Monsanto

MILLIWATT GENERATOR HEAT SOURCE

PROGRESS REPORT

January 1 6 , 1978 - A p r i l 1 5 , 1978

Wayse R. ~ m o s P r o g r a m Manager

MiOUND FACILITY I

Miamisburg, Ohio

operated by

a subsidiary of Monsanto Company MO4lSANTO RESEARCH CORPORATION

for the 8U. S. DEPARTMENT OF ENERGY Contract No. EY-7642-04-0053

MASTER I

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I.

11.

MILLIWATT GENERATOR HEAT SOURCE

PROGRESS REPORT

Introduction

Activities at MRC associated with the Milliwatt Generator Heat Source efforts over the period January 16, 1978, to A p r i l 1 5 , 1978, are presented below.

*Pu02/Titanium Compatibility Studies (P. E. Teaney, A. R. Kiefer and D. L. Roesh)

Continuing are the compatibility studies of various materials as previously described (Section IV, MWG Progress Report, April 16 - July 15, 1977). were the metallographic and microprobe analyses of the Pu02/ titaniyn compatibility specimens. The specimens were tested at 800 C and 1000 C as shown in the test matrix (Table I). Compatibility specimens were tegted for time periods ranging from 32 daysoto 720 days at 800 C, and from 30 days to 180 days at 1000 C.

Completed during the report period

Temp. (OC)

Table I

Ti/Pu02 Compatibility Test Matrix

Time (Days)

800 32 61 90* 180 361 720 1000 30 60 go* 180

* duplicate specimens and a blank were tested for 90 days at each temperature

The configuration of the compatibility specimen is shown in Figure I. The specimen consisted of three (3) capsules. The inner (titanium) capsule was gas tungsten arc welded after being loaded with fuel. sequently electron beam welded in a tantalum capsule followed by enclosure in an outer cont-ainer of Hastelloy-X. The outer container provided oxidation resistance for the high tempera- ture heat treatment in air. ,

The fueled titanium spechen was sub-

The purpose of the tantalum DECLAIMER

Thii report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi- bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom- mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any ag%cy thereof. -

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Titanium

Configuration of Ti tani um/Plutonium Dioxide Compatibility Specimens

E B We1 d

E B Weld

GTA Weld I

Hastelloy-X

Tantalum

L 2 3 8 ~ ~ 0 ~

FIGURE 1

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capsule was t o pro tec t the t i tanium l i n e r from possible ni t rogen d i f fus ion through the Hastelloy-X during the long term-high temperature exposure. a b a r r i e r t o prevent an eu tec t i c reac t ion between the t i tanium and the Hastelloy-X.

The tantalum a l so served as

Pr ior t o assembly, the tantalum and t i tanium capsules were chemically cleaned i n a lOml HF, l O m l HN03, 3Oml l a c t i c acid so lu t ion t o assure t h a t no pro tec t ive oxide b a r r i e r exis ted on the surface of the specimens.

The impurity content of the f u e l used f o r the tests i s shown i n Table 11. The f u e l contained less than 1 . 9 weight percent t o t a l impuri t ies .

All of the specimens t e s t ed a t 1000°C were bulged, especial ly i n the area of the specimen t h a t was not i n contact with the fue l . A blank (non-fueled) specimen t h a t w a s t e s t ed f o r 90 days w a s bulged i n a l l areas of the specimen. r e su l t ed from i n t e r n a l pressure due t o the high temperature aging. The area of the fueled capsules t h a t w a s i n contact with the f u e l w a s not as d i s t o r t e d , but w a s embri t t led with respect t o the upper port ion of the capsule and contained numerous stress cracks. One of the most severe conditions i s shown i n Figure 2. apparently w a s embri t t led by s o l i d state d i f fus ion of oxygen from the f u e l ea r ly i n the tes t . Therefore, during the tes t the upper (more duc t i l e ) port ion of the capsule deformed while the lower port ion developed stress cracks.

