Shielding computations for establishing a radial gamma scanning system in RML hot cell

The paper describes the gamma shielding computations of concrete cell, housing the specimens of Fast Breeder Test Reactor (FBTR) MARK I fuel irradiated to a burn up of 155 GWD/T and 150 d cooled, for performing radial gamma scanning (RGSS) through a modified service plug in the wall of hot cell in Radio Metallurgical Laboratory (RML). As per the regulatory requirement the contact dose rates outside the concrete wall shall be ≤ 1 μSv/h in full occupancy areas for performing the experiment. The shielding adequacy checks have been performed using QAD-CGPIC computer code. The computations have been performed for handling a single fuel pin as well as a subassembly housed inside the hot cell, though a cut section (L=10 mm) of the fuel pin will actually be used. It is found that the gamma dose rates just outside the concrete wall along the beam line when a sub-assembly, single fuel pin and its cut section are aligned and are in contact with the plug are 380,1027 and 96.5 μSv/h respectively. At other locations outside the concrete wall, the dose rates are very much below the regulatory limit. (author)