ML20101N208
| ML20101N208 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 04/04/1996 |
| From: | Mccoy C GEORGIA POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-96-001, IEB-96-1, LCV-0788, LCV-788, NUDOCS 9604080289 | |
| Download: ML20101N208 (17) | |
Text
Georgia Power Company 40 invemess Center Parkway
,. Post Office Box 1295 B rmingham, Alabama 35201 i
Telephone 205 877-7122
- c. K. uccoy Georgia Power
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yogve the southern electre systen April 4, 1996 LCV-0788 Docket Nos.: 50-424 50-425 U. S. Nuclear Regulatory Commission ATTN:' Document Control Desk Washington, D. C. 20555-0001 VOGTLE ELECTRIC GENERATING PLANT 30-DAY RESPONSE TO NRC BULLETW 96-01 CONTROL ROD INSERTION PROBLEMS Gentlemen:
By letter dated March 8,1996, the NRC issued Bulletin 96-01, "Cor. trol Rod Insertion Problems," requiring actions to be taken by utilities regarding the su sceptibility and evaluation of the Rod Control System to the phenomena of contrci rod failure to insert completely. The Bulletin was issued to accomplish two goals. First, to alert addressees to -
problems encountered during recent events in which control rods failed to insert completely when tripped and second, to assess the operability of control rods, particularly in high burnup fuel assemblies.
The Georgia Power Company 30-day response for the Vogtle Electric Generating Plant is summarized in Attachments 1 and 2. Georgia Power Company considers that the control rods in both units are operable based on our review of current industry data and based on successful reactor trip and drag test data in VEGP-1 in March 1996 in high burnup fuel.
Georgia Power Company will continue to follow the Westinghouse Owners Group and industry effort to determine the root cause of the problems experienced at the identified plants, and will factor the results of this effort into any future plans.
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9604080289 960404 PDR ADOCK 05000424 l
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I GeorgiaPower b U. S. Nuclear Regulatory Commission Page 2 Mr. C. K. McCoy states that he is a vice president of Georgia Power Company and is authorized to execute this oath on behalf of Georgia Power Company, and to the best of his knowledge and belief, the facts set forth in this letter are true.
GEORGIA POWER COMPANY l
By:
l C. K. McCoy i
Sworn to and subscribed before me this day of
.1996.
i ll n { %.
Notary Pubfic CKM/SHK '
Attachments 1 and 2 cc: Georgia Power Company Mr. J. B. Beasley, Jr.
Mr. M. Sheibani NORMS U. S. Nuclear Regulatory Commission Mr. S. D. Ebneter, Regional Administrator Mr. L. L. Wheeler, Licensing Project Manager, NRR Mr. C. R. Ogle, Senior Resident Inspector, Vogtle l
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LCV-0788 l
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9 ATTACRMENT 1 VOGTLE ELECTRIC GENERATING PLANT NRC BULLETIN 96-01 CONTROL ROD INSERTION PROBLEMS Reauired Response (th which states:
"Within 30 days of the date of this bulletin a report certifying that control rods are determined to be operable; actions taken for Requested Actions (1) and (2) above; and the plans for implementing Requested Action (3) and (4)."
Response
A report certifying that control rods are determined to be operable.
Response
Control rods at Vogtle Electric Generating Plant Unit 1 (VEGP-1) were operable at the end of Cycle 6, which completed operation on March 3,1996, as evidenced by the fact that prompt, complete control rod insertion occurred when the unit was tripped from low power, to end the cycle. Control rods in bank D were at 174 i
steps, per demand indication, at the time of the trip. For VEGP-1 Cycle 7, control rods will be determined to be operable by rod drop time tests prior to reactor startup and periodic Rod Cluster Control Assembly (RCCA) stepping during i
operation, as required by the Technical Specifications. Additional testing of rod operability will be performed as described below in the Response to Requested Action (3).
Control rods at Vogtle Electric Generating Plant Unit 2 (VEGP-2), which is currently in Cycle 5, are operable. The last shutdown for VEGP-2 was on July 23, 1995 when the unit tripped from full power. No control rod anomalies were observed, and all control rods inserted fully. Additionally, no abnormal control rod operation has been observed during reactor operation. Operability will continue to be demonstrated through periodic RCCA stepping as required by j
Technical Specifications. Rodded assembly burnups are bounded by rodded
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assembly burnups previously attained in VEGP-1, and are projected to remain bounded through the end of Cycle 5.
