ML20133N382

Summary of 970109 Meeting W/Hl&P Re Response to NRC Bulletin 96-01, Control Rod Insertion Problems. List of Attendees & Licensee Handout Encl

ML20133N382
Person / Time
Site:	South Texas
Issue date:	01/17/1997
From:	Alexion T NRC (Affiliation Not Assigned)
To:	NRC (Affiliation Not Assigned)
References
IEB-96-001, IEB-96-1, NUDOCS 9701230267
Download: ML20133N382 (18)

Text

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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20066-0001

• • • • • ,e January 17, 1997 LICENSEE: Houston Lighting and Power Company (HL&P), et al.

FACILITY: South Texas Project, Units 1 and 2 (STP)

SUBJECT:

StMiARY OF JANUARY 9, 1997, MEETING ON HL&P'S RESPONSE TO BULLETIN 96-01, " CONTROL ROD INSERTION PROBLEMS" On January 9, 1997, representatives of HL&P and NRC met to discuss the above subject. Meeting attendees are listed in Attachment 1. A handout provided by the licensee is Attachment 2.

The Nuclear Regulatory Comission (NRC) opened the meeting with the following background discussion summary. In a previous meeting on May 24, 1996, HL&P indicated that due to 2 new indications of incomplete rod insertion (Iol) in lower burnup assemblies in Unit 1, HL&P was strongly considering performing a mid-cycle rod drop test in January 1997, when rodded assembly burnups approached the value corresponding to the lowest burnup fuel assembly with the observed IRI condition (32 GWD/MTU). By letter dated November 27, 1996, HL&P provided the results of testing on selected assemblies and concluded that the cause of IRI is excessive guide tube distortion in the dashpot due to the in-vessel axial compressive load. HL&P further concluded that the since fuel assemblies are built as designed, the most likely cause of guide tube bowing is inadequate resistance to buckling in the fuel assembly design. In the same letter, HL&P indicated that future STP loading will limit end-of-cycle (E0C) fuel assembly burnups under all control rods to the extent practical, that rod drop testing will be performed at E0C and at each outage of sufficient duration where more than 1250 MWD /MTU burnup has accumulated since the most recent test, and that the results of their evaluation indicates there is substantial shutdown margin in Unit 1 Cycle 7, and therefore, there is no need for additional testing.

During NRC's review of HL&P's letter dated November 27, 1996, (prior to this meeting), NRC was concerned with the proposed deletion of the previously considered Jsnuary 1997, rod drop testing because (1) the existing fuel assembly design is inadequate for buckling, and no substantial design modifications have been made to address this, (2) rodded assembly burnups in Unit I have now approached the value corresponding to the lowest burnup fuel assembly with the observed IRI condition during the last cycle, and (3) 49 of 57 assemblies in rodded locations in Unit I will exceed 32 GWD/MTU by E0C (to date, Unit 2 has not experienced IRI). NRC concluded that HL&P should i reconsider its proposed deletion of the January 1997, rod drop test, and I communicated this position to HL&P. HL&P then requested a meeting with NRC.

During the January 9, 1997, meeting HL&P indicated that it will perform a mid- {

cycle rod drop test in Unit I en January 18, 1997, unless cold weather /

conditions force them to postpone the test for 1 week. Also, the E0C for Unit 2 is set for February 8, 1997, at which time HL&P will conduct a rod-drop test in Unit 2. With these 2 new sets of data, HL&P indicated that it will be able to define the need for further testing.

g 9701230267 970117 PDR ADOCK 05000498 O PDR

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HL&P indicated that their findings of previous tests are that (1) control rod i drag is related to burnup, (2) guide tube drag and distortion is maximum in l the dashpot, (3) assembly growth is consistent with design predictions, (4) ,

maximum rod drop time (to dashpot entry) in Unit 1 Cycle 6 was well below the l l Technical Specification limit, (5) recoil behavior of rod drop traces during I Unit 1 beginning-of-cycle (BOC) Cycle 7 was much better than Cycle 6, and l (6) high core residence time (accumulated effective-full-power days (EFPD)) i was observed in all fuel with IRI. Based on their findings, HL&P's corrective actions include limiting Unit 1 Cycle 7 (U1C7) rodded fuel assembly burnups to l 38 GWD/MTU at E0C, limiting U2C6 to 32.5 GWD/MTU and 1001 EFPD, limiting UIC8 i to 28 GWD/MTU and 900 EFPD, and working with the fuel vendor for long-term fuel design changes. Some preliminary long-term design changes currently under consideration include (1) using zirlo guide tubes, (2) having the fuel rods resting on the bottom nozzle, (3) using a bottom grid that rests on the dashpot region, and (4) using a thicker guide tube wall. The earliest that HL&P would possibly begin to implement these design changes is for VIC8.

