Patent Number: 051026180
Section: description

Referring to FIG. 1, tritium is extracted from heavy or light water rich in tritium by a reactor comprising a number of stages, four stages being shown for simplicity. Each of the stages comprises essentially an evaporator 10, a superheater 11, a catalytic reactor 12 and a condenser 13. These components of the various stages are interconnected by piping as shown in FIG. 1, and their respective functions are as follows. In the description which follows, specific reference is made to the extraction of tritium from tritium-rich heavy water according to the reaction EQU DTO+D.sub.2 .fwdarw.D.sub.2 O+DT However, it is to be understood that the apparatus is useful in the extraction of tritium from tritium-rich heavy or light water according to any of the following reactions: EQU DTO+D.sub.2 .fwdarw.D.sub.2 O+DT EQU HTO+H.sub.2 .fwdarw.H.sub.2 O+HT, EQU HTO+HD.fwdarw.HDO+HT, or more generally EQU QTO+Q.sub.2 .fwdarw.Q.sub.2 O+QT where Q denotes either of the hydrogen isotopes H and D. The tritium-rich heavy water (DTO) from a nuclear reactor, or heavy water (D.sub.2 O) from a preceding stage, is delivered into the evaporator 10 by a metering pump (not shown). The evaporator converts the water to steam which is mixed with tritium-lean deuterium (D.sub.2) delivered from the subsequent stage, or in the case of the final stage with tritium-lean deuterium from a supply tank. This mixture is fed to the superheater 11 where it is superheated to 200.degree. C. for subsequent catalytic exchange. The superheated gas-steam mixture passes to the catalytic reactor 12 where in contact with a platinum catalyst the following reaction takes place: EQU DTO+D.sub.2 .fwdarw.D.sub.2 O+DT Isotopic equilibration takes place and part of the tritium is transferred from the tritium-rich heavy water to the tritium-lean gas. The equilibrated mixture passes to the condenser 13 where the tritium-lean water is condensed and separated from the tritium-enriched gas. The condensed water is fed to the evaporator of the succeeding stage, or in the case of the final stage to the lean water return. The tritium-rich gas is fed back to the evaporator 10 of the preceding stage, or in the case of the first stage is fed to a cryo-distillation unit. As will be apparent from the scheme shown in FIG. 1, the design of such a plant based on convention practice requires extensive piping interconnecting the components of the various reactors, with many joints which are potential sources of leakage of radioactive substances such as tritium gas and tritiated water. According to the present invention the components of each stage are integrated into a single casing structure, thus eliminating the piping between its components. This construction has the further advantage of compactness to facilitate enclosure of the system in a secondary pressure vessel, as may be required for safety reasons in high tritium applications. As shown in FIG. 2, the casing structure is made up of a number of casing sections 20, 21, 22 and 23. The casing section 21 consists of a vertical steel cylinder having upper and lower flanges 24, 25 to which the casing section 20 having a flanged opening 26 and the casing section 22 having a flanged opening 27 are respectively bolted. The casing section 23 having a flanged opening 28 is bolted to a flanged opening 29 of the casing section 22. The four casing sections when joined together as illustrated form a unitary pressure vessel housing the components of the reactor. The joints between sections must be leaktight to prevent leakage of steam and gases; this may be achieved by seal welding the flanged joints between the sections. The vertical cylinder 21 houses the superheater 31, the catalytic reactor 32, and the condenser 33. Cooling fluid for the condenser 33 is supplied from a header within the casing section 20, the latter having inlet and outlet connections 34. The casing section 22 houses the evaporator 35, which in the present example comprises a tubular heat exchanger. The tubes of the heat exchanger extend horizontally, steam being admitted to the tubes from the casing section 23 having inlet and outlet connections 36, 37 for the steam. Tritium-rich water to be treated is admitted to the casing section 22 from the condenser of the preceding stage, or in the case of the first stage from the nuclear reactor itself, through an inlet pipe 38. The casing section 22 of the evaporator has a neck portion 39 defining a mixing and entrainment separation chamber 40 adjacent to the superheater 31. The neck portion 39 has an inlet 41 through which tritium-lean gas is supplied to the mixing chamber 40 from the subsequent stage or, in case of the final stage, from a source of deuterium. In operation of the reactor, the mixture of tritium-lean gas and steam from the evaporator section is passed to the superheater 31. The superheater 31 in the