All rodded fuel assemblies in VEGP-1 Cycle 6, VEGP-1 Cycle 7, and VEGP-2 Cycle 5 are Westinghouse Vantage 5.
The response below to Requested Action (2) contains further discussion of control rod operability.
Actions taken for Reauested Action (1) which states-
"Promptly inform operators of recent events (reactor trips and testing) in which control rods did not fully inert and subsequently provide necessary training, including simulator drills, utili2ing the required procedures for responding to an event in which the control rods do not fully insert upon reactor trip (e.g., boration of a pre-specified amount)."
Resoonse:
Shift briefings were held with each operating crew to promptly advise operators of the recent events, of the potential for less than full control rod insertion, and of the proper compensatory actions in the event ofless than full control rod insertion. In addition, the potential for less than full control rod insertion will be covered in the next segment of Licensed Operator Requalification training to further reinforce operators' understanding of the recent events and of the proper compensatory actions. The simulator was modified to permit exercises involving less than full control rod insertion of some rods. Simulator exercises involving less than full control rod insertions of some rods will be included in the next segment of Licensed Operator Requalification training. The next segment of Licensed Operator Requalification training is scheduled fbr April 15,1996 through May 20, 1996.
Actions taken for Requested Action (2) which 11A191 "Promptly determine the continued operability of control rods based on current information. As new information becomes available from plant rod drop tests and trips, licensees should consider this new information together with data already available from Wolf Creek, South Texas, North Anna, and other industry experience, and make a prompt determination of control rod operability."
Response
Control rods at VEGP-1 were operable at the end of Cycle 6, which completed operation on March 3,1996, as evidenced by the fact that prompt, complete control rod insertion occurred when the unit was tripped from low power to end the cycle. For VEGP-1 Cycle 7, control rods will be determined to be operable by rod drop time tests prior to reactor startup and periodic RCCA stepping during operation as required by Technical Specifications. Additional testing of rod
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operability will be performed as described below in the response to Requested Action (3). Based on currently available information, control rods at VEGP-2 are operable, and will continue to be operable for the remainder of Cycle 5. Rodded assembly burnups are bounded by rodded assembly burnups previously attained in VEGP-1. Operability will continue to be demonstraN through periodic RCCA stepping as required by Technical Specifications. No aonormal rod behavior has been observed at VEGP-2. All rodded fuel assemblies in VEGP-1 Cycle 6, VEGP-1 Cycle 7, and VEGP-2 Cycle 5 are Westinghouse Vantage 5.
On March 3,1996, VEGP-1 was shut down for a refueling outage. With the reactor at low power, rods were tripped into the core to achieve shutdown. At the time of the trip, bank D rods were at 174 steps, per demand indication. All rods promptly indicated full control rod insertion, and there were no indications of control rod sticking. At the time of the trip, four assemblies in bank C had burnups in excess of 50,500 MWD /MTU, and four assemblies in bank D had burnups in excess of 48,900 MWD /MTU.
On March 16-17,1996, following core offload, RCCA drag testing was performed in the spent fuel pool for all 53 assemblies which were rodded during Cycle 6 operation. Drag tests were performed using the same RCCA that resided in the assembly during Cycle 6. All 53 assemblies exhibited low drag forces in the guide tube above the dashpot.
Two assemblies did exhibit drag forces in the dashpot region which were higher than that permitted by Westinghouse specification F-5.1, Instructions. Precautions.
and Limitations for Handling Rod Cluster Control Assemblies and Core Component Assemblies, for RCCAs in rodded assemblies at the beginning of a cycle. Both assemblies had burnups in excess of 50,800 MWD /MTU. In the dashpot region both assemblies exhibited breakaway drag forces of approximately 170 to 185 pounds and dynamic drag forces of approximately 110 to 135 pounds as compared to the F-5.1 specification value of 100 pounds. Out of the dashpot region, both assemblies exhibited drag forces which were well within the F-5.1 specification value of 40 pounds. The high drag forces in the dashpot region did not adversely impact the operability of the control rods in these assemblies as evidenced by the fact that prompt, complete control rod insertion occurred at the March 3,1996 trip. In addition, information provided by the Westinghouse Owners Group (WOG) indicates that all assemblies which have experienced insertion problems have had drag force values above the Westinghouse specification F-5.1 values both in and out of the dashpot region. The WOG information indicates that no assembly that had drag force test values below the Westinghouse specification values in one region of the guide tube, either in the dashpot or out of the dashpot, has experienced insertion problems. I I
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Based on review of the VEGP-1 drag test data, Westinghouse concluded that the behavior observed in the assemblies ac VEGP-1 was not similar to that observed in i
the assemblies with the insertion anomaly at Wolf Creek, and that the assemblies at VEGP-1 do not have the thimble tube distortion observed at Wolf Creek. In addition, Westinghousejudged that the same burnup can be achieved again I
without concern for RCCA insertion.