Based on the substantially lower E0C fuel burnup and core residence time than Cycle 6, improved rod drop recoil performance at BOC, and previous testing results (which show that guide tube distortion is limited to the dashpot i region, therefore, rod drop times and shutdown margin can be met with  !

substantial margin), HL&P concluded with a high degree of confidence that l control rod safety limits will be met with substantial shutdown margin during I operation of UIC7. The NRC indicated that the meeting was very informative '

and requested that HL&P provide the NRC staff with the restart criteria that HL&P will use following the January 18, 1997, rod drop test. HL&P indicated that it would provide the restart criteria by January 15, 1997.

({T'q)j) hh Thomas W. Alexion, Proj(ct Manager Project Directorate IV-1 Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation Docket Nos. 50-498 and 50-499 Attachments: 1. List of Meeting Attendees

2. HL&P Meeting Handout cc w/atts: See next page

t l Houston Lighting & Power Company South Texas, Units 1 & 2 I CC:

! Mr. David P. Loveless Jack R. Newman, Esq.

1 Senior Resident Inspector Morgan, Lewis & Bockius i U.S. Nuclear Regulatory Commission 1800 M Street, N.W.

/. O. Box 910 Washington, DC 20036-5869 i Bay City, TX 77414 i Mr. Lawrence E. Martin

, Mr. J. C. Lanier/M. B. Lee General Manager, Nuclear Assurance Licensing

City of Austin Houston Lighting and Power Company l Electric Utility Department P. O. Box 289 l 721 Barton Springs Road Wadsworth, TX 77483

Austin, TX 78704

! Rufus S. Scott

! Mr. M. T. Hardt Associate General Counsel Mr. W. C. Gunst Houston Lighting and Power Company City Public Service Board P. O. Box 61867

P. O. Box 1771 Houston, TX 77208 San Antonio, TX 78296 Joseph R. Egan, Esq.

Mr. G. E. Vaughn/C. A. Johnson Egan & Associates, P.C.

j Central Power and Light Company 2300 N Street, N.W.

P. O. Box 289 Washington, DC 20037 i Mail Code: N5012

] Wadsworth, TX 74483 Office of the Governor j ATTN: Andy Barrett, Director INP0 Environmental Policy Records Center P. O. Box 12428

700 Galleria Parkway Austin, TX 78711 1 Atlanta, GA 30339-3064 1 Arthur C. Tate, Director 3

Regional Administrator, Region IV Division of Compliance & Inspection j U.S. Nuclear Regulatory Commission Bureau of Radiation Control 4 611 Ryan Plaza Drive, Suite 400 Texas Department of Health Arlington, TX 76011 1100 West 49th Street Austin, TX 78756 Dr. Bertram Wolfe 15453 Via Vaquero J. W. Beck Monte Sereno, CA 95030 Little Harbor Consultants, Inc.

44 Nichols Road Judge, Matagorda County Cohasset, MA 02025-1166 Matagorda County Courthouse 1700 Seventh Street Texas Public Utility Commission Bay City, TX 77414 ATTN: Mr. Glenn W. Dishong 7800 Shoal Creek Blvd.

