IL33599A - Thermo-electric generator - Google Patents

Description

THERMO-ELECTRIC GENERATOR : : ATOMIC LIMITED This invention relate s to apparatus for the utilization of radiation energy from radioisotope sour ce s and for the production of electrical power by means of the thermo -ele ctric conver sion of said radiation energy.

The need for a simple and reliable electrical power generator has been recogni zed for year s . Such units have been required on remote site s or where the pre sence of maintenance supervi sion is impractical, for example in marine equipment such as marker s , buoys , beacons and the like.

In the utili zation of radioisotope source s , such equipment must be free from bilogical hazards both during shipment and when renewing the source. The pre sent invention envisages freedom from such biological haz ards and the ability to change the source with the utmost convenience without the need to disturb either any hermetic sealing associated with thermo -electric conver sion units or thermal contacts as sociated therewith.

It is an object of one feature of the invention to provide a simple electrical power source.

In accordance with the foregoing object the invention comprise s : a radioisotope electrical power generator , comprising: (i) a source -receiving enclosure for the reception of at least one sealed capsule of a radioactive isotope , (ii) radiation attenuation means completely surrounding item (i) , the said attenuation means , in use , having a temperature rise due to an attenuation proces s therein, (iiij a plurality of heat sink means at least partly surrounding and spaced from item (ii), (iv) a plurality of electrically inter connected semi-conductor thermopile s each having a heat receiving surface in thermal contact with item (ii) and a heat discharging surface in thermal contact with item (iii) whereby each thermopile , in use , is subject to a thermal gradient, and (v) an evacuable container for item s (i), (ii), (iii) and (iv).

A preferred embodiment of the invention will now be de scribed with reference to the accompanying drawings , in which: Fig. 1 is a side view, in section, of the power generator and a Fig. 2 is a horizontal section, taken along the linell-II in Fig- 1, Fig. 3 is a horizontal section, taken along the line III -III in Fig. 1, Fig. 4 is an end view of a source cage, Fig. 5 is a vertical section, taken along the line V-V in Fig.4, Fig. 6 is a vertical section of a fuel capsule assembly, Fig. 7 is a vertical section of the power generator and heat sink, Fig. 8 is a side view, partly in section, of the complete assembly.

Referring now to the drawings, in Fig. 1 there is shown the internal structure of a thermo-electric power generator, generally indicated at 1. At the centre there is a source cage 102, formed of pure nickel (cold drawn Nickel "200"), containing up to seven capsule assemblies 104, to be described hereinafter, each containing Cobalt 60 radioactive isotope. The source cage 102 is received in a tubular portion 106 comprising the inner wall of a heat block 108 having outer walls 110, an outer base 112, an inner base 114, and a top annular plate 116. All these items with the exception of the heat block are formed from sheet of an alloy, known under the trade mark DELORO "C" and which comprises Cr-17% W-5%; C-0.1%; Ni-55%; Mo-17%; Fe-6%. The heat block 108 is filled with an alloy of depleted uranium and 8% molybdenum 118. A plug 120 of a suitable high density material, for example tungsten is disposed above the source cage 102.

Referring again to Fig. 1 and to Fig. 2 which is a section taken along the line II- II in Fig. 1, it will be seen that the outer cylindrical surface of the heat block 110 is provided with six flat surfaces 122A-122F. Four rows of semi-conductor thermopiles 124 are arranged six to a row, abutting the flats at one end and against heat sink leg assemblies 126 at the other end thereof. T¾e-s^-w-ee» i*efe©^feke¾H¾-©^l^^ -A-P'P-Ueafei-ewi-Ne* . —filed; formed of a high thermal conductivity metal such as copper and are metal-lurgically bonded to six of the flats 122A - 122F and the six heat sinks 126 and the thermopile as semblie s are held together by means of tension hoops 128 and turn buckle 130.

