ML20101P245

Forwards Response to NRC Bulletin 96-001, Control Rod Insertion Problems

ML20101P245
Person / Time
Site:	Wolf Creek
Issue date:	04/05/1996
From:	Maynard O WOLF CREEK NUCLEAR OPERATING CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
IEB-96-001, IEB-96-1, WO-96-0058, WO-96-58, NUDOCS 9604090312
Download: ML20101P245 (10)

Text

{{#Wiki_filter:_. 1 l l i LF CREEK Wf) NUCLEAR OPERATING l Otto L. Maynard Vice President Plant Operations i April 5, 1996 l WO 96-0058 l l U. S. Nuclear Regulatory Commission ATTN: Document Control Desk l Washington, DC 20555-0001

Subject:

Docket 50-482: Response to NRC Bulletin 96-01, " Control Rod Insertion Problems" I Gentlemen: I On March 8, 1996, the NRC issued NRC Bulletin 96-01 concerning recent control rod insertion problems at three Westinghouse-designed plants, including the Wolf Creek Generating Station (WCGS). NRC Bulletin 96-01 requested all Licensees of Westinghouse-designed plants to provide, within 30 days, a l written response to the bulletin, pursuant to Section 182a, the Atomic Energy [ Act of 1954, as amended, and 10 CFR 50. 54 (f). Attached is WCNOC's response to 1 l that request. l l If you have any questions concerning this matter, please contact me at (316) 364-8831, extension 4450, or Mr. Richard D. Flannigan at extension 4500. Very truly yours, l I l-Otto L. Maynard OLM/jra Attachment cc: L. J. Callan (NRC), w/a i W. D. Johnson (NRC), w/a J. F. Ringwald (NRC), w/a J. C. Stone (NRC), w/a 9604090312 960405 PDR ADOCK 05000402 G PDR PO. Box 411/ Burlington, KS 66839 / Phone: (316) 364-8831 An Equal opportunity Employer M/F/HC/ VET l

4 I i STATE OF KANSAS ) ) SS COUNTY OF COFFEY ) Otto L. Maynard, of lawful age, being first duly sworn upon oath says that he is Vice President Plant Operations of Wolf Creek Nuclear Operating Corporation; that he has read the foregoing document and knows the content thereof; that he has executed that same for and on behalf of said Corporation with full power and authority to do so; and that the facts therein stated are true and correct to the best of his knowledge, information and belief. By kNO Otfo'L. Mal / nard' / Vice President Plant Operations SUBSCRIBED and sworn to before me this 5 day _of $6i 19ss. A NW Notary Public Expiration Date I A-15-NM ' DIANA S. CLARKSON ' Notary Public-State of Kanses ,My Appt. Expires Q-{ M 9

'Attachmsnt to WO 96-0058 I

• Page'1 of 8 i

RESPONSE TO NRC BULLETIN 96-01,

• CONTROL ROD INSERTION PROBLEMS" A.

Requested Actions and Required Information NRC Bulletin 96-01 requented each Licensee to take the following actions: (1) Promptly inform operators of recent events (reactor trips and testing) in which control rods did not fully insert and subsequently provide t necessary training, including simulator, drills, utilizing the required l 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 I amount). (2) 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 I control rod operability. I (3) 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. l 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). (4) For each reactor trip during calendar year 1996, verify that all control rods have promptly fully inserted (bottomed) and obtain other available l information to assess the operability and any performance trend of the rods. In the event that all rods do not fully insert promptly, conduct tests to measure and evaluate rod drop times and rod recoil. ] l In addition to the above requested actions, NRC Bulletin 96-01 also requires, per 10 CFR 50.54 (f), the following written information be submitted under oath 4 or affirmation: (1) 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 inplementing Requested Actions (3) and (4). (2) Within 30 days of the date of this bulletin,

a. core map of rodded fuel l

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 j information for the next cycle. l