Mr. William T. Cottle Suite 400N Executive VP & General Manager Nuclear Austin, TX 78757-1024 Houston Lighting & Power Company South Texas Project Electric Generating Station P. O. Box 289 Wadsworth, TX 77483

MEETING BETWEEN HL&P AND NRC ON BULLETIN 96-01 January 9, 1997

! Hamg Oraanization T. Cloninger HL&P 4

D. Leazar HL&P j R. Dunn HL&P E. Kee HL&P S. Head HL&P L. Connor for STS A. Wyche Bechtel

, J. Roe NRC l W. Beckner NRC i J. Lyons NRC

{ M. Chatterton NRC H. Conrad NRC

, F. Grubelich NRC j J. Rajan NRC

. K. Thomas NRC T. Alexion NRC l

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ATTACMENT 1 1

s SOUTH TEXAS PROJECT PRESENTATION: i

DISCUSSION OF CONTROL ROD INSERTION ISSUES  ;

TO NRC t

January 9,1997

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VISION: STP -- A WORLD-CLASS POWER PRODUCER

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i PURPOSE hmmunicate STP-specific information regarding incomplete rod insertion, and present the reasons why Unit 1 Cycle 7 operation will meet control rod safety limits through end of cycle STP Team:

Ted H. Cloninger - Vice President, Nuclear Engineering David A. Leazar - Manager, Nuclear Fuel & Analysis Roland F. Dunn - Supervisor, Reactor Engineering Ernie J. Kee - Unit 1 Reactor Engineer Scott M. Head - Supervisor, Nuclear I;ic nsing L-

i j STP UNIT 1 INCOMPLETE ROD INSERTION (IRI) BACKGROUND l

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! Steps above rod bottom / Fuel burnup (gwd/mtu)/ Core j residence time (efpd)

E10 E11 0/23/747 0 /27/ 856 0/30/926 4

F25 N09 0/40/979 i

! F26 F10 0 /41/ 979 l F29 K10 0/42/979 0/45/1088

F41 F06 0 /41/ 979 0/44/1088 i

F47 ,

C07 0/40/979 0/44/1088 0/46/1157 F53 D08 0/38/979 0/41/1088 F59 C09 0 /41/979 F60 K08 0 /26/979 0/30/1088 0 /33/1157 F64 N07 0/40/979 R27 C05 0/35/979 0/38/1088 0 /41/1157

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STP PREVIOUS TESTING CONCLUSIONS  !

Fuel Testing:

. Show that RCCA drag is related to burnup

. Guide tube drag and distortion is maximum in dashpot, essentially no drag above the dashpot

- Consistent with fuel design (i.e., makes sense physically due to dashpot reduced diameter and length)

- Causes incomplete insertion at the bottom of RCCA travel

. Assembly growth consistent with design predictions and well below design limit

- All fuel assemblies offloaded in Cycle 6 were measured

- Low growth minimizes spring compression effect seen at Wolf Creek

- Increases as burnup increases

- No anomalous growth at low burnup observed 147P 9 i

STP PREVIOUS TESTING CONCLUSIONS l

RodDrop Time Testing: '

. Rod drop traces provide information regarding the rod's residual energy (if any) at i rod bottom  :

- Unit 1 BOC Cycle 6 recoil behavior is statistically significant to future performance-7 of 11 RCCAs with low BOC recoil had IRI on 03/02/96 8 of 11 RCCAS with low BOC recoil had IRI at EOC  ;

- Unit 1 Cycle 7 loading pattem produced significantly more recoils at BOC than Cycle 6: ,

i BOC Cycle 6 BOC Cycle 7 7 RCCAs = 0 recoil 0 RCCAs = 0 recoil  !

4 RCCAs = 1 recoil 1 RCCA = 1 recoil 46 RCCAs > 2 recoils 56 RCCAs > 2 recoils

. No degradation in Tech Spec rod drop time and no slowing down above dashpot I

- All rod drops showed significant margin to the 2.8 seconds Tech Spec limit

- Maximum rod drop time in Cycle 6 was 1.65 seconds

. High core residence time (accumulated core burnup in EFPD) observed in all IRI  !

fuel (thrice-burned) ,u

STP UNIT 1 CYCLE 6 VS. CYCLE 7 FUEL BURNUPS AND CORE RESIDENCE TIME EFPD Cycle 6 Reactor Trip on 08/29/95, zero stuck rods:

Fuel Bumup Core efpd # of Rodded # of Stuck gwd/mtu F/As Rods 6 134 8 0 18 -22 489 12 0 23 -26 698 -747 5 0 26 979 4 0 34 - 35 979 8 0 37 - 41 979 20 0 -

