ML20134P959
| ML20134P959 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 11/21/1996 |
| From: | Ohanlon J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 96-591, IEB-96-001, IEB-96-1, NUDOCS 9612020003 | |
| Download: ML20134P959 (11) | |
Text
_
j
-c o
VIRGINIA ELucTHIC AND Powna COMPANY Hicnwown,Vinornir caust November 21, 1996 United States Nuclear Regulatory Commission Serial No.96-591 Attention: Document Control Desk NL&OS/ETS Washington, D. C. 20555-0001 Docket Nos. 50-338,339 License Nos. NPF-4,7 l
i Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 SUBMITTAL OF CONTROL ROD DROP 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 red recoil data for all control rods during 1996 outages of sufficient duration. This letter provides the rod drop j
time tests results for recent Unit 1 and Unit 2 shutdowns.
I North Anna Unit 2 was shutdown on October 21,1996 for a secondary system repair and had operated less than seven effective full power days (EFPD) since the beginning of Cycle 12 operation.
Following the unit shutdown, the individual rod position indication (IRPI) system indicated that four control rods were greater than 10 steps withdrawn. Control rod drop times were measured on October 23. Based on the control rod drop time test results and the fact that recoil was observed on the timing traces for all control rods in the North Anna Unit 2 core, it was concluded that all 48 control rods promptly, fully inserted during the reactor shutdown. All control rod drop times were within the internal operational drop time limit of 2.13 seconds.
1 Unit 2 resumed power operation on October 25 and subsequently tripped on November 12,1996 after approximately 17 EFPD had elapsed since power operation resumed. Following the November trip, the control board rod position indication (IRPI) system indicated that one of the control rods was greater than 10 steps withdrawn. An attemate reading of this IRPI provided by the process computer printout indicated that the rod was less than 10 steps withdrawn. Shortly after the trip, the control board IRPI indication changed and indicated a rod position that was less than 10 steps withdrawn which was consistent with the process computer printout indication.
Control rod drop times were measured on November 13. Similarly, based on the control rod drop time test results and the fact that recoil was observed on the timing traces for all control rods in the North Anna Unit 2 core during the test, it was concluded I
fok20$0a$ $ oo$338 h
j' G
i that all 48 control rods promptly, fully inserted during each reactor shutdown. All control rod drop times were within the intemal operational drop time limit of 2.13 seconds.
An evaluation of the drop time test results for Unit 2 Cycle 12 which were performed on j
October 23 and November 13 is included as Attachment 1.
in addition to the Unit 2 outages in October and November, North Anna Unit 1 tripped on October 24,1996. There were no anomalous control rod insertion indications by examination of the individual rod position indicators (IRPIs) following the trip. The control rod drop times were measured during the outage. An evaluation of the drop time test results for Unit 1 Cycle 12 which were performed on October 24 is included as. All control rod drop times were within the intemal operational drop time i
limit of 2.13 seconds. 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 all 48 control rods promptly, fully inserted during the reactor trip. The l
drop time test data indicate that there has been no significant change in the control rod drop behavior during Cycle 12 operation since the control rods were tested in August 1996 and during the startup of Cycle 12 in March 1996.
Should you have any questions or require additional information, please contact us.
Very truly yours, kttlk 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. D. McWhorter NRC Senior Resident inspector North Anna Power Station
J l
4 1
1 I
i 1
j i
~
l 4
i 1
i i
1 1
4 5
l ATTACHMENT 1 W
i
.i i
VIRGINIA POWER j
4 NORTH ANNA UNIT 2 CYCLE 12 CONTROL ROD DROP TIME TEST RESULTS 1
1 I
i I
4
.I j
l 1
4 4
4 s
4 1
4
Eyjiuation of North Anna Unit 2 Cycle 12 Control Rod Drop Time Tests Eerformed on October 23.1996 and November 13.1996 4
Rod Drop Time North Anna Unit 2 Cycle 12 achieved initial criticality on October 12,1996 and had i
operated less than seven effective full power days (EFPD) since the beginning of Cycle 12 when the reactor was shutdown on October 21,1996 to repair a leak in the secondary i
steam system. All control rods inserted into the core following the unit shutdown (i.e., the rod bottom lights were on), but the individual rod position indication (IRPI) system indicated that four control rods were greater than 10 steps withdrawn. The IRPls that indicated greater than 10 steps withdrawn corresponded to core locations H14, G7, G13, and G3. The IRPI system is an analog system and is sensitive to temperature changes.
It is typical to observe drift in one or more IRPIs, particularly following a reactor shutdown.
After obtaining satisfactory test results for the control rods and repairing the steam leak, i
Unit 2 resumed power operation on October 25,1996 and operated for approximately 17 EFPD when the unit tripped off-line on November 12,1996. All control rods inserted into the core following the trip (i.e., the rod bottom lights were on), but the IRPI system control board meter for the control rod in core location D4 indicated that the control rod in this l
location was greater than 10 steps withdrawn. An attemate reading of this IRPI provided by the process computer printout indicated that the rod in location D4 was less than 10 l
steps withdrawn. Shortly after the trip, the IRPI control board IRPI meter for location D4 changed its indicated value to be less than 10 steps withdrawn. 'This type of meter behavior could be caused by a residual static charge in the edgewise meter housing or instrumentation drift associated with the IRPI system.
Rod drop time tests were performed during these two outages under hot, full flow conditions on October 23,1996 and November 13,1996. Figure 1-1 compares the drop time test results from the beginning-of-cycle (BOC) tests and the tests conducted on i
October 23 and November 13. As can be seen on Figure 1-1, for any given control rod, there is very little variation in the drop times that were measured at BOC, October 23, and November 13. The rod drop times for any given control rod are all within *0.08 seconds of each other with most test results being within *0.02 seconds of each other. All rod 4
drop times for the tested control rods were within the intemal operational drop time limit of 2.13 seconds. Therefore, by examination of the rod drop time test results, there has been no significant change in the drop time behavior of the control rods during operation of Cycle 12.
Figure 1-2 shows the rodded assembly bumup for North Anna Unit 2 Cycle 12 as of October 31,1996. Since the assembly bumup values were calculated as of October 31, they are slightly higher than the assembly burnup at the time, of the October 23 tests and slightly lower than the bumup at the time of the November 13 tests.
l P
q Rod Recoil Recoil was observed for all rod drop tests. 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 control rod drop time measurements that were performed during both Unit 2 outages and the fact that recoil was observed on the timing traces for all control rods in the North Anna Unit 2 core during both sets of tests, it is concluded that all 48 control rods promptly, fully inserted during each reactor shutdown. All rod drop times for the control rods were within the intemal operational drop time limit of 2.13 seconds. Based on the test data, the anomalous IRPI indications for core locations H14, G7, G13, and G3 j
following the shutdown on October 21 and the IRPI indication for core location D4 following the trip on November 12 were not indications of incomplete control rod insertion.
The anomalous IRPI indications were likely to be the result of either instrumentation drift i
which is commonly seen with large temperature changes or residual static charge in the j
control board meter housing.
1 4
4 W
I r
l North Anna Unit 2 Cycle 12 Recent Control Rod Drop Time Measurements (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 1 66 1.E 8 1.76 3
1.66 1 69 1.74 1.67 1 65 1.75 i
M M
1.65 1,68
.l t
1 3
1 64 1.66 i
1.63 1.67 C
B B
C 1 72 1 63 1.78 1.52 4
1.72 1.64 1.77 1.53 1.73 1 62 1.77 1 52 l
SB SB 1 68 1.67 5
1.68 1.66 1 68 1.66 A
B D
C D
B A
1.95 1.66 1 66 1.66 1.67 1 68 1.65 6
1.06 1.66 1.68 1.65 1.70 1.67 1.66 2 00 1 64 1.66 1 67 1 67 1.71 1,66 SA SB SB SA 1.69 1.63 1.61 1.61 7-1.69 1.63 1 63 1.63 1 68 1.62 1 61 1.60 9
c c
D j
[
1.82 1.62 1.69 1.74 8
1.64 1.59 1.66 1.77
)
1 84 1.62 1 68 1.74 SA SB SB SA 1.54 1.63 1 60 1.69 9
1.54 1.64 1 60 1.67 1.54 1.63 1.59 1 68 i
A B
D C
D B
A 1.73 1.69 1.62 1.66 1 67 1.62 1.74 10 1.76 1 69 1.65 1.63 1 67 1.65 1.72 1.75 1 67 1.62 1 65 1.66 1.02 1.74 SB SB 1.64 1.70 11 1.64 1.69 1.64 1.66 C
B B
C 1.75 1.61 1 64 1.70 i
13 1.75 1.68 1 65 1.70 1.73 1 60 1.64 1.71 SA SA i
1.70 1.66 13 1.68 1.66 l
1.68 1 65 A
D A
l 1 80 1.75 1.67 14 1.78 1.74 1.91 1.78 1 74 1.88 13 Legend Bank ID BOC Test 10/23/96 Test 11/13/96 Test i
Figure 1-2 North Anna Unit 2 Cycle 12 Rodded Assembly Burnup as of October 31,1996 A
B C
D E
F G
H J
K L
M N
P R
1 i
A D
A l
2 23299 19039 23535 M
SA t
3 23071 22891
\\
l c
B B
c 4
24456 23302 24032 24638 SB SB 9
19602 20010 A
B D
C D
B A
6 23464 24345 24801 23399 24198 23943 23688 SA SB SB SA 7
22895 19867 19991 23092
-i e
D c
c D
8 19299 23682 23713 19552 SA SB SB SA 9
23337 19590 19931 22452 A
B D
c D
B A
10 23454 23409 24966 23580 24703 23966 23511 SB SB 11 20238 19629 s
c B
B c
S2 24510 24020 24282 24604 SA SA l
j 13 22837 22916
~
A D
A 14 23590 19181 23534 13 Legend Bank ID Bumup as of10/31/96 (MWD /MTU)
.j l
I I
)
i ATTACHMENT 2 l
VIRGINIA POWER NORTH ANNA UNIT 1 CYCLE 12 CONTROL ROD DROP TIME TEST RESULTS l
l 1
Evaluation of North Anna Unit 1 Cycle 12 Control Rod Drop Time Tests Performed on October 24.1996 i
Rod Drop Test North Anna Unit 1 tripped off line on October 24,1996. All control rods inserted into the core following the trip (i.e., the rod bottom lights were on), and no anomalous control rod
)
insertion behavior was observed on the independent rod position indication (IRPI) system.
