Design and development of a new filter head assembly for Continuous Air Monitor (CAM)

Air monitoring plays a vital role in the radiation protection program of any nuclear facility in controlling the internal exposures. Hence a robust and reliable Continuous Air Monitor (CAM) with rapid detection and measurement capabilities become indispensable to promptly warn the workers of any increase in air activity in the work environment. The commercial filter head assemblies, key component in a CAM, have a filter compartment and detector compartment which are coupled together by threaded joints to form the assembly. These metal to metal joints ought to be leak tight to achieve good collection efficiency. It may be noted that the replacement of the filter in the system every shill require opening and closing of the filter heads, resulting in wear and tear, cross threading and consequent leak path. The leak paths developed result in the reduction in collection efficiency which in turn result in increase in the minimum detectable activity of the system, failing to warn the worker at lower levels of air activity. To circumvent this a new CAM filter head was indigenously designed and developed with minimal thread joints, achieving leak tightness by means of jack mechanism. The new CAM filter head is shown. The outer base of the filter head was fabricated using aluminium while the filter and detector compartment was fabricated in S.S.A. commercially available screw jack was used to ensure leak tightness. Leak tightness was tested in the HEPA filter test facility using DOP aerosols. The new design addresses all the problems encountered in the earlier designs and ensures leak tight performance in the long run. Also, operators can change filter papers much easier and faster compared to older mechanisms. The design, development and testing of the new filter head is highlighted in this paper. (author)