Parts of nuclear reactors

84.01 - Nuclear reactors; fuel elements (cartridges), non-irradiated, for nuclear reactors; machinery and apparatus for isotopic separation. 8401.10 - Nuclear reactors 8401.20 - Machinery and apparatus for isotopic separation, and parts thereof 8401.30 - Fuel elements (cartridges), non-irradiated 8401.40 - Parts of nuclear reactors (I) NUCLEAR REACTORS The term nuclear reactor covers, in eneral, all the apparatus and ap liances inside the area screened off b the biological shiel including, where appropriate, t e shield itself. It also includes any o er apparatus and appliances outside that area, provided they form an integral part of those contained inside the screen. d L R A nuclear reactor generally comprises : (A) The core, consisting of: (1) The fuel (fissile or fertile). This may be dissolved or dispersed in the moderator (homogeneous reactor) or concentrated in he1 elements (cartridges) (heterogeneous reactors). (2) The moderator and, where ap ropriate, the neutron reflector (e-g.,byl!ium, graphite, water, heavy water, certain hyd? ocarbons such as diphenyl or terpheny s) (3) The coolant. This serves to remove the heat generated by the reactor (carbon dioxide, helium, water, heavy water, molten sodium or bismuth, a molten sodium-potassium mixture, molten salts, certain hydrocarbons, etc., are frequently used for this purpose). The moderator, however, also often acts as a coolant. (4) The control rods, of materials with a high neutron absorption capacity (e.g., boron, cadmium, hafnium) or of alloys or compounds of such materials. (B) The mechanical structure for exam le, the reactor vessel; the he1 element (cartridges) loadin grid; the piping an tubing or the conveyance of the coolant; the valves; the contro rod operating mechanism, etc.). 6 - P (C) The measurin checking and automatic-control instruments (e.g., neutron sources, ionisation cham ers, thermocouples, telecameras, pressure or flow meters). k (D) The thermal and biological shields (of steel, concrete, lead, etc.). r Certain other machinery, apparatus and ap liances ma also be used in nuclear plant and may even be located inside the area screened o by the bio ogical shield. These are not regarded as having thereby acquired the essential character of parts of a nuclear reactor and must therefore be classified in their own appropriate headmgs (see exclusions (c) to (ij) below). The nature, characteristic features and manner of assembly of the component parts of nuclear reactors may, however, differ considerably. The various types of reactors are generally distinguished by reference to : (1) The energy of the neutrons propagating the chain reaction (e.g., thermal (or slow), intermediate or fast reactors). (2) The distribution of the fissile material in the core of the reactor (e.g., homogeneous reactors or heterogeneous reactors). (3) The intended use (e , research reactors, isotope roducing reactors, material testing reactors, reactors for e conversion of fertile materi s into fissile material converters or breeders), propulsion reactors, thermal or electrical energy producing reactors . f \ I (4) The nature of the materials used or the princi le of operation e.g., natural uranium, enriched uranium, uranium-thorium, sodium-grap ite, gaseous-grap ite, pressurised water, pressurised heavy water, boiling water, swimming pool, organic moderator type reactors). ! In general, the size of a reactor is so calculated as to be at least " critical ", so that any outward loss of neutrons shall never be sufficient to interrupt the chain reaction. However, for research urposes, " subcritical " reactors, which require additional sources of neutrons, may sometimes e! used. These reactors are also included in this heading. Separately presented parts of nuclear reactors are, in general, classified in accordance with the provisions of Note 2 to Section XVI. Control rods and the corresponding mechanisms, the neutron sources fitted to initiate the fission reaction of the reactor, the vessel, the grid for insertion of the fuel elements (cartridges) and the pressurisers for pressurised water reactors are, therefore, classified in this heading as parts of nuclear reactors. The following goods are, however, not regarded as parts of nuclear reactors : (a) Blocks of gra hite (heading 38.01 or 68.15), beryllium (heading 81.12), or beryllium oxide (heading 69.18. @) Metal tubes and pipes, in special forms, or merely shaped but not otherwise worked, resented unassembled, whether or not identifiable as for the construction of nuclear reactors (Section V). (c) Steam and other vapour generating boilers (heading 84.02). (d) Heat exchangers (heading 84.04 or 84.19). (e) Steam turbines and other vapour turbines (heading 84.06). (0 Pumps (heading 84.13 or 84.14). (g) Blowers (heading 84.14). (h) Apparatus for extracting minerals from water (generally heading 84.19 or 84.21). (ij) Handling machinery for changing or extracting the fuel elements and travelling cranes (generally heading 84.26). (k) Mechanical remote control manipulators for radioactive products (heading 84.28). (11) MACHINERY AND APPARATUS FOR ISOTOPIC SEPARATION This oup covers all mechanical, thermal or electrical apparatus and