ML19209B626

Submits Design Criteria for Removeable Adge Absorber Rod Re Tab Stress Analysis for Alternate Absorber Matl Control Blade Test Program

ML19209B626
Person / Time
Site:	Peach Bottom
Issue date:	10/01/1979
From:	Brugge R GENERAL ELECTRIC CO.
To:	Verrelli D Office of Nuclear Reactor Regulation
References
MFN-245-79, NUDOCS 7910100248
Download: ML19209B626 (5)

Text

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4 g1 C . f'UCLEAR POWER SYSTEMS DIVISION GENERAL ELECTRK CCMPANY,175 CURTNER AVE., SAN JOSE, CALIFORNIA 95125 P fa2, (408) 925-3360 MFN-245-79 October 1, 1979 ROB-056-79 9 , &-

U. S. Nuclear Regulatory Commission Division of Operating Reactors Office of Nuclear Reactor Regulation Washington, D.C. 20555 Attention: Mr. David M. Verrelli Operating Reactors Branch 3 Gentlemen:

SUBJECT:

TAB STRESS ANALYSIS FOR PEACH BOTTOM III ALTERNATE ABSORBER MATERIAL CONTROL BLADE TEST PROGRAM

Reference:

NEDO-24213, " Proposed Peach Bottom Atomic Power Station Unit 3 Alternate Absorber Control Blade Test Program,"

August 1979 The time required to obtain material performance data in the BWR environ-ment is extremely long. Since the control blade is not designed to be disassembled once it is fabricated, no interim data can be obtained without destructive examination of the control rod. To avoid destructive examination and still obtain some data as soon as possible, the structural design of the control blade has been modified to allow the removal of the edge absorber rod in each wing. The design of the removeable rod feature was required to meet the following crit.pria:

(a) The design shall maintain structural integrity for all normal and abnormal events anticipated over the design life of the test blade.

(b) The design shall not require major redesign of tte existing control blade structural components (minor modification of existing hardware is allowed prnvided form, fit and function are not impacted).

(c) The design shall be capable of allowing the removal of the absorber rod by remote means under 12 to 20 feet of water.

(d) The design shall have a high probability of allowing successful removal of the absorber rod and proside a mechanism for capturing a replacement rod.

(e) The design shall be easy to fabricate. j/Q 7010ea0 io &' 4

[

U. S. Nuclear Regulatory Commission Page 2 Within the constraints of the above design criteria, the design selected incorporates a tab which allows the removal of the edge absorber tube.

The modifications to the control blade required to backfit this design are minimal and do not impact the structural integrity of the existing control blade components. The tab, in its assembled position, maintains the edge absorber rod in position during all phases of operation. The tab allows easy removal of the edge absorber rod which is 10nger than the other absorber rods so that a sufficient length of rod is available to attach a tool for removal of the rod. Once the absorber rod has been removed, a new rod (slightly shorter in length) will be inserted in the edge rod position and the structure below the tab will be modified to hold the new rod ';n place.

The design provides that with the reactor at power, there are no loads on the tab, and that during manufacturing the tab is bent and then annealed. Thus, there is no applied or residual stress in the tab. The tab is loaded only during scram and occurs when there is a scram and the buffer in the control rod drive fails to slow the drive before reaching the mechanical limit. Under these conditions, and assuming the control rod structure does not dissipate any of the load, the stress on the tab is .67 (Appendix I) of the ASME,Section III, allowable (the control rod is not a code component, but code limits were used as a conservative approach). The fatigue limits were also calculated. Under the worst case loading the code allows about 700 failed buffer scrams. Forty-five (45) is a conservative estimate of the number of scrams in a three year period that would cover the life of the tab. Therefore, the tab is considered adequate to place in Peach Bottom 3 core for a single cycle of operation.

Very truly yours, R. O. Brugge, Manager Services Licensing Safety and Licensing Operation R08:gmm/519-520 cc: L. S. Gifford (GE-Bethesda) 1126 1/1

GENER AL @ ELECTRIC APPENDIX I TAB EVALUATION A. LIMITING CASE Assumptions:

1. The most limiting event is a failed buffer. A failed buffer scram is only a problem when the reactor is not pressurized. At pressures of 500 lbs/in2nd higher the failed buffer scram imparts less load than a normal cold scram.

NOTE: A failed buffer scram is extremely unlikely because: La) no GE operating reactor has ever had such an event; (b) the design of the Peach Bottom 3 control rod drive requires extensive breakage of the buffer seals to reach a postulated failed buffer condition.

2. The short duration of the tab life (one 18 month fuel cycle), the probability of the event occurring and the short time duration of the event, if it does occur, places this event in the same cate-gory as the SSE event. Therefore, the ASME Section III rules for the SSE event may be applied (i .e., stress allowable = 2.4 Sm)

3. Loading of the tab is directly proportional to the loading of the control blade. No credit is taken for friction, hydrodynamic effects, or energy absorption in the materials.

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GENER AL @ ELECTRIC APPENDIX I - continued ANALYSIS:

4 II

-W" ---

.044

~

t

-)

t load Load Load Moment = Load x .044"= M L L

MAX. STRESS IS AT POINT "B" B

//////

~

S B* I Y"Y t = .056 + .003 t = .053" min SI 3 ~

M =

B I=t" 12 w = .200 + .020-L t

~

2

• min = .180 2

2S BtW3 Stw B

"L 12t 6 S ' '

B Allswable

= 72.000 x .0532 x .18" = 6.06 in.lb.

6 M' Allowable M

Load Allowable =L A

.0 b " " 137.7 lb.

Failed Buffer Load = 10,000 lb. at coupling Hafnium Rod Wt. = V Hf O Hf =( r x .

x . 81 l bm/in

= 1.99 lb max or about 2 lb.

Control Rod Wt. = 218 lb. (218 used because 10,000 lbs. is based on 218. Not wt. of test C.R.)

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G EN E R A L ($ E LECTRIC APPENDIX I - continued ANALYSIS: (continued) 28 x 10,000 = 91.7 lb. = Max. Load Applied Load Acolied , 91.7 - *67 Load Allowed 137.7 Based on the assumptions listed on Sheet 1, the tab will withstand a failed buffer load.

B. Normal Conditions The terminal scram velocities under 1ormal conditions are:

Cold: 6 - 8 in/sec Hot - <6 in/sec The small amount of energy, about .16 in-lb, will be absorbed within the sheath and the tab will see no lead.

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