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#REDIRECT [[L-MT-14-021, Proposed Alternative in Accordance with 10 CFR 50.55a Request RR-008 Associated with the Fifth Ten-Year Inservice Inspection (ISI) Interval]]
| number = ML14064A185
| issue date = 02/28/2014
| title = Monticello, Proposed Alternative in Accordance with 10 CFR 50.55a Request RR-008 Associated with the Fifth Ten-Year Inservice Inspection (ISI) Interval
| author name = Fili K D
| author affiliation = Northern States Power Co, Xcel Energy
| addressee name =
| addressee affiliation = NRC/Document Control Desk, NRC/NRR
| docket = 05000263
| license number = DPR-022
| contact person =
| case reference number = L-MT-14-021
| document type = Inservice/Preservice Inspection and Test Report, Letter
| page count = 26
}}
 
=Text=
{{#Wiki_filter:ý&XcelEnergye Monticello Nuclear Generating Plant2807 W County Road 75Monticello, MN 55362February 28, 2014L-MT-14-021 10 CFR 50.55aATTN: Document Control DeskU.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Monticello Nuclear Generating PlantDocket 50-263Renewed Facility Operating License No. DPR-22
 
==Subject:==
 
10 CFR 50.55a Request RR-008 Associated with the Fifth Ten-Year Inservice Inspection (ISI) Interval
 
==Reference:==
 
1)Letter from Northern States Power Company, a Minnesota corporation (NSPM), d/b/a Xcel Energy to Document Control Desk, "Fifth Ten-YearInservice Inspection Plan", dated February 28, 2012 (ADAMSAccession No. ML12060A298).
Pursuant to 10 CFR 50.55a(a)(3)(ii),
Northern States Power Company, a Minnesota corporation (NSPM), doing business as Xcel Energy, the licensee for the Monticello Nuclear Generating Plant (MNGP), hereby requests NRC authorization of the enclosed10 CFR 50.55a request associated with the Fifth Ten-Year Inservice Inspection (ISI)Interval for MNGP (Reference 1).NSPM proposes an alternative to visually inspect all accessible surfaces on both the topand underside of Shroud Support Plate Welds H8 and H9, which have known flaws, forall refueling outages in each of the three periods in the Fifth Ten-Year ISI Interval (2015,2017, 2019, and 2021) without disassembly of fuel cells or jet pump assemblies.
Asubset of the flaws on the underside of both welds will be selected and monitored indetail each refueling outage for any visually apparent change to the flaws. Based onthe inspection
: results, NSPM will determine the need for additional evaluations and/orany resulting actions and implement them accordingly.
Implementation of thealternative, as described herein, will provide reasonable assurance of structural integrity of the MNGP Reactor Vessel Shroud Support Plate.Enclosure 1 to this letter entitled, "Proposed Alternative in Accordance with10 CFR-50.55a(a)(3)(ii),
10 CFR 50.55a Request RR-008",
proposes an alternative tothe requirements of American Society of Mechanical Engineers (ASME) Boiler andPressure Vessel Code, Section Xl, "Rules for Inservice Inspection of Nuclear PowerPlant Components,"
(ASME Section Xl), 2007 Edition with the 2008 Addenda,IWB-2420(b),
as applied to the flaws in Shroud Support Plate Welds H8 and H9. Inconsideration of the unusual difficulty obtaining access to examine all areas with flawsin the H8 and H9 welds and pursuant to 10 CFR 50.55a(a)(3)(ii),
NSPM requests NRCauthorization of the proposed alternative provided in the enclosure because complying
,&uý--7VCCL.
Document Control DeskPage 2with the requirements of ASME Section XI, IWB-2420(b) would result in hardship orunusual difficulty without a compensating increase in the level of quality and safety.Enclosure 2 to this letter entitled, "Monticello Shroud Support Structure Flaw Evaluation Review and Support Plate Weld Inspection Recommendations",
provides supporting detail and technical justifications.
NSPM requests that the NRC authorize this 10 CFR 50.55a request by March 1, 2015to support the 1 R27 MNGP refueling outage.If you have any questions or require additional information, please contact Mr. RandyRippy at 612-330-6911.
Summary of Commitments This letter makes no new commitments and no revisions to existing commitments.