devices specially designed for e enrichment of a chemical element or of a compound of that element in one of its isotopes, or for the complete separation of the constituent isotopes. The most important are those used for the production of heavy water (deuterium oxide) or for the enrichment of uranium in U 235. The apparatus and devices used for the production of heavy water by enrichment of natural water include : comprisin a very lar e number of (1) Special fractional distillation and rectification sllght CIIference in oiling point ates arranged in clusters and in cascade and which are continually more getween heavy water and normal water to depleted in heavy water and tail fractions which are continually more enriched. Pr x % (2) Apparatus which, b low-tern erature fiactional distillation of liquid hydrogen, separates the deuterium, whic can then e combusted to obtain heavy water. \ (3) Ap~aratusfor the production of heavy water or deuterium compounds, based on isotopic exc ange, sometimes in the presence of catalytic agents, for example by the " dualtemperature " method or by contact of different liquid or gaseous hydrogenous phases. (4) Electrolytic cells intended for the production of heavy water by water electrolysis, and apparatus combining electrol sis with isotopic exchange between the hydrogen produced and the originating water itse f. For the enrichment of uranium in U 235, the following apparatus is most often used : (1) Special centrifuges called " gas " (uranium hexafluoride) centrifuges, whose cylindrical rotor (" bowl "), of plastic material or steel, rotates at very high speeds. These centrifuges are treated internally against the corrosive effects of uranium hexafluoride. In practice, a very large number of units is used, arranged in cascade and operating down-current or counter-current. (2) Uranium isotope separators (gaseous diffusion type). In this equipment, gaseous uranium hexafluoride is separated into two fractions, with slightly different contents of uranium 235 diffusion through a porous membrane (" barrier ") inside a be tubular). By repeating the operation many times pure (3) " Nozzle " ap aratus (Becker process), in which a stream of gas (uranium hexafluoride and helium or hy ogen) is injected at high speed into a highly incurved nozzle. A " paring tube " at the outlet separates the enriched fraction of uranium hexafluoride. % Calutrons for electro-magnetic separation are also classified in this heading. Sub'ect to the general provisions regarding the classification of parts (see the General Exp anatory Note to Sechon XVI), parts of the machines and apparatus of this group are also covered. (111) FUEL ELEMENTS (CARTRIDGES) NON-IRRADIATED, FOR NUCLEAR REACTORS Fuel elements (cartridges), non-irradiated, for nuclear reactors consist of fissile or fertile material contained in a sheath, generally of base metal e.g., of zirconium, aluminium, magnesium, stainless steel), fitted with special attachments for andling. h metallic state or as compounds uranium 235 or 233 or in plutonium, either in plutonium. Fertlle fuel elements at the periphery of the reactor to Fuel elements are of different types, for example : (1) Combustible metals or alloys thereof in the form of bars or tubes sheathed in base metal. This metallic sheath ma be flan ed to facilitate heat exchange, and the element may be fitted with a support an a head or convenience of insertion xnto and extraction fiom the reactor. B f (2) Dispersions of the fissile fuel in graphite in the form of bars, plates or spheres encased in gra hite or consistin of other types of dispersions and cermets. These are flanged or fitted m e same way as tl? e fuel elements (cartridges) described in (1) above. & (3) An assembly of: (i) A series of sandwiched plates consisting of the fissile or fertile he1 (metal or ceramic compound) coated on the outside with inert metal. (ii) Inert metal tubes filled with pellets of uranium dioxide or carbide. (iii)Concentric fissile metal tubes sheathed with inert metal. es of he1 elements (cartridges) are fitted with supports which also serve to keep space apart and fixed in lace; they often have an outer casing. All the sub-elements themthese *I1 constituting these fie1 elements fcartridges) are mounted on a cormnon base and attached to a common head. 9' Presented se arately, these sub-elements (e.g., stainless steel sheaths filled with nuclear fuel and sealed) are c assified as parts of fuel elements (cartridges). f Micros hefes of nuclear @el coated with layers of carbon or-silicon carbide, intended for introduction into sp%encal or pr~smat~c fuel elements, and spent (irrad~afed) fuel elements (cartridges), fall m heading 28.44. The heading also excludes : (a) Furnaces for the separation of irradiated nuclear fuel by pyrometallurgical processes (heading 84.17 or 85.14, as the case may be). (b) Separators for irradiated fuels or for processing effluents, operating by fractional distillation (other than those for the production of heavy water) (heading 84.19). (c) Air filters specially designed to eliminate radioactive dust charcoal purifiers for retaining radioactive elements, including such a fuels or for processing effluents, (heading 84.21).