Indian Journal of Pure & Applied Physics Vol. 56, August 2018, pp. 583-586 Neutron attenuation studies with borated polyethylene slabs containing 30% natural boron and its comparison with hydrogenous materials D Venkata Subramanian*, Adish Haridas, D Sunil Kumar, A John Arul & P Puthiyavinayagam Reactor Design Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India Received 9 May 2018 Providing suitable shielding for neutrons is one of the challenging tasks in fast reactor fuel reprocessing facilities. The shield material should have good moderating and absorbing properties. In order to find cost effective prospective materials, a series of neutron attenuation measurements are performed with hydrogenous materials at the south beam end of Kalpakkam Mini (KAMINI) reactor to understand their attenuation characteristics. In the present experiment, the neutron attenuating properties of borated polyethylene (BPE) containing 30% natural boron have been studied. The thermal and fast neutron flux attenuation characteristics of the material have been compared with 5% and 10% BPE and other hydrogenous materials. The thermal/epithermal neutron flux attenuation obtained with 30% BPE for a thickness of 30 cm is 1.5 times more than 5% and 10% BPE and 10 times more than normal polyethylene. It is also observed that there is no significant difference in the fast flux attenuation of 30%, 10% and 5% BPE. The outcome of the study indicates that if 30% BPE is used instead of normal polyethylene in fuel reprocessing facilities, 50% reduction in volume of shields can be achieved for thermal and epithermal neutron flux attenuation and 16 to 22% reduction in volume shields for fast neutron flux attenuation. Keywords: KAMINI, Borated polyethylene, Polyethylene, Neutron flux, Attenuation 1 Introduction A shield is interposed between source of radiation and the object to protect and to mitigate the radiation damage. Selection of shield for a particular application depends on the type of radiation and its energy dependent cross sections. For gamma ray shielding, high Z materials (like lead, tungsten, etc) are utilized and for attenuating neutrons, moderating (low Z) and absorbing (like boron, cadmium, etc) materials are preferred. Designing cost effective low volume shields for different types of radiations, especially for neutrons is a strenuous task. To understand the neutron attenuation characteristics of shield materials, a series of experiments are performed at the south beam end of KAMINI reactor. Apart from prospective shield materials such as ferro boron 1 , ferro tungsten 2 etc., hydrogenous materials are also studied. Hydrogen content in hydrogenous materials makes thema better neutron shield at lower temperatures (<80 o C). They have potential shielding applications in the fast reactor fuel cycle facility (FRFCF) being built at Kalpakkam and also in irradiated material shipping casks. The present experimental study was conducted with 30% BPE blocks. BPE is a product typically used forradiation shielding applications. It is made from high density polyethylene plastic with various boron weight percentages ranging from 5% to 30%. It is available in standard-sized sheets as well as in blocks, slabs, and custom-size sheets. BPE is easy to work with, fabricate, and install, making it ideal for shielding applications. The experiment was conducted by stacking 30% BPE slabs of thickness 40 cm at the south beam end of KAMINI reactor. KAMINI is a 233 U‑fueled, light water moderated; natural convection cooled, and beryllium oxide reflected research reactor. It is located at the Indira Gandhi Centrefor Atomic Research, Kalpakkam, India. Because of the highly efficient reflector material BeO, it has a very low fuel inventory (~612 g). The reactor is designed to operate at a nominal power of 30 kW. The neutron flux available atthe South beam end is ~10 6 –10 7 n/(cm 2 s). Various activation foils 3 were fixed in between the BPE slabs and activated when subjected to neutron flux. The measurement of their induced activities at different locations and their ratios provided information on the neutron flux attenuation behavior of thermal, epithermal and fast neutrons with respect to BPE containing 30% natural boron. ——————— *Corresponding author (E-mail: dvs@igcar.gov.in)