Patent GB-1257250-A (GB)
IPC: G21H1/10
Filed: 1969-12-22
Abstract: 1,257,250. Thermoelectric devices. ATOMIC ENERGY OF CANADA Ltd. 22 Dec., 1969 [30 Sept., 1969], No. 62353/69. Heading H1K. A radioisotope powered thermoelectric generator comprises a heat source in the form of an enclosure for receiving at least one sealed capsule of a radio-active isotope, surrounded by a radiation attenuator which produces a temperature rise, a plurality of heat sinks surrounding the heat source, a plurality of thermopiles each in thermal contact with the heat source and one of the heat sinks and an evacuable container enclosing the thermopiles and heatsinks. As shown, Fig. 1, the fuel assembly comprises a nickel cage 102, having seven longitudinal bores in each of which is inserted a sealed capsule 104 containing the radio-active isotope cobalt-60, surrounded by a heat block 108 comprising an alloy of depleted uranium and 8% molybdenum which absorbs radiation and produces a temperature rise. The heat block 108 is enclosed in sheet metal walls 106, 110 and the cavity containing the final assembly is closed by a tungsten plug 120. The heat block 108 is generally cylindrical but has six longitudinally extending flats on its outer surface against which are mounted thermopiles 124. Each longitudinal column of thermopiles is provided with a separate heat sink leg 126 connected to a main heat sink 140 (only part of which is shown) by means of flexible foils 142. The thermopiles 124 are electrically insulated from the heat block 108 and heat sink legs 126 by sheets 125 of beryllium oxide, aluminium oxide or heavily anodized aluminium, and the arrangement is compressed by loops 128 tightened by turnbuckles (130). Three thermopiles 132 are also mounted between the lower face 112 of the heat block and the main heat sink 140. The thermopiles are enclosed by a tubular casing secured at one end to the main heat sink 140 and closed at the other end by means of a thin foil 160 secured to the top edge of the heat block 108. The thermopiles are provided with electrical connection to the outside by a cable which extends through a helical bore in the heat sink 140 (Fig. 7, not shown), the bore also enabling the space surrounding the thermo-elements to be evacuated. A thermally insulating pad 182 enclosed in a hermetic jacket 180, 181 closed by a foil 183 is placed on top of the assembly. The lower part of the assembly 1 is clamped inside a radiation screen (1414) of lead or of uranium 8% molybdenum enclosed in steel walls and the connector 184 on the cap containing the insulating pad 182 is screwed into a radiation screen plug (1430) which is bolted to the main screen. The plug (1430) is of the same construction as the main screen and has a duct extending from the connector 184 to the outside to enable the thermal pad to be evacuated. The main screen is provided with pins 1418 and rests on skids 1426. The device is assembled by arranging the thermopiles and heat sink legs round the heat block, packing the voids with microporous insulating material and evacuating the enclosure. The fuel cage is then loaded with electric heaters instead of nuclear fuel capsules and inserted into the heat block. The remaining components are assembled and the voids around the fuel area are evacuated and backfilled with helium. The assembly may then be tested. To load with nuclear fuel it is merely necessary to lift out the radiation screen filing (1430) to which the thermal pad 182 is secured and replace the electric heaters with the cage containing the fuel capsules. This does not involve disturbance of the thermopiles or of the heat flow paths and does not necessitate breaking the vacuum.