On March 20,1996, prior to loading of the VEGP-1 Cycle 7 core, the RCCAs from the two assemblies described above were drag tested in their Cycle 7 host assemblies. Drag tests in both Cycle 7 host assemblies found low drag forces in l
the dashpot region as well as out of the dashpot region.
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A review of historical trip data (since 1991) for VEGP-1 and -2 found no instances of control rods failing to insert fully after a trip. In addition, recorded red drop times show no indications of control rod sticking. A review of burnup data for VEGP rodded assemblies was performed to determine the highest burnup l
in rodded assemblies during reactor trips since 1991. Burnups in excess of 50,800
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MWD /MTU in Westinghouse Vantage 5 fuel and 41,900 MWD /MTU in Westi ighouse LOPAR fuel were present during trips with no instances of a failure of a control rod to insert fully.
Rodded assembly burnups at the conclusion of VEGP-2 Cycle 5 will be bounded i
by the maximum rodded assembly burnup observed for VEGP-1 Cycle 6, assuming VEGP-2 Cycle 5 operates as currently projected. For VEGP-1 Cycle 7, which is scheduled to start operation in April 1996, the end of Cycle 7 burnup in one rodded assembly has the potential to exceed the maximum rodded assembly burnup observed for VEGP-1 Cycle 6 by about 1100 MWD /MTU. However, the rodded assembly burnups for all other assemblies in VEGP-1 Cycle 7 are projected to be bounded by the maximum VEGP-1 Cycle 6 rodded assembly burnup. Details of current and projected assembly burnups for VEGP are provided in Attachment l
2.
VEGP cores use fuel with a standard 12-foot active fuel length. Both cores use Westinghouse Vantage 5 and Westinghouse LOPAR fuel. All rodded assemblies in current VEGP cores and in VEGP cores under design are Vantage 5. This configuration is different from the configuration of the cores at any of the plants identified as having this problem.
South Texas Project uses a 14-foot active fuel length core design consisting of Standard XL, Standard XLR, and Vantage SH fuel. The dashpot region is 10 inches longer than in the standard 12-foot active fuel length assembly design and comprises a double dashpot. i s
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Both North Anna and Wolf Creek use Vantage 5H fuel. To date, there have e
been no reported instances ofincomplete control rod insertion occurring at plants with Vantage 5 or LOPAR fuel.
Both VEGP-1 Cycle 7 and VEGP-2 Cycle 5 have shutdown margin in excess of the minimum required by Technical Specification 3.1.1.1 (which accounts for the most reactive control rod stuck fully withdrawn from the core). This excess shutdown margin could be used to offset any loss of shutdown margin that resulted from the failure of control rods to insert fully.
Georgia Power Company will continue to follow the Westinghouse Owners Group and industry effort to determine the root cause of the problems experienced at the identified plants, and will factor the results of this effort into any future plans.
Plans for imolementing Requested Action m which states:
" Measure and evaluate at each outage of sufficient duration during calendar year 1996 (end of cycle, maintenance, etc.), the control rod drop times and rod recoil data for all control rods. If appropriate plant conditions exist where the vessel head is removed, measure and evaluate drag forces for all rodded fuel assemblies.
a.
Rods failing to meet the rod drop time in the technical specifications shall be deemed inoperable.
b.
Rods failing to bottom or exhibiting high drag forces shall require prompt corrective action in accordance with Appendix B to Part 50 of Title 10 of the
{
Code of Federal Regulations (10 CFR Part 50)."
Response
l Georgia Power Company plans to perform rod testing during 1996 as outlined below.
