Powder sandwich technique: A novel method for determining the thoron emanation potential of powders bearing high 224Ra content

A new methodology has been developed to measure Rn-220 (thoron) emission from Ra-224-bearing powders handled in nuclear fuel cycle. In this method, a 'powder sandwich' is made by enclosing the powder in between two filter papers in sandwich geometry. This arrangement ensures that the thickness of powder sample is much less than the thoron diffusion length, avoiding any loss of thoron due to matrix absorption and supports complete removal of thoron gas emanated from the powder. The technique utilizes a closed loop setup in which thoron emanated from the powder sandwich is removed using flow through arrangement and is measured using suitable thoron detector. The thoron mass exhalation rate for the powder is estimated using a mass balance model from the measured equilibrium thoron concentration. Subsequently, the thoron emanation coefficient is estimated using the thoron mass exhalation rate and Ra-224 content of the powders. The applicability of the methodology has been demonstrated for three different powders. (C) 2012 Elsevier Ltd. All rights reserved.