ML20195D534

Forwards Description of Vermont Yankees Plans for Insp of & Mods to Certain Reactor Vessel Internals

ML20195D534
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	05/27/1999
From:	Leach D VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BVY-99-73, NUDOCS 9906090190
Download: ML20195D534 (9)

Text

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.YERMONT YANKEE- l NUCLEAR POWER CORPORATION i

,o P.O. Box 157, Governor Hunt Road May 27.1999 (y')

b Vemon, Vermont 05354-0157 -

BVY 99-73 (802) 257-7711

' U.S. Nuclear Regulatory Commission 1 ATTN: Document Control Desk Washington,DC 20555

Reference:

(a) Letter, VYNPC to USNRC," Vermont Yankee Plans for the 1998 and 1999 Refueling 1 Outages Regarding Reactor Vessel Internals," BVY 97-123, dated September 30,1997.

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Subject:

Vermont Yankee Nuclear Power Station License No. DPR-28 (Docket No. 50-271)

Reactor Vessel Internal Plans for the 1999 and 2001 Refueline Outanes In Reference (a), Vermont Yankee informed the staff of our Spring 1998 and Fall 1999 refueling outage plans as they relate to the BWRVIP. Vermont Yankee submits this letter to update our plans for the 1999 and 2001 refueling outages. The attachment to this letter describes Vermont Yankee's plans for inspection I of and modification to certain reactor vessel internals. Of note an: our plans to defer replacement of the core j spray piping internal to the reactor vessel from the 1999 refueling outage.

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Vermont Yankee reaffirms our mtent to mstall top guide and core plate wedges and ultrasonically inspect  !

140 accessible Jet Pump Mixer / Diffuser / Adapter welds during the 1999 outage. The remaining 20 welds I inaccessible to UT capability will be inspected using enhanced visual inspection techniques (EVT-1). The attachment addresses all of the current BWRVIP guidelines regarding inspection scope and scheduling as i they apply to the reactor vessel internal components.

We trust that the attached information is responsive to your concerns. If you have any questions on this transmittal, please contact Mr. Thomas B. Silko at (802) 258-4146.

i Sincerely, VERMONT YANK - NUCLEAR POWER CORPORATION I i

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(Daff &cli' Vic President, Engmeenng l

Attachments \

cc: USNRC Region 1 Administrator USNRC Resident inspector-VYNPS h )

USNRC Project Manager- VYNPS r.

Vermont Depanment of Public Service , t, e Od l 9906090190 990527 6 <

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.- , BVY 99-73 Attachment i Vermont Yankee Nuclear Power Station Reactor Vessel Internal Plans for the 1999 and 2001 Refueling Outages

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'BVY 99-73 / Attachment I / Page !

Reactor Vessel Internal Plans for the 1999 and 2001 Refueling Outages Core Sorayfjpjag In the Fall of 1996, Vermont Yankee (VY) performed ultrasonic inspection of 39 core spray piping circumferential welds and visual inspection of five circumferential welds that were not accessible for ultrasonic inspection. Rose 44 welds represented 100% of the accessible core spray piping welds. He inspections met the guidelines of the Boiling Water Reactor Vessel Internal Project (BWRVIP) Core Spray Internals inspection and Flaw Evaluation Guidelines (BWRVIP-18) for a baseline examination. Two non-pressure boundary mechanical welds, where the core spray piping penetrates the core shroud (P8b welds),

were ultrasonically found to have indications of possible intergranular stress corrosion cracking. The flaw analysis evaluated several possible conditions of the core spray piping, including the limiting case where all four mechanical collar welds were completely failed. NRC evaluated the analysis and authorized operation i

for one cycle , with the stipulation that operation beyond the 1998 refueling outage would depend on the satisfactory evaluation of the reinspection results or by implementing repairs during the 1998 refueling 2

outage. VY responded with its plans for reinspection in 1998 and replacement in 1999. NRC issued a 8

Safety Evaluation Report on the basis of these plans.

