Advanced fuel cycles for use in PHWRs H.P. Gupta * , S.V.G. Menon, S. Banerjee Theoretical Physics Division, Central Complex, Bhabha Atomic Research Centre, Mumbai 400 085, India article info abstract Pressurized heavy water reactors (PHWRs) were originally designed for employing once through fuel cycles with natural uranium. The excellent neutron economy and on-line fueling due to limited excess reactivity are important characteristics of these reactors. However, PHWRs have the main drawback of low burn-up, approximately 7500 MWd/T, due to the use of natural uranium. Use of neutron absorbers for control and power flattening further deteriorates the burn-up. All these aspects, specific to PHWRs, also lead to management of large quantities of: (i) initial fuel (ii) irradiated fuel, and (iii) radioactive wastes. Some of these drawbacks can be alleviated with high burn-up fuel, which also improves fuel uti- lization. Slightly enriched uranium and plutonium have been under consideration for this purpose. In situ production of U 233 , by using thorium along with appropriate fissile feed, is one possibility. Alternatively, U 233 can be generated externally in fast breeder reactors. It has been recognized that, when used along with thorium, PHWRs can also serve as efficient burners of excess plutonium accumulated over the years. Fuel cycles have been designed so as to completely reverse the isotopic composition (fissile to fertile ratio) which exists at the beginning of a cycle. These cycles also envisage producing proliferation resistant fuels containing high gamma-active decay products. Most of the reactor physics aspects of the various fuel cycles can be analyzed using simple methods of neutron physics and fuel burn-up. Multi-group tech- niques and explicit representations of the PHWR cluster geometry are essential. However, core physics and fuel management calculations can be simplified at an exploratory stage. Nevertheless, it is necessary to make sure, using core analyses, that the new fuel cycles do satisfy all the constraints of flux peaking, controllability, coolant void reactivity, etc. The main aim in this paper is to provide a comparative eval- uation of the various advanced fuel cycles that are feasible in PHWRs. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Nuclear power is once again in great demand due to the grow- ing energy needs of the world population, particularly in the devel- oping countries. The limited availability and environmental issues associated with fossil fuels are other contributing factors [1]. Two types of thermal reactor systems, namely, the light water reactors (LWRs), which include both pressurized water reactors (PWRs) and boiling water reactors (BWRs), and PHWRs, have been developed well and commercially proven. While PWRs requires about 3% U 235 enrichment, PHWRs use natural uranium together with heavy water as moderator. Enhanced neutron economy of PHWRs, because of the negligible neutron absorption in heavy water, is one of its important characteristics. Even so, natural ura- nium provides only a small excess reactivity and hence low burn- up, thereby leading to on-power fueling. These aspects, specific to PHWRs, also require large quantities of initial fuel. As a result, it also produces large quantities of irradiated fuel and radioactive wastes. Use of neutron absorbers for control and power flattening further deteriorates the fuel burn-up. On-line fueling provides sev- eral possibilities in introducing new fuel cycles, even though it generates a few operational and engineering problems associated with the fueling machine. The above considerations lead to a genuine interest in extend- ing burn-up in PHWRs, which can be done by increasing the fissile content in the fuel. Slightly enriched uranium and plutonium have been under consideration for this purpose. Several other possibili- ties emerge with the Th–U 233 cycles. In situ production of U 233 , by using thorium along with appropriate fissile feed, is one such pos- sibility. Alternatively, U 233 can be generated externally in fast bree- der reactors. Due to the good neutron economy, PHWRs also show the possibility of self-sustained Th–U 233 cycles, however with lower burn-up. Lastly, there is the possibility of using spent fuel from PWRs, containing nearly 1.56% fissile material, in PHWRs, thereby reduc- ing the waste burden. There is no reprocessing in the DUPIC fuel, except removing the volatile fission products [2]. However, in the TANDEM cycle, uranium and plutonium together are separated and blended with Nat-U [3]. 0022-3115/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2008.08.004 * Corresponding author. Tel.: +91 22 2559 3779; fax: +91 22 25505151. E-mail address: hpgupta@barc.gov.in (H.P. Gupta). Journal of Nuclear Materials 383 (2008) 54–62 Contents lists available at ScienceDirect Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat