ML20114D922

Forwards Supplement to 910930 Response to NRC Request for Addl Info to Resolve 920618 Telcon Request for Relief from Inservice Insp Program.Justification Re Removal of Insulation Panels from Bracket Welds Encl

ML20114D922
Person / Time
Site:	Quad Cities
Issue date:	08/28/1992
From:	Schrage J COMMONWEALTH EDISON CO.
To:	Murley T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
References
NUDOCS 9209100166
Download: ML20114D922 (10)

Text

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Ccmm:nw:alth Ediscn -

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Downers Grove, Illinois 60515 1

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August 28,1992 i

Dr. Thomas E. Murley, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission l

Washington, D.C. 20555 ATTN: Document Control Desk

Subject:

Quad Cities Stat!on Units 1 and 2 Resolution of Questions Pertaining to 2

Relief Request for Inservice inspection Program NRC_DscheLNcs. 50-2fL4_anift0-265 1

References:

(a)

Teleconference on June 18,1992 between l

Ccmmonwealth Edison (J.L. Schrage) and NRR (L.N. Olshan).

(b)

J.L.- Schrage to T.E. Marley letter cated September 30,1991.

(c)

J.L. Schrage to T,E. Murley letter dated March 12,1992.

Dr. Murley:

In Reference (a), Commonwealth Edison (CECO) submitted a p;oposed.

i Relief Request to the inservice inspection (ISI) program. - Additioncl infor~ation i

pertaining to this relief request was provided in Reference (b). Subsegunt to the j

sub. ittal of the Reference (b) Information, NRR informed CECO that additional '

justificat:an for the proposed Relief Request would be required prior to approval '

(Reference (c) teleconference). The additional justification should describe the basis for evaluating the impracticality of esmoving insub. ion panels which cover the Reactor Vessel Stabilizer Bracket welds.

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9 Dr. T.E. f.lurley August 28,1992 The additional justification requested by NRR is provided in the attachment. If there are any further questions or comments, please direct them to John L. Schrage at 708-515-7283.

Sincerely,/

/hGfekguy

, -hn L. Schrage Nuclear,

'nsing Administrator Attachment cc:

A. Bert Davis, Reolonal Administrator - Rill L.N. Olshan, ProJ50t Manager - NRR T.E. Taylor, Senior Resident inspector - Quad Cities D. Smith, NRR Technical Staff Office of Nuclear Safety -IDNS l

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f BASIS FOR EVALUATING THE _ IMPRACTICALITY OF - REMOVING' INSULATION PANELS WHICH = COVER THE REACTOR VESSEL-STABill2ER BRACKET _ WELDS il'[

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There are eight Reactor Vessel Stabilizer Brackets for each unit at Quad Cities Station. These are located on the fourth elevation of the drywell. The Unit 1 brackets are rectangular blocks which bevel to a point at the weld i

location. The physical configuration and dimensions of the Unit 1 brackets are described in Figure 1. The Unit 2 brackets are similar in construction with the exception of a vertical"U shaped" indentation:.t the weld side of the i

bracket. The outer edges of the indented area (the welded surface) are also beveled to a point. The physical j

configuration and dimensions of the Unit 2 brackets are described in Figure _2.

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The brackets are welded directly to the reactor vcssel at the beveled areas on each side of the bracket /

The weld material forms a welded surf ace along the top and bottom edges of the bracket (see Figures 3 and 4).

The bottom welded edge of the bracket is in close proximity to the top of the Biological Shield (see Figure 5), The brackets are connected to the Biological Shield by a stabilizer bar and associated connectors (see Figure 5). uThis :

t-bar passes horizontally through the center of "le bracket, and is approximately 4 inc! n in diameter.

j The reactor vesselitself is covered with an interlocked system of 0.05 inch thick stainless steel mirror i

insulation panels. The panels are attached to each other with stainless steel screws on each edge. The l

dimension of the insulation panels range from approximately one by three feet to three by three feet. Each

- insulation panel provides support for the directly adja ont panels (le; panels directly above and on each side).

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. Movement and/or removal of a single panel has the potential or directly affecting the position and configuration of l

the three adjacent panels.

In the area of the reactor vessel which is surrounded t y the Biological Shiekt, the insulation fits between j

the shield and the reactor vessel. When necessary (ie: to surport inservice inspection activities) the insutstion j

panels are removed, replaced, and/or adjusted by physicall( reaching through. variou's hinged openings in the Biological Shield. These activities are extremely time consarnng in that there is minimal physical space between i

- the vessel and shield wall to manipulate the insulation panels (approximately 12 inches).

