GB1281979A - Low capacity nuclear reactor and fuel elements therefor - Google Patents

Abstract

1281979 Fuel elements BROWN BOVERI/ KRUPP REAKTORBAU GmbH 9 Dec 1970 [16 Dec 1969] 58551/70 Heading G6C A fuel element for a low capacity nuclear reactor consists of a moulded plastics body acting as a moderator and particles of fissile material contained within the body, each of the particles having a gas-tight envelope, and the particles deing distributed in the moulded plastics body in such a manner that zones of predetermined densities of fissile material are established, whereby an inhomogeneous distribution of fissile material is created in the fuel element. The coated fuel particles may be embedded in the moulded plastics body, contained loosely in cavities in the body, or contained in the cavities in the form of bonded particles. The diameter of the particles is typically 0À5 mm. and the thickness of the gas-tight envelopes 0À3 mm. Polyethylene is a particularly suitable plastics material because of its high thermal conductivity. In the reactor shown in Fig. 5, plate-like fuel elements 1 are provided with the fuel particles forming a layer in each element. The elements 1 are fixed relatively to each other by means of pins inserted in complementary holes 4. Each element 1 contains appropriate holes constituting absorber-rod passages 5, cooling passages 6 and one or more irradiating passages 7. The heat generated in the fuel elements 1 can be conducted to the container wall 8 by way of the moderator and a heatexchanging medium, e.g. water, contained in the cooling passages 6 or other gaps between the fuel elements and dissipated by means of a coolant circulating through cavities 10 in the wall 8. For higher reactor capacities, however, it may be advantageous to cool the reactor core direct by means of a coolant circulating in the above-mentioned passages 6. The gaseous or liquid coolant is fed to and from the passages 6 via ports 11 and chambers 12, flow restrictors 13 being provided in the upper and lower coverplates 14 of the reactor container. In an alternative arrangement (Fig. 3, not shown), the fuel particles are not distributed over a layer but are contained in uniformly disposed cylindrical cavities, the axes of which are at right angles to the planes of the plate-like elements 1. In a further embodiment (Figs. 6 and 7, not shown), the fuel particles are accommodated in the hollow interiors of rod-like or spherical fuel elements. In the case of the rod-like fuel elements, the ends of the elements are tapered to enable the elements to be centered in conical recesses in the two cover-plates of the reactor container. The particles used in the abovedescribed fuel elements may conveniently have a core of UC (20% enriched U) and a coating of pyrolytic carbon.