The bulging

The bottom port ion of the capsule

The guel- l iner i n t e r f ace of a specimen a f t e r 30 days a t 1000 C i s shown i n Figure 3 . Reaction along the ins ide edge of the specimen i s indicated by the presence of porosi ty and a two-phase microstructure which ranged i n depth from 50 t o 85 pm from the fuel /metal in te r face . The react ion zone has a Widmanstatten s t ruc tu re consis t ing of plutonium and ti- tanium. Electron microprobe analysis indicated t h a t the l i g h t e r phase w a s predominately t i tanium (approximately 95 weight percent) while the darker phase consis ted of approxi- ma te ly 33 weight percent plutonium i n t i tanium. One of the

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Table I1

Fuel Impurit ies (Percent as Metal)

Ni - 0.05

Fe - 0.36

Sn - t race

A1 - 0.11 Ca - 0.07

B - 0.04

Mn - 0.06

Pb - 0.23

S i - t race

C r - 0.41

MO - ~ 0 . 1 4

CU - ~ 0 . 0 4

CO - 0.28

Mg - 0.07

Zn - 0.04

N a - t r ace

Total ~1.90%

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Liner Sidewall

Titanium Compati- bi 1 i ty Capsul e after 181 days at I O O O ~ C

Y PuO,/Ti interface

Y Bottom o f titanium capsule

w Tantal urn barrier

Figure 2 25X (as polished)

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.

PuO,/Ti Reaction after 30 days at 1000°C

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- .

250X (as polished)

Figure 3

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sites of e lec t ron microprobe analysis i s shown i n Figure 4A i n addi t ion t o photomicrographs from the cathode ray tube display of the e lec t ron microprobe. A densi ty d i s t r i b u t i o n of the a rea scanned w a s obtained using backscattered elec- trons from the sample (Figure 4B) while the concentrations of plutonium i n the area are shown i n Figure 4 C (obtained using plutonium ma x-radiat ion) . tonium (4C) corresponded t o the higher densi ty areas i n 4 B and t o the darker phase areas i n 4A. Most of the pores i n the specimen did not contain a react ion product. However, when a reac t ion w a s p resent , i t w a s enriched i n plutonium and depleted i n t i tanium with respect t o the matr ix . addi t ion t o the observed r eac t ion , plutonium diffusion was detected t o a depth of 325 pm from the fuel-metal i n t e r f ace .

The concentrations of plu-

I n

0 Reactions i n the remaining 1000 C specimens w e r e s i m i l a r t o those i n the 30 day specimen. and reac t ion increased with addi t iona l time a t 1000°C. Plu- tonium penetrated the gra in boundaries of the specimens more severely i n some areas of the specimens than i n o thers . Plu- tonium penetrated e n t i r e l y through the l i n e r (80 mils) a t one s i t e i n a 90 day specimen and a t four locat ions i n the 181 day specimen. with highly s t ressed locat ions i n the l i n e r . Disregarding these local ized penetrat ions of plutonium, an attempt w a s made t o measure the general dgpth of plutonium di f fus ion i n the specimens t e s t e d a t 1000 C. The r e s u l t s are summarized i n Table 111.

However, t he amount of porosi ty

The areas of severe reac t ion appeared t o coincide

Table 111

Plutonium Diffusion i n Titanium (lOOO°C)

- Time (hr) Depth of Bulk Diffusion

of 2 3 e P ~ i n um (AX) AX2 o r pm2

30 60 90 90 181

325 pm 550 575 710 755

105625 302500 330625 504100 570025

#

250X ( a s p o l i s h e d )

A ) Specimen a f t e r 30 Days a t 1 O O O O C (showing s i t e o f e l e c t r o n microprobe a n a l y s i s )

B ) Dens i ty D i s t r i b u t i o n o f t h e Area f rom F i g u r e 4A

F i g u r e 4

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C ) P l u t o n i u m D i s t r i b u t i o n o f t h e Area f rom F igure 4A

These data were f i t t e d t o the parabol ic r a t e equation AX2 = k t + b where AX i s the reac t ion depth i n microns, t i s the time i n hours and k and b are constants . r e su l t i ng ra te curve (AX2 = 118t + l . l x 1 0 5 ) i s shown in 'F igure 5 . The curve i s meant t o simply i l l u s t r a t e a t rend i n the data , and i s not intended t o prove t h a t a parabol ic ra te l a w i s being followed.

