Gammaspectrometry of R139-66/3

A continuous series of irradiation experiments, with steel specimens for determination of post-irradiation mechanical properties of various steels and weld materials, is being performed within ECN materials testing programme on nuclear construction materials during many years. The recent irradiation experiments R139-66/1-4 are different from previous ones in that they contain about 6 times as many specimens as usual capsules do. Specimens are densily packed in open holders, such that the specimens are cooled by means of direct contact within the primary coolant water of the HFR. For detailed monitoring of irradiation conditions (temperature, neutron flux distribution and thermal to fast neutron flux density ratio) of the specimens, the capsules are extensively instrumented with thermocouples, monitors for neutron metrology and scan wires. The latter for additional gamma spectrometry measurements to determine the gradient of the thermal and fast flux distribution along the vertical length of the capsules (length of the specimen stack). The 4 experiments of the 66 series are fully identical with the exception of target dose levels (irradiation periods). Two experiments, 66/1 and 66/4, are targeted at dose level 5 dpa (more than one year of continuous irradiation) and the other two experiments, 66/2 and 66/3, are aimed at 0.5 dpa (1 HFR cycle). In this report the results of R139-66/3 are presented. In section 2 a brief description of the gammascan wires is given. A description of the gammascan facility is given in section 3, whereas the experimental results are given in section 4. (author). 2 refs.; 76 figs.; tabs