I l

• Attachm:nt to WO 95-0058

' Page'2 of.8 (3) 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. 9 E. RESPONSES TO REQUIRED RESPONSE ITEMS ITEM 1 i Wolf Creek Nuclear Operating Corporation (WCNOC) has determined that for Cycle f 9, all control rods are considered operable based on (1) the redesign of the Cycle 9 core loading pattern preventing control rods from being located in high burnup fuel, and (2) extensive testing of control rods in their Cycle 9 l locations. I An inspection program was undertaken by WCNOC and Westinghouse to address the i incomplete Rod Cluster Control Assembly (RCCA) insertion that occurred at Wolf Creek Generating Station (WCGS) near the end of Cycle 8. These activities I included the preparation, review and implementation of a test plan and the formation of a. root cause team. A summary of the tests and examinations i j. - performed is provided below: l

1. Rod Drop testing at 195 F.

This test was performed o determine } RCCA behavior in a simulated reactor trip.

2. Drag testing in vessel with upper internals in place.

This test was performed to determine the impact of the upper internals on the RCCA drag. l

3. Drag testing in the spent fuel pool.

RCCA's were tested. in their t l host assembly and in a new reference assembly. 4. Eddy current testing of selected RCCAs. i

5. Drag testing using a short RCCA (13" long rodlets) to determine if-l the top of the fuel assembly was the location of the interference.

I 6. Fuel assembly length measurements. l 7. Fuel assembly bow measurements. l 8. Boroscope inspection of thimble tubes of selected assemblies. l

9. Single tube probe testing of thimble tubes.

l l A root cause team was organized with representativer-of WCNOC, Houston Lighting and Power Company, and several Westinghouse divisions. The root i cause - analysis determined that the incomplete RCCA insertion was caused by l problems in the fuel assemblies. The fuel assemblies affected were thrice burned assemblies with burnup exceeding 49,000 Megawatt-Days per Metric Ton ( Uranium (MWD /MTU). (NOTE: A complete report on the testing and analysis of l the incomplete RCCA insertions was submitted to the NRC in Letter WO 96-0051, dated March 20, 1996, from Otto L. Maynard to the NRC). i i f l t

• Attachmant te WO 96-0058

' Page"3 of 8 Following the January 30, 1996 reactor trip, WCGS entered the eighth refueling outage. As a result of the conclusions of the root cause team, the Cycle 9 core loading pattern was revised with the express intent of lowering the burnup of assemblies in control rod locations. Fuel in rodded locations in the Cycle 9 core it in its first or second cycle of operation. The projected assembly burnup for the 53 control rod locations at the end of Cycle 9 is: Number of Control Rods Burnun Range (MWD /MTU) 44 18,000 to 30,000 1 30,000 to 34,000 8 40,000 to 41,000 The redesigned Cycle 9 core loading pattern should eliminate the possibility of a re-occurrence of incomplete control rod insertion during Cycle 9. At the time this response was written WCNOC was working to complete the eighth refueling outage including rod drop testing per surveillance Requirement 4.1.3.1.3. The results of the rod drop testing for Cycle 9 will be reviewed for control rod operability. Drag testing was performed on the control rods in their Cycle 9 locations. No excessive drag was observed in any assembly. The Technical Specification requirement to maintain 1300 pcm shutdown margin was analyzed for the redesigned Cycle 9 loading pattern. This calculation was performed as part of the normal reload design process. The placement of fuel assemblies with reduced burnup, relative to previous WCGS cycle designs, yields increased trippable rod worth. As a result the redesigned Cycle 9 loading pattern has increased excess shutdown margin relative to recent cycles. In fact, the WCGS cycle 9 design has 584 pcm excess shutdown margin to the 1300 pcm requirement at the most restrictive time in core life. Actions taken for Requested Action 1 On March 20, 1996, the Manager Operations provided key Operations personnel with a copy of NRC Bulletin 96-01 and a written summary of the North Anna event described in the bulletin. In addition, a review of NRC Bulletin 96-01 will be presented to WCNOC Licensed Operators in licensed operator requalification cycle 96-3. This cycle will be held from June 10 through July 19, 1996. Simulator training on control rod insertion problems will be presented to the Licensed operators during this same requalification cycle. This training will include an event in which the control rods do not fully insert upon a reactor trip and in which the required procedures for such an event will need to be utilized. Actions taken for Requested Action 2 Based on the discussion provided above, WCNOC considers the control rods to be operable. As new industry information becomes available, WCNOC will consider this new information in conjunction with current data to make continued determination of control rod operability. l

