Patent GB-1082052-A (GB)
Title: Energy absorbing devices
Inventor: CAIRNS WALTER JOHN
IPC: G21C7/20
Filed: 1964-05-07
Abstract: 1,082,052. Reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. April 26, 1965 [May 7, 1964], No. 19151/64. Heading G6C. [Also in Division F2] In a nuclear reactor an energy absorbing device (see Division F2) is provided for limiting the free fall of a body member of a fuel element assembly 29 within a tube 2 extending into the core of the reactor and comprises a sleeve member 15 in the tube having at least one continuous guiding groove 16 extending along the length of the sleeve member in zigzag manner, at least one guide pin 25 which is arranged slidably to move in engagement with the groove or grooves of the sleeve member 15 with longitudinal movement of the body member within the tube so as to impart an oscillatory motion to the body member about its longitudinal axis such that the sleeve member is deformed when the kinetic energy of the body member 29 exceeds a predetermined value, the guide pin or pins deforming the groove or grooves of the sleeve to effect random crumpling of the sleeve member to jam the body within the tube. In a vertically oriented fuel element channel of a steamcooled heavy water moderated nuclear reactor shown in Fig. 1 a composite pressure tube 1 is provided with upper and lower sections 2, 3 respectively of stainless steel and a centre section 4 of zirconium. The pressure tube 1 is supported on an upper shield tank 8 containing light water and the centre section extends downwardly into the core of the reactor bounded by a cylindrical calandria vessel 27 containing heavy water. The lower section 3 penetrates a lower shield tank 28 containing light water and a zirconium liner 9 is also secured to the upper and lower tube sections 2, 3 such that together with the centre section 4 there is defined an annular duct 10 through which light water is passed and vaporized to provide a cooling medium for the zinc zirconium section 4. A stainless steel inner liner 11 is secured in the upper section 2 and slidably guided in the lower section 3 such that the liners 11 and 9 define a second annular duct 12 containing a static volume of steam which serves to insulate the zirconium section 4 and the liner 9 from the heat radiated from the nuclear fuel in the centre section. The upper section 2 supports a tubular member 13 having a sleeve member in the form of a lining 15 defining guide grooves 16 of zigzag formation. Fig. 2 shows the construction of a body member 29 of a fuel element assembly comprising a seal plug 18 from which depends a stainless steel tubular rod 19 carrying a neutron shield plug 20 of stainless steel of helical formation below which is carried the nuclear fuel rods 22 which depend from a support grid 23 and are tied together by zirconium straps 24 at the upper and lower ends of the fuel rod cluster 21, on the shield plug 20, and on the rod 19 are sets of angularly spaced guide pins 25 which co-operate with the guide groove 16 in the lining or sleeve member at 15 of the fuel element channel. In the event of accidental release of a fuel element assembly during charging or discharging from the channel and the kinetic energy is in excess of a safe value the guide pins plastically deform the lining 15 at the ends of the grooves and the sleeve member 13 deforms radially inwardly to contact the assembly and absorb the frictional resistance when the crumpling action becomes sufficient to jam the body within the tube.