ML20141C081

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Summary of 970424 Meeting W/Util to Discuss Hl&P Plans Re Incomplete Control Rod Insertion at Stp,Units 1 & 2.Meeting Attendees & Handout Provided by Hl&P,Encl
ML20141C081
Person / Time
Site: South Texas  STP Nuclear Operating Company icon.png
Issue date: 05/14/1997
From: Alexion T
NRC (Affiliation Not Assigned)
To:
NRC (Affiliation Not Assigned)
References
NUDOCS 9705160135
Download: ML20141C081 (16)
v • d • e


Text

{{#Wiki_filter:. _ _ . _ _ _ . _ _ _ _ _ _ . _ _ _ _ . _ _ _ - . . . _ _ _ . . _ _ _ _ . _ _ l . p ur 6b 498 

 ,                          't '                                             UNITED STATES                                       ;

L' ' e fi NUCLEAR REEULATORY COMMISSION WASHINGTON. D.C. 30806 0001 

        %*****/                                                                       May 14, 1997 LICENSEE: HOUSTON LIGHTING AND POWER COMPANY (HL&P)

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

SUBJECT:

SUMMARY

OF APRIL 24, 1997, MEETING ON INCOMPLETE CONTROL R00 INSERTION (IRI) AT STP On April 24, 1997, HL&P met with the Nuclear Regulatory Commission (NRC) to discuss HL&P's plans regarding IRI at STP. Meeting attendees are listed in Attachment 1. Attachment 2 is a handout provided by HL&P. I During a January 25, 1997, rod drop test on Unit 1, which took place during the middle of Cycle 7, 2 control rods stuck at 6 steps. During a subsequent test on April 5, 1997, 4 control rods stuck at 6 steps (the same 2 from th6 January test plus 2 others). HL&P attributes the root cause to fuel assembly thimble tube distortion caused by excessive axial compressive loads, with irradiation metallurgical effects as a contributing factor. HL&P has been addressing this problem by limiting fuel assembly burnups in rodded fuel assemblies. In addition, HL&P is planning to augment their approach with Phase I and Phase II fuel design changes. Phase I plans include using Zirlo fuel cladding, thimble tubes and mid-grids to reduce fuel assembly growth and corrosion, and adding a debris grid at the fuel assembly bottom to reduce assembly skeleton axial loading. Phase I is scheduled for Unit 1 Cycle 8 (September 1997). Phase II plans include increasing the thimble tube outside diameter and increasing the tube wall thickness for improved buckling resistance, and using a single (versus a double) dashpot to lower the top of the dashpot and remove a transition. Phase I is scheduled for Unit 2 Cycle 7 (October 1998). HL&P noted that they have not approved Phase II at this time. Other design changes under consideration include decreasing the top nozzle spring force and reducing the-control rod rodlet outside diameter. Regarding the current operating cycle for Unit 1, HL&P presented a graph that compares the shutdown margin limit of 56 IRIS at 6 steps with a predicted equivalent number of IRIS at 6 steps during Cycle 7, based on Cycle 6 data and  ; Cycle 7 data observed to date. Based on this graph, which HL&P believes shows substantial safety limit margin, HL&P plans to perform only one additional rod drop test (on June 28,1997) between now and the end of Cycle 7 (September 13, 1997). From this graph, HL&P is predicting the equivalent of 8 IRIS at 6 steps during the June test and 14 IRIS at 6 steps during the end of Cycle 7  ; test. HL&P indicated that if the June test results are substantially l different from what they are expecting, they will reevaluate their plan. 1 

                                                                                                                               \ l Regarding the current operating cycle for Unit 2, HL&P indicated that Unit 2 has not experienced IRI when standard fuel is limited to burnups of 30 GWD/MTV h[I and Vantage SH fuel is limited to burnups of 25 GWD/MTU. The current Unit 2 cycle burnups are projected to slightly exceed these values, and therefore,
HL&P may decide to do a rod drop test just prior to Unit 2 end of cycle. I l \

l 160044 NRC FILE CENTER C0Ff 9705160135 970514 PDR ADOCK 05000498 ) l P PM

The NRC expressed concerns that under HL&P's proposed plan for Unit 1, the proposed burnup deltas since the last rod drop test (i.e., 3009 MWD /MTU for the June test and 2769 MWD /MTV for the end of Cycle 7 test) will exceed the 2500 MWD /MTV minimum burnup increment between successive tests that was proposed by the Westinghouse Owners Group in response to Bulletin 96-01, 

 " Control Rod Insertion Problems." The NRC also expressed concern with the possibility of control rods sticking in the upper part of the core, since rod drop traces are showing evidence of slowing down in this area. The NRC indicated that they will consider HL&P's plan and provide feedback.

