ML20006B904

Responds to NRC Bulletin 89-003, Potential Loss of Required Shutdown Margin During Refueling Operations. Refueling Boron Concentration Will Be Calculated W/Provisions for One Shuffle Alteration

ML20006B904
Person / Time
Site:	Prairie Island
Issue date:	01/29/1990
From:	Parker T NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
References
IEB-89-003, IEB-89-3, NUDOCS 9002060076
Download: ML20006B904 (8)

Text

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. ;, i p Northem States Power Company  ;

414 Nicollet Mall . .

Minneapohs, Minnesota $54011927 :

Telephone (612) 330 5500 January 29, 1990 .NRC Bulletin 89 i l

Director'of Nuclear. Reactor Regulation f U S Nuclear Regulatory Commission l Attn; Document Control Desk ll Washington, .DC -20555 PRAIRIE ISLAND' NUCLEAR CENERATING'PIANT  :!

Docket Nos. 50-282'- License Nos. DPR p 50 306 DPR 60 i t

Response to NRC. Bulletin 89-03' '

Potential Loss of Required Shutdown ,

Marcin Durine Refue!1jg Operations i Our response to Bulletin 89-03 is attached.

s Picase. contact us if you have any questions related to our' response.

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.i Thomas M Parker Manager ,

4 Nucicar Support Services 3 c: Regional Administrator - Region III, NRC Senior Resident Inspector, NRC .(

NRR Project Manager, NRC

!- G Charnoff-

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l Attachments: 1. Affidavit i

2. Response to Bulletin No. 89-03 i

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4 9002060076 900129 PDR ADOCK 05000282 a PDC

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UNITED STATES NUCLEAR REGULATORY COMMISSION NORTilERN STATES. POWER COMPANY. ,

-t PRAIRIE' ISLAND NUCLEAR GENERATING PLANT DOCKET NO. 50-282 -

50-306 -

POTENTIAL IDSS' 0F REQUIRED ' s SilUTDOWN MARGIN DURING REFUELING OPERATIONS Northern States Power Company, a Minnesota corporation, with' this let'ter is submitting information requested.by NRC Bu11etin;89-03.

This letter contains no restricted or other defense information.  :

NORTHERN STATES POWER COMPANY By

' Thomas M Parker f Manager,! Nuclear Support Services Onthis@ day of r e- /9fobefore me a notary public in'and for said County,personallya][p' eared Larson, Vice President Nuclear Generation, and being first duly sworn ' acknowledged that he is authorized . to execute this document on behalf of Northern States Power Company, that he knows the contents -

thereof, and that.to the best of his: knowledge, information, and belief the =

statements made in it are true and that it is not interposed for'delayc D

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' MARCIA K. LaCORE NOTARY PUN 10 -MINNESOTA HENNEHN COUNTY i My Commseen Empires Sept 24.1993 l wwwwwwwwwwwwwwwwwwvn -

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Attachment 2 Page 1 of 6 PRAIRIE ISLAND RESPONSE TO BUTTRTIN No. 89-03 Prairie Island has reviewed NRC bulletin 89-03, " Potential : loss :of Required.:

Shutdown Margin ~During' Refueling Operations"L and developed-an action plan to-address all :ofD the issues raised . by the bulletin. This: bulletin - concerned refueling procedures that allow fuel assemblies to be placed in intermediate _ core locations without prior explicit analysis: to ensure that thef required' shutdown margin is maintained. The bulletin' requested assurance that; adequate. shutdown margin is maintained through the following actions:

1. . Assure that any intermediate fuel' assembly configuration (including' control rods) intended to,be used during refueling is identified and-evaluated to maintain . sufficient refueling boron concentration to result in a minimum shutdown margin of approximately 5%.

2. Assure that fuel loading procedures only allow those intermediate fuel .

assembly configurations .that do not violate the allowable shutdown margin'and that'these procedures are strictly adhered to. ~

3. Assure that the staff responsible for refueling operations is trained in the procedures recommended iti Item 2 above and understand' the J

potential consequences of violating <these procedures. ;This training. i should . include the fundamental - aspects of - criticality control with l higher enriched assemblies.

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i BACKGROUND ON PRAIRIE ISLAND REFUELINGS During all Prairie Island refuelings, procedures require the operability of two! a source range detectors for monitoring core multiplication (typically, four are j available). During all fue1~ aeditions to the core , ._ procedures - require ' 1/M ~

plotting utilizin5 two source range monitors. In addition, one monitor; is

'l required to have audible indication to the refueling machine operator for on line i monitoring of core suberitical multiplication. 'During refueling activities, the Reactor Coolant System is borated to a concentration to assure the final core

design remains 5% shutdown with an additional 100 ppm for conservatism.  ;

Prairie Island normally performs a fuel shuffle to reload the core. This involves -

moving the fuel from the old location directly to' the new position.

