESULTS IN ACCORDANCE WITH NRC BULLETIN 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 dudng 1996 outages of sufficient duration. North Anna Unit 2 completed Cycle 11 on September 8,1996. The commitments made in our response to NRC Bulletin 96-01 require control rod drop time testing to be performed at outages of sufficient OJration and to evaluate Control rod drag forces during outages when the vessel head is removed. Both of these tests were performed during the Cycle 11 to Cycle 12 refueling outage following the September 8 unit shutdown. Attached is an evaluation of the data obtained from the control rod drop time tests completed on September 8,1996 and the control rod drag force measurements completed on September 16,1996.
Should you have any questions or require additional information, please contact us.
Very truly yours, James P. O'Hanlon
);/
Senior Vice President - Nuclear I
Attachment 9610220177 961015 PDR ADOCK 05000339
/
O PDR 220043
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U. S. Nuclear Regulatory Commission Region 11 i
4 101 Marietta Street, N. W.
Suite 2900 Atlanta, Georgia Mr. R. D. McWhorter NRC Senior Resident inspector North Anna Power Station f
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EyAhtafon of North Anna 2 Eind of Cycle 11
@ntrol Rod Drop Time Tests and Control Rod Drag Tests i
North Anna Unit 2 completed Cycle 11 on September 8,1996. The commitments made in our response to NRC Bulletin 96-01 require control rod drop time testing to be performed at the end of a cycle and to evaluate control rod drag forces during outages when the vessel head is removed. Both of these tests were performed during the Cycle 11 to Cycle 12 refueling outage following the September 8 shutdown. The following is an evaluation of the data obtained from the control rod drop time tests and the control rod drag force measurements.
i Qntrol Ro1LDrop Time and Recoil Evaluation Control rod drop time tests were performed on September 8 shortly after Unit 2 was shut down for refueling. The measured drop times were within the intemal operational limit of 2.13 seconds which is less than the Technical Specification limit of 2.7 seconds. Figure 1 i
compares the drop time test results obtained from the end-of-cycle (EOC) tests to the drop time test results that were obtained at the beginning of Cycle (BOC) 11. As can be seen on Figure 1, there is very little variation in the drop times that were measured at EOC compared to the drop times measured at BOC. On average, the EOC drop times are approximately 0.02 seconds less per rod than the drop times measured at BOC.
Therefore, by examination of these data, there was no significant change in the drop time behavior during the operation of North Anna 2 Cycle 11.
Recoil was observed for e I rod drop tests. Recoil is the control rod bounce that occurs when the spring pack on tse control rod impacts the top nozzle of the fuel assembly. The existence of recoilis positive indication that the control rod has fully inserted.
i By examination of the control rod drop time data and the existence of recoil, it is concluded that all 48 control rods were capable to proraptly, fully insert during operation of Cycle 11.
Control Rod Drag Measurement Evaluation Control rod drag measurements were performed in the spent fuel pool on September 16 following the offload of the North Anna 2 Cycle 11 (N2C11) core using the actual rodded fuel assemblies from Cycle 11 with their respective control rods. The acceptance criteria for the drag tests are: (a) the maximum drag load of a control rod in a fuel assembly should not exceed 100 pounds in the dashpot region, and (b) the maximum drag load of a control rod in a fuel assembly should not exceed 40 pounds in the upper guide tube region (region above the dashpot). All 48 rodded fuel assemblies from N2C11 had less than 100 pounds of control rod drag force in the dashpot region. Two fuel assemblies slightly exceeded the criterion for drag force in the upper guide tube. The remaining 46 rodded fuel assemblies from Cycle 11 had less than 40 pounds of control rod drag force in the dashpot region.
Assemblies-SM6 (46,264 MWD /MTU) and SM0 (46,149 MWD /MTU) exceeded the drag force acceptance criterion of 40 pounds in the upper 4
guide tube by 4 pounds and 1 pound, respectively.