De BWRVIP-18 core spray piping reinspection frequency for visual inspection is one cycle. Therefore, the five wekts that were inspected visually in the Fall of 1996 were visually reinspected in the Spring of 1998.

In addition, VY also visually reinspected the two core spray piping welds that, via UT, exhibited cracking during the Spring 1998 outage. As in 1996, no cracking was detected visually.

VY assigned engineering resources and initiated work on the pipe replacement project in February 1998.

VY and our pipe replacement vendor have aggressively pursued a design to replace the core spray invessel piping, including the safe-ends intemal to the reactor vessel nozzles, through and including, the core shroud penetrations. However, despite the early planning, we have realized that full system replacement is a significantly larger effort than sectional replacements performed to date and that adequate prototype testing could not be completed in time to support the outage. Accordingly, VY has elected not to perform replacement of the core spray piping in 1999 in consideration of the significant risk to our outage schedule.

VY intends to complete the design portion of this project in 1999.

VY is informing NRC that the Safety Evaluation Report may warrant revision relative to the two flawed core spray piping structural welds that were previously documented and evaluated. Both welds are collar-to-shroud welds, identified as P8b welds per the BWRVIP. These welds are not pressure retaining welds.

In 1996 engineering analyses were performed which demonstrated that the annulus piping would perform its safety function if all four collar-to-shroud welds were completely failed. Given that if a P8b weld completely failed, the core spray annulus piping could be displaced % inch axially and 0.028 inches vertically and horizontally. In such a case, the stresses in the core spray system annulus piping were determined to be within AEME Section III allowable stress limits. %ese welds are redundant to the sparger tee-box-to-shroud pipe welds, identified as P9 welds per the BWRVIP. The P9 welds are the actual pressure-retaining welds. All other pressure-retaining welds in the internal core spray piping system were

' Letter, USNRC to VYNPC," Review of Core Spray System Piping Collar to-Shroud Weld Flaw Evaluation and Core Spray System inspection Plan at Vennont Yankee Nuclear Power Station (TAC Nos. M96671 and M96689)," NVY 96 176, dated November 20,1996.

8 Letter, VYNPC to USNRC, " Vermont Yankee Plans for the 1998 and 1999 Refueling Outages Regarding Reactor Vessel intemals," BVY 97-123, dated September 30,1997.

8 Letter, USNRC to VYNPC, " Plans for the 1998 and 1999 Refueling Outages Regarding Reactor Vessel Intemals - Vermont Yankee Nuclear Power Station," NVY 98-44, dated March 25,1998.

VEltMoNT YA%Itti Nt ci.i Ast Pows it Coeu*onxitoN

• BVY 99 73 / Attachment I / Page 2

- ultrasonically examined and were identified to be free of flaws. Based upon these results the P9 welds can be considered to be fully functional with'a high level of confidence.

In addition, the flaws found by ultrasonic inspection in the P8b welds could not be verified using enhanced visual inspection techniques. No portion of the flaws extend to the surface of the shroud or thermal sleeve and therefore we believe, based upon further assessment of the weld configuration, that the flaws are likely

' fabrication-related.

, VY will reinspect the Core Spray Piping Intemal Welds in accord .ce with the BWRVIP guidelines.

BWRVIP-18 specifies that certain target welds be reinspected, of which VY has 32. De BWRVIP core spray piping reinspection frequency for ultrasonic inspection is two cycles.; Consequently, of the 44 welds that were inspected ultrasonically and visually in 1996,32 will require reinspection in 1999. VY intends to perform Enhanced Visual Inspection (EVT-1) of these welds, J I

The core spray piping bracket welds, up until the 1998 refueling outage, were inspected 'with a modified VT-1 inspection technique. Since that time, the BWRVIP committee has agreed with the NRC to revise ,

BWRVIP-18 and perform EVT-l's of these attachment welds. Therefore, for future inspections VY will perform EVT-l's of the core spray piping bracket welds. The BWRVIP-18 recommended inspection frequency is every four cycles for these welds. The next inspection is scheduled for 2001, although not necessary until the currently scheduled outage of 2004.