Occasionally, a fuel assembly must be moved to a , device used to change out control rods. Then, the assembly is typically moved directly back to-its new position. Periodically, a complete core offload is used to perform ISI- and ,

miscellaneous testing on the reactor vessel. '

This results in reloading. the -

assemblies directly into their new location. Thus, intermediate locations are A

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Attachment 2 l Page 2 of 6-only used as contingency plans when difficulties are encountered during fuel '

movements typically.

1 Prairie Island has made several changes in the recent past that_have resulted in a significant reduction in the need for contingency actions. By reducing the '

number of fuel. assembly -inserts, the number and complexity of the moves are reduced thus minimizing the chance of encountering an abnormal ~ situation. This <

has been completed by > eliminating the use of.90 thimble : plugs , 2 sourcei ~

assemblies and all burnable poison inserts. Integral -Sadolinia rather. than burnable poison inserts.is used to control the initial reactivity. I

, J PROCEDURE CONTROLS ON REFUELING ,

There are two specific procedures that control the actin tics _ associated with refueling operations. Instruction SWI-NE-8 is a specific: instruction for the nuclear engineering staff that provides instructions for generating the fuel move t sequence. Procedure D-5_ establishes the requirements a prior to and during a refueling activities. This procedure is used by the plant operations group:to ensure that all requirements related to the movement of fue11 during refueling'  !

are adhered to. This includes Technical Specification requirements as well as pre-fuel movement surveillance, shift manning, equipment operability and all

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j other procedural requirements.  ;

The requirements of procedure -D 5 that are applicable to' fuel' movement control f are as follows:

"1. Movement of any fuel assembly or insert SHALL only be made with a Fuel Transfer Log, generated por SWI-NE-8,. and which has 'been signed _ by two Nuclear Eng , or by a. Nuclear Eng 'and a SR0" "2. Any changes or additions to the Fuel Transfer Logs require the approval ~I" of two Nuclear Eng., or a Nuclear Eng. andta SRO."-

"3. The Fuel Transfer Log shall be signed off as each step is' completed,

' where the Control Room copy has all steps to be ' signed off and the SFP and Containment copies have only the steps in the respective areas j signed off."  :

RESPONSE TO BULLETIN 89-03 Based on the information contained in NRC Bulletin 89- 03, Prairie _ Island _ j completed a review of all operations related to refueling that could effect the i core shutdown margin. This review involved the site Nuclear Engineers, the Plant chemistry Group, as well as the general office Nuclear Analysis Department, j Nuclear Analysis Department is the group responsible for the Prairie Island core  ;

designs as well as all reactor physics and transient safety analyses, with the ,

exception of LOCA analysis. This review resulted in the following three areas  ;

being addressed: t i

1. All procedures were reviewed to ensure that fuel movements are o 1

Attachnunt 2 Page 3 of 6 controlled'by adequate means.

2.: -NRC and Industry experiencewere reviewed to learn how other vendors j and licensees were addressing this issue.

3. A detailed' study was performed by. Nuclear Analysis Department? to determine the effect that intermediate core >1oading sequences have on refueling Shutdown Margin. The results.are discussed in Appendix A'.

From these studies, two key procedural changes are necessary at PrairieTIsland1 to ensure that adequate Shutdown Margin will be maintained. First the refueling boron concentration will be. increased to a concentration that will: ensure ~that.

any one fuel assembly can be safely positioned in an intermediate core location without challenging the required Shutdown Margin. Nuclear Analysis' Department will calculate this boron concentration onT a cycle' specific basis, ; unless a.

bounding gene-ic calculation is developed in 'the' future. ; Second, the procedures.

used to generate the. fuel-loading sequence was changed to read as follows:

" Core Shuffle and reloads.shall be, written so that fuelLis-not placed in

intermediate core locations except as designated below-(fuel shall be moved l directly to the core design location):

a. One assembly may be.in any intermediate core location to facilitate abnormal situations, l

b. Assemblies may. be,. located in -intermediate core 1'ocations ' 'if ' the l assembly to be placed in a- specific location has' less- reactivity than {

the reactivity of the assembly in that location in; the final core-

-i design."

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Provided the above controls are adhered to, adequate Shutdown Margin can be l assured. O

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SUMMARY

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! In summary, the Prairie Island responses to address the concerns of NRC Bulletin 'l l 89-03 are as follows: ;j

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1. Assure thac any intermediate fuel assembly configuration (including.  !

control rods) intended to be used during refueling'is identified =and' j

evaluated to maintain sufficient refueling boron concentration to result 1 in a minimum shutdown margin'of approximately 5 %. ;l i

1 RESPONSE: Calculations will be performed to determine what refueling ]

! boron concentration will be required to maintain-5% Shutdown Margin

! with any one fuel assembly in a limiting intermediate location.(This }

will include the routine 100 ppm added for conservatism). For any Li configuration that will require more than one fuel assembly to be in  ;

an intermediate location, the "misloaded" assembly will be required l to have less reactivity than the reactivity of the assembly in that  !

