Patent GB-929838-A (GB)
Title: Improvements in and relating to nuclear reactors
Inventor: BUTLER GRAHAM FREDERICK
IPC: G21C17/04
Filed: 1959-12-07
Abstract: 929,838. Nuclear reactors. NUCLEAR POWER PLANT CO. Ltd. Nov. 16, 1960 [Dec. 7, 1959], No. 41529/59. Class 39 (4). [Also in Group XXIX] A burst slug detection system for a nuclear reactor comprises means for continuously passing to fission product detection means mixed samples of cooling fluid from each of a series of groups of fuel channels, together with means for passing samples of cooling fluid from each fuel channel of a group in turn, the sampling of individual channels and groups of channels taking place simultaneously. Fig. 1 is a section through a sampling valve comprising an optically flat member 1 containing two sets of ports arranged in separate concentric rings. The ports 2 of the outer ring are each connected to a fuel channel through a sampling pipe 3 and at their other end communicate with a common space 4 which is connected through a duct 5 to fission product detection means. The ports 6 of the inner ring extend between the space 4 and a channel 7 which is connected by a duct (not shown in Fig. 1) to fission product detection means. A rotatable plate 10 slides over the surface of member 1, coming to rest at intervals for a given time to connect one of the ports 2 to one of the ports 6 by means of a bridge member (not shown in Fig. 1) whilst sealing the ends of the remaining ports 6 by studs 12. The member 10 may be rotated in steps by a ratchet mechanism driven by a gas-operated bellows, Fig. 6 (not shown). Thus the output from duct 5 is a mixture of the gas samples from all channels except one in a group, and the output from channel 7 is a gas sample from each individual channel in turn. To provide an indication of the position of the selector there may be one less port 2 than the number of rest positions of the. selector, so that in one position the selector does not connect a port 2 to a port 6. By suitable design of the bridge member there need be only half as many ports 6 as ports 2. The valves may be arranged in groups of 12, each group having a fission product detector of high sensitivity and one of low sensitivity. Fig. 8 shows two such groups A1-A12 and B1-B12. The outlets 9 for the individual samples are connected in turn to a high sensitivity detector SSA and SSB, respectively, under the control of solenoid-operated valves AC1-AC12 and BC1- BC12. At the same time the mixed sample outlets 5 of the valves are connected in turn to a low-sensitivity detector FSA or FSB each for a period of 30 seconds under the control of solenoid-operated valves AD1-AD12 and BD1 -BD12. In case one of the detectors FSA or FSB fails it may be arranged that for one cycle group A feeds to detector FSA and for the next cycle to detector FSB, and vice versa for group B. If a reading of a low sensitivity detector indicates a fault the valve concerned can be controlled to hunt through its positions passing the single samples to either of two separate highsensitivity detectors HC 1  or HC 2  until the channel containing the fault is located. When a fault is discovered during the slow scan of individual channels the channel is known immediately and the selector valve concerned can be kept in a position so that it continuously passes a sample from the faulty channel to one of the detectors HC 1  or HC 2 . To guard against failure of one of the detectors SSA or SSB spare lines may be provided so that one of the detectors HC 1  or HC 2  can be switched into circuit as a replacement for SSA or SSB. The outputs of the detectors may be fed to recording means provided with separate recording charts for individual channels and for groups of channels. The recording means may be provided with means for setting individual alarm levels for each group and channel, an alarm being actuated when these levels are exceeded.