Com Spray Spargers With the Spring 1998 outage, VY committed to follow the guidance of the BWRVIP-18 for inspection of -

core spray spargers. In 1998, following the published guidance for a geometry-tolerant plant, VY  !

performed a modified VT-1 (with cleaning) of the core spray sparger circumferential welds and a VT-3 of  !

the nonles and brackets in 1998. No flaws were found. Since that time, the BWRVIP has agreed with the  !

NRC to mvise BWRVIP-18 and discontinue the designation of geometry-tolerant plant status. Derefore, in i the future, VY will perform EVT-l's of the sparger circumferential and bracket welds and a VT-1 1 inspection of the nonle welds. De reinspection frequency for sparger circumferential welds is two cycles.

De reinspection fmquency for nonle welds is 50% every two cycles, and the reinspection frequency for i sparger bracket welds is four cycles, as defined by BWRVIP-18. Derefore, the sparger circumferential '

i welds and 50% of the nonle welds will be reinspected in 2001.

Core Shroud VY performed an ultrasonic irspection ofits circumferential welds in the Spring of 1995. As a result of that inspection, a'four tie-rod modification was installed on the shroud in 1996 which provided full circumferential weld structural replacement. In conjunction with the 1996 repair, ultrasonic and eddy  ;

current inspections of the repair design-reliant welds were performed. De design-reliant welds consist of portions of eight vertical welds, six ring-segment welds and portions of welds H8 and H9 at the jet pump baffle plate.' No cracking was found in any of these welds.

He' 1996 vertical and ring segment weld inspections meet the proposed BWRVIP Guidelines for Reinspection of BWR Core Shmuds (BWRVIP-07) for a baseline inspection of repaired shrouds, even as j they are now being revised (as a result of Nine Mile Point i vertical weld cracking). Because VY has performed a full baseline inspection of repair design-reliant welds, the BWRVIP reinspection frequency does not recommend performance of an inspection in either the 1999 or 2001 outages, with the possible exception of portions of welds H1 and H2.

VEntovr YAmst Nect.r.AH Powut ColuaonAnoN "BVY 99-73 / Attachment 1./ Page 3 4

- De first cycle inspection of all four tie-rods.was conducted during the Spring 1998 refueling outage. . The

' inspection consisted of a visual examination to critoria approved by the repair designer. Dere were no inspection findings.1 Because the tie rods were re-torquod in 1998 to a higher value to support future increased core flow initiatives; all four tie-rods will be reinspected in 1999.

Shroud Support No cracking was identified during the Fall 1996 ultrasonic and eddy current inspections of welds H8 and

.H9. De Fall 1996 inspections satisfy the guidance of BWRVIP-38 for a baseline examination._ ne BWRVIP-38 seinspection frequency does not recommend reinspection in either the 1999 or 2001' outages.

Access hole cover welds will continue to be inspected each refueling outage until the BWRVIP provides guidance in this area.

Top Guide VY plans to install top guide wedges during the Fall 1999 refueling outage. His is being done in order to eliminate inspections of the top guide aligner assemblies, the top guide hold-down assemblies, and the top guide rim . weld as recommended by BWRVIP-26. For plants with top guide wedges, BWRVIP-26 recommends verification that the wedges are in place.

We will continue examination, as recommended by General Electric Service Information Letter (SIL) 554, of a sample of top guide grid beams. VY has repeatedly examined these locations and has not found any indication of flaws.

Core Plate VY also plans to install core plate wedges during the Fall 1999 refueling outage. His is being done in order to eliminate inspections of the core plate rim hold-down bolts secommended by BWRVIP-25. For plants with core plate wedges, the only inspection recommended by BWRVIP-25 is to verify that the wedges are in place.

. Jet Pumn Assemblies VY completed baseline inspection per BWRVIP-41 of the 30 jet pump riser circumferential welds in 1998.