present embodiment of the invention comprises a tubular heat exchanger the tubes of which are vertically oriented within the casing 21. Heating fluid is supplied to the tubes of the heat exchanger via inlet and outlet connections 42, 43. It will be appreciated that the heating of the evaporator section and/or the superheater section of the reactor may alternatively be accomplished by electrical heating elements instead of heat exchangers supplied with heating fluids from external sources as shown. The superheated mixture of tritium-lean gas and tritium-rich steam passes to the catalytic reactor bed 32 at a temperature of approximately 200.degree. C. where an exchange of isotopes takes place. The tritium-lean gas receives tritium from the steam while part of the tritium of the steam is replaced by deuterium. The resultant mixture passes to the condenser 33. The condenser 33 comprises a vertically oriented tubular heat exchanger mounted within the upper part of the cylindrical casing 21. As previously mentioned, cooling fluid is supplied to the tubes of the condenser from a header within the casing section 20. Cooling of the steam/gas mixture results in separation of the condensed steam. The depleted water passes to the evaporator section of the subsequent stage, or in the case of the final stage to the lean water return, via an on output pipe 44. The tritium-enriched gas passes via an outlet pipe 45 to the mixing chamber of the preceding stage, or in the case of the first stage to the cyro-distillation unit. All the stages of the tritium separation plant are constructed in the same manner, the stages being interconnected as described so as to effect countercurrent flow of the deuterium and the tritiated water from stage to stage. Thus, tritium-rich water is fed to the evaporator section of the first stage, the depleted water being taken from the condenser section of the final stage, while tritium-lean deuterium gas is fed to the evaporator section of the final stage, the enriched deuterium being taken from the condenser section of the first stage and passed to the cryo-distillation unit. In a modification of the tritium separation plant described with reference to FIG. 2, the evaporator section of the first stage is omitted, the water to be treated being passed directly from the nuclear reactor to the evaporator section where it is mixed with the tritium-lean deuterium gas. An alternative VPCE reactor constituting one stage of the tritium separation plant is illustrated in FIG. 3. In this reactor the evaporator casing 22' is a vertical cylinder aligned with the casing section 21, the tubes of the evaporator 35' being vertically oriented within the casing section 22'. Otherwise, the construction of the reactor is essentially as described with reference to FIG. 2 and corresponding parts are denoted by the same reference numerals. FIG. 4 shows schematically an arrangement of reactors of the kind shown in FIG. 3, the essential components of the four stages and their various connections being denoted by the same reference numerals as are shown in FIGS. 1 and 3 to identify the corresponding parts. In this arrangement the first, second, third and fourth stages are identified by the references A, B, C and D respectively. The reactors of the four stages are vertically oriented, the condensed water flowing from the respective condenser sections under gravity. FIG. 5 shows schematically an alternative arrangement of reactors of the kind shown in FIG. 3, wherein the reactors are inverted so that the evaporators are at the top of each stage and the condensers are at the bottom. In this arrangement pumps 47 are used to pump the condensed water from each stage to the evaporator of the subsequent stage. This provides convenient flexibility in the layout of the tritium separation plant and it will be particularly noted that the reactors of the various stages may be arranged horizontally instead of vertically as previously described. FIG. 6 shows schematically yet another alternative arrangement in which the reactors are of the kind shown in FIG. 2, but in which the evaporators 10 are omitted from the integrated casing structures of the various stages and replaced by independent evaporator sections 50 which are interconnected with the respective superheater sections 12 by piping 51. As shown in the fragmentary view in FIG. 7, the evaporator section of the first reactor stage may be omitted altogether, the water to be treated being received directly from the nuclear reactor as steam and fed directly to the superheater 11 of the first stage by piping 42. As previously mentioned, the reactors are useful in the extraction of tritium from heavy or light water by catalytic reaction with either or both of the hydrogen isostopes (H) and (D). In the following claims the term "water" means heavy or light water and the term "hydrogen" means light hydrogen (H) or deuterium (D).