Referring to Fig. 3 , three additional thermopile s 132 are base mounted beneath the heat bl0ck/l l 2 and in mechanical and thermal contact with a module firing plate 134 fastened to a main heat sink 140, to be described, by six screws 138. The heat sink leg as semblie s 126 are r th^mally joined to the main heat sink 140 by means of foil package s 142 closely fastened to the main heat sink 140 as by pre s sure plate s 144 and bolts 146. are so de signed and electrically interconne cted, that the relatively small individual electrical outputs collectively provide a useful voltage and adequate current. In order that the mechanical and thermal structure doe s not inter fere with desired electrical connections, each of the thermopile s 124, 132 are insulated from the structure by very thin sheets of high thermal con-ductivity electrical insulating material, such as beryllium oxide or aluminum oxide or heavily anodized aluminium shown at 125 in Figs. 1 and 2. The wiring of the thermopile s has been omitted from the drawings for simplicity. However , in Fig. 7 there is shown a helical bore 1408 which is used for housing the electrical outlet.

The source cage 102 will now be de scribed in more detail with reference to Figs. 4 and 5. The cage , generally indicated, at 102 com -prise s an ih *//egral cylinder of cold drawn Nickel " 200" , or other high temper ature high thermal conductivity oxidation re sistant material, having six hexagonally spaced longitudinal hole s 1022 and a similar centrally located hole 1024. All seven hole s extend from one end of the cylinder to adjacent fuel capsules 104 may be supported. A recess 1028 is formed in the central hole 1026, adjacent the end thereof; to accommodate remote handling equipment.

Referring now to Fig. 6, there are shown details of the fuel capsule assembly, generally indicated at 104. The capsule comprises inner and outer walls 1041 and 1042, lower end caps 1043 and 1044, and upper end caps 1045 and 1046. Cap 1046 is counter -bored as at 1047 to receive a remote handling tool attachment by means of which encapsulated fuel can be loaded into the unit. The inner wall 1042 may be formed from any suitable corrosion resistant material compatible with the radioisotope fuel at the device operating temperature and preferably acceptable for reactor irradiation purposes, for example, ZIRCALLOY -2 R (an alloy of Zr-98%; Sn-1.45%; Fe-0.125%; Cr-0.100%; Ni-0.050%) or possibly Type 316-L stainless steel.

The outer wall 1041 and end caps 1043-1046 may be formed from any suitable high temperature and corrosion resistant material, such as: DELORO "C" @ (an alloy of Cr-17%; W-5%; C-0.1%; Ni-55%; Mo-17%; Fe-6%), HASTELLOY "C", ®(an alloy of Cr-15.5%; W-4%; C-0.06%; Ni-59%; " o-16%; Fe-5%; V-0.2%), HASTELLOY "X" S) (an alloy of C-0.1%; Cr-22%; Co-1.5%; Mo-9%; Fe-18%; W-0.6%; Ni-49%) or HAINES-25 (R) (an alloy of Crr 20.45%; W-15.10%; Fe-1.95%; C-0.07%; Si-0.07%; Ni-9.93%; Al-1.03%; P-0.016%; S-0.011%; Co-51.37%; Mn-1-2%).

Referring again to Fig. 1, the top of the enclosure 1 is provided with a thermal barrier comprising a foil 160 formed of HASTELLOY "C" (ξ^ which is welded to the walls 4·¾9 of the enclosure 1. The centre of the foil 160 is held firm against the top annular plate 116 by means of a ring 161 and cap screws 162, the foil being welded between annular discs 164, 166 the lower of which 166 i s in contact with an "O" ring 168 „ The outer periphery of the foil 160 i s welded between a lower flange m ember 170 and an upper flange member 172. To prevent heat los s from the top of the fuel and enclo sure 1 , a pad of thermal insulation 182 is enclosed in a hermetically sealed metal jacket comprising a center rece s s 181 a Hastelloy " C" , ^thermal barrier foil 183 and a top section 180. The foil section 183 is secured to the centre rece s s 181 by being welded to 181 and a lower supporting annular disc 185. The outer periphery of the foil 183 is welded between a lower flange member 187 and an upper flange member 189. The whole of thi s insulation as sembly is connected to the upper shield plug 1430 (Fig. 8) by a connection 184 to allow evacuation and is thus removed whenever the plug 1430 is removed.