The

All of the specimens t e s t ed a t 800°C were i n t e g r a l and the re were no v i s i b l e s igns of capsule d i s t o r t i o n due t o i n t e r n a l pressure. appeared t o be f r i a b l e i n nature af ter exposure t o the f u e l . mater ia l f lak ing off i n t o the f u e l . fue l - l i ne r reac t ion a f t e r 32 days a t 8OO0C w a s a s l i g h t (<sum) loss of material from the in s ide edge of t he l i n e r . The 6 1 day specimen w a s a l so s l i g h t l y i r r e g u l a r along the ins ide edge. small plutonium enriched p r e c i p i t a t e s del ineated the gra in boundaries t o a depth of 28 pm from the ins ide edge.

The in s ide edge of the 8OO0C specimens

All specimens (except blanks) showed indicat ions of The only ind ica t ion of

I n addi t ion a t one loca t ion i n the l i n e r ,

Duplicate specimens were t e s t e d f o r t he 90 day t i m e period. One specimen showed no evidence of reac t ion except f o r f laking o r loss of material from t h e in s ide edge. maining specimen w a s s i m i l a r t o t he 6 1 day specimen w i t h local ized g ra in boundary penetrat ion of plutonium t o a depth of 280 pm.

The re-

NO plutonium di f fus ion o r gra in boundary p rec ip i t a t ion w a s detected i n the 180 day specimen. along the ins ide edge of the l i n e r indicated approximately 1 0 pm loss of material i n t o the f u e l .

However, i r r e g u l a r i t y

Plutonium enriched g ra in boundary p rec ip i t a t e s w e r e detected t o a depth of 170 pm i n one area of t he 361 day specimen. Plutonium diffused t o a depth of 300 pm i n t o the t i tanium matrix a t t h a t locat ion.

The only tes t a t 8OO0C showing general migration of plu- tonium i n t o the t i tanium matr ix w a s t he 720 day specimen.

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A t the shor te r t i m e per iods, plutonium penetrated the matr ix only a t widely sca t t e red locat ions. The typ ica l appgarance of the fuel-metal i n t e r f ace a f t e r 720 days a t 800 C i s shown i n Figure 6 . i s indicated by the i r r e g u l a r i t y along the ins ide edge. Voids and plutonium enriched inclusions are present gen- e r a l l y f o r a depth of approximately 320 pm. Plutonium penetrated the gra in boundaries t o a depth of 850 pm i n local ized areas of the specimen.

Loss of material i n t o the f u e l

In summary, t he data show t h a t t i tanium i s ngt a desirgble encapsulant f o r plutonium dioxide i n the 800 C t o 1000 C temperature range. This i s not surpr is ing. Thermodynami- c a l l y , reac t ion between the materials would be expected. A t 927OC, the f r e e energy of react ion f o r the equation

4Pu0, + T i -+ TiO, + 2Pu,O,

i s -29.8 Kcal'. There w a s the p o s s i b i l i t y , however, t h a t the reac t ion product might form a pro tec t ive layer i n h i b i t - ing fu r the r reac t ion . The r e s u l t s show t h a t t h i s did not occur. Also, i t w a s hoped t h a t i f a reac t ion did occur, a r a t e could be determined t h a t might allow use of the material as an encapsulant with a predictable l i f e expec- tancy. Unfortunately, the e r r a t i c nature of the plutonium grain boundary reac t ion , espec ia l ly i n the highly s t r e s sed areas of t h e specimen, made t h i s determination impossible.

111. Hardware Production (R. W . Saylor)

The l i n e r cap blanking d i e has been modified with a hardened tool s t e e l punch replacing the previous carbide mater ia l . Carbide chipping i n the blanking d i e punches has been a common occurrence and t o da te , four d i e s have been modified i n the above manner. Additional dies have performed wel l , requir ing only rout ine maintenance.

An addi t iona l (unscheduled) 45 s t rength member bodies were fabr ica ted t o replace hardware l o s t through engineering

'F. L. Oetting, Chem. Rev., 67:3, 261 (1967)

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I_- -. . .