.___-._-m Attachment to WO 96-0058

• page'4 of 8 I

Plana for Implementino Reauested' Action (3) For any outage occurring during 1996 which allows time to properly setup and test the control rods by established plant procedures without restraining the j plant restart, WCNOC will measure and evaluate the control rod drop times and [ recoil data for control rods in fuel assembly locations in their second cycle of operation and having high burnups greater than 25,000 MWD /MTU. This minimum burnup was establiPhed after reviewing the performance of Control. rods during the prev 3ous cycle and the examinations performed during the eighth ( refueling outage. A reactor trip occurreu during Cycle 8 with second cycle fuel assemblies in rodded locations at burnups between 26,400 and 30,100 MWD /MTU. All control rods fully inserted during this trip. The end of cycle 8 performance for one-cycle assemblies with a burnup of 15,000 MWD /MTU and two-cycle assemblies with burnups in the range of 39,000 to 44,000 MWD /MTU was normal. The rod drop . times for these assemblies were much less than the Technical. Specification j requirement, even though the tests were conducted at cold temperatures.- The decrease in the number of recoils observed in the twice-burned assemblies correlated with a slightly higher drag force measurement in the dashpot of l these assemblies. The Cycle 9 startup tests of drag forces with assembly burnups up to 17,570 MWD /MTU indicates acceptable performance of all rodded l locations. Therefore, excluding fuel in their first cycle of operation is l supported by the performance and examination data at WCGS. Limiting the testing of second cycle fuel to burnups greater than 25,000 MWD /MTU will { [ provide data to assess the operability and performance trend of ~ the control rods. L I Once this data has been collected, it will be repeated during an outage of l l sufficient duration only af ter an additional 2500 MWD /MTU burnup has been achieved on those rodded locations. For the same conditions as described above, drag forces will be measured and evaluated for outages when the vessel head is removed. Plann for Imnlementina Recuested Action (4) i l For each reactor trip during calendar year 1996, WCNOC will verify that all l control rods have promptly, fully inserted. For any control rods that do not fully insert, control rod drop tests will be performed and the results evaluated. l WCNOC plans to meet the intent of Requested Actions 3) and 4) from NRC Bulletin 96-01. This will be accomplished by following the actions described above until such time as Westinghouse and the Westinghouse Owners Group (WOG)

have identified the appropriate data required to support a root cause determination. WCNOC will provide an update of our Bulletin 96-01 response if' our plans for implementing Requested Actions 3) and 4) are modified to support the collection of appropriate data for the root cause determination.

1 3 4 .n.,,..

. Attachment to WO 96-0058

• Paga*5 of 8 ITEM 2 WCGS is currently in tho eighth refueling outage.

As such the current core l configuration with current burnups are reflected in Figure 2. Figure 1 shows the WCGS Cycle 9 loading pattern. Of the 53 RCCAs, 36 are located in new Region L assemblics, 16 in once-burned Region K assemblies, and 1 in a once-burned Region A assembly. Design-information for the fuel assembly types is shown in the following table. l Table 1 Fuel Assembly Design Information Region A fuel Region K and L fuel Fuel Type 17x17 Standard 17x17 Vantage 5H Fuel Cladding-Material Zircaloy-4 Improved Zircaloy-4 l Guide Tube Inside Diameter (in.) 0.450 0.442 j. Dashpot Inside Diameter (in.) 0.397 0.397 l Guide Tube Material Zircaloy-4 Improved Zircaloy-4 { l Top Grid Inconel Inconel IFM Grids None Improved Zircaloy-4 l Middle Grids Inconel Improved Zircaloy-4 [ Bottom Grid Inconel Inconel Protective Grid None Inconel ), l l Figure 2 shows the burnup for the rodded locations at the beginning of Cycle 9. Figure 3 shows the projected burnup for the rodded locations at the end of Cycle 9. The maximum projected burnup in a rodded location is i l 40,883 MWD /MTU. t i t l I l -l i ,. - - - ~ -.. -. -.,..... -.