Karen D. FiliSite Vice President, Monticello Nuclear Generating PlantNorthern States Power Company -Minnesota Enclosures (2)cc: Administrator, Region III, USNRCProject Manager, Monticello, USNRCResident Inspector, Monticello, USNRCMinnesota Department of Commerce ENCLOSURE IMONTICELLO NUCLEAR GENERATING PLANTPROPOSED ALTERNATIVE IN ACCORDANCE WITH 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a REQUEST RR-008(23 pages follow)
Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008ASME Code Component(s)
AffectedCode Class:1Component Numbers:H8 Weld: Shroud Support Plate to Shroud Weld* ISI Component ID's:" C-3E (Shroud Shelf 0-180 deg)" C-3F (Shroud Shelf 180-360 deg)H9 Weld: Shroud Support Plate to Reactor Vessel Weld* ISI Component ID's:" C-3C (Shroud Shelf H9 Weld 0-180 deg)" C-3D (Shroud Shelf H9 Weld 180-360 deg)B-N-2, Welded Core Support Structures and InteriorAttachments to Reactor VesselsB13.30 Interior Attachments beyond Beltline RegionB13.40 Core Support Structure Alternative to ASME Section XI, IWB-2420(b)
Successive Inspections Examination Category:
Item Number(s):
 
==
Description:==
: 2. Applicable ASME Code Edition and AddendaThe Monticello Nuclear Generating Plant (MNGP) began the Fifth 10-yearInservice Inspection (ISI) Program Interval on September 1, 2012. The Code ofRecord for the Fifth Interval is the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section Xl, "Rules for Inservice Inspection of Nuclear Power Plant Components,"
(ASME Section Xl), 2007Edition with the 2008 Addenda.3. Applicable Code Requirement ASME Section XI, 2007 Edition with the 2008 Addenda, IWB-2420(b)
Page 1 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008The 2007 Edition with the 2008 Addenda IWB-2420(b) states:If a component is accepted for continued service in accordance withIWB-3132.3 or IWB-3142.4, the areas containing flaws or relevantconditions shall be reexamined during the next three inspection periodslisted in the schedule of the Inspection Program of IWB-2400.
Alternatively, acoustic emission may be used to monitor growth of existingflaws in accordance with IWA-2234.
: 4. Reason for RequestIWB-2420(b)
When a component has been accepted for continued service using analytical evaluation (IWB-3142.4),
as written in IWB-2420(b),
"the areas containing flawsor relevant conditions shall be reexamined..."
NSPM understands this to mean all the areas containing flaws or relevantconditions shall be reexamined.
MNGP has areas of flaws on the underside ofthe core shroud support in the H8 and H9 weld metal. The core shroud supportwelds are located in the reactor pressure vessel (RPV) interior, and the flawshave been accepted for continued service by analytical evaluation.
: However, allareas with the relevant condition are not fully accessible for reexamination.
The limited accessibility conditions were recognized following initial flawidentification with visual examination, and were accounted for in the applicable evaluations.
The analyses provided reasonable assurance that the components' structural integrity would be maintained during continued operation.
The flaws were reported to the NRC in the ISI Summary Reports for the 2011and 2013 refueling
: outages, and the analytical evaluations were also submitted as required by IWB-3144(b).
(References 1, 2, and 3)IWB-3144(b)
Evaluation analyses of examination results as required byIWB-3142.4 shall be submitted to the regulatory authority having jurisdiction at the plant site.Page 2 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008Although IWB-2420(b) allows acoustic emission monitoring as an alternative toreexamination, NSPM does not consider the interior of an operating reactor to bea suitable environment for the application.
Obtaining access to examine all areas with flaws in the H8 and H9 welds wouldbe unusually difficult due to the inherent design and interferences of the RPVinterior structures (see Attachments A, B, and C), several of which are described later in this request.