For VEGP-1, the following actions will be performed:
Rod drop time tests including observation of rod recoil will be performed prior to Cycle 7 reactor startup.
If the unit trips in 1996, timely complete rod insertion will be confirmed per normal reactor trip response procedures. Rod drop time tests including observation of rod recoil will be performed only if timely complete rod insertion does not occur.
No further testing will be performed during 1996 because burnups in rodded assemblies will be relatively low (less than 42,500 MWD /MTU).. -.
For VEGP-2 prior to the scheduled Fall 1996 refueling outage, the following actions will be performed:
If a planned shutdown occurs in 1996 prior to the scheduled refueling l
outage, the unit will be ramped to low power and tripped. Rod insertion will be observed. Rod drop time tests including observation of rod recoil will be performed for the first shutdown only, unless timely complete rod insertion does not occur.
If the unit trips in 1996 prior to the scheduled refueling outage, timely complete rod insertion will be confirmed per normal reactor trip response procedures. Rod drop time tests including observation of rod recoil will be performed for the first shutdown only, unless timely complete rod insertion does not occur.
For the planned Fall 1996 outage on VEGP-2, the following actions will be performed:
The unit will be ramped to low power and tripped. Rod insertion will be observed.
Rod drop time tests including observation of rod recoil will be performed prior to cooling down.
Control rod drag testing will be performed either in the reactor vessel prior to core offload or in the Spent Fuel Pool after core offload.
Rod drop time tests including observation of rod recoil will be performed prior to Cycle 6 reactor startup.
Following the Fall 1996 outage on VEGP-2, the following actions will be performed:
No other testing will be performed on the unit in 1996 due to low burnup, unless timely complete rod insertion does not occur following a reactor shutdown or trip.
The actions of Technical Specification 3.1.3.4 will be met for rods with drop times exceeding the limit. Rods that meet operability requirements of the Technical Specifications but fail to bottom during a reactor trip or exhibit high drag forces will be subject to those actions necessary to provide confidence that they will perform satisfactorily in service in accordance with 10 CFR 50 Appendix B. Rods determined to require corrective action or failing to insert fully or promptly will be i
reported to the NRC in accordance with NRC Bulletin 96-01. :
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l Plans for implementing Reauested Action (4) which states:
"For each reactor trip during calendar year 1996, verify that all control rods have promptly fully inserted (bottomed) and obtain other available information to assess the operability and any performance trend of the rods. In the event that all rods do not fully insen promptly, conduct tests to measure and evaluate rod drop times and rod recoil."
Resoonse:
i If either unit trips in 1996, timely complete rod insenion will be confirmed per normal reactor trip response procedures. If timely complete rod insertion is not observed, rod drop time tests including observation ofrod recoil will be performed.
Reauired Response (2). which states:
"Within 30 days of the date of this bulletin, a core map ofrodded fuel assemblies indicating fuel type (materials, grids, spacers, guide tube inner diameter) and current and projected end of cycle burnup of each rodded assembly for the current cycle; when available, provide the same information for the next cycle."
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Response
The requested information is provided in Attachment 2 for the following VEGP cycles-I i
VEGP-1 Cycle 6, which completed operation on March 3,1996; VEGP-1 Cycle 7 which t
is anticipated to begin operation in April 1996; and VEGP-2 Cycle 5, which is currently operating. The requested information for VEGP-2 Cycle 6 is not currently available, as that design is not sufficiently finalized and is still subject to change. The requested information will be provided for VEGP-2 Cycle 6 within 30 days following criticality of that cycle, which is currently anticipated in October 1996.
For VEGP-1 Cycle 6, Attachment 2 contains a core map indicating for each rodded location the control rod bank identification, the assembly identification number, and the burnup of the assembly at the end of cycle. Attachment 2 also contains a table of the physical assembly characteristics of the two regions of fuel which contained control rods during Cycle 6.
For VEGP-1 Cycle 7, Attachment 2 contains a core map indicating for each rodded l
location the control rod bank identification, the assembly identification number, the L
current (beginning of cycle) burnup, and the projected end of cycle burnup. - Attachment 2 also contains a table of the physical assembly characteristics of the two regions of fuel which will contain control rods during Cycle 7.
