International Journal of Nuclear Energy Science and Engineering (IJNESE) Volume 5, 2015 doi: 10.14355/ijnese.2015.05.001
www.ijnese.org
Thermal Performance of UO2‐BeO Fuel during a Loss of Coolant Accident Shripad T. Revankar1,2, Wenzhong Zhou3, Deepthi Chandramouli1 School of Nuclear Engineering, Purdue University, 400 Central Drive, West Lafayette, IN 47907 USA
1
Division of Advanced Nuclear Engineering, Pohang University of Science and Technology, Pohang, Gyeongbuk 784‐790, Republic of Korea 2
Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon Tong, Hong Kong 3
*1
shripad@purdue.edu; 2wenzzhou@cityu.edu.hk; 3deepthi1223@gmail.com
Abstract A ceramic‐ceramic composite nuclear fuel consisting of UO2 as matrix and BeO additive has high thermal conductivity compared to UO2. In this study performance of UO2‐BeO composite under transient conditions such as loss of coolant accident (LOCA), using RELAP5 code was carried out. To model performance of this composite, the thermo‐physical properties such as thermal conductivity, specific heat capacity and specific enthalpy were modified to account for the presence of the 10% volume BeO in UO2. Simulation were carried out with REPLAP5 MOD3.3 code for pressurized water reactor (PWR) with 2% cold leg break to study temperature patterns, pressure, core water level and void fraction. Results from RELAP‐5 showed about 20% drop in average fuel temperatures of UO2‐BeO composite fuel compared UO2 fuel. Keywords UO2‐BeO Composite Fuel; Enhance Thermal Conductivity; Thermal Performance; RELAP5 MOD3.3; LOCA
Introduction Nuclear power plants currently use UO2 as a primary nuclear fuel which has demonstrated several desirable characteristics including high melting point, fission gas retention and stability under irradiation. But UO2 has a low thermal conductivity that leads to a large centreline temperature and high temperature gradient across the fuel pellet. This limits the operational performance of the reactor due to thermal stresses causing pellet cladding interaction and the release of fission product gases (Belle 1961, Holden 1966, Frost 1982, Bailly et al. 1999). As a solution to this, enhanced thermal conductivity nuclear fuel have been proposed to decrease fuel temperatures and improve reactor performance. Decrease in fuel temperatures facilitates reduction in pellet‐cladding interaction through lessening thermal stresses that result in fuel cracking, relocation, and swelling, and decrease in fission gas release allowing for higher fuel burn‐up (Frost 1982, Bailly et al. 1999). Some developments on high thermal conductivity fuel have considered UO2, UO2‐ThO2 or UO2‐ PuO2 ceramic particles dispersed in a stainless steel or zirconium alloy metal matrix (Lambert 1966, Frost 1982, Revankar 2001, McDeavitt, et al. 2002), and aligned metal fibres dispersed in a ceramic fuel matrix (Rust and Boyle 1972). There are also developments of ceramic‐ceramic composite fuel where a small fraction of compatible and high thermal conductivity ceramic such as SiC and BeO is added to UO2. In this regard UO2‐BeO composite fuel has been considered for many years and has been studied for its performance with different fractions of BeO in UO2 including irradiation (Titus and Saling 1963, Johnson and Mills 1963, Manly 1964, Goodjohn 1964, Nishigaki and Maekawa 1964, Hanna et al. 1964, Mills et al. 1964, Freed et al. 1965, Ishimoto et al 1996). Recently Solomon et al. (2005) have developed UO2‐BeO fuel using green granules method and have found that this composite fuel with 10% vol. BeO has enhanced thermal conductivity up to 50% higher than UO2 fuel. This composite fuel has been studied by Sharma et al 2006, Latta et al. 2008, McCoy and Mays 2008, Revankar and Zhou 2009, McDevitt et al. 2010, 2011, and Chandramouli and Revankar 2014. These authors have experimentally studied UO2‐BeO fuel thermal performance and have performed computational studies on
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