Patent GB-1108054-A (GB)
Title: Fuel element for a nuclear reactor
Inventor: MOGARD JOHAN HILDING
IPC: G21C15/04
Filed: 1965-07-20
Abstract: 1,108,054. Fuel elements. ATOMENERGI A.B. 20 July, 1965 [24 July, 1964], No. 30797/65. Heading G6C. A fuel element comprises a hollow tubular body of fissile fuel having protective coatings on the inner and outer surfaces, one surface having spaced recessed portions and the coating on that surface contacting the non-recessed portions while being spaced from the recessed portions to provide gas-filled or evacuated spaces constituting a heat insulating layer. In the embodiment described, a fuel element consists of three tubular bodies 1a, 1b 1c enclosed between an outer protective coating 2 and an inner protective coating 3 with a lower extended portion 15 having a conical portion 6 supported on a conical seat 16 of an opening 24 in the bottom 4 of a reactor core. The fuel element supports on its top a funnel-shaped member 7 having its upper edge abutting the inside of a tube 8 surrounding the element. Water in the space 27 outside the tube 8 acts as a moderator and flows from below into the space 28 between the tube 8 and the fuel element, flowing upward through this space while boiling. A mixture of steam and water flows out through a series of openings 21 in the tube 8, the steam flowing back into the tube 8 through a further series of openings 20 and down through the fuel element while being superheated. When the fuel element is to be changed, the opening 24 is closed by means of a valve 26, the plug 17 in the top of the tube 8 is removed, and cooling water is supplied to the tube 8 through a pipe 19. Pressurized water is then supplied through a duct 23 in the core bottom 4 which communicates with a groove 22 in the conical seat 16, resulting in the fuel element being lifted from the seat 16. The fuel element is lifted up from the tube 8 by a lifting member in a known manner. The inner surface of the fuel body la (Fig. 2, not shown) has vertical grooves of semicircular cross-section, the grooves being gas-filled and the cylindrical surface of the fuel body between. two adjacent grooves being in contact with the protective coating 3. The fuel body 1b (Fig. 3, not shown) also has vertical grooves but these have such a shape as to produce a wavy structure on the surface of the fuel body, only the tips of the wave crests being in contact with the coating 3. The inner surface of the fuel body 1c (Fig. 4, not shown) has vertical grooves of a large width, separated by narrow portions which are in contact with the coating 3. These grooves have a uniform depth. The heat insulating capacity of the grooves increases in the downward direction from fuel body la to fuel body 1c and consequently a comparatively large part of the heat produced in the fuel body 1c is directed outwardly to heat the water in the boiler space 28, whereas a comparatively small part is utilized for superheating the steam, the converse being true in the case of the fuel body 1a. This is consistent with the natural cooling capacity, as the water has its highest cooling capacity at the bottom of the fuel element, whereas the steam has its highest cooling capacity at the top of the fuel element.