Four flaws were discovered in thermal sleeve-to-elbow welds. De NRC recently issued a revised Safety Evaluation . Report' which allows operation until the 2001 refueling outage, in 2001, these four welds will

. be reinspected. In 1998, VY also completed baseline inspection, per BWRVIP-41, of 50% of the riser to-restrainer welds,50% of the riser brace welds,50% of the inlet clamp bolted conrations, and 50% of the restrainer assemblies. No flaws were identified in these components.

In ecceid.nce with ' recommendations in NUREG/CR-3052 and the guidance of BWRVIP-41, VY also performed inspection of 100% of the jet pump hold-down beams during the 1998 refueling outage. One Letter, USNRC to VYNPC," Jet Pump Circumferential Weld Inspections at Vermont Yankee Nuclear Power

- Station (TAC No. MA5109)," NVY 99 46, dated April 29,1999.

U Vranos t Yma: NecuAn Powen Couronxuos I GVY 99 73 / Attachment I / Page 4 l

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l. beam was replaced as a result of a UT indication. In.accordance with BWRVIP-41,50% of the jet pump )

hold-down beams will be inspected during the 1999 and 2001 refueling outages.

In 1999, VY will complete the baseline inspection of the jet pump circumferential welds. He 30 riser 1- circumferentia* welds were inspected in 1998. A total of 140 circumferential welds in the mixer, diffuser i and adapter sections of thejet pump will be ultrasonically examined from the ID of thejet pumps. Access is l l gained for inspection tooling through the mixer inlet throats. -Twenty (20) circumferential welds are 1 l . inaccessible for UT inspection and will be examined using the EVT-1 visual technique.

With the exception of the hold-down beams, the four flawed riser welds, and the possible inspection ofjet

. pump thermal sleeve welds (ifinspection capability becomes available), no inspection of any otherjet pump components is recommended in 2001 per BWRVIP-41.

Standbv Liauid Control System Per BWRVIP-27, the nozzle-to-safe end weld extemal to the vessel is the only inspection location within the scope of the BWRVIP that is critical to its function. The guidelines state, "A volumetric examination of the

, nozzle-to-safe end weld should be performed, if accessible, at the next outage when inspection tooling is available and appropriate pre-outage planning can be done." The BWRVIP Inspection Committee and EPRI are currently woiting on volumetric NDE techniques for these small diameter dissimilar metal welds, but it is not clear when a technique will be ready. VY intends to perform this examination when a demonstrated technique becomes available. In the interim, VY will continue to perform enhanced leakage examination of thisjoint in accordance with BWRVIP-27. It should be noted that at VY the Standby Liquid

' Control System safe end is fabricated with low carbon (0.019%) stainless steel, and thus is not considered to be susceptible toIGSCC.

Lower Plenum BWRVIP-47 governs inspection of the components in the lower plenum. This document identifies inspection of five items, which are integral of the control rod drive assembly. %ese are the guide tube i

. body-to-sleeve welds; the guide tube base-to-body welds; the guide tube sleeve-to-alignment lug welds; and I

. the fuel support alignment pin-to-core plate weld and the pin itself. VY will perfonn these examinations as a part of the blade change-out procedure beginning in 2001. This will satisfy the minimum sample

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l guidelines in BWRVIP-47 for these components.

FeedwaterNozzle Inner Radii I 1

In 1995, VY performed a unique examination of the four feedwater nozzle inner radii in accordance with a Relief from~.NUREG-0619. This was performed from the inside of the reactor vessel using tooling that manipulated ultrasonic transducers in the annulus between the feedwater thermal sleeve and the nozzle. He NRC issued an SER8 that approved an inspection frequency of four cycles. Derefore, in 2001 this examination will be repeated.

j .s1 Letter, USNRC to VYNPC,"Feedwater Nozzle Inspection Relief Request - Vermont Yankee Nuclear Power l- Station," NVY 95-142, dated October 12,1995.

l. Letter, USNRC to VYNPC," Erratum to the Safety Evaluation of Vermont Yankee Nuclear Power

- Corporation's Request for Relief from NUREG-0619 Feedwater Nozzle Inspection Requirements - Vermont

Yankee Nuclear Power Station," NVY 96182, dated December 5,1996.