React ions along Fuel-metal I n t e r f a c e of T i t a n i u m Specimen a f t e r 720 Days a t 8 O O 0 C

1

I. .

- \

t ri a . * *

. .

t

Ili4 '. e

P

T

..

L

A

t -

*

* &

6 2 5 X a S P

250X

10 '1 i s e d

p o l i s h e d )

F igure 6

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evaluation and the abnormally high dye penetrant rejects found in the Sheet 16, Lot 7 raw material (Section 11, MWG Progress Report, October 16, 1977 - January 1 5 , 1 9 7 8 ) .

Efforts are underway to standardize all gage masters at the low limit of the product tolerance range. system for mastering gages will simplify their use and lessen the chance for error.

A uniform

Two lathes equipped with a digital readout system and optical comparator are now operating continuously to meet production commitments. An EE Monarch lathe is being upgraded with this equipment to provide back-up in case of problems on the present lathes.

Hardware continues to be produced on schedule with high acceptance rates for each of the seven components. Shown in Table IV are the number of components produced to date and the acceptance rates. defectiveness and the dollar percent defectiveness values.

Also shown are the cost of

IV. Encapsulation (C. E. Burgan)

Twenty-five pressure burst capsules were fabricated from Lot8 T-111. for production usage.

Also fabricated were ten simulant units (filled with a mixture of tungsten and molybdenum). units will be used as mock-ups for fueled units in estab- lishing impact gun parameters for an upcoming reimbursable or der.

These units will be used to qualify the T-111

A portion of these

A new torch drive system was installed for the strength member and clad welding operations.

Encapsulation of production subassemblies and assemblies continues on schedule with high acceptance rates. 472 units have been encapsulated through the liner, 429 units through the strength member, and 386 units through the clad.

To date,

DOE has now accepted a total of 243 heat sources.

Shown in Table V is the Quality Report on Assemblies and the dollar percent defectiveness values. To date, for the entire program (hardware and encapsulation), the total cost of defectiveness is $ 2 0 , 1 3 6 , the total value of all product is $ 9 1 9 , 1 7 0 , and the dollar percent defectiveness is 2.2%.

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Table I V

Quality Report on Hardware

Number Process Number Example Eng. Number Yield

Component Fabricated Prime Weld Eval. Scrap (7)

6 1 1 - 4 9 9 . 3 - Liner Shim 615

615 612 3 - 0 1 0 0 . 0 Liner Cap

Liner Body 570 557 11 - 2 9 9 . 6

Strength Member Cap 630

Strength Member Body 630

607 1 7 6 9 9 . 0

532 69 1 2 17 9 7 . 3

555 546 7 - 2 9 9 . 6

555 540 7 - 8 9 8 . 6

Clad Cap

Clad Body

Overall Process Yield 99.0%

Dollar Value of Fabricated $190 ,193 Hardware

Cost of Defectiveness $ 1 , 9 7 3

Dollar Percent Defectiveness . 1.0%

Table V

Quality Report on Assemblies

Liner Assembly Fabricated Re j ec ted Yield cost of

Value of

$ % Defective

Defectiveness

Fabricated Units

Strength Member Fabricated Assembly Rejected

Acceptable Yield c o s t of

Value of

$ % Defective

Defectiveness

Fabricated Units

572 6 l

98.7%

$ 3 , 7 2 0

$288,920 1.3%

429

418 112

97.4%

$6,754

$187,682 3.6%

Clad Assembly Fabricated 386 Rejected 11 3 Acceptable 375 Yield 97.2% cost of Defectiveness $7,689

Value of Fabricated Units $252,375

$ % Defective 3.0%

Remarks :

3 - dye indications 1 - power failure 1 - bad weld 1 - fuel problem

211 - ultrasonic indications in the weld area 310 - outside diameter in the heat affected zone too large 1 - nick on outside diameter of cap

V. Pres'sure Burst Capsule Evalu.ation (D. A. Pawlak)

Twenty-five pressure burst capsules were fabricated for production qualification of Lot 8 T-111, and testing of these capsules has been initiated. Results to date are shown in Table VI.