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For VEGP-2 Cycle 5, Attachment 2 contains a core map indicating for each rodded location the control rod bank identification, the assembly identification number, the burnup as of February 29,1996, and the projected end of cycle burnup. Attachment 2 also contains a table of the physical assembly characteristics of the two regions of fuel in Cycle 5 which contain control rods.
Reauired Response (3). which states:
"Within 30 days after completing Requested Action (3) for each outage, a report that summarizes the data and that documents the results obtained; this is also applicable to Requested Action (4) when any abnormal rod behavior is observed."
Response
Drag Test Results for VEGP-1:
Drag testing was performed in the Vogtle Spent Fuel Pool on March 16-17,1996 on all assemblies which were rodded during VEGP-1 Cycle 6. Results of this testing are provided in the response to Requested Action (2) above Results for Subsequent VEGP Tests:
Results for subsequent VEGP tests will be submitted when required by the above evolutions performed in 1996.
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f ATTACIBfENT 2 1
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Vogtle 1 Cycle 6 R
P N
M L
K J
H G,
F E
D C
B A
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SA B
C B
SA SG43 sw28 5H01 5H44 SG41 40729 26FJ1 25944 26291 41223 3
SD SB SB SC 5H52 5H06 5H08 5H59 29326 28252 28036 28;24 SA D
SE D
SA 5G48 SG58 SG03 5G55 5G47 41160 49406 42552 49493 41178 SC SD 5H73 5H54 28977 28928 B
C A
C B
5H39 5G80 5H64 SG82 5H40 26177 50805 27795 50677 26070 SB SB g
5H09 5H11
/
27842 28125 C
SE A
D A
SE C
SH02 5G04 5H71 5H12 5H57 SG01 5H03 25716 42524 27563 28351 27678 42390 25824 13 SB 3C SH13 27923 27928 i
B C
A C
B 5H26 SG67 5H81 5G70 SH43 26865 50852 27638 50586 27256 SD SC 5H75 5H53 30270 28631 SA D
SE D
)
5G40 5G63 SG02 5G56 SG51 41624 49270 42382 48909 41503 1
)
5H63 5H07 5H10 SH77 28852 27994 27818 29183 i
LEGEND SA B
C B
SA l
5G50 5H42 5H04 5H38 SG44
- ROD BANK 41130 26465 25828 26801 41632 1
- ASSY NUMBER
- EOC 6 BURNUP ACTUAL (MWD /MTU)
1 l
PIIYSICAL CIIARACTERISTICS OF RODDED ASSEMBLIES PLANT VOGTLE UNIT 1 CYCLE 6 l
REGION 5G REGION 5H Assembly Type Vantage-5*
Vantage-5*
Clad Material Zirc-4 Zirc-4 Grid Material Mid-span grids Zirc-4 Zirc-4 Bottom / Top grid Inconel-718 Inconel-718 l
Guide Tube Material Zirc-4 Zirc-4 Guide Tube O.D. (inches)
Above dashpot 0.4740 0.4740 At dashpot 0.4300 0.4300 Guide Tube I.D. (inches)
Above dashpot 0.4420 0.4420 l
At dashpot 0.3970 0.3970 l
l
- 17x17 assemblies with optimized fuel rod O.D. of 0.360 in. and with intermediate flow mixing (IFM) grids
Vogtle 1 Cycle 7 R
P N
M L
K J
H G
F E
D C
B A
1=
SA B
C B
SA SH67 5J14 SJ28 SJ16 5H58 29114 o
o o
29039 42521 25100 27100 25016 42534 SD SB SB SC BJ43 SJ56 SJ59 SJri o
e o
o 29128 29589 29559 29063 SA D
SE D
SA A
SH62 5H43 5H28 SH42 5H72 29079 27256 29801 26485 29053 42538 49365 48208 49355 42521 SC SD 5J81 SJs4 e
o 29063 29123 B
C A
C B
