ML19282A927

Rept of Reconstitutable-B4C Type Control Element Assembly Design for Use in Bg&E Reactor, Nonproprietary

ML19282A927
Person / Time
Site:	Calvert Cliffs
Issue date:	02/01/1979
From:	Anthony A, Keefer C ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY
To:
Shared Package
ML19282A925	List: ML19282A924 ML19282A927
References
CEN-105(B)-NP, NUDOCS 7903080338
Download: ML19282A927 (10)

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- COMBUSTI0f1 EflGINEERIf4G, IfiC.

SUPPLEf4EffT 1-ffP to B-PH 627 . _.

Calvert Cliffs Unit 1 Cycle 4 Refueling License Amendment C-E POWER SYSTEf1S Windsor, Connecticut g

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t C-E POWER SYSTEMS COMBUSTION ENGINEERING, INC.

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REPORT OF A RECONSTITUTABLE - 84C TYPE CEA DESIGN FOR USE IN THE BG&E REACTOR Prepared by: %I) b t. Date: //2.e /7S C/B. Keefer

Approved by: 0t 8 / TL.a Date: //26/77' A[J! Anthpy Report No.: CEN-105(B)-NP Issued: J-i s

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LEGAL NOTICE b

This report was prepared as an account of work sponsored by Combustion Engineering, Inc. ' Neither Combustion nor any person acting on its behalf: .

a. Makes any warranty or representation, express or implied including the warrantins of fitness for a particular pur-pose or merchantability 3 with respect to the accuracy.,

completeness, or usefulness of the information contained in this report, or that the use of any informatica, ap-paratus, method, or process disclosed in this report may not infringe privately owned rights; or

b. Assumes any liabilities with respect to the use of, or for damages resulting from the use of, any information, apparatus, method or process disclosed in this report.

CRITERIA FOR PROPRIETARY INFORMATION Information contained in this report which is delineated by means of surrounding brackets is proprietary to Combustion Engineering, Inc. , for the following reasons:

The use of the information by a competitor would substan-tially decrease his expenditures, in time and resources, in designing, producing or marketing a similar product.

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1.0 INTRODUCTION

This report presents the mechanical design of a new stainless steel clad - B C4 type control element assembly for use in the Baltimore Gas and Electric - Calvert Cliffs Unit One reactor.

The new CEA design in"olves a change in cladding material and specially designed reconstitutable poison rods which serve as a lead

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for all future poison rod designs. The purpose of the poison -

rod design is to demonstrate that the silver-indium-cadmium con-

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> tained in the tips of the poison rods in all future CEA's can be replaced with B 4C. Both the change in cladding material and the replacement of Ag-In-Cd with B4 C are being made for reasons of economics and to improve material availability. Included in this report are justifications for the derign changes.

2.0 S"!?/J'Y .

C-E has reviewed the present CEA design and has faund that certain material changes can be made without changing design criteria or compromising design margin in any way. The changes include using cold worked type 316 stainless steel cladding instead of Inconel 625 material ( ,

. ]The new control rod design is such that the outer diameter of the lower end of the cladding will not change over the life of the rod. The four outer poison rods enter the buffer region of the CEA guide tubes where the diametral clearance is raduced from 0.087 inches to 0.020 inches. Therefore,

.. in these positions it is important to maintain the same clad outer diameter over the life of the CEA.

eY The strength, ductility, corrosion resistance, compatibility with other materials, and weldability of cold worked 316 stainless steel is comparable to Inconel 625. Also, considering both the change in cladding material and revised poison rod design, there is no significant change in rod worth.

3.0 DISCUSSION C-E is considering revising the design of CEA's for all future reactors and for replacement rods for earlier plants when needed.