1 l . Attachment to WO 96-0058

• Page'6 of 8 FIGURE 1 CYCLE 9 CORE LOADING PATTERN 1

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~ . Attachment to WO 96-0058 Page'7 of 8 FIGURE 2 PROJECTED EXPOSURE AT BEGINNING OF CYCLE 9 1 2 3 4 6 6 7 8 9 10 11 12 13 14 15 A A27 A47 Ass mis Asi A4s As2 A 12,927 , I8 B ust Los Les Ls1 ~ Loi us2 B ggg 1 Y j. 'T T. C nas nio L74 K42 Los x4s x72 C Lso x11 D 37,7,2 ,"8,7, if,$3 D L72 L34 x4s x4e x71 K44 L4s L71 7 "l " L,1 : E As4 Lo4 Lao Lss ni? L2s x2s ts7 nos Ls4 L27 Los Ass E j Kas K27 Mas [' Ks4 x74 xss K2s K0s A:s F F Air G Aso L*4 uso L21 mas Las x4s Las un L22 Kso Les As2 G T d*s'7, '5- ' 5,$'7. T j 8 H nos uss H tso x12 x21 xo x41 1 Las ks4 L47 mar Las ust Le7 x74 (42 usi '8j J A12 ts: Les A14 J L Lf L' ' j K As4 x79 g Koi Kst x2s A4s K x19 ns2 no7 uss "of L Ass to Los Ass L Lss Ls2 Kos Ls2 xas L4s no4 ts7 tro

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( _m. _._m._ l l Atta,chment to WO 96-0058 I Page 8 of 8 FIGURE 3 i PROJECTED EXPOSURE AT END OF CYCLE 9 l l l i .1. 2 3 4 5 6 7 8 9 10 11 12 13 14 15 l A A27 A47 A38 K13 As1 A43 A32 A ty, . to,, t,,,, ,n,,, Ks2 B B Kos Lu m m m C Ks3 K10 L74 K42 LSO K11 Le9 K48 K72 C gy 73, y 2F O D D K71 K44 L48 L71 L72 L34 K43 K4e l d'8, L40 Ls3 K17 L2s K23 U7 K09 Ls4 LN LO3 A63 E E AS4 LO4 i 4 l K33 K27 K36 K64 K78 K3s K24 K08 Ais F ] O F A17 27 p ggg 27 000 4 ,Lae t,, t,, t,, g,7 t,, g,, Ls3 As2 G G As0 Ls4 m n as i 1 .K.,o,s 'Le,e,, La La 27, s,. ,A,,s,s,, 37,.s ,Ka,s,, Li.e,- n Lss 3., K3e H H K0s K02 K41 Ls0 K12 K21 g sy% Ks4 L47 K87 L8s K31 L87 K74 L42 Ks1 ,y gay L64 A14 J J A12 ts2 'LES ~ Las LS1' . LB4' ,L7,,, 37 m Kas 37,sse K79 ,y p K01 K39 K28 23.279 A4s K K A44 Kie K32 K07 i L As4 LO2 L39 Ls2 KO3 L32 K29 L43 K04 Ls? L20 LOS A63 L i 27 .K.,i,e,, K4,e,e Ke7- ,K,22 M ,n,1 - Kse Kas L33 L7s 'm M L70 Lie K40 Ks0 4,, 1 L13 L31 L45 L16 I N K7s K30 L73 K47 gy,gyy L49 27.733 K24 27 4 L7s Kid K63 N pg ,,L8,1,, Lif L88 K78

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