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

2. Licensee Handout cc w/atts: See next page DISTRIBUTION:

HARD COPY E-MAIL Docket File SCollins/FMiraglia (SJC1/FJM) RZimmerman (RPZ) PUBLIC JRoe (JWR) EAdensam (EGAl) PD4-1 r/f TAlexion (TWA) CHawes (CMH2) OGC WBeckner (WDB) PGwynn (TPG) ACRS GHolahan (GMH) JLyons (JEL) MChatterton (MSC1) HConrad (HFC) FGrubelich (FXG) Document Name: ST042497.MTS [9I 0FC. PM/PD W k LA/PD4-1 ( A)BC/S'PSB NAME TAlexih(CHawesOdN JLyoY DATE h/97 $/5/97 I /Ih97 COPY hES)10 YES/NO YES/N0 U OFFICIAL RECORD COPY

_- .= . . .- - - . - _ _ . - . . . _ . 1 The NRC expressed concerns that under HL&P's proposed plan for Unit 1, the proposed burnup deltas since the last rod drop test (i.e., 3009 MWD /MTV for the June test and 2769 MWD /MTU for the end of Cycle 7 test) will exceed the 2500 MWD /MTU minimum burnup increment between succersive tests that was proposed by the Westinghouse Owners Group in response to Bulletin 96-01, 

      " Control Rod Insertion Problems." The NRC also expressed concern with the possibility of control rods sticking in the upper part of the core, since rod drop traces are showing evidence of slowing down in this area. The NP.C

, indicated that they will consider HL&P's plan and provide feedback. i r J . Thomas W. Alexion, Proje t Manager Project Directorate IV-1 Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation Docket Nos. 50-498 and 50-499 _ 1 Attachments: 1. List of Meeting Attendees

2. Licensee Handout cc w/atts: See next page l

\ l

Houston Lighting & Power Company South Texas, Units 1 & 2 l CC* l l Mr. David P. Loveless Jack R. Newman, Esq. Senior Resident Inspector Morgan, Lewis & Bockius l U.S. Nuclear Regulatory Commission 1800 M Street, N.W. l P. O. Box 910 Washington, DC 20036-5869 l Bay City, TX 77414 [ Mr. Lawrence E. Martin ! Mr. J. C. Lanier/M. B. Lee General Manager, Nuclear Assurance Licensing City of Austin Houston Lighting and Power Company Electric Utility Department P. O. Box 289 721 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. Central Power and Light Company 2300 N Street, N.W. P. O. Box 289 Washington, DC 20037  : Mail Code: N5012 Wadsworth, TX 74483 Office of the Governor ATTN: Andy Barrett, Director i INP0 Environmental Policy Records Center P. O. Box 12428 700 Galleria Parkway Austin, TX 78711 Atlanta, GA 30339-3064 Arthur C. Tate, Director Regional Administrator, Region IV Division of Compliance & Inspection U.S. Nuclear Regulatory Commission Bureau of Radiation Control 611 Ryan Plaza Drive, Suite 400 Texas Department of Health Arlington, TX 76011 1100 West 49th Street Austin, TX 78756 i Dr. Bertram Wolfe I 15453 Via Vaquero Texas Public Utility Commission Monte Sereno, CA 95030 ATTN: Mr. Glenn W. Dishong 7800 Shoal Creek Blvd. l Judge, Matagorda County Suite 400N  ! Matagorda County Courthouse Austin, TX 78757-1024 i 1700 Seventh Street Bay City, TX 77414 Mr.' William T. Cottle Executive VP & General Manager Nuclear

Houston Lighting & Power Company l South Texas Project Electric

! Generating Station l P. O. Box 289 l Wadsworth, TX 77483 i

MEETING WITH HL&P ON INCOMPLETE CONTROL R0D INSERTION April 24, 1997 Nama Draanization T. Cloninger HL&P S. Head .HL&P D. Leazar HL&P R. Dunn HL&P G. Holahan NRC J. Lyons NRC M. Chatterton NRC H.-Conrad NRC F. Grubelich NRC T. Alexion NRC i D. i l 4 i ATTACHMENT 1

i SOUTH TEXAS PROJECT i MEETING WITH THE NUCLEAR REGULATORY COMMISSION TO DISCUSS INCOMPLETE ROD INSERTION STATUS APRIL 24,1997 i i VISION: SOUTH TEXAS PROJECT - - A WORLD CLASS POWER PRODUCER  ! . a  ! 4 5! t s  ! 

      ~                                                                                      j t

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SOUTH TEXAS PROJECT l. Puroose 

    . Communicate STP-specific information regarding:
           -Incomplete rod insertion (IRI)
           - Planned STP fuel assembly design changes to prevent iRI
           - Proposed Unit 1 rod drop testing schedule to monitor IRI
    . STP Team                                                                                                                                                                    !

