GB947104A - Neutron flux measuring apparatus - Google Patents

Abstract

947,104. Nuclear reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Oct. 17,1962 [Oct. 27,1961], No. 38479/61. Heading G6C. Neutron flux measuring apparatus comprises an irradiation unit of low neutron absorption displaced at a locality at which the flux is to be measured, a flowpath for a neutron activatable fluid through the unit between an inlet and an outlet, a monitor to measure the radio-activity of the fluid, and an outlet tube connecting the outlet to the monitors, the flowpath through the unit being such that the time taken for the fluid to pass through the unit is large relative to the time taken for the fluid to pass through the outlet tube so that the activity of the fluid measured by the monitor affords a measure of the of the neutron flux at the locality. In the drawing the irradiation unit 10 comprises a thin walled chamber of magnesium alloy provided with inlets 12 at one end, an outlet 13 at the other end and thin transverse porous partitions 17 in its interior. The outlet 13 and a reference outlet 19 are connected by fine bore capillary tubes housed in a braided cable 21 to counters 22, the outputs of which are compared in unit 23 and fed to a recorder 24. In operation a reduced pressure is maintained at the counters so that gas surrounding unit 10 is drawn through inlets 12 and reaches outlet 13 after about 50 seconds; the gas then takes about one second to travel from the outlet 13 to the counter 22. The gas may be argon or carbon dioxide and may be the reactor coolant. The unit 10 may be lowered into an empty fuel channel of a nuclear reactor by means of cable 21 and winch 29, and to scan the flux distribution along the channel the wind may be operated to cause the unit 10 to move up or down the channel at a constant speed, e.g. 0. 3 cm/sec., with continuous recording of the activity of the fluid passing through it. A plurality of units may be provided at various localities in the reactor core. The fluid passing through the irradiation unit need not be the reactor coolant or the gas surrounding the unit; a conduit may join outlet 19 to inlets 12 so that activatable fluid can be supplied through one of the capillary tubes in cable 21.