SJ17 5H22 SJ58 SH21 BJ18 o
21871 o
21954 e
2s01a 44944 29464 eased 25100 SB SB T
T 7
29559 C
SE A
D A
SE C
SJ34 SH26 SJ69 5H12 SJ65
$H40 SJ31 o
26865 o
as351 o
2e07o o
O 27100 48208 29468 51919 29456 48208 27100 SB SB O
BJ75 SJ57 o
o J
295R9 29559 B
C A
C B
SJ19 5H23 SJ62 SH18 SJ13 o
21154 o
21993 o
25100 44944 29456 44944 25016 SD SC T
T 11 29128 29063 SA D
SE D
SA SH80 5H44 5H38 5H39 SH74 28981 26291 26801 26177 28786 42521 49355 48209 49365 42538 SC SB SB SD LEGEND 7
7 7
Y 29063 29559 29589 29128 SA P
c B
- ROD BANK SH76 m
SJ39 BJ15 5H86 29007 o
e o
28915
-ASSY. NUMBER 42538 2s01s m 0s 25100 42521
-CURR.BURNUP*
-PROJ.BURNUP QEOC7**
- Actual EOC 6 (MWD /MTU)
- Based on Design
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PHYSICAL CIIARACTERISTICS OF RODDED ASSEMBLIES PLANT VOGTLE UNIT 1 CYCLE 7 l
REGION 5H REGION 5J Assembly Type Vantage-5*
Vantage-5*
Clad Material Zirc-4 Zirc-4 l
Grid Material l
Mid-span grids Zirc-4 Zirc-4 Bottomffop grid Inconel-718 Inconel-718 l
Guide Tube Material Zirc-4 Zirc-4 Guide Tube O.D. (inches) l Above dashpot 0.4740 0.4740 At dashpot 0.4300 0.4300 Guide Tube I.D. (inches)
Above dashpot 0.4420 0.4420 At dashpot 0.3970 0.3970
- 17x17 assemblies with optimized fuel rod O.D. of 0.360 in, and with intermediate flow mixing (IFM) grids
Vogtle 2 Cycle.5 R
P N
M L
K J
H G
F E
D C
B A
~
1:
SA B
C B
SA sS3ssiis sT22 sT29 sS39 3s113 16339 16877 16024 34880 40041 25936 26797 25844 39962 SD SB SB SC sTss sT34 sise siss 18968 1903s 18930 18686 29n9 29957 29930 29698 SA D
SE D
SA A
sS47 sS13 sT37 sS27 sS49 Q
34863 39004 19827 39280 34974 39962 47348 29833 4N8 40041 SC SD sin sm 18769 18881 29698 29nt B
C A
C B
sT14 5309 sT69 sS08 sT32 18070 3s901 193s4 3se68 16317 v
25844 43967 30618 43967 25936 SB SB sT42 sT43 188s7 18910 a
29930 29957 C
SE A
D A
SE C
sT26 ST33 sT60 sS44 sTR2 sT44 sT23 1684s 18880 19407 40786 19376 18800 16709 26787 29833 30618 48830 30618 29833 267t*
SB SB O
sT3s sT40 18998 18na f
29957 29930 B
C A
C B
sT21 sS10 sT79 sSos sT13 16s17 3s498 19466 3s361 18136 25936 43967 30618 43967 25844 SD SC 5734 sT81 19202 18711 29779 29696 SA D
SE D
SA sS42 sS29 ST41 sS14
$$40 3s209 38762 18933 38916 34926 40041 47348 29833 47348 39962 SC SB SB SD sis 6 sT38 sT39 sT86 LEGEND 18ses teses 18911 19092 29698 29930 29957 29779 SA B
C B
- ROD BANK sS46 sT27 stir sT30 sS37 34986 16287 1673s 16s97 3s270
-ASSY. NUMBER 3,,62 25s44 267sr 25938 40041
-CURR.BURNUP*
-PROJ.BURNUP OEOC5"
- As of 2/29%
(MWD.WTU)
" Based on Design
P r
PHYSICAL CHARACTERISTICS OF RODDED ASSEMBLIES PLANT VOGTLE UNIT 2 CYCLE 5 REGION 5S REGION 5T Assembly Type Vantage-5*
Vantage-5*
Clad Material Zirc-4 Zirc-4 Grid Material Mid-span grids Zirc-4 Zirc-4 Bottomfrop grid Inconel-718 Inconel-718 Guide Tube Material Zirc-4 Zirc-4 Guide Tube O.D. (inches)
Above dashpot 0.4740 0.4740 At dashpot 0.4300 0.4300 Guide Tube I.D. (inches)
Above dashpot 0.4420 0.4420 At dashpot 0.3970 0.3970
- 17x17 assemblies with optimized fuel rod O.D. of 0.360 in. and with intermediate flow mixing (IFM) grids
)