Radioactive contamination measurements of the primary sodium pipes in FBTR by gamma spectrometry

Abstract

Gamma spectrometric measurements were carried out in the primary sodium pipes of FBTR, twice during shut down state of the reactor with sodium circulating at 180 °C and once after draining the primary sodium from pipes. However, the first two measurements were mainly the feasibility studies of undertaking gamma spectrometric measurements inside the primary sodium cells and to establish a reference on the build up of radiation field in the cells due to the deposition of radionuclides on the walls of the primary sodium pipelines. For estimating the specific activity of radionuclides in the circulating sodium as well as deposited ones on the interiors of pipes, calibration curves were generated by simulating the geometry conditions. Third spectral measurement was performed after 651 EFPD of reactor operation under two scenarios, sodium circulating at 180 °C and sodium drained out from the primary sodium pipes. The radionuclides observed before draining of sodium are 54Mn, 58Co and 60Co due to corrosion products and 203Hg, 22Na and 24Na due to activation products of coolant and the soluble impurities in it. Trace quantities of 65Zn, 59Fe and 124Sb were also seen. Once the primary sodium is drained from the pipelines, the major radionuclides deposited inside the walls of the pipelines and their specific activities are, 54Mn (17,700 kBq/m 2), 22Na, 60Co and 58Co (∼350 kBq/m 2 each) and 65Zn (250 kBq/m 2). These results indicate that the handling of components for maintenance work inside the cells housing primary sodium pipes, if warranted, is not much of a radiological concern.