Patent GB-1084712-A (GB)
Title: Nuclear rector
Inventor: ACKROYD RONALD TUNSTALL
IPC: G21C1/00
Filed: 1964-01-28
Abstract: 1,084,712. Reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Jan. 7, 1965 [Jan. 28, 1964], No. 3708/64. Addition to 922,498. Heading G6C. A nuclear reactor core comprises a plurality of core units of which each is in the form of relatively rotatable concentric cylindrical fuel elements, each such element having eccentric regions of differing infinite multiplication factor. In the water-cooled reactor illustrated, the core incorporates three cylindrical core units 11, 12, 13 each of which has three concentric fuel elements 14, 15, 16. The fuel elements are relatively rotatable in that they comprise a central rotary drum 14, a stationary annulus 15, and a rotary annulus 16, each of which is divided diametrically into multiplying regions 14a, 15a, 16a and non-multiplying regions 14b, 15b, 16b. In the reactor described, the regions 14a, 15a, 16a are only multiplying when they are permeated by water; on the other hand, for an un-moderated fast reactor, these regions would be multiplying in the absence of moderator. The active core area has a boundary 17 within which the interstices 18 between the core units are constructed as multiplying regions. The multiplying regions are constituted by upright fuel pins which consists of uranium dibxide pellets stacked in stainless steel sheaths supported between top and bottom grids which are perforated for the passage of coolant water. The rotary fuel elements 14, 16 have their top and bottom grids mounted on bearings and connected to drive mechanisms. The non-multiplying regions are constituted by dummy fuel pins which contain non-fissile material. The rotary non- multiplying regions 14b, 16b are lined with shells 19 of neutron-absorbing poison such as boron-steel, while shells 20 of neutron-absorbing poison are mounted in the stationary non- multiplying region 15b and in the region surrounding the core. The reactivity is controlled by relative rotation of the fuel elements, being a maximum when the multiplying regions of all the core units are located within the active core area (as shown for units 11, 12) and a minimum when the multiplying regions are relatively dispersed (as shown for unit 13). The reactivity is reduced not only by the dispersion of the nuclear fuel but also by the interposition of neutron absorbing material between multiplying regions. This reactivity control may be employed for power level control, long term control, or safety shut-down of the reactor. If the reactor core size is to be greatly increased, the interstitial multiplying regions 18 may approach critical size and to counter this possibility, it is proposed to use a number of core units of different sizes which can be fitted together alongside each other in such a way as to reduce the size of the interstitial regions to the point of being sub-critical. The invention may be employed with spectral shift reactors, in which case the eccentric regions would comprise neutron moderating regions of greater and less effect, for example some of the dummy fuel pins in the non-multiplying regions could be of a moderator material with the remaining dummy pins replaced with fuel pins.