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Tha insulation which covers the reactor vessel at the stabilizer brackets Consists of two vertically adjacent '

L panels. These panels surround the stabilizer brackets and cover the welded surfaces; The two panels are joined to each other at a verticallecation which is approximately one third of the way up frcm the bottom of each bracket.

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The two nsulation panels fit together with matching horizontal edges, and an overlapping band for the screws..

(see Figne 6). The screws connecting the two panels are at the same vertical position as the stabilizer bar, with approximately three inches of clearance between the bar and the insulation. The bottom panel extends down the.

vessel, behind the Biological Shield, and I" connected to lower insulation panelsf These lower insulation panels i'

re at the same level as the Core Spray and Feedwater nozzle penetrations.

In order to perform the required surface examir'ation of the stabilizer bracket welds (100% of the weld i

surface), both of the adjacent upper and lower insulation panels must be removed; Removal of the upper panel.

. would allow access to the top surface weld, and approximately 67% of the left and right side surface weld.

Removal of the lower panel would allow access to the remaining 23% of the side surface welds.' A surface-

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'xamination of the bottem surface weld is impractical due to the proximity of the bottom we d to the top surface of -

' Riological Shield (approximately one inch).

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- Basis for impracticality of Removing the insulation Panels-

_ _ - In order fo physically remove the upper and lower insulation panels at each of' the eigtit stabilizer brackets,.

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the lower insulation panel must be removed (and eventually replaced) through the openings in the Biological ^

l Shield at the Core Spray and Feedwater nozzles.- This would require removal (and eventual reinstallation) of additionalinsulation panels at the level of. the nozzles.

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Removal of the upper and lower insulation panels requires removal of the stainless steel screws which connect the two panels. The clearance between the insulation and the stabilizer bar (approximately three inches) does not allow for non-destructive removal of these screws (ie: the screws must be removed by breaking off the-head of the screw with a hammer and a chisel). Commonwealth Edison has penormed a test to evaluate the impact of this type of manipulation on the integrity of the stainless steelinsulation. The results of the test indicate that the destructive removal of the screws will result in permanent defom1ation of the screw holes of the lower insulation panel. This deformation would require replacement oi the lower insulation panel at each stabilizer bracket. Once the lower panelis replaced, the minimal clearance between the stabilizer bar and the insulation precludes the -

reatta'hment of the upper insulation panel to the lower insulation panel.

The imprPcticality for the removal of insulation panels is based upon the cumulative occupatienal radiation exposure which would be incurred:

• during removal, reinstallation, and alignment of the lower insulation panels at each of the eight stabilizer bracket locations:

during realignment of the lower panel subsequent to future manipulations of the insulation panels surrounding the Feedwater nozzles (to support ISI activities on the nozzles).

As stated above, removal of the screws would result in the need to completely replace the lowerinsulation panel, and would not allow for reattachment of the lower panel to the upper panel. The removal of the lower insulation panel for all eight stabilizer bracket locations would require approximately 32 person-hours of work in close proximity to the Core Spray and Feedwater nozzles. Reinstallation and alignment would take approximately 192 person-hours; Realignment of the lower stabilizer bracket panels woc!d also be necessary subsequent to the performance of ISI activities on the Feedwater nozzles. Since the lower panels would not be reattached 'o the upper panels (at the elevation of the stabilizer brackets) the lower panels would shift and move upon removal of panels adjacent to the nozzles CECO estimates that approximately 192 person hours would be required to realign insulation panels which have shifted an@or rnoved.

These time estimates are based upon previous CECc experience removing, reinstallationplacing, and aligning insulation panels v>ith simihr positional constraints (ie: removal / reinstallation placement in and around vessel penetrations). The working dose rates at the Core Spray and Feedwater nozzles (with the doors of the Biological Shield open) range f rom 200 mrem / hour to 900 mrenyhour. Therefore the initial cumulative exposure (utilizing an average dose rate of 500 mrem /hr) to remove, replace, and align the Iowar panels would be 112 person-rem. Subsequent 1st activities requ: ring realignment of the insulation would incur approximately 96 person-rem every other refuel outage.

Based upon these cumulative occupational radiation exposure estimates, CECO has determined that the removal of the insulation is impractical. The estimated values 10r cumulative exposure (on a per unit basis) represent 20% and 17% respectively of the annual exposure goaliTherefore, the performance of the required surf ace inspection of the top and side surface welds is impractical (the impracticality of performing a surf ace examination of the bottom surface weld c _ussed above) As described in Reference (c), CECO has -

determined that approximatety 100% of the v weld s"rf ace and 78% of Qe side weld surfaces are accessible to a visuul examinatior, gv7 -1).

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