Nuclear Engineering and Design 240 (2010) 2066–2074 Contents lists available at ScienceDirect Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes Utilization of TRISO fuel with reactor grade plutonium in CANDU reactors Sümer S ¸ ahin a,∗ , Hacı Mehmet S ¸ ahin b , Adem Acır b a ATILIM University, Faculty of Engineering, Department of Mechanical Engineering, 06836 ˙ Incek, Gölbas ¸ ı, Ankara, Türkiye 1 b Gazi University, Faculty of Technology, 06503 Teknikokullar, Ankara, Türkiye article info Article history: Received 31 December 2009 Received in revised form 5 April 2010 Accepted 9 April 2010 This paper is dedicated to the memory of beloved Prof. Dr. Necmettin HACIEM ˙ INO ˘ GLU (1933–1996), University of ˙ Istanbul, ˙ Istanbul, Türkiye. abstract Large quantities of plutonium have been accumulated in the nuclear waste of civilian LWRs and CANDU reactors. Reactor grade plutonium and heavy water moderator can give a good combination with respect to neutron economy. On the other hand, TRISO type fuel can withstand very high fuel burn-up levels. The paper investigates the prospects of utilization of TRISO fuel made of reactor grade plutonium in CANDU reactors. TRISO fuels particles are imbedded body-centered cubic (BCC) in a graphite matrix with a volume fraction of 68%. The fuel compacts conform to the dimensions of CANDU fuel compacts are inserted in rods with zircolay cladding. In the first phase of investigations, five new mixed fuel have been selected for CANDU reactors com- posed of 4% RG-PuO 2 + 96% ThO 2 ; 6% RG-PuO 2 + 94% ThO 2 ; 10% RG-PuO 2 + 90% ThO 2 ; 20% RG-PuO 2 + 80% ThO 2 ; 30% RG-PuO 2 + 70% ThO 2 . Initial reactor criticality (k ∞,0 values) for the modes , , , and are calculated as 1.4294, 1.5035, 1.5678, 1.6249, and 1.6535, respectively. Corresponding operation lifetimes are ∼0.65, 1.1, 1.9, 3.5, and 4.8 years and with burn ups of ∼30 000, 60 000, 100 000, 200 000 and 290 000 MW d/tonne, respectively. The higher initial plutonium charge is the higher burn ups can be achieved. In the second phase, a graphical-numerical power flattening procedure has been applied with radially variable mixed fuel composition in the fuel bundle. Mixed fuel fractions leading to quasi-constant power production are found in the 1st, 2nd, 3rd and 4th row to be as 100% PuO 2 , 80/20% PuO 2 /ThO 2 , 60/40% PuO 2 /ThO 2 , and 40/60% PuO 2 /ThO 2 , respectively. Higher plutonium amount in the flattened case increases reactor operation lifetime to >8 years and the burn up to 580 000 MW d/tonne. Power flattening in the bundle leads to higher power plant factor and quasi-uniform fuel utilization, reduces thermal and material stresses, and avoids local thermal peaks. Extended burn-up grade implies drastic reduction of the nuclear waste material per unit energy output for final waste disposal. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Alternative fuels can open new dimensions for conventional nuclear reactors with well established technology and long oper- ational experiences. One of the primary interests is to reduce plutonium inventories, because of the serious public and political concern in the world about misuse of this plutonium and about acci- dental release of highly radiotoxic material in to the environment. Over the past 50 years, nuclear power plants have been accumu- lating reactor grade plutonium (RG-Pu) in form of nuclear waste exceeding 1700 tonnes. In that respect, various studies have been performed for Canada Deuterium Uranium (CANDU) reactors. Previous work has investigated the incineration of plutonium in CANDU reactors in ∗ Corresponding author. Tel.: +90 312 586 43 04; fax: +90 312 212 43 04. E-mail address: ssahin@atilim.edu.tr (S. S ¸ ahin). 1 http://www.me.atilim.edu.tr/show staff.php?lang=en&id=40. combination with thorium extensively in detail (S ¸ ahin et al., 2004a, 2006a,b,c, 2008). It has been shown that plutonium would supply the initial reactor criticality and then thorium will bred sufficient 233 U to keep the reactor operational over very long periods and extended burn up due to the unique feature of higher neutron econ- omy of CANDU reactors. It was calculated that only a small amount of RG-PuO 2 (∼4%) mixed with 96% ThO 2 would allow very long operation periods (>8 years) with unprecedented high burn-up values (>160 000 MW d/tonne) (S ¸ ahin et al., 2006a). Conventional CANDU reactors use nuclear fuel in form of pellets in zircolay cladding. It was pointed out that conventional reactor fuel rods would not withstand such high burn ups due to the swelling prob- lems arisen from the gaseous fission products and fuel deformation. A conservative recommendation was to renew the fuel rods peri- odically, coupled with a simplified reprocessing after certain burn ups, such as 50 000–60 000 MW d/tonne (S ¸ ahin et al., 2006a). On the other hand, high temperature reactor (HTR) fuel can withstand very high burn ups. One of the primary candidates as HTR fuel is known as TRISO fuel. Along with the intensive 0029-5493/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nucengdes.2010.04.008