ML20114B624

Requests Approval for Reuse of Channel Boxes in Cycle 16,per NRC SER of NRC Bulletin 90-002, Loss of Thermal Margin Caused by Channel Box Bow, Transmitted Via . Strategy for Channel Box Reuse in Cycle 16 Encl

ML20114B624
Person / Time
Site:	Monticello
Issue date:	08/25/1992
From:	Parker T NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
IEB-90-002, IEB-90-2, NUDOCS 9208310005
Download: ML20114B624 (5)

Text

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414 IOcset Mall

%nneapolis, Minnesota 55401 1927 Telephone (612) 3345500 August 25, 1992 NRC Bulletin 90-02 U S Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Reauest for %nrovel for the Reuse of Channel Boxes in Cycle 16

References:

1. Letter dated October 22,199') from William 0 Long, NRC to Thomas M Parker, titled: Safety Evaluation Report - Loss of Therrual Margin Caused by Channel Box Bow. 4 Ve request your approval for the reuse of channel boxes in Cycle 16.

Reference 1 requires your evaluation of reuse of channel boxes on a cycle-specific basis. This evaluation must be completed prior to startup of Cycle 16 per Reterence 1. Startup for Cycle 16 is planned for March 2, 1993. Our eva?iation is actaened.

P, lease contact us it you have questions concerning this submittal.

/

l]f1,Yshw '

Thomas M Pa ker Manager Nuclear Support Services

, c: Regional Administrator Region III, NRC Senior Resident Inspector, NRC

, NRR Project Manager, NRC J E Silberg i

/r' 9208310005 920025 PDR O

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i ATTACHMENT MONTICELLO NUCLEAR GENERATING PLANT Stratery for Channel Box Reuse in Cvp,Je 16 In Cycle 16, there will be 92 reused channels (Cycle 15 contained 200 reused channels). Cycle 16 will contain the following number of bundle types:

Number of Cycles Number Number of i Fuel Type of Operation of Bundles Reused Channels CE8X8EB 4th 92 92 CE8X8NB 3rd 128 0 -

CE8X8NB3 2nd 136 0 CE8X8NB3 1st 128 0 Total 484 92 The attached core map (Figure 1) shows_the-locations of the fuel bundles utilizing reused fuel channels in the anticipated core loading for Cycle 16 at Monticello. Of these 92 bundles, 66 bundles have channels with exposures significantly lower than a typical second bundle lifetime reused channel.

These lower exposures primarily result from intentional channel shufflin6 done at the last two refueling outages to lower channel exposures for higher power

'oundle s . The other 26 bundles have channels with exposures typical of a full second bundle lifetime reuse. These are the final remaining reused channels ,

in the Monticello core.

Bundles with reused channels are to be loaded on the low power core periphery.

A bounding approach, consisting of- conservative adjustments to the MAPLHGR and MCPR operating limits for bundle types in any 4-bundle cell containing one or more reused channels, will be employed in the process computer databank for '

Cycle 16. This is the same approach that was used for the low-power-peripheral bundle locations with reused channels in the current operating cycle (Cycle 15).

I Channel Bow Calculations l Figure 1 shows all 4-bundle cells which will contain one or more reused channels. General Electric will assume a channel bow of -350 mils for all-bundles with reused channels. The -350 mils value is a reasonabla nominal

- bounding value to use for these locations and is the same va'_ue assumed for -

peripheral cells in the Cycle 15 analysis. Figure 2 shows estimated channel exposures at the end of Cycle 16 for these locations. Full second-bundle

! lifetime channels have exposures of 60-71 GWD/MT. Cell-average channel exposures for any 4-bundle cell are less than they were for peripheral cells for the Cycle 15 core loading.

• The total of 160 bundles residing in the 40 4-bundie cells (both shaded areas

_ _ ._ . _., _ . - _ ,. .. , _ ....,- _ ..~._.._.__.....m._.~.-.__.___..___ _,_.m___._._

Attachment August 25, 1992 Page 2 on Figure 1) with one or more reused channels witl have their MAPLHCR anu MCPR operating limits conservatively adjusted, a) Fourth and third cycle fuel in any 4-bundle cell with a water face on the core periphery (the lighter shaded cells on Figure 1) will use a cell-average channel bow of 350 mils and will have their OLCPR (Operating Limit CPR) value increased by 20% (i.e.,

unitiplied by 1.2). These same bundles will have their MAPLHGR limits reduced by 17.6% (i.e.,-divided by 1.176).

b) Bundles in the eight remaining cells will be treated slightly differently.

The fourth-cycle bundles will use a 350 mils bow and the same OLCPR and MAPLHGR limit adjustment as in "a" above.

Second-cycle and fresh fuel bandles will use-a cell average bow of 129 mils and will have their OLCPR value increased by 20% and 23%

respectively. The 129-mil cell average bou results from assuming 350-mil bow for 1 reused channel and the 5' mil bow for tho other 3 first bundle lifetime channels in each ot those 8 cells. If a very conservative 350-mil cell average bow were to be used for these 8 cells, bundles in these 8 cells would become unnecessartly limiting. MAPLHGR limits in these 8 cells will be reduced by 17.6%. Reducing the MAPLHCR limits will also assure adequate margin for LHGR limit for all bundles.

In summary, an increast- in OLCPR by 20% will bound channel bow effects in all ce.Is containing reused channels, except fresh fuel in the 8 non-water face cei ' where OLCPR will be increased by 23%. A reduction in MAPLHCR limits by 17.6% will bound channel bow effects in all cells containing reused channels.

These adjustments in OLCPR and MAPUlGR limits are the result of evaluations performed specifically for Cycle 16 by GE Nuclear Energy and are calculated relative to channels with zero bow. These penaltics on the peripheral bundles will not force these bundles to become most limiting since preliminary control rod pattern analysis shows approximately 45% margin for MCPR and 30-40% margin for MAPLHGR for these edge locations.

A review of the impact of channel bow in Cycle 16 upon MCPR safety limit concludes that the same conclusions reached.for Cycle 15 are again appropriate for Cycle 16. The process of assuming conservativo channel bows and h

calculating t ermal margin impact introduces no additional uncertainty that would impact the safety limit MCPR. The use of conservative channel bow assumptions introduces an overall conservative bias in thermal sargin

, evaluations.

Future Cycles In '.uture cycles, we do not plan to reuse fuel channels.

Figure 1 Reuse Channel Box Locations for Cycle 16

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^ontrol Ceils 350-mil cell average tcw will be used in these locations -

129-mil cell average bow will be used in these locations Numbers "1" "2" "3" and "4" identify bundle locations containing fuel bundles in their first, second, third and fourth cycles of operations, respectively, Reuse channels are all on "4" type bundles.

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