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Attachment 2

- Page 4 of 6 location in the final loading pattern. l i

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2. Assure that fuel loading procedures only allow those intermediate fu<

assembly configurations that do not violate ~ the allowable . shutdown - ,

margin and these procedures'are strictly adhered to. 1 RESPONSE: The refueling boron concentration will be calculated'with ,

provisions for one shuffle alteration. This is. presently; beingl ,

addressed in the Unit 1 core reload 10CFR 50.59 safety evaluation and-'

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will be incorporated into the L routine Nuclear Analysis. Department ~

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procedures before the next scheduled refueling outage. Procedure DJ5' l requires verification of the required refueling boron concentration ~

before moving fuel and. also requires adherence __ to the - Fuel' Transfer-Logs. This procedure ' required no. changes. Instruction SWI-NE 8 ' '

provides instructions for generating the fuel movement sequence. This. '

procedure has been changed to ' provide additional instructions that -

assure no more than one shuffle alternation is used unless the assembly has a reactivity that is.less than.the reactivity of the assembly in

.j that location in the final core design. Thus procedures'will'be-adequate to assure required shutdown margin is maintained.

3. 1 Assure that the staff responsible for refueling operations is trained in the procedures recommended in' Item 2 above - and understand the potential consequences of violating these procedures. The-training  :

should include the' fundamental . aspects of critic'ality control' .with '

t higher enriched fuel' assemblies. >

. . t RESPONSE: The. Operations department' is responsibleLfor-implementing,  ;

procedure D-5 (Refueling Operations). An SRO from this department'is '

responsible for all core geometry changes. During' license' training cycle 90 01, a member of the site reactor engineering' staff performed' training on the importance of adhering to the Fuel Transfer-Logs and' 3 l discussed the basis as it existed in previously' issued NRC Information Notice 89-51. This training'is complete. The site. Nuclear Engineering staff is responsible for implementing instruction SWI-NE 8 (Generation of Fuel Transfer Logs) . The entire Nuclear Engineering staff . was actively involved in addressing this bulletin. The final bulletin draft and the changes to instruction SWI-NE 8 were discussed with each member of the Nuclear Engineering staff. This training isfcomplete.

The Nuc1 car Analysis Department procedures used to calculate the-required refueling boron concentration will be revised to include provisions for one shuffle alteration before the next scheduled: Unit p 2 refueling outage.

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Attach ent 2 Pye $ of 6 1

-6PPENDIX'A THE EFFECT OF INTERMEDIATE CORE IhCATIONS10N SHUTDOWN MARGIN -

I The Nuclear Analysis Department determined the required boron concentration for a serieslof core shuffle alternations. For Unit l' Cycle 14,zthis resulted ina the-following required boron concentrations:

5% Shutdown Mars i n Required Boron Concentration

1. of Alterations IReaufred Boron for the'Limitine'AlterationsF -;

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0  : 2114 ppm i 1 2212 ' ppm - ,

2 2355 ppm- i 2490 ppm 3

4 2623 ppm maximum 3127 ppm =

The following assumptions were used in'the analysis:

1. All control rods were fully. withdrawn. ,

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2. No water holes existed in the core, i

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.3. The most reactivo. assemblies were moved.

The removal of all control rods is a very significant conservatism, i.e. , ;600 -

ppm. Control rods are only moved within fuel-assemblics. There'are two fixtures ,

to change control rods from one fuel assembly-to another. The1 normal maximum,

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number of control rods (and accompaning fuel assemblies) removed from the core  ;

is four. All control rods are removed during a full core'off load, but,this is not of concern since they are removed with fuel as the core is ' unloaded and reloaded.

During a refueling shuffle, the number of water holes is minimized. 'However, other than the initial configuration . or the final configuration 1there would -

seldom be a configuration. with no water holes. A water hole adds negative reactivity (assuming all control rods are withdrawn from tho' core) . -Therefore,

using .no water holes in the analysis is conservative.

The base core used to analyze the shuffle alterations was 'the final c. ore pattern.

The core pattern for the next cycle is more' reactive than the core pattern at beginning of the refueling. The final core pattern may not be the most reactive possible configuration (this is shown in extreme by the " Maximum" case in the  ;

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. 1 Attachment 2 Page 6 Of 6 above table). Therefore, shuffle alterations may cause configurations that are more reactive than the final configuration.

The fuel shuffle is developed with no intermediate fuel locations. Therefore, a given core fuel assembly location will only have one of two possible fuel:

assemblies, the fuel assembly in that location et the' end of the previous ' cycle )

or the fuel assembly that will be there at the start up of the-next cycle. The- i most reactive configuration during the shuffle must be evaluated. -If -: this  ;

configuration is not used in the shuffle alteration analysis, a conservative a adder must be considered. - For the Unit 1 Cycle 14, the final core configuration. "

was the most reactive configuration. t A calculation conservatism of 100 ppm 'is added . to the ' calculated boron concentration. This is included in the concentrations in the above table.- ,

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