Contents lists available at ScienceDirect Atmospheric Research journal homepage: www.elsevier.com/locate/atmosres Study on CCN activity of fission product aerosols (CsI and CsOH) and their effect on size and other properties Gaurav Mishra a , S.N. Tripathi b,c, ⁎ , T. Saud d , Manish Joshi e , Arshad Khan e , B.K. Sapra e a Nuclear Engineering and Technology Programme, Department of Mechanical Engineering, IIT Kanpur 208016, India b Department of Civil Engineering, IIT Kanpur 208016, India c Centre for Environmental Science and Engineering, IIT Kanpur 208016, India d National Aerosol Facility, IIT Kanpur 208016, India e Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Mumbai 400085, India ARTICLE INFO Keywords: CCN Cloud Condensation Nuclei CsI CsOH Fission product aerosols ABSTRACT This paper discusses the size resolved cloud condensation nuclei (CCN) properties of two cesium bound com- pounds viz. CsI and CsOH. These properties are important in context of risk analysis and management of probable environmental releases during postulated nuclear reactor accident conditions. If released as fission product aerosols, these particles have potential to act as CCN, when exposed to humid environment. On acti- vation, their evolution-deposition dynamics and consequently fate is expected to be affected in closed and/or open atmosphere. Size resolved CCN efficiency spectra (20–300 nm) are obtained for 0.2–1% supersaturation (SS) for pure CsI and CsOH particles employing a DMT-CCN counter. The essential parameters estimated from these measurements are activation diameter and size-averaged hygroscopicity (κ) at targeted SS levels. Experimental results were also compared with the standard theories available in the literature. Accuracy of the deposition rates for these particles (if released) in reactor component systems estimated by nuclear reactor accident analyses codes will improve when CCN properties are also taken into account. CCN efficiency spectra and activation diameters at specific SS for CsI and CsOH particles are being reported for the first time. Information on these properties strengthen the database which is vital for simulating behavioral characteristics of these particles. This in turn has capability to improve environmental source term estimations in the most unlikely scenario of containment breach during severe reactor accident conditions. 1. Introduction In the event of a postulated nuclear reactor accident, the core of the reactor melts and fission products are released rapidly through the re- actor coolant system to the containment building. In the containment, the aerosols of fission products may grow in the humid atmosphere and eventually settle onto the floor and water pools (Jokiniemi, 1988). In such an accident, the worst scenario is containment failure, where the integrity of the reactor building is lost soon after the accident before the fission products have had time to settle. An estimate reveals that as much as 80% of the fission products released from the reactor core may get deposited to the surfaces of the primary coolant circuit (Wright, 1994). Due to the decay heat of the reactor fuel, the deposited fission products may release at a later stage of an accident and emerge from the reactor coolant system days or even weeks after the accident (Wright, 1994). In case of a late containment failure it could lead to a major release of volatile fission products like cesium, iodine and tellurium to the environment. Radioactive cesium, contributes to both external and internal ra- diation doses, has a half-life of 30 years and has contaminated > 2,00,000 km 2 of Europe after Chernobyl Disaster (Ramana, 2006). Studies have shown that around 6% of the European territory has been contaminated for more than 20kilo - becquerel/m 2 after the Chernobyl accident. The total amount of deposited cesium-137 in Europe is 8 * 10 16 becquerel and the major part of this amount affects European countries in the following manner: Belarus 33.5%, Russia 24%, Ukraine 20%, Sweden 4.4%, Finland 4.3%, Bulgaria 2.8%, Austria 2.7%, Norway 2.3%, Romania 2.0%, Germany 1.1% (Izrael et al., 1996). Vast studies have been done in order to understand the effect of cesium in food chain, air, water and soil contamination as well as on livestock after Chernobyl Disaster (Paasikallio et al., 1994; Thomas and Martin, 1986; Mattsson and Moberg, 1991; Davidson et al., 1987; Lavi et al., 2006; Vakulovsky et al., 1994; Koulikov and Ryabov, 1992). Radionuclides of cesium were identified in large amounts at https://doi.org/10.1016/j.atmosres.2019.104816 Received 8 July 2019; Received in revised form 7 November 2019; Accepted 19 December 2019 ⁎ Corresponding author at: Department of Civil Engineering, IIT Kanpur 208016, India. E-mail address: snt@iitk.ac.in (S.N. Tripathi). Atmospheric Research 236 (2020) 104816 Available online 24 December 2019 0169-8095/ © 2019 Published by Elsevier B.V. T