i Rod drop time tests were performed under hot, full flow conditions on October 24,1996.
Figure 2-1 compares the drop time test results from the beginning-of-cycle (BOC) tests and the tests conducted on August 28,1996. As can be seen on Figure 2-1, for any given control rod, there is very little variation in the drop times that were measured at BOC, October 23, and November 13. The rod drop times for any given control rod are all within *0.10 seconds of each other with most test results being within *0.04 seconds of i
each other. All rod drop times for the tested control rods were within the intemal operational drop time limit of 2.13 seconds. Therefore, by examination of the rod drop time test results, there has been no significant change in the drop time behavior of the 4
control rods in the Unit 1 Cycle 12 core.
i Figure 2-1 shows the rodded assembly bumup for North Anna Unit 1 Cycle 12 as of October 31,1996. Since the assembly bumup values were calculated as of October 31, they are slightly higher than the assembly bumup values at the time of the October 24 i
control rod drop time tests.
i Evaluation Recoil was observed for all rod drop tests. 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.
I Conclusion i
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. All rod drop times for the tested control rods were within the intemal operational drop time limit of 2.13 seconds. There has been no significant change in the drop time behavior of the control rods during Cycle 12 operation.
1 4
1
~
Figure 2-1 North Anna Unit 1 Cycle 12 Recent Control Rod Drop Time Measurements (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 1.73 1 60 1.73 3
1 62 1.60 1.70 1.70 1 62 1.72 SA SA 1.74 1.71 3
1.66 1.66 1.67 1.68 C
B B
C 1.75 1.71 1.65 1.73 4
1.67 1.69 1.64 1,72 j
1.69 1.73 1.66 1.73 SB SB 1.70 1.75 5
1.06 1.73 1.69 1.78 A
B D
C D
B A
2.03 1.75 1.72 1.77 1.69 1.73 1.64 6
2.04 1.74 1.70 1.78 1.69 1.74 1.60 2.06 1.73 1.72 1.78 1.70 1.78 1.61 SA SB SB SA 1.74 1 66 1.65 1.73 7
1.70 1.62 1.68 1.68 -
1.71 1.69 1.68 1.70 D
C C
D 1.82 1.69 1.72 1.78 1
8 1.83 1 64 1.69 1.75 1.88 1.69 1.72 1.79 SA SB SB SA 1.58 1.71 1.63 1.78 0
1.56 1.70 1.62 1.68 1 58 1.75 1.69 1.70 A
B D
C D
B A
1.84 1.71 1.73 1.70 1.64 1.73 1.79 10 1 81 1.70 1 70 1.70 1 61 1.74 1.72 1 84 1.71 1 74 1.71 1.65 1.74 1.72 SB SB l
1 69 1.80 11 1.66 1.81 1.70 1 82 C
B B
C i
1.75 1.67 1.79 1.69 12 1.72 1.63 1.75 1.66 1.73 1 68 1 80 1.67 SA SA 1.72 1.71 13 1.66 1.69 a
1.66 1.70 A
D A
4 1.79 1.73 1.97 14 1.72 1.72 1 94 e
l 1.74 1.76 1.96 15 Legend Bank ID BOC Test 8/28/96 Test 10/24/96 Test
Figure 2-2 North Anna Unit 1 Cycle 12 Rodded Assembly Burnup as of October 31,1996 A
B C
D E
F G
H J
K L
M N
P R
1 A
D A
3 30098 28596 29568 SA SA 3
33612 33140 C
B B
C 4
32592 34592 35112 32079 SB SB 0
31243 31569 A
B D
C D
B A
6 29964 35469 35859 34412 35409 35210 30012 SA SB.
33256 30324 30585 33744 D
C C
D 8
28905 34443 34468 28887 SA SB SB SA 9
33820 30132 30106 32804 A
B D
C D
B A
10 30676 34427 35947 34101 36064 34952 30135 SB SB 11 31983 31573 C
B B
C 12 32830 35114 35336 32770 SA SA 13 33056 33413 A
D A
14 30049 28488 30163 15 Legend Bank ID Burnup as of10/31/96 (MWD /MTU)