SE306377B - - Google Patents

Abstract

1,066,264. Reactors. UNITED STATES ATOMIC ENERGY COMMISSION. Sept. 21. 1964 [Nov. 15, 1963], No. 38494/64. Heading G6C. In a large pressurized-water power breeder reactor there are no neutron absorbers in the core apart from safety rods, and control is effected by moving fuel to vary the ratio of neutrons used for fission and breeding. The core is formed of a number of core assemblies, each being independently critical, and containing both fissile and fertile material, U 235 or U 233 , and U 238 or Th 232 respectively, and all being in dioxide form. It is envisaged that the reactor will operate at its full power of 1720 MW(th) for 10 years without refuelling. Reactor.-Coolant enters the spherical pressure vessel 20 through a pipe 35 which leads to an inlet plenum chamber 31. 40% of the coolant enters ports 36 and passes upwards within the movable centres of the core assemblies, out through the ends of these parts to the stationary part of the core assemblies, and finally through outlets 49. Tile remainder of the coolant enters the core assemblies through ports 53B and makes three passes through each before leaving. The core weight is transmitted to the pressure vessel by the inlet plenum chamber. Core assemblies (Figs. 1, 3).-The core of the reactor is assembled basically from a number of circular section units 42 each surrounded by three chevron section units 38. These units are arranged on a triangular lattice. The innermost section, 41, is the movable portion of the assembly and is surrounded by the fixed annular portion 42. Both sections comprise a plurality of rods 44 containing fertile and/or fuel material. An annular neutron absorbing safety element 43 is insertable between the sections 41 and 42. Each blanket segment 38 contains fertile rods 55 and has an internal baffle 58 forming two of the coolant passes referred to earlier, the third pass being through the fixed annular section 42. Thus the critical units of the reactor core each comprise a group formed by members 41, 42. and three members 38. Each rod in the central region of section 41 is entirely of fertile material, and the remaining rods of section 41 have upper portions of fertile material and lower portions of fissile material. The relative lengths of fissile and fertile material in the rods are so arranged that, referring to Fig. 10, the central rod 41 has fertile material 45 and fissile material 46. A similar arrangement of the rods in the annular section 42 results in that part of the assembly having a fissile region 46 and a fertile region 45. Reactor operation.-All reactivity control, other than emergency shut-down, is achieved by moving the centre core assembly sections 41. Initially, all power is generated by the fissile material, but towards the end of the reactor lifetime about 65% of the power will be derived from the originally fertile loading. At start-up, the movable sections are set at positions of maximum reactivity, are moved to minimum positions after about 30,000 hours and gradually returned to their original positions in about 70.000 hours.