Cycle 6 Reactor Trip / Rod Testing on 12/18-19/95,four stuck rods:

Fuel Bumup Core efpd # of Rodded # of Stuck gwd/mtu F/As Rods 11 243 8 0 1 22 - 27 598 12 0 27 -29 807 - 856 5 0 30 1088 4 0 38-42 1088 16 0 44 - 45 1088 12 4 Cycle 6 RodDrop Testing on 03/02/96, seven stuck rods:

Fuel Bumup Core efpd # of Rodded # of Stuck gwd/mtu F/As Rods 14 312 8 0 24-29 667 12 0 29-31 877-926 5 0 33 1157 4 0 41 1157 8 0 t i%m-43-47 1157 20 7

STP UNET 1 CYCLE 6 VS. CYCLE 7 FUEL BURNUPS AND CORE RESIDENCE TIME EFPD Cycle 6 EOC Rod Drop Testing on 05/18/96, eleven stuck rods:

Fuel Bumup Core efpd # of Rodded # of Stuck gwd/mtu F/As Rods 18 387 8 0 26 - 33 742 12 0 32 - 33 952 2 0 32 1001 3 1 36 1232 4 1 i 43 -47 1232 16 2 49 -50 1232 12 7 ,

Cycle 7 FuelBurnup and Core EFPD on 01/17/97:

Fuel Bumup Core efpd # of Rodded gwd/mtu F/As 10 220 8 24 - 27 607 36 29-30 784 5 31 - 32 962 8 Cycle 7 Fuel Burnup and Core EFPD at EOC, 09/97:

Fuel Bumup Core efpd # of Rodded gwd/mtu F/As 20 451 8 33 - 37 838 36 36 -38 1015 5 l 37 -38 1193 8 m-

m,m.h._m,6-Am4*aw&emhe- ae4--MA--a-wwhe-4---44*a4--- h4 +-M**h- , - -N +-h=%>e STP INCOMPLETE ROD INSERTION ROOT CAUSE o IRI is caused by excessive guide tube distortion in the dashpot due to in-vessel axial compressive loading and inadequate resistance to buckling in the fuel assembly design o Contributing factors include irradiation and time at temperature o Based on this root cause, STP dashpot design, and results of our testing program, incomplete rod insertion at STP is limited to the lower dashpot - safety evaluations demonstrate meeting control rod safety limits with substantial margin i

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t STP UNIT 1 CYCLE 7 ANALYZED SHUTDOWN MARGIN CASES WITH HYPOTHETICAL STUCK RODS i All cases assume the highest worth stuck rod is fully withdrawn BOC and EOC shutdown margin and trip reactivity met for the following cases:

1. Stuck rods

• Position **

Case 1 12 18 Case 2 20 12 Case 3 56 6

• no core location or fuel burnup restrictions, e.g., any 12 or any 20 rods

• • based on digital rod position indication (DRPI) - includes 4 step uncertainty lm .,-

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STP IRI Corrective Actions  :

U1 C7 rodded fuel assemblies limited to less than 38 gwd/mtu at EOC ,

U2 C6 rodded fuel assemblies limited to less than 32.5 gwd/mtu and 1001 EFPD at EOC U1 C8 rodded fuel assemblies limited to less than 28 gwd/mtu and 900 EFPD at EOC Working with fuel vendor to identify long term fuel design changes by 04/97 Perform U2 C5 EOC rod drop testing on 02/08/97 Expect incomplete rod insertion results to be similar to U1 EOC-6 (e.g.,11 RCCAs -

2 @ 12 steps,9 @ 6 steps)

Projected Cycle 5 Fuel Burnup and Core EFPD at EOC, 02/97:

Fuel Bumup Core efpd # of Rodded t gwd/mtu F/As 19 439 8 32 914 4 39-40 914 20 39-40 1292 8 l 44 - 53 1292 17 MMIN @

