[en] The possibility of decreasing the reactivity drop in the TVR-M modernized heavy water cooled reactor for the time between fuel reloadings using a burnable absorber is studied. Natural gadolinium is applied as burnable absorber material. It is placed in a form of a rod or a bush in the center of a fuel assembly. Geometry and gadolinium amount ensuring the least devivations in the multiplication factor during the reactor operating cycle are determined. It is shown that the multiplication factor variation for the period between fuel reloadings is to be a mnnimum one if rods with gadolinium of the greatest size are used. A noticeable effect on the calculation results is exerted by the neutron spectrum hardness value which in a reactor of small dimensions differs from the cell hardness. The spectrum adjustment can be realized by varying a moderator amount in a cell