The present CEA designs are adequate, but the cost of katerial used in their manufacture has risen drastically and later problems with material availability seem likely. With this in mind, C-E has performed a detailed study and has found that certain material changes can be made in the CEA design without affecting the integrity of the design. The guide lines that have been followed in revising the original design include:

1. The design criteria shall .not be changed.

2. The present design margin shall not be changed.

The revised CEA is shown on drawings number E-1168-162-001, Rev. 01 and E-1168-162-002, Rev. 01. The poison rods have been modified in three ways. First, the new design ultilizes cold worked (23 + 5%)

_ type 316 stainless steel with a wall thickness 1 mil greater than the original design. The wall thickness was increased so that the collapse strength of the cladding would be at least as high as it was for the Inconel 625 cladding. The 0.D. was increased by 1 mil I and the I.D. decreased by 1 mil to provide the increased cladding

- thickness with the least effect on the overall design. The stain-less steel cladding is used on three of the five rods. Two of the rods use the present Inconel 625 cladding which will previde a direct comparison.

B There is ample evidence that stainless steel cladding is satis-factory for in-reacter F* 5tainless steel clad control elements have been used in. most not all non C-E reactors for many years.

The in-reactor data used by C-E to justify the adequacy of cold-worked 316 stain 1<'s .ee l cladding were taken from HEDL reports.1,2

. The cata show 316 stainless steel to have equal or better end-of-life tensile preperties than that of Inconel 625. The unirradiated yield strength of 316 stainless steel meets the specified mini 5um require-

• ments for Inconel 625 and the-collapse strength against external pressure is equal to that of Inconel 625. There is also ample evidence that the corrosion resistance of 316 stainless steel and its compatibility with B4 C ~and zircaloy-4 in a reactor environcent are equal to that of Inconel 625. The excellent weldability of cold worked 316 stain-less steel is well known and has been verified by fabricators of control rods used in the FFTF reactor. Nevertheless, the quality of'end cap welds has been carefully verified by a detailed qualifica-tion program prior to fabrication of the CEA poison rods. Tests were also performed on tube samples from the specific run of

' tubing that were used in fabricating the CEA poison rods to check tensile properties and to verify the collapse strength of the cladding against external pressurization. There is no increase in tritium release to the coolant when Inconel 625 is replaced with 316 stainless steel.

A second change is in the connection of the four outer rods to the CEA spider. The present connection consists of threading the poison rods into blind holes in the spider leg. The connection is prevented from loosening by a dowel pin which is plug welded in place. In the new design, a thru hole is machined in the spider leg. [ .

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] New or previously used rods can be remotely reinstalled on the CEA spider during normal shut dov;n periods, so that the CEA can be used continuously. Rods removed after one or more cycles, can be examined at pool side or in a hot cell.

The third design change involves' the lower tip section of the .

rods. Figure 2 shows the comparison between the present and reviseddesign,f(( .

This blanked out section described in detail the design changes made to the lower tip section of the CEA poison rcds. The description is -considered proprietary information.

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3 The combined end-of-life stress on the cladding resulting from hydraulic forces, maximum helium release and pellet growth [

]is less than 2/3 the unirradiated yield strength of the cladding at 650 F. The criterion for poison rod cooling that there be no bulk boiling within the guide tube is met, since the heat generation in the tips is equal to or less than that produced in the Ag-In-Cd tip. The criterion for CEA scram time

- that the CEA's travel 90 percent of the active core height in less than 2.5 seconds is also met because there is essentially no change in CEA weight and less than a one percent change in the annular clearance between the poison rods and guide tubes. The net change in CEA rod worth .considering both the cladding change and the change in the lower end of the center poison rod is less than 0.5%. -u :  ; . ..;

It is planned that the new features of the CEA be dimensionally characterized so that later monitoring of the design can be properly done. This CEA, therefore, will serve as a lead unit for later CEA's of similar design. Details of the revised design, including tolerances, specifications, and special requirements are listed on drawings E-1168-162-001, Rev. 01 and E-1168-162- -

002, Rev. 01.

I Post Irradiation Tensile Properties of Reference 20 Percent Cold Worked Type 316 Stainless Steel, HEDL-SA-1030, R. L. Fish, October 1975.

.' 2 " Semi-Annular Progress Report, Irradiation Effects on Reactor Structural Materials, August 1974 to February 1975," HEDL-TME 75-23, pp. HEDL -74 to -78.

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