Technical note Adaptive fuzzy system for fuel rod cladding failure in nuclear power plant Antonio C.F. Guimara ˜es * , Celso M.F. Lapa Instituto de Engenharia Nuclear – Divisa ˜o de Reatores/CNEN, Ilha do Funda ˜o s/n, 21945-970, P.O. Box 68550, Rio de Janeiro, Brazil Received 14 July 2006; received in revised form 16 August 2006; accepted 30 November 2006 Available online 1 February 2007 Abstract A new approach to the study of ballooning that causes cladding failure in fuel rods using an adaptive neural fuzzy inference system (ANFIS) is presented in this paper. By mapping input/output patterns describing cladding failure phenomena through average inner cladding temperature and fuel rod gas pressure, ANFIS shows a great potential to modeling this problem in alternative to the traditional approach. A typical pressurized water reactor fuel rod data was used to this application. The results confirm the potential of ANFIS comparatively to experimental calculations. Ó 2007 Elsevier Ltd. All rights reserved. 1. Introduction Artificial intelligence (AI) approaches and methodolo- gies have been successfully applied to many complex prob- lems related to project, operation and improvement of the safety level in nuclear power plants. In Guimara ˜es (2003a) was used the fuzzy logic methodology to establish inservice inspection priorities for nuclear components. In Guimara ˜es (2003b) was developed a new methodology for the study of flow accelerated corrossion (FAC) phenomenon based on a fuzzy rule system. In Guimara ˜es and Lapa (2004a) were studied the effects analysis fuzzy inference system in nuclear problems using approximate reasoning. In Guimara ˜es and Lapa (2004b) was considered the fuzzy inference system for evaluating and improving nuclear power plant operating performance. Now, loss of coolant of accident (LOCA) in nuclear power plant (NPP) and subsequent straining and ballooning of the cladding with failure from excessive strain or departure from nucleate boiling has motivated the development of a new approach in AI. A light water reactor (LWR) fuel rod typically consists of UO2 fuel pellets enclosed in Zircaloy cladding, as shown in the Fig. 1 (Cunningham et al., 2001a). The primary func- tion of the cladding is to contain the fuel column and the radioactive fission products. If the cladding does not crack, rupture, or melt during a reactor transient, the radioactive fission products are contained within the fuel rod. During some reactor transients and hypothetical accidents, how- ever, the cladding may be weakened by a temperature increase, embrittled by oxidation, or over stressed by mechanical interaction with the fuel. These events alone or in combination can cause cracking or rupture of the cladding and release of the radioactive products to the coolant. Furthermore, the rupture or melting of the clad- ding of one fuel rod can alter the flow of reactor coolant and reduce the cooling of neighboring fuel rods. This event can lead to the loss of a ‘‘coolable’’ reactor core geometry. More detailed descriptions can be found in Cunningham et al. (2001a). The pressure of the gas in the fuel rod must be known in order to calculate the deformation cladding and the trans- fer of heat across the fuel-cladding gap. The pressure is a function of the temperature, volume and quantity of gas. Because the temperature is spatially non-uniform, the fuel rod must be divided into several smaller volumes so that 0306-4549/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.anucene.2006.11.012 * Corresponding author. Tel.: +55 21 22098080; fax: +55 21 22098259. E-mail addresses: tony@ien.gov.br (A.C.F. Guimara ˜es), lapa@ien. gov.br (C.M.F. Lapa). www.elsevier.com/locate/anucene Annals of Nuclear Energy 34 (2007) 233–240 annals of NUCLEAR ENERGY