Development and applications of energy-specific fluence monitor for field monitoring D.N. Krishnakumar n , K.M. Somayaji, R. Venkatesan, V. Meenakshisundaram Radiological Safety Division, Radiological Safety and Environmental Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamilnadu, India article info Article history: Received 18 January 2011 Accepted 31 January 2011 Available online 1 March 2011 Keywords: CsI detector Radiation instrument Argon plume dispersion Environmental survey abstract A portable energy-specific fluence monitor is developed for field monitoring as well as to serve as stand- alone data acquisition system to measure dose rate due to routine releases at various locations in and around Nuclear Power Reactors. The data from an array of such monitors deployed over a region of interest would help in evolving a methodology to arrive at the source term evaluation in the event of a postulated nuclear incident. The other method that exists for this purpose is by conducting tracer experiments using known release of a gas like SF 6 into the atmosphere and monitoring their concentrations downwind. The above instrument enables one to use the routine release of 41 Ar as a tracer gas. The Argon fluence monitor houses a CsI(Tl) detector and associated miniature electronics modules for conditioning the signal from the detector. Data logging and in-situ archival of the data are controlled by a powerful web enabled communication controller preloaded with Microsoft Windows Compact Edition (WIN CE). The application software is developed in Visual Basic.NET under Compact Framework and deployed in the module. The paper gives an outline of the design aspects of the instrument, associated electronics and calibration of the instrument, including the preliminary results obtained using the instrument. The utility of the system is established by carrying out field survey around Madras Atomic Power Station (MAPS), consisting of two Pressurized Heavy Water Reactors (PHWR), by mapping the 41 Ar plume. Additional features such as enhancing the monitor capability with embedded GPS along with real-time linking using wireless networking techniques are also being incorporated. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction Model prediction of environmental dose rates from an atmo- spheric release of radioactive materials relies on the availability of meteorological dispersion parameters and the information on the amount and composition of the release (source term). During a radiological emergency, the source term may not be directly accessible. In this case, off-site radiation monitoring data may be used to provide the estimate of the source term. Dose rate monitors placed around nuclear installations provide on-line data, which can be used to estimate the source term (Martin Drews et al., 2004). While dispersion models run with current meteor- ological parameters injected in real time, actual dose rate monitor- ing at various locations in the site would give us a methodology to estimate source term during radiological emergency. Data received from such measurement can be used to test atmospheric disper- sion and dose rate models. A source term estimation methodology was evolved by working back from a number of field measure- ments of dose rate, knowing the site specific atmospheric parameters (Bent Lauritzen et al., 2003). Studies revealed that the method for estimation of atmospheric dispersion of radionuclides from a nuclear research reactor using a set of experimental radiation monitoring data from 41 Ar releases was found to provide good estimates with theoretical values (Martin Drews et al., 2005). The Kalpakkam site is located at the east coast of India at 12.5011N and 80.1011E. It consists of two Pressurized Heavy Water Reactors that release 41 Ar in controlled quantities through a stack of 100 m height. A Prototype Fast Breeder Reactor (PFBR) is also being constructed in the site. Analysis of the environmental radiological impact under design-based probable accidental releases for any proposed nuclear plant is a regulatory requirement and therefore, as a part of it, a study of atmospheric dispersion of radionuclides and the consequent dose to the public is carried out (Srinivas and Venkatesan, 2005) The meteorological condition at Kalpakkam, like any coastal site, is non-stationary and non-homogeneous due to thermally driven land–sea breeze circulation, which gives rise to a variety of complex atmospheric dispersion conditions. Ground level concentration and sky-shine dose due to radio- active emissions from a nuclear power plant at a coastal site have been estimated using the standard Gaussian Plume Model (GPM) and the modified GPM suggested by Misra (1980), which incorpo- rates fumigation effect under sea breeze condition. The difference in results between these two models is analyzed in order to Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/apradiso Applied Radiation and Isotopes 0969-8043/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2011.01.042 n Corresponding author. Tel.: + 91 44 27480062; fax: + 91 44 27480235. E-mail addresses: nkkumar@igcar.gov.in, krishnakumard@yahoo.com (D.N. Krishnakumar). Applied Radiation and Isotopes 69 (2011) 1039–1045