VatuoNT YANKEE Nt'cuan Powrn Com onAuoN BVY 99-73 / Attachment I / Page 5 -

Internal Attachment Welds Other than the jet pump and core spray attachment welds discussed above, no vessel internal attachment welds are scheduled for inspection in 1999 or 2001.

Other ReactorInternals Components There are no safety-related reactor internals components other than the ones discussed above.

1 As described in the forgoing discussion and demonstrated by previous initiatives, VY believes in an

- aggressive and conservative approach in performing reactor vessel intemal inspections and implementing repairs or replacements. VY is also proactive in following the BWRVIP emerging recommendations and has demonstrated our intent in meeting thest. recommendations at the earliest possible times.

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t-l VituMoNT YANK :n Nt ci.r.Au Powru CouronArtoN 'l e

Docket No. 50-271

. .. BVY 99-73 i

Attachment 2 Vermont Yankee Nuclear Power Station Reactor Vessel Internal Plans for the 1999 and 2001 Refueling Outages

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'BVY 99-73 / Attachment 2 / Page i

SUMMARY

OF VERMONT YANKEE COMMITMENTS The following table identifies commitments made in this document by Vermont Yankee. Any other actions disenssed in the submittal represent latended or planned actions by Vermont Yankee. They are described to the NRC for the NRC's information'and are not regulatory commitments. Please notify the Licensing Manager of any questions regarding this document or any associated commitments.

COMMITMENT COMMITTED DATE OR" OUTAGE"

1) VY will reinspect the Core Spray Piping Internal target welds in  : 1999 refueling outage accordance with the BWRVIP guidelines.

2) VY will perform EVT-l's of the core spray piping bracket welds. 2004 refueling outage

.- (A1, P2)

3) VY will perform EVT-l's of the [ core spray] sparger circumferential 2001 refueling outage and bracket welds and a VT-1 inspection on 50% of the nozzle welds. (A1, P2)

4) VY will perform EVT-l's of the [ core spray] bracket welds. 2004 refueling outage

' (A1, P2)

5) All four [ core shroud] tie-rods will be reinsputed. (Al, P3) 1999 refueling outage

6) Access hole cover welds will continue to be inspected each refueling Each refueling outage outage until the BWRVIP provides guidance in this area. (A1, P3)

7) We will continue examination, as recommended by GE SIL 554, of a 1999 refueling outage sample of top guide grid beams. (A1 P3) 8; These four [ jet pump thennal sleeve-to-elbow welds with flaws] will 2001 refueling outage be reinspected. (Al, P3)

9) In accordance with BWRVIP-41,50% of thejet pump hold-down 1999 refueling outage beamswillbeinspected (A1,P3)

10) in accordance with BWRVIP-41,50% of thejet pump hold-down 2001 refueling outage beams will be inspectal. (A1, P3)

11) VY will complete the baseline inspection of thejet pump 1999 refueling outage -

circumferential welds. A total of 140 circumferential welds in the mixer, diffuser and adapter sections of thejet pump will be ultrasonically examired from the ID of thejet pumps. Twenty (20) circumferential welds are inaccessible for UT inspection and will be examined using the EVT-1 visual technique. (A1, P4)

12) Perform enhanced leakage examination of thisjoint (nozzle-to-safe Each refueling outage end weld) in accordance with BWRVIP-27, until a demonstrated i volumetric NDE technique becomes available. (A1, P4)

13) VY will perfonn these examinations (guide tube body-to-sleeve 2001 refueling outage welds; the guide tube base-to-body welds; the guide tube sleeve-to-alignment lug welds; and the fuel support alignment pin-to-core plate weld and the pin itself) as a part of the blade change-out procedure beginning in 2001. (A1, P4)

14) Perform a unique examination of the four feedwater nozzle inner 2001 refueling outage radii in accordance with o Relief from NUREG-0619. (A1, P4)

Note: A = Attachment #, P = Page #