Patent GB-1066402-A (GB)
Title: Improvements in and relating to nuclear reactors
IPC: G21C1/20
Filed: 1965-01-13
Abstract: 1,066,402. Reactors. SOCIETE BELGE POUR L'INDUSTRIE NUCLEAIRE BELGONUCLEAIRE S.A. Jan. 13, 1965 [Jan. 17, 1964; April 14, 1964], No. 1485/65. Heading G6C. The housing for the core of a fast or intermediate nuclear reactor comprises a plurality of juxtaposed modules, i.e. casings, resistant to high temperature and high pressure, and adapted to receive and enclose fuel elements and to act as ducts for the flow of heat-carrying fluid. The modules may enclose cylindrical fuel elements arranged in clusters or spherical fuel elements of the cermet type, the matrices of which are of steel and the fuel of mixed uranium - plutonium oxide. The fuel may be displaced along the axes of the modules, natural uranium introduced at one end becoming progressively enriched in plutonium during its displacement. The juxtaposed modules of the invention are particularly advantageous for use in superheating dry water vapour in power reactors. The modules may be arranged either in layers or in clusters which may be formed by welding individual metallic modules together or by drilling parallel channels through a plate or block. The whole assembly of juxtaposed modules may be considered as a multicellular housing, the outer wall of which alone is of considerable thickness, the walls separating the modules serving only as a reinforcement. The steam may pass axially through the modules. However, the multicellular housing allows of perforating holes to form passages between neighbouring modules, without endangering the strength of the assembly. Such holes may extend the entire length of the modules occupied by the fuel and the steam then passes through the modules perpendicular to their axes. Fig. 9 (not shown) shows a simplified section of such an assembly, an inner sheathing 15 supplying steam which passes through the modules in the direction of the arrows to be collected by a doublewalled outer sheathing 14. An equivalent arrangement (Fig. 10, not shown) uses two superposed layers, the axes of the modules of one layer being at right angles to those of the other layer. In the embodiment of Fig. 11 (not shown), the housing is constructed from modules 3 and the steam enters at 1 and leaves through an outlet 2. Stoppers 4 welded with lock-nuts support the coolant pressure and a tube 5 serves for the fuel handling. This arrangement allows of charging and discharging under water by completely drowning the modules 3. The water may flow through and be cooled outside the reactor, the tube 5 acting as a dam and the water it contains forming a protection against radiation. An alternative reactor construction (Fig. 12, not shown) allows the fuel to be handled while the reactor is operating. In case of accident involving the total or partial fusion of the fuel, the modules provide a barrier against the spreading of contamination and prevent re-formation of a critical mass. An undesirable excess of reactivity due to accidental invasion by a moderator (for instance, total or partial flooding by water) is avoided by an arrangement of thermal and/or epithermal absorbers inside spaces between the modules.