Therefore, NSPM is proposing an alternative to therequirements of IWB-2420(b) that will monitor the flawed areas of accessible surfaces and welds for potential changes and provide reasonable assurance thatthe component's structural integrity will continue to be maintained withoutexamining all the areas containing the flaws. The proposed alternative isdescribed later in this request.Component Description and Configuration The subject welds, referred to throughout this documentation as H8 and H9, arelocated in the reactor pressure vessel (RPV) interior and are part of the coreshroud assembly; specifically, the shroud support structure (see Attachments Dand E).H8 and H9 are weld identifiers designated by the Boiling Water Reactor Vesseland Internals Project (BWRVIP) in the BWRVIP-38
: document, "BWR ShroudSupport Inspection and Flaw Evaluation Guidelines,"
(Reference
: 4) and are usedfor their applicability to the ISI Program components for ASME Code ItemsB13.30 and B13.40 designated as the Shroud Shelf.The shroud support assembly includes a horizontal ring plate that is weldedbetween the bottom of the core shroud and the upper region of the reactorbottom head, and vertical support legs that are welded between the bottom of thecore shroud and the bottom of the bottom head.The horizontal ring plate is referred to as the shroud support plate (synonymous with baffle plate, or shroud shelf) and is made of Inconel (ASME SB-168).
TheH8 weld is the horizontal weld that joins the support plate to the Inconel coreshroud cylinder.
The H9 weld is the horizontal weld that joins the support plate toa weld buildup pad on the RPV bottom head. The H8 and H9 weld material isInconel 182, and the weld buildup pad on the RPV is Inconel 82 and 182. Thearea below the support plate and core shroud is the RPV lower plenum.Page 3 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008The purpose of the shroud support plate in connection with the other reactorinternals is to maintain an adequate distribution of coolant flow during normaloperations, seismic disturbances and design basis accidents.
The shroudsupport plate specifically is part of the core coolant envelope needed to maintaintwo thirds core height in the event of a recirculation line break loss of coolantaccident (LOCA). In connection with the shroud support legs, the shroud supportplate also provides lateral support for the core shroud during normal and accidentconditions.
Due to inherent design configuration of the reactor vessel internals with a weldedcore shroud and support assembly, fuel core and core support components, coreinstrumentation, sparger piping in the upper vessel regions, and jet pumpassemblies in the annulus region (see Attachment A), gaining access to thelower plenum is unusually difficult, and to gain further access would requireextensive disassembly of the fuel cells or jet pumps, which, as described below,would create a hardship without a compensating increase in the level of safety orquality.Access considerations and Inspection Technique NSPM has successfully inspected MNGP shroud support components in theregion below the shroud support plate, on a limited basis, by lowering high qualitycamera heads and auxiliary lighting into the jet pump inlets, and down throughthe jet pump to the vessel lower plenum. With this method, which does notrequire disassembly of jet pump or fuel cell assemblies, the flaws on theunderside of the H8 and H9 welds were coincidentally discovered during theMNGP 2011 refueling outage while inspecting the shroud support legs.When the inspections were performed on the underside of H8 and H9 welds inthe lower plenum, the common areas within a jet pump pair were accessible forinspection.
Those areas on either side of the access hole covers and the areasbetween the pairs could not be inspected due to the rigidity of the equipment andthe limited maneuverability as it passes through the jet pump and the opening inthe shroud support plate. (See Attachments C and E)In order to gain additional coverage on the underside of the welds, extensive reactor internal disassembly is required.
The jet pumps and/or fuel cells wouldhave to be disassembled and removed.
As described in BWRVIP-38, thePage 4 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008potential problems created by disassembly of fuel cells or jet pumps mayoutweigh the inspection benefit.As noted in BWRVIP-41, "BWR Jet Pump Assembly Inspection and FlawEvaluation Guidelines,"
(Reference
: 5) flow induced vibration (FIV) caused byleakage between the slip joint of the mixer and diffuser can cause damage to jetpumps. The FIV caused by slip joint leakage does not occur as long as the jetpumps are properly assembled, as designed and originally installed.
Disassembly and reassembly for the inspection may alter the alignment andaffect the stability of the jet pumps and increase the risk for damage with limitedimprovement in inspection coverage.
Disassembly and reassembly of the jet pumps would also have refueling outageimpacts with regard to additional outage time, costs, and dose. Estimates indicate that disassembly and reassembly of a jet pump pair would takeapproximately 20 to 24 hours. Applying the estimated time for 10 jet pump pairsresults in approximately 200 to 240 additional hours (-8-10 days) over and abovethe inspection time.In 2013, general area dose rates were approximately 1 to 3 millirem per hour(mR/hr) on the refuel floor near the refuel cavity. Applying 1 to 3 mR/hr to thelower time estimate of 200 hours for disassembly and reassembly of all 10 pairs,3 workers per shift, 2 shifts per day, the estimated dose would be 600 to 1800mR.Based on 2013 refueling outage costs of approximately
$60,000 per day for therefueling and in-vessel vendor, jet pump disassembly and reassembly activities would cost roughly $480,000
-$600,000.
