ML19340A530

Process Development Fabrication of B4C Powder Control Rods for Alternate Plant Design

ML19340A530
Person / Time
Site:	Dresden
Issue date:	08/06/1958
From:	Weyers J GENERAL ELECTRIC CO.
To:
References
GEAP-3042, NUDOCS 8008130158
Download: ML19340A530 (14)

Text

v ENGYNEERfrG REPORT GEAP-3042 S

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PROCESS DEVELOPMENT FABRICATION OF B4C POWD C3iTROLJODS N.

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ALTERNATE DRESDEN DESIGN August 6, 1958

.1 J. W. Weyers FUELS AND MATERIALS DEVELOPMENT SUB-SECTION ENGINEERING SECTION 1

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RETURN TO RE0,LATW GENIMt. HES

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4 / / Q) (\\ N GENERAL ELECTRIC ATOMIC POWER EQUIPMENT DEPARTMENT SAN JOSE, CALIFORNIA 9

900 1130157

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4 ENGINEERING REPORT i

GEAP-3042 4

1 PROCESS DEVELOPMENT FABRICATION OF BeC POWDER COtERCL RODS FOR f

ALTERNATE DRESDEN DESIGN I

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Fuels and Materials Development Operation August 6, 1958 bb i

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DISTRIBlTTION :

H. A. Brammer H. M. Connelly J. R. Dickson V. A. Elliott A. N. Holden R. A. Huggins K. W. Kepner Library

-S V. D. Nixon E. W. O'Rorke R. B. Richards W. R. Smith F. E. Tippets A. C. Van Dyk D. A. Venier J. W. Wevers - 5 J. R. Wolcott i

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TABLE QF CONTENTS I.

Summary II.

Design Basis III. Preliminary Fabrication and Blackness Tests IV.

VBWR Control Rods A.

Design B.

Fabrication C.

Costs and Schedules V.

Dresden A. ternate Design VI.

Fabrication A.

Fabrication Experience en Original Design B.

Redesign Fabrication Experience C.

Inspection Results D.

Costs VII.

Irradiation Test Results VIII. Enclosures Figure I

- Critical Assembly Control Rod Blackness Test Piece #1 Figure II

- Critical Assembly Control Rod Blackness Test Piece #2 Dwg. #612D321-VBWR B4C Powder Control Rod Figure III

- Dwg. #141F569a Original Dresden Prototype Design Figure IV

- Final Dresden Prototype Design Table I

- Inspection Results Dwg. #141F569-Alternate Dresden Control Rods

4 i

i I.

Summary An alternate control 7 od design and prototype fabrication ef fort was requested as a backup for the Dresden Boron Stainless reference design.

This backup was considered necessary since the material suppliers were having dif ficulty fabricating boron stainless plate, and the irradia-tion stability of control rods fabricated from boron stainless left something to be desired.

B4C control rods were fabricated in two configurations; one type (flat blades) for VBWR, and the second type (cruciform) for the Dresden pro-totype.

4 The program consisted of design, preliminary fabrication of blackness test samples, fabrication of full size components, and inspection and/or testing.

II. Desion Basis The design criteria was established as follows :

A.

Must have a minimum control rod life of five years.

B.

Must have structural stability during repeated scram at 1000 psi, 6000F boiling water.

4 C.

Must be fabricable within Dresden core tolerance requirements, and must be dimensionally stable.

D.

Must cost less than Boron Stainless rod.

E.

Must suf fer no irradiation damage.

F.

Must be blacker than 2% Beron Stainless.

III. Preliminary Fabrication and Blackness Tests The analysis of the design parameters indicated that boron carbide powder encapsuled in stainless steel tubes with a structural cover.

holding the tubes into orientation might be the best approach. A blackness test sample was fabricated as shown in Figure I (Critical Assembly Control Rod Blackness Test #1).

Fabrication studies consisted of determining the correct mesh size powder to use to obtain the maximum fill density. Both -325 mesh and 14F mesh were tried with the coarser 14F mixture giving the higher fill density as shown below:

Powder Size Wt. Der 11-3/4" tube Wt/cc

% T. Density 14F mesh 10.1 grams 1.64 grams 66

-325 mesh 8.0 grams 1.30 grams 53 Tubes were filled with powder vibrated with a small electric vibrator markino tc t, and tube ends were plugged with corks. Periodic checks indicated that no settling or stratification occurred once the tube was filled in this manner, when the 14F mesh powder was used. The finer

-325 mesh powder did not flow freely and sometines " hung up" in the fill

funnel, i

-,.---n Blackness testing was done in the VAL critical assembly facility. The slab (Figure 1) was compared with the same size slab cf cadmium, 2%

Bcron stainless, and the slab shown in Figure II.