Ted H. Cloninger - Vice President, Nuclear Engineering  ! Dovld A. Leazar - Manager, Nuclear Fuel & Analysis Roland F. Dunn - Supervisor, Reactor Engineering Scott M. Head - Supervisor, Nuclear Ucensing l l l l t i i r i Page 2 of II i 

    ..   ..                                                                                  ... . :l SOUTH TEXAS PROJECT i

STP Unit 1 Cycle 7 incomotete Rod Insertion (IRD Backaround l l Steps above rod bottom / (All V5H) Fuel burnup(gwd/mtu) i l H05 C-9 0 / 17  ; l H47 K-8 0/18 H10 l C-7 0/17 0 / 26 H46 l F-8 0 /18 l 0 / 27 l i l l i l

  • l

' Page 3 or i1 l l . 

                                                                                                                                                                                                                 .:l f

SOUTH TEXAS PROJECT l 1 . 

                                                                                                                                                                                                                    ?

STP Fuel Assembly Deslan Chanaes to Prevent IRI i< 

   . The root cause of incomplete rod insertion has been identified as fuel assembly thimble tube distortion caused by excessive axial compressive loads, and a contributing factor includes irradiation metallurgical effects e  Therefore, in addition to fuel assembly burnup management under control rods, the following Phase I and ll fuel                                                                                               !

design changes are planned to address the above cause, and provide our long term correction to the IRI l condition  ! I I I l t i i Page 4 of 1I i i

SOUTH TEXAS PROJECT l t f l STP Fuel Assembly Desian Chanaes to Prevent IRI i 1 3 l Phase I-Implementation planned for Unit 1 Cycle 8 (September 1997) t I e ZlRLO fuel cladding, thimble tubes, and mid-grids  ! I t 

                   - reduced creep rate                                                                                                                                                                                                                      ;

I 

                   - reduced oxial assembly growth                                                                                                                                                                                                           ;
                   - reduced corrosion
                   - requires Tech Spec change
             . Debris grid added at bottom (Performance +)                                                                                                                                                                                                  >
                   - reduced assembly skeleton oxial loading from fuel rods                                                                                                                                                                                  ;

t i t i Page 5 of 1I '

1 SOUTH TEXAS PROJECT f ! STP Fuel Assembly Desian Chances to Prevent IRI Phase II- Implementation planned for Unit 2 Cycle 7 (October 1998) l l The following proposed changes are being evaluated by the STP-W design team: l e Tnimble tube OD from top to bottom is some diameter i 

         - OD above dashpot is .008" larger than V5H XL fuel, some as standard XL
         - OD in dashpot is .052" larger than V5H or standard XL fuel
         -improved buckling resistance in dashpot area compared to V5H and standard XL fuel                                                                  i
         - improved buckling resistance above dashpot compared to V5H XL fuel                                                                                !

e Thicker thimble tube wall  ! i 

         - thimble tube wall thickness above dashpot increases by .004~
         - thimble tube wall thickness in dashpot increases by .026"                                                                                         ;
         -improved buckling resistance compared to V5H and standard XL fuel e  Dashpot is single vs. double
         - removes a transition and lowers the top of the dashpot by about 4~ (equivalent to six steps) i Page 6 of II                                                                         '

_ _ ~ [ l l SOUTH TEXAS PROJECT . STP Fuel Assembly Desion Chonoes to Prevent IRI Additionallong Term Actions STP has requested the following to be evoluoted by the W design team: 

   . Decrease top nozzle spring force
         - Condition 11, loss of load /RCP overspeed event with fuel assembly liftoff may be limiting e Reduce RCCA rodlet OD
         - STP is planning to replace RCCAs with chrome-plated cladding at 10 year ISI outage Page 7 of II

 .. ..                                                                                                                                                                       ..         . :i i

SOUTH TEXAS PROJECT STP Unit 1 Cycle 7 Shutdown Morain Cooability All cases assume the highest worth stuck rod is fully withdrawn BOC and EOC shutdown margin and trip reactivity met for the following cases: l 

                                                     # 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                                                                                        '

Page 8 of 11 

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l .. .. .: .. SOUTH TEXAS PROJECT l l Planned Test Schedule o Rod drop test on 6/28/97, burnup delta of 3009 mwd /mtu since last test e Rod drop test at End-of-Cycle on 9/13/97, burnup delta of 2769 mwd /mtu since 6/28 These dates are acceptable for the following reasons: e IRI condition progresses slowly with core burnup e Significant safety limit margin exists e Unit 1 operation remains bounded by previous fuel cycle IRI experience e STP will continue to use Restart Evaluation Criteria for the next Unit 1 rod drop test 

          - monitors rod drop time, changes in rod drop time, and shutdown margin
          - evaluates reduction of burnup interval prior to next rod drop test, if required Page 10 or 11

SOUTH TEXAS PROJECT t i i t Meetina Summarv i e Described STP's long term corrective actions to prevent incomplete rod insertions j 

            =   Presented STP safety limit margin for incomplete rod insertions
            . Described planned Unit 1 Cycle 7 rod drop test schedule i

i I i i i i Page1IofI1 ' 

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