1
Thp. control rod drop times for assemblies SM6 and SMO indicate that the ability of the control rods to perform as designed was not affected by their upper guide tube drag forces. The EOC control rod drop times in assemblies SM6 and SMO were 1.69 seconds and 1.67 seconds, respectively. The EOC control rod drop time in SM6 was 0.03 seconds greater than its BOC drop time. There was no difference between the EOC and BOC measured control rod drop times in assembly SMO. Recoil was observed for both j
control rods during the drop tests. It is therefore concluded that the drag force of 44 j
pounds and 41 pounds in the upper guide tubes of these assemblies did not impede the ability of the control rods in assemblies SM6 and SMO to perform as designed.
A Fuel Anomaly Form was issued documenting that the drag force in assemblies SM6 and SMO exceeded the acceptance criterion for drag force in the upper guide tube region.
These two fuel assemblies are not scheduled for reuse. However, these two assemblies are restricted from use in a core location that requires an insert component should they be selected for use in a future core design.
Table 1 is a list of the N2C11 rodded assemblies, corresponding EOC bumup, Cycle 11 core location, and drag test results. Figure 2 is a core map comparing the average assembly burnup at BOC and EOC for rodded fuel assemblies in N2C11. Figure 3 is a chart of measured control rod drag force versus fue! assembly burnup for the rodded assemblies in N2C11.
CAonclusior)
Based on the control rod drop time tests and control rod drag force measurements that were performed following the shutdown of N2C11, it is concluded that all 48 control rods were capable to promptly, fully insert as designed during operation of Cycle 11. The conclusion is supported by the following:
i The 48 control rods in the N2C11 core were within the internal operational limit of 2.13 seconds and the Technical Specification limit of 2.7 seconds for drop time to the dashpot.
j Control rod recoil was observed during the EOC control rod drop time tests for each of the 48 control rods in the core. The presence of recoil verifies that the control rod fully iriserted when tripped into the core.
The drag test results of the N2C11 rodded assemblies with the exception of SM6 and SMO were within the acceptance criteria of 40 pounds in the upper guide tube and 100 pounds in the dashpot.
Two assemblies (SM6 and SM0) exceeded the drag force acceptance criterion of 40 pounds in the upper guide tube by 4 pounds and 1 pound, respectively. The EOC control rod drop times and the presence of recoil indicate that the drag force of 44 pounds and 41 pounds in the upper guide tubes of these assemblies did not impede the ability of the control rods in assemblies SM6 and SMO to perform as designed. These two fuel assemblies are not scheduled for reuse. However, they are restricted from use in a core location that requires an insert component should they be selected for use in a future core design.
2
Tcbla 1 North Anna 2 CycI211 C:ntral Rod Dr;:g Tc;t Rruit3 Assembly N2C11 Core Bumup Dashpot Drag Guide Tube Drag ID Location (MWD /MTU)
Force (Ibf)
Force (Ibf)
IM8 F6 48055 46 19 2M4 K10 47904 42 27 2M5 F10 47415 64 28 1M1 K6 47246 21 3
i 3M9 D6 47162 16 4
i 3M4 M6 46948 9
1 3M1 K4 46903 21 4