The slab shown in Figure II was f abricated and tested to determine the ef fect of closing the " window" between the poison areas with 24 baron stainless strips.

Blackness test results were as follows :

Gecmetry and Material Relative Blackness A.

Cadmium slab 1

B.

24 Boron Stainless slab 1.13 C.

54C per Figure 1 1.11 D.

B4C per Figure I corrected for 1/4" undersize in length and 1/4" undersize in width 1.17 E.

BaC per Figure IT 1.17351 IV.

VB..

Cont rol Reds Repl, ement control rods were needed for VBWR because the boron carbide pressed blocks used for startup showed evidence of excessive breakdown under water flow and irradiation, A program was established to design and fabricate the replacement rods using the B C powder-tube configura-4 tion.

A.

Desian - The detail design is shown on the attached Drawing No. 612D321 - VBNR B C Powder Control Rod. The design had to 4

be detailed such that the rod would have the same outside struc-tural shape as the original control rods, attach to existing control rod drives, have approximately 42" of poison height, and not weigh in excess of 100 lbs.

The blackness tests (see paragraph III abcve) indicated that BaC powder in stainless tubes had suf ficient poison, and the concept was incorporated in the detail design.

Pressure Calculation - Using 1800 psi yield strength af 6000F for 304 S.S. welded and drawn tubing,.020 wall thickness,

.250 0.D., ar internal. pressure of 3000 psi can be contained.

Internal gas buildup due to fission of boron was calculated at 803 psi, maximum for a 5-year life.

A heliarc (T.I.G.) plug weld was used to seal the tube ends, and a test pressure (at room temperature) of 3000 psi was used as a weld proof test on each tube.

Coolant - Steam or water drain holes in the outside skin were added to maintain safe operating temperatures of the tubes, and to serve as pressure equalizers on both sides of the skin.

i B.

Fabrication - Standard sheet metal fabrication techniques were used on the structural components. Loading tubes with powder was performed as in paragraph III Luve, using a funnel and vibrator to obtain the fill density of 1.6 gm per cc minimum.

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Welds on tube ends were tested at 3000 psi hydrostatic, and were mass spectrometer _ leak tested. Only seven leaks were found, and these were, where the B4C powder was too close to the end plug. thus contaminating the molten weld pool.

C.

Costs and Schedules - Six rods were designed and built on D.O.S. 120-064 in the two-week period between March 7 and March 21, 1958, at a cost of $5,700.

f V.

Dresden Alternate Desion Using the design parameters as outlined in paragraph II, above, and the design and fabrication experience gained from producing the blackness e

test samples and VBWR prototypes, the design evolved as depicted on the enclosed Drawing No.141 F569 - Alternate Dresden Control Rods.

Alternate 3 was chosen for fabrication since no special bending or weld-ing fixtures would be required. It should be noted that alternate #1 could also be easily fabricated should physics analysis show that a poison center or core is required.

VI.

Fabric ation As stated in paragraph V, above, no special bending er welding fixtures were required, and standard sheet metal fabrication techniques were used. Because of the tube length, (9 ft long), a special mass spec-tremeter test fixture had to be built.

A.

Fabrication Experience on Oricinal Desian - Alternate 3 was selected on Drawing No.141F569 to be built on D.O.S. 120-067.

I Detail cross segt(on is shown in Figure III. Excessive warpage and distortioE[during fusion welding the sheath to the center bar. The assembly was redesigned as shown in Figure IV.

Fabrication E perience on Redesian - The center bar was B.

1 lengthened, on each web, so that a resistance weld joint could be used to eliminate the distortion during fusion welding as described in paragraph VI-A above.

C.

Inspection Results

. Inspection results are shown in Table I, attached.

D.

Costs - The cost limitation on the D.O.S. was $3,500 of which approximately $2,500 was used.

VII.

Irradiation Test Results Four VBWR rods were inserted at VAL on May 1,1958, and have been used as shut-down control, only. During operation, these rods are above the core in the steam zone. Several 12-inch tubes filled with B4C powder are now awaiting'a license permit before being inserted into the core for. irradiation testing to accurately measure internal gas buildup.

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