It will be appreciated that acce ss to the source is accomplished by removal of the main shield plug 1430 with the thermal insulation attached and the plug 120. It is not nece s sary to break down the state of evaucation of the enclosure 1 during source - changing operations.

Referring now to Fig. 7, there i s shown the enclosure 1 fastened to the copper main heat sink 140, by means of a flange 1402 and screws 1404. An "O" ring 1406 i s provided at the joint. The main heat sink 140 is provided with a helical bore 1408 through which electrical connector s 1410 and 1412 may pas s.

Fig. 8 shows the enclosure 1 rooow-e-dr-within a biological container . The latter comprise s a mas s of lead, or an uranium 8% molybdenum alloy, 1414 within outer steel walls 1416, a bottom plate 1420, and a top plate 1421. The fins 1418 form part of a cooling radiator as sembly, fabricated on a base plate 1422, which in turn is supported by channel member s 1424 and skids 1426. The top of the entire structure i s closed by a weather cover 1428. Part of the shielding is formed as a plug 1430 which is provided with a lifting eye 1432.

A s sembly of the power generator will now be described. portions 122A, 122B . . . etc, on the heat block -Θ by means of the heat sink leg as semblie s 126 , the hoops 128 and the turn buckle 130. Those thermo -electric module s 132 disposed beneath the heat block are placed in position on the copper base plug 134. The heat conducting foil links 142 are then clamped to the heat sink 140 by the clamp screws 146.

All voids are then packed with high quality microporous ther mal insulation such as icrotherm (a trademark of Spectar Engineering Ltd. , of Kidderminster , England). The thermo element vacuum enclosure generally indicated at 1 is then fitted, after installing the "O" ring 1406 , and fastened to the heat sink 140 by means of s crews 1404. This step includes fastening the foil discs 164, 166, by means of the clamp ring 161 , to the top of the heat block 1 10. The thermo-electric chamber is then purged and sealed via the helical base 1408 and metal tubing 1409. Preliminary te sts to inve stigate the thermo dynamic characteristics of the assembly are then carried out. The se te sts involve placing the nickel source spacer 102 into the heat block and with electric heater s placed within the spacer. / 1414 The main biological shielding, le s s its top plug 1430 , is fir st positioned around the generator , followed by installation of the top plug.

The voids around the fuel area are then evacuated and backfilled with helium , after which the heat input nece s sary for the de signed performance is determined using the electric heater s.

The top plug 1430 and thermal barrier as sembly 182 are then removed and a selected quantity of encapsulated radioisotope is loaded into the heat block by means of shielded remote handling equipment. The thermal barrier as sembly 182 and the top plug 1430 are then replaced. 60 In operation, the radiation from the source, usually Co, is attenuated by the one -inch thickne s s of depleted uranium 8% molybdenum alloy heat block. Since the heat block is thermally insulated, by the micro -porous thermal insulation and the semi - conductor thermopile s , from the heat sink, a thermal gradient i s developed between the block and the sink and thermo-conductively in contact with the block and the sink and are therefore subject to the abovementioned thermal gradient. The other set of semiconductor thermopiles, disposed between the underside of the heat block and the copper base plug operate similarly.

Advantages of the invention include the following: (a) access to the fuel is possible without in any way disturbing the semiconductor thermo-element assembly or interrupting the main path for rejection of heat. As a result, the precise assembly of semiconductor components can be carried out inactively and tested and does not then require attention under active conditions; also opening the device for fuel attention, etc. , will tend to increase the rate of loss of heat, so no excursions of the hot surface of the thermo-couples above the designed temperature occur. (b) the thermo-element units are relieved of undesirable stress, which could be set up by either thermal expansion or mechanical misfit, by the flexible link to the bottom plug. (c) the device can be fuelled by a field loading facility thus eliminating the need on initial fuelling for a shielded remote handling cell and allowing for possible refuelling in the field after prolonged operation instead of returning the complete device to the manufacturer.

Claims (1)

1. insufficientOCRQuality