l SM7 F12 46826 43 34 3MO F8 46639 44 14 4M6 K12 46569 36 19 4M8 M10 46530 21 9
SM8 DIO 46360 25 6
SM6 F4 46264 57 44 SMO H10 46149 48 41 3M7 H6 46009 34 25 4M5 K8 45877 30 16
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3M2 E11 44496 20 13 EM3 C9 44390 14 4
4M2 G3 44316 19 10 6M1 N7 44110 12 3
3M3 J3 43883 22 9
4 SM3 L11 43742 12 5
3M6 C7 43638 15 5
4MO L5 43508 30 10 SM2 G13 43391 31 18 4M7 E5 43338 23 13 4M4 J13 43243 17 13 6MO N9 43174 17 11 5M5 J7 41771 19 9
SM1 G9 41676 49 29 2M3 D12 41634 30 9
SM4 J9 41619 33 24 OM1 M12 41485 29 6
SM9 G7 41370 31 20 1M4 D4 40544 22 12 1M3 M4 40176 19 6
6M2 P8 37905 18 3
4M9 B8 37886 8
1 OM7 F14' 37824 17 6
2MO K14 37743 22 6
1M7 B10 37735 7
2 4M3 H14 37385 12 4
6M4 H2 37336 12 3
2M8 P6 37158 7
0 2M7 B6 37133 7
2 OM3 K2 36807 18 5
OMS P10 36721 29 10 I
2M6 F2 36550 15 7
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Figure 1
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North Anna Unit 2 Cycle 11 BOC Contr:I Rod Drop Tima Me2:urem:nt3 Compared to EOC Rod Drop Time Measurements (Drop times are measured to the dashpot and ara represented in seconds)
A B
C D
E F
G H
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L M
N P
R 1
i A
D A
2 1.71 1.69 1.75 1.64 1.68 1.72 SA SA 3
1 69 1 71 1.64 1.64 C
B B
C 4
1.75 1.66 1.79 1.55 1.73 1.69 1.76 1.48 SB SB 5
1.68 1.67 1.66 1.65
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B D
C D
B A
i 6
. 95 1.66 1.66 1.67 1.67 1.69 1.67 1.89 1.64 1.67 1.62 1.62 1.67 1.61 SA SB SB SA 7
1.73 1.63 1.61 1.65 1.69 1.67 1.60 1.58 D
C C
D 8
1.85 1.63 1.68 1.73 1.80 1.60 1.67 1.71 SA SB SB SA g
1.54 1.65 1.60 1.72 1.50 1.69 1.62 1.68 A
B D
C D
B A
10 1.79 1.69 1.65 1.67 1.64 1.65 1.72 1.72 1.66 1.68 1.67 1.60 1.63 1.73 SB SB 11 1.64 1.68 1.64 1.66 C
B B
C 12 1.77 1.64 1.65 1.70 1.74 1.66 1.66 1.69 SA SA
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13 1 71 1 70 1.73 1.66 A
D A
14 1.84 1.75 1.91 1.77 1.74 1.84 l
l 15 Legend BankID BOC Test EOC Test i
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Figura 2 North Anna Unit 2 Cycb 11 Rodded Fuel A:sembly Burnup Map Average Assembly Burnup at BOC and EOC (Burnup is expressed in MWD /MTU)
A B
C D
E F
G H
J K
L M
N P
R 1
i A
D A
2 24896 20784 25228 36550 37336 36807 SA SA 3
23764 23142 44316 43883 C
B B
C 4
25841 24551 25403 25525 40544 46264 46903 40176 SB SB 5
20686 20827 43338 43508 A
B D
C D
B A
6 25574 25588 26166 24352 25709 25353 25552 37133 47162 48055 46009 47246 46948 37158 SA SB SB SA 7
23030 19411 19963 23324 43638 41370 41771 44110 D
C C
D 8
20856 24853 24637 21366 37886 46639 45877 37905 i
23597 19820 19848 22827 44390 41676 41619 43174 A
B D
C D
B A
10 25762 24568 25822 24846 26298 24992 25303 37735 46360 47415 46149 47904 46530 36721 SB SB 11 21441 21049 44496 43742 C
B B
C 12 26172 25130 24990 26606 41634 46826 46569 41485 SA SA 13 22756 22752 43391 43243 A
D A
14 26119 20751 26198 37824 37385 37743 15 Legend BankID BOC Bumup EOC Bumup 5
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Figure 3 North Anna 2 Cycle 11 End-of-Cycle Drag Force Measurements 100 90 80 70
[1 60 a Dashpot Region u
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x Upper Guide Tube Region f
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35000 37500 40000 42500 45000 47500 50000 Fuel Assembly Burnup, MWD /MTU 6
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