.l STP IRI Conclusions for Unit 1 Cycle 7 Operation o A fuel assembly's core residence time is an important contributor to IRI; Cycle 7 EOC rodded fuel burnups and core residence time are substantially lower than Cycle 6 o Testing shows guide tube distortion is limited to the dashpot region, therefore, rod drop times and shutdown margin (SDM) can be met with substantial margin Assumed SDM cases with hypothetical stuck rods show that control rod safety 4

limits can be met for bounding conditions, e.g., N-1 rods stuck at 6 steps j Cycle 6 experience shows IRI at a maximum of 12 steps for fuel with ,

substantially higher burnup and residence time than all Cycle 7 rodded fuel o BOC rod drop recoil is an indicator of a rod's ability to achieve full insertion, Cycle 7 recoil data indicates significantly better performance than Cycle 6 o Based on substantially lower EOC fuel burnup and core residence time than Cycle 6, improved rod drop recoil performance at BOC, and previous STP testing results, STP has a high degree of confidence that control rod safety limits will be met with  ;

substantial margin during operation of Unit 1 Cycle 7 h

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STP Future Testing Plans

. Results of Unit 1 mid-January 1997 and Unit 2 Cycle 5 end of cycle rod drop test results will be evaluated to determine whether future testing is necessary

. STP will submit written test reports for the above rod drop tests, similar to those sent previously t

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4 DISTRIBUTION: Meeting held on January 9, 1997 iard Co)v L3ectat; ,ile!

PUBLIC PDIV-1 r/f OGC ACRS E-Mail i FMiraglia (FJM)

RZimmerman-(RPZ)

JRoe (JWR) l WBeckner (WDB)

TAlexion (TWA)

CHawes (CMH2)

EJordan (JKR)

MChatterton (MSC1)

HConrad (HFC)

FGrubelich (FXG)

JRajan (JRR)

KThomas (KMT)

JDyer, RIV (JED2)

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g a HL&P indicated that their findings of previous tests are that (1) control rod drag is related to burnup, (2) guide tube drag and distortion is maximum in

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the dashpot, (3) assembly growth is consistent with design predictions, (4) maximum rod drop time (to dashpot entry) in Unit 1 Cycle 6 was well below the Technical Specification limit, (5) recoil behavior of rod drop traces during Unit I beginning-of-cycle (BOC) Cycle 7 was much better' than Cycle 6, and (6) high core residence time (accumulated effective-full-power days (EFPD))

was observed in all fuel with IRI. Based on their findings, HL&P's corrective actions include limiting Unit 1 Cycle 7 (UlC7) rodded fuel assembly burnups to 38 GWD/MTU at E0C, limiting U2C6 to 32.5 GWD/MTU-and 1001 EFPD, limiting UIC8 to 28 GWD/MTU and 900 EFPD, and working with the fuel vendor for long-term fuel design changes. Some preliminary long-term design changes currently under consideration include (1) using zirlo guide tubes, (2) having the fuel rods resting on the bottom nozzle, (3) using a bottom grid that rests on the dashpot region, and (4) using a thicker guide tube wall. The earliest that HL&P would possibly begin to implement these design changes is for UIC8.

Based on the substantially lower E0C fuel burnup and core residence time than Cycle 6, improved rod drop recoil performance at B0C, and previous testing results (which show that guide. tube distortion is limited to the dashpot region, therefore, rod drop times and shutdown margin can be met with substantial margin), HL&P concluded with a high degree of confidence that control rod safety limits will'be met with substantial shutdown margin during operation of UIC7. The NRC indicated that the meeting was very informative and requested that HL&P provide the NRC staff with the restart criteria that HL&P will use following the January 18, 1997, rod drop test. HL&P indicated ,

that it would provide the restart criteria by January 15, 1997.

ORIGINAL SIGNED BY:

Thomas W. Alexion, Project Manager Project Directorate IV-1 Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation Docket Nos. 50-498 and 50-499 Attachments: 1. List of Meeting Attendees

2. HL&P Meeting Handout -

cc w/atts: See next page DISTRIBUTION: See next page ,

Document Name: ST010997.MTS .

OFC PM/PQk W b(A)LA/PD4-1 (A)BChRXB.

NAME TAlexio h CHawesM)d JLyN '

DATE lb797 )N/97- l /l1/97 -

COPY YES)NO YES/N0 YES/N0 v

0FFICIAL RECORD COPY

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