Table VI

Pressure Burst Test Results

Lot 8 T-111 Capsules (lOIO°C) of

CaDsule

MPT-O1H

MPT-02H

Internal Pressure Rupture Time (psia) (hrs) Failure Location

8001.2

6500.5

24.49

90.38

Cap/body weld - body interface Cap /body weld

Rupture times compare favorably with prior data from Lot 7 capsules (both the lot qualification values and the TMS values).

VI. Surveillance (D. A . Pawlak)

A portion of the surveillance activities include the long range storage (at 21OoC and 410OC) of pressure burst capsules, with subsequent testing of the stored units at various time intervals to FY2003 (STA BB Drawing 309768). Protection of the T-111 from air oxidation during these long time periods at elevated temperatures will be accomplished by encapsula- tion of each pressure burst capsule in a Hastelloy C-276 sleeve with end caps.

Each constant temperature oven will contain direct drive mechanisms, which will eliminate malfunctions due to bearing, pulley, or belt problems. Each will also contain solid state proportioning control systems, with uniformity within +0.75% - of the set point and a control accuracy of +0.5O. - Although the Hastelloy C-276 and the constant temperature ovens have been on order for several months, vendor delays

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VII.

VIII.

X.

have resulted in deliveries now projected for June, 1978. Upon receipt of the materials and equipment, the first surveillance pressure burst capsules will be put on test.

Ultrasonics (W. A. Dudley)

Efforts are being made to ultrasonically evaluate pressure burst capsule welds. This presently cannot be done because of pressure burst capsule stem interference with the ultra- sonic fixturing. An order has been placed for a specially built ultrasonic transducer.

Also being investigated is the feasibility of non-destructively evaluating T-111 sheet material for microinclusions by acous- tical microscopy. A contract was placed with Sonoscan, Inc. The initial results of their study with "typical" T-111 sheets of .040" thickness are expected in May 1978.

Reimbur s ab 1 e s

Fabricated and delivered to LASL for the U.S. Navy were five heat sources of the MWG design, with the exception that the wattage level was 4.5 watts (E-45064). (A total of six were delivered because wattage requirements were not met in one unit - the sixth unit will be returned to Mound.) Essentially completed is a Sandia reimbursable order (E-40549) for fabrication and delivery of 32 fueled units. has been made on 21 units, with the remaining 11 units to be shipped to GEND in late April, 1978.

Recently received from SLA were two more reimbursable orders. One is for disassembly of two RTG's and evaluation of the non-Mound fabricated heat sources (E-45062). The other order calls for fabrication,. impact, and evaluation of eight fueled units (E-45061).

Shipment

The total prograuanatic FY-78 reimbursables to date is 204.6K.

GEND TMS Units

Fabricated and evaluated were 25 WR heat sources for GEND TMS activities. These units, which will be shipped to GEND

IX .

in late April, 1978, were fabricated as part of the overall P&S funding. This completes Mound's obligations to GEND (delivery of capability, feasibility, and TMS units) until shipment of production units is initiated in late FY-78.

Savannah River Interface

With the first encapsulation responsibilities being trans- ferred to Savannah River in FY-80, communications between the sites have been initiated to simplify the eventual technology transfer. Copies of the hardware drawings, welding fixtures, alpha boxes, and associated purifying systems, have been sent to Savannah River personnel in addition to all the operation sheets for liner welding and non-destructive testing.

Many of the technical details were discussed at meetings at Savannah River in mid-February and mid-April, with Mound personnel in attendance. Six persons representing SRP and DuPont engineering visited Mound on February 24, 1978, and two SRP personnel observed the liner welding operations on March 15, 1978. Another Mound visit of SRP, SRL, and DuPont engineering personnel is tentatively planned for May 10, 1978.

In late June, 1978, SRP will ship to Mound sufficient oxide for encapsulation of 12 sources. jected to various compatibility and impact tests, identical to those previously performed on Mound units. from these 12 units will then allow comparison between SRP oxide (oxalate process) and Mound oxide (hydroxide process). Although some of the compatibility tests will not be completed for two years, the initial data is expected to provide sufficient information for meaningful long range predictions.

These units will be sub-

The data

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