This does not factor in other relatedcosts such as inspection, radiation protection
: support, mobilization anddemobilization, etc.Regarding fuel cell disassembly and reassembly activities, it is Monticello's viewpoint that disassembly of the fuel cells for inspecting the underside of the H8and H9 welds through the core support plate has slightly less risk thandisassembling the jet pumps. Vacating a fuel cell for access to the lower plenumto perform inspections, similar to jet pump disassembly, would have time anddose impacts to a refueling outage. Estimates indicate that the disassembly andreassembly steps for each cell, including fuel moves, would take approximately Page 5 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-00816 hours and would likely require replacement of some of the affectedcomponents.
Additionally, if there is fuel in the vessel during these activities, higher risk conditions may exist for "Operations With A Potential For DrainingThe Reactor Vessel" (OPDRV) while performing the related under-vessel activities, thereby requiring additional steps extending the time to complete theactivities.
Considering that there are 24 peripheral fuel cells to be vacated, the estimated time to complete the work is 384 hours (16 days). Although a portion of that workand related dose may be performed coincidental with some normal refueling activities, there would still be a substantial impact to refueling outage duration, vendor costs, worker dose, and replacement part cost.Using 2013 dose levels on the refuel floor, at 1 to 3 mR/hr, 3 workers per shift, 2shifts per day, for 384 hours, estimated dose for the refuel floor workers would beapproximately 1150 to 3450 mR. To vacate a fuel cell, a crew of workers is alsorequired under the vessel to perform removal and reinstallation of the ControlRod Drives (CRDs). Using 2013 dose levels for CRD changeouts, the changeout crew received roughly 200 mR combined dose per drive changeout.
Therefore, for changeout of 24 drives necessary to disassemble and reassemble the fuelcells, combined dose would be approximately 4800 mR. When added to therefuel floor dose, total dose would be approximately 5950 to 8250 mR.Based on 2013 combined costs for the refuel floor and under-vessel vendors of$74,000 per day, the cost for 16 days of fuel cell disassembly and reassembly activities would be approximately
$1,184,000.
This does not factor in otherrelated costs such as inspection, radiation protection support,mobilization/demobilization, etc.Vacating fuel cells for performing inspections on H8 and H9 under the shroudsupport plate, although slightly less risky than jet pump disassembly, would stilllikely result in limited accessibility.
Of the two welds, the H9 weld is locatedwhere the shroud plate joins the reactor vessel bottom head and would be themore difficult of the two to access for inspection.
As shown on Attachments A, B,and C, remote tooling for inspection from a disassembled fuel cell would need totravel from the nearest fuel cell across the width of the annulus to reach the H9weld. The opening in core support plate for each fuel cell is only 10.875" indiameter.
Inspection equipment would have to be maneuvered through thePage 6 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008narrow opening and have enough flexibility to maneuver across the shroudsupport plate from the underside to inspect the H9 weld. Considering theunusually difficult measures to perform an inspection in this manner, and with thelikely result of not being able to examine all areas of each weld to satisfy therequirements of IWB-2420(b),
there would not be a compensating increase in thelevel of quality or safety.The access hole covers are welded to the shroud support plate and function toperform a leak-tight barrier between the annulus and lower plenum. These arenot intended to be disassembled.
Disassembly of any reactor internals includes increased risk of generating foreignmaterial into the core or lower plenum, issues with reassembly that may have anunforeseen effect on future operation, and potential need for replacement/repair options for infrequently disassembled parts.The visual inspection technique deployed through the jet pump inlets for theunderside of the H8 and H9 welds is currently viewed by NSPM as the bestavailable technique for inspection of the area even with its limited coverage.
With the exception of limited areas at the N1A and N1B recirculation suctionnozzles, MNGP does not have access from the outer diameter to interrogate theflaws volumetrically.
UT of the RPV base material adjacent to the H9 weld, inlimited areas available at the N1A and N1 B nozzles, was performed in 2011 and2013. This will be explained in more detail in the Basis For Use section.The insulation package design on the exterior surface of the reactor vesselseverely limits access to perform a volumetric inspection of the H9 weld from theRPV outside surface.
There is no annulus or gap between the insulation and theRPV outside diameter (OD) surface based on MNGP's experience from previouswork activities on the vessel OD, as well as past discussions with the outageinsulation vendor. In addition, except for removable insulation panels around thevessel nozzles, the insulation package is interlocked with adjoining insulation sections and is held in place with metal banding.It should also be noted that in the qualitative
: analysis, as stated in Enclosure 2,the entire underside of both the H8 and H9 welds is assumed to be flawed forevaluation purposes.
Any activities to improve visual inspection coverage on thePage 7 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008underside of the welds would have no effect on the assumptions or conclusion inthe existing analysis.
Because there would still likely be access limitations that preclude the ability toinspect all of the H8 and H9 welds, MNGP could not meet the literal requirements of IWB-2420(b).
Therefore all the additional work, time, dose, and replacement part costs required to disassemble and reassemble reactor vessel internalcomponents for inspection, in order to satisfy IWB-2420(b),
would result in ahardship or unusual difficulty without a compensating increase in the level ofquality or safety.Flaws requiring reexamination per IWB-2420(b)
As previously described, the flaws on the H8 and H9 welds, visible cracks on theunderside surface of the weld metal, were accepted by analytical evaluation under ASME Section XI IWB-3142.4.
This Code sub-paragraph requiressubsequent examination of all areas containing flaws in the next three inspection periods following initial discovery under IWB-2420(b).
The flaws were initially discovered in 2011 which was the last refueling outage in Period 3 of the Fourth10-Year ISI Interval.
A small subset of flaws on the underside of both the H8 and H9 welds werereexamined in 2013, as well as performing examinations on the topside of thewelds. Analytical evaluations were performed again following this inspection toconfirm acceptance of the component for continued service.There are two refueling outages in Period 1 of the Fifth 10-Year Interval, 2013and 2015. Although a limited scope of inspections was performed at MNGP in2013, which was in Period 1 of the Fifth 10-Year ISI Interval, these exams werenot intended to fulfill the requirements of IWB-2420(b).
They were performed toverify the indications observed in 2011 were in fact flaws, by utilizing a newlyfabricated cleaning tool to remove surface deposits.
Therefore, the firstsuccessive inspection applicable to IWB-2420(b) would be scheduled for thesecond refueling outage in Period 1, which is the 2015 refueling outage (RF027).The flaws reinspected in 2013 were initially inspected in their as-found condition with indications being easily visible on a layer of surface deposits on the welds.Following a specialized cleaning process that cleaned the surface to bare metal,the same locations were reexamined.
The underlying cracks that produced thePage 8 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008linear indications on the surface deposit were readily apparent and wereessentially identical to the as-found indications seen prior to cleaning.
It was described that the indications in the surface deposit were very similar tothe conditions produced during a liquid dye penetrant examination, where thebleed out from the underlying flaw is highly visible on the background provided bythe developer.
Although the cleaning provided validation that the indications were relevant and were emanating from cracks in the weld metal, examination with the surface deposit in place was equally effective for identifying the flawsand the extent of cracking.
(see Attachments F and G)The flaws on the H8 and H9 welds were identified on all of the accessible regionsinspected on the underside of the welds using access provided through the jetpump inlet and openings into the lower plenum of the vessel. During theinspection in 2011, it was noted that the flaws appeared to continue beyond theregions accessible for inspection on the underside of the welds, as shown inAttachment H. Therefore, for evaluation
: purposes, it has been assumed thatthere are similar flaws in all the uninspected regions of both the H8 and H9welds.5. Proposed Alternative and Basis for UseProposed Alternative:
Pursuant to 10 CFR 50.55a(a)(3)(ii),
compliance with the successive inspection requirements under IWB-2420(b) of the 2007 Edition with the 2008 Addenda ofthe ASME Section Xl Code would result in a hardship or unusual difficulty withouta compensating increase in the level of quality and safety.NSPM proposes to visually inspect all accessible areas of the topside andunderside of both the H8 and H9 welds during each remaining refueling outage inthe three periods of the Fifth ISI Interval (2015, 2017, 2019, 2021). Due to theextensive nature of the flaws, detailed mapping of all flawed areas is notpractical.
NSPM intends to continue accessing the lower plenum via the jetpump inlets to perform the visual inspections.
In addition to inspecting allaccessible areas of the H8 and H9 welds for changes in the general condition ofthe welds, MNGP will select four areas with known, distinct indications on thePage 9 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008underside of the shroud support plate in the H8 and H9 welds to monitor for anyvisually apparent changes in the flaw. The areas selected will include twolocations on each weld, and will be located in different quadrants of the vessel.The selected locations will be mapped (by photo, video, or other effective method) and visually compared to the previous inspection.
The flaw locations will be examined for visual evidence of new branching, visual evidence of lengthchanges (e.g. flaws that once only covered a portion of the weld now completely cross the weld, etc.), and visual evidence of any flaws that extend into the reactorvessel low alloy steel or the shroud support plate itself. The accessible topsideof the welds will also be inspected to verify no cracking has penetrated throughthe thickness of the weld (e.g. crack-like indications on the topside that could beconnected to cracking on the underside).
Based on the inspection
: results, NSPMwill determine the need for additional evaluations or any resulting actions andimplement them accordingly.
NSPM and Monticello are members of industry organizations that address issueswith reactor vessel internal structures and attachments.
These organizations perform research and develop inspection techniques and guidelines to addressthe issues on behalf of the industry.
Involvement in these organizations, as wellas contact with other stakeholders and in-vessel inspection service providers willbe used at MNGP to further assess the conditions of the shroud support platewelds and develop inspection strategies going forward.By performing detailed mapping and monitoring of a representative sample of theflaws and investigating more refined inspection techniques, Monticello willcontinue to monitor the condition of the welds and meet the intent ofIWB-2420(b).
The proposed alternative to the requirements of IWB-2420(b) willdemonstrate, with reasonable assurance, that the structural integrity of theshroud support plate and its welds will be maintained, and that the assumptions used in evaluations remain valid. The alternative can be implemented withoutimposition of undue hardship or unusual difficulty that would not provide acompensating increase in the level of quality and safety.Page 10 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008Basis for Use:Since 2011, when the flaws in the H8 and H9 welds were initially discovered, extensive analysis was performed regarding the flaws and how they may affectthe structural integrity of the shroud support assembly.
These analysesdemonstrated that the flaws in the H8 and H9 welds have a negligible effect onthe ability of the shroud support assembly to perform its design and safetyfunctions during normal and accident conditions.
One of the evaluations performed for the H8 and H9 welds included the potential for the flaws in the H9 weld to grow into the low alloy steel of the reactor vessel.The probability of flaw growth into the low alloy steel of the reactor vessel is lowbased on the water chemistry environment in the lower plenum in the MNGPreactor vessel and the low residual stress in the reactor vessel. Note that noneof the observed flaws in the visual inspections were found to extend beyond theboundary of the H8 and H9 weld metal.Monticello has very limited OD access to the reactor vessel for Ultrasonic Testing(UT) due to the design of the RPV insulation package.
There are small areas ofaccess near the recirculation suction nozzles (N1A and N1B) where theinsulation is designed to be removable, and UT can be performed.
In 2011, asingle-sided UT inspection was performed from the outer diameter (OD) of thereactor vessel in the N1B recirculation suction nozzle window using a procedure qualified according to the Performance Demonstration Initiative (PDI) for reactorvessel welds. Due to the interference of the permanent insulation, Monticello could only perform axial scans which would identify any potential circumferential flaws in the low alloy steel of the reactor vessel at the H9 weld. No indications were found. In 2013, a similar single-sided UT inspection was performed in theN1A nozzle window, and again no indications were found. A combined total ofapproximately 129.5 inches of the reactor vessel was scanned in 2011 and 2013.The UT results help demonstrate the conclusion that the probability of flawgrowth into the low alloy RPV material is low.The primary concern related to the H8 and H9 welds is uplift of the plate in theevent of a design basis LOCA event. The uplift of the shroud support plate wouldbe driven by the vertical seismic loads and reactor internal pressure differences across the plate. The evaluations done in 2011 and 2013 assume veryconservative flaw profiles including complete circumferential cracking of both thePage 11 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008H8 and H9 flaws with cracking in the depth direction of approximately 75%through the weld thickness (through-wall).
In the 2013 evaluation, usingconservative flaw profiles and consideration of the loading acting upon theshroud support plate in the reactor vessel, only 18% of the total weld surface isrequired to be free of through-wall indications to overcome the uplift loads actingon the shroud support plate. Considering such extensive flaw profiles, theevaluations demonstrate that the structural integrity of the shroud support plateand its ability to resist uplift remain intact for at least 12 years and maintain thecore coolant envelope.
See Enclosure 2 for additional details of evaluations performed to date.Based on flaw tolerance estimates provided in BWRVIP-38, the MNGP shroudsupport assembly is inherently flaw tolerant by design. In addition to the flawtolerant design, MNGP implemented hydrogen water chemistry (HWC) in 1989and recently implemented Online Noble Metal Chemistry (OLNC) in 2013. Theenvironment of the lower plenum is well mitigated against flaw growth andinitiation based on the water chemistry controls implemented in accordance withBWRVIP-190 "BWR Water Chemistry Guidelines" (Reference
: 6) via the MNGPStrategic Chemistry Plan.All of the evaluations done to demonstrate the structural integrity of the shroudsupport assembly, including the shroud support plate H8 and H9 welds and theshroud support leg H10 welds, have been summarized and are further described in Enclosure 2, "Monticello Shroud Support Structure Flaw Evaluation Reviewand Support Plate Weld Inspection Recommendations."
The documentevaluates whether reduced inspection coverage is technically justifiable in lieu ofthe implicit requirement to inspect all flawed areas of the H8 and H9 welds asdescribed in IWB-2420(b).
The document recommends minimum inspection requirements based on the conservatisms built into the evaluations performed todate, MNGP water chemistry in the lower plenum of the reactor vessel, and crackgrowth potential of the flaws. The minimum inspection recommendations provided in Enclosure 2 are as follows:1. At least 15% coverage of the top side of welds H8 and H9 with theobjective of identifying at least 13% of the top side weld length to beunflawed.
Page 12 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008a. The extent of top side coverage should be increased until atleast 13% of the weld length for both H8 and H9 are shown tobe unflawed.
: 2. 5% coverage of the bottom side of welds H8 and H9 in areas withknown flaws with the objective of monitoring for unexpected change offlaw appearance.
Note that in 2013, Monticello was able to inspect 32% of the topside of the H8weld and 35% of the topside of the H9 weld with no relevant indications.
Basedon a review of previously inspected regions on the underside of the H8 and H9welds, the areas accessed through the jet pump inlets, will be used to meet the5% coverage recommendation.
NSPM proposes to visually inspect all accessible areas of the top and underside of the H8 and H9 welds without disassembly of jet pumps or fuel cells. Byinspecting all of the accessible areas of H8 and H9 welds for the next threesuccessive periods and performing detailed monitoring and comparisons on asubset of the flaws on the underside of the welds for visually apparent changes,NSPM will meet the intent of the IWB-2420(b).
The proposed alternative to therequirements of IWB-2420(b) will demonstrate, with reasonable assurance, thatthe structural integrity of the shroud support plate and welds will be maintained, and that the assumptions used in evaluations remain valid.Page 13 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008Summary:In summary, the evaluation provided in Enclosure 2 provides a technical basis tojustify a lesser amount of examination of flawed areas than implied byIWB-2420(b).
NSPM proposes an alternative to visually inspect all accessible surfaces on boththe top and underside of the H8 and H9 welds for each remaining refueling outage in the three periods of the Fifth 10-Year ISI Interval (2015, 2017, 2019,2021) without disassembly of fuel cells or jet pump assemblies.
A subset of theflaws on the underside of both welds will be selected and monitored in detail forany visually apparent change to the flaws. Based on the inspection results,NSPM will determine the need for additional evaluations or any resulting actionsand implement them accordingly.
The proposed alternative will providereasonable assurance that the structural integrity of the reactor vessel shroudsupport plate will be maintained.
Continued involvement in industry organizations that address issues with reactorvessel internals, as well as contact with other stakeholders and in-vessel inspection service providers will be used at MNGP to further assess theconditions of the shroud support plate welds and develop inspection strategies going forward.Pursuant to 10 CFR 50.55a(a)(3)(ii),
NSPM requests the NRC to authorize use ofthe proposed alternative to ASME Section Xl, IWB-2420(b).
Complying withIWB-2420(b) at MNGP for flaws or relevant conditions on the underside of the H8and H9 welds of the RPV Core Shroud Support Plate would result in hardship orunusual difficulty for NSPM without a compensating increase in the level ofquality and safety.Page 14 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-0086. Duration of Proposed Alternative The proposed alternative will be used for the Fifth 10-Year Inservice Inspection Interval of the ASME Section Xl Inservice Inspection Program for the MNGP thatis expected to end on May 31, 2022.7. Precedents None identified
: 8. References
: 1. NSPM Letter L-MT-11-046 to NRC, "Cycle 25 Inservice Inspection SummaryReport,"
dated August 23, 2011, ADAMS Accession No. ML1 12351222.
: 2. NSPM Letter L-MT-13-102 to NRC, "Cycle 26 Inservice Inspection andIn-Vessel Visual Inspection Summary Reports,"
dated October 11, 2013,ADAMS Accession No. ML13308B206.
: 3. NSPM Letter L-MT-13-040 to NRC, "Supplemental Information Regarding Cycle 25 Inservice Inspection Summary Report -Core Shroud Support FlawEvaluation,"
dated July 2, 2013, ADAMS Accession No. ML13191A766.
: 4. Boiling Water Reactor Vessel and Internals
: Project, "BWR Shroud SupportInspection and Flaw Evaluation Guidelines" (BWRVIP-38),
Rev. 0, September 1997.5. Boiling Water Reactor Vessel and Internals
: Project, "BWR Jet PumpAssembly Inspection and Flaw Evaluation Guidelines,"
(BWRVIP-41),
Rev. 3,September 2010.6. Boiling Water Reactor Vessel and Internals
: Project, "BWR Water Chemistry Guidelines
-2008 revision" (BWRVIP-1 90), 2008 Revision, October 2008.Page 15 of 15 Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008Attachment A -Reactor Vessel and Internals OverviewSteam DryerTop GuideJet Pump Inlet'Core Shroud -Core Support PlateRecirculation Outlet -(Typical of NIA and NIB)Shroud Support PlateShroud Support LegsTypical FuelCellConfiguration Page El-A Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008Attachment B -Area Below Top GuideFuelSupportPieceEGuide TubeH9 WeldH8 WeControl Rod.Drive HousingTypical Fuel Cell" Configuration Vacating a fuelcell requirestotaldisassembly andremoval of allcomponents within redrectangle forinspection ofshroud supportplate weldsPage El-B Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008Attachment C -Tooling Insertion PathsVCurrent Path..........
> Used for VisualInspection through Jet PumpPath Through OpenFuel Cell -Requires> disassembly andIremoval of allcomponents in fuelV I icell and maneuverbetween shroudsupport legsCore Shroud dShroud SupportPlateH9 Weld H8 WeldShroud SupportLeg (Typical
-14 Total AroundCircumference of Shroud)Page El-C Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008Attachment D -Monticello Shroud Support Structure Illustration 13/4*Shroud Baffle PlateShroud LedgeW,,H8 WeldH10Wl Shroud SupportStubs (14Total)
Page E1-DI Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008Attachment E -Monticello Shroud Support Plate Underside Illustration (Shroud Support Legs Not Illustrated)
Access Hole CoverJet Pump Opening inShroud Support PlateReactor PressureVesselReactor CoreCore Shroud -Access Hole CoverJet Pump PairsJPI /JP2JP3/JP4JP5/JP6JP7/JP8JP9/JP10JP11 /JP12JP13/JP14 JP15/JP16 JP17/JP18 JP19 I JP20Areas indicated in red are inaccessible for inspection due tothe rigid nature of the inspection equipment and limitedmaneuverability within the jet pumps.Page E1-E Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008Attachment F -Indications at 680 Before and After Cleaning of H8 Weld (2013)Note that the indication is clearly visible prior to cleaning.
The red arrows show thebranching pattern indicating that the before and after photos are the same flawBefore CleaningAfter CleaningPage E1-F Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008Attachment G -Indications at 2920 Before and After Cleaning of H9 Weld (2013)Note that the indication is clearly visible prior to cleaning.
The red arrows show thebranching pattern indicating that the before and after photos are the same flaw.BeforeCleaningAfter CleaningPage E1-G Monticello Nuclear Generating PlantProposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(ii) 10 CFR 50.55a Request RR-008Attachment H -H8 and H9 Weld Showing Indications Past Field of View of Camera(2011)H8 WeldIndication at 700-Note Indication appears tocontinue pastfield of view ofthe cameraH9 WeldIndication at 3000-Note Indication appears tocontinue pastfield of view ofthe cameraPage E1-HI}}

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