Nuclear Engineering and Design 239 (2009) 1148–1154 Contents lists available at ScienceDirect Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes Benchmark results for the “BWR-PB” fuel assembly based on pebble-bed coated particles with uranium dioxide and gadolinia poison Abdelfettah Benchrif ∗ , Abdelouahed Chetaine, Hamid Amsil Physic Reactors Group, Department of Physics, Faculty of Sciences, University Mohamed V Agdal, 4 Avenue Ibn Battouta POB 1014, Rabat, Morocco article info Article history: Received 26 September 2008 Received in revised form 29 January 2009 Accepted 6 February 2009 abstract This paper presents an innovative concept for a long life, boiling water reactor with pebble-bed coated particles (BWR-PB), small nuclear reactor without open-vessel refuelling. Small nuclear reactors without the need for on-site refuelling have a greater simplicity, better com- pliance with passive safety systems and are more adequate for countries with small electric grids and limited investment capabilities. Besides, it will help the developing countries to develop their economy, but at the same time these reactors must not lead to the proliferation of a nuclear material, which could be used to fabricate weapons. This study contributes to the evaluation of some neutronic parameters with the aim of predicting both their static and dynamic behaviour before starting on concrete processes, an optimization of fuel assembly parameters for fuel cycle characteristics improvement and a possibility of assembly lifetime extension. In this work, all the parameters as well as infinite multiplication factor, spectrum index, neutron spectra and instantaneous conversion ratio were calculated for the fuel assembly with gadolinia poison and without any poison. The evaluation of this parameters shows that the fuel assembly life time can be extended for a reasonably period without outside refuelling. So, the aim of BWR-PB concept was verified. © 2009 Elsevier B.V. All rights reserved. 1. Introduction To draw more attention to the small and medium sized reac- tors (SMRs) which use the coated particle fuel, the first Research Coordination Meeting of the International Atomic Energy Agency’s Coordinated Research Project (CRP) on “Small Reactors without On- site Refuelling” was held from 21st to 25th November 2005 at the Agency’s Headquarters in Vienna. The small reactors without on- site refuelling are defined as reactors which have a capability to operate without refuelling for a reasonably long period (of 8–30 years), and with any fresh and spent fuel being stored at the site outside the reactor during its service life. In the BWR-PB reactor core calculation, the calculation of an assembly average effective cross-section is required because it is used commonly in core design (Tsuyoshi et al., 2002). The pro- posed concept of an innovative boiling water reactor (BWR-PB) uses a microfuel particle. The latter is a set of small pebble-bed coated particles type TRISO which was originally used in high- temperature gas-cooled reactors (HTGR), and is directly cooled by boiling light water. The microfuel particles are spherical UO 2 ker- nels surrounded by graphite coating layers needed to provide a ∗ Corresponding author. Tel.: +212 6 62 24 71 43. E-mail address: abenchrif@gmail.com (A. Benchrif). fission product containment, and the anti-corrosion barrier to keep water out of the fuel kernel (Senor et al., 2007). The coated part of graphite is selected for a moderation effect. The graphite is helpful to reduce the fuel temperature rise by its large heat capacity in case of a coolant loss accident (Tanihira and Shimazu, 2007). The main advantage of this concept is that the excess reactivