Method and apparatus for determination of the content of fissionable material in from nuclear reactor fuel assemblies or fuel samples taken

摘要

1,235,324. Measuring fuel element fissile material content. KERNFORSCHUNGSANLAGE JULICH G.m.b.H. June 11, 1968 [June 22, 1967], No. 27761/68. Heading G1A. [Also in Divisions G4-6] The amount of usable fissile material remaining in a fuel element is determined by removing the element from the reactor, irradiating the element to produce short-lived fission products, and then comparing the drop in activity over a predetermined time with that for a similarly irradiated element of known fissile material content. In the arrangement of Fig. 3, a fuel element is removed from the reactor 18 and conveyed to a station 19 where a rough activity measurement is carried out and moderator elements are separated from it for return on line a to the reactor. The fuel element is conveyed through the reactor on line b where on passage through station 20 it is irradiated. The element then passes through the activity measurement stations A, B, where the activity drop over a short time of the fission products formed during the irradiation, is measured. In the arrangement shown, this comprises two scintillation counters, the time taken for the element to be conveyed from one to the other, constituting the predetermined time over which the activity drop occurs. Alternatively, the activity at two separate times is measured by the same scintillation counter. The activity drop is compared with that for a fuel element of known fissile material content to decide at station 21, if the element is to be returned, on line e, to the reactor, or rejected, at d. Timing and sequencing are controlled by arrangement 22. The alternative activity measurement arrangements are described in detail with reference to Figs. 1 and 2 (not shown). In the two detector arrangements, the detector outputs feed amplifers (8), pulse energy discriminators (10) and counters (11), the difference of the two outputs being recorded in data processing unit (12), being modified by the output of dead-time analysis (9). The arrangement has facility for dealing with a sequence of samples. All calculations are carried out in data processing unit (12). In the single detector arrangement, the counts are printed out (17) for subsequent evaluation manually or recorded on a reversible counter. The fuel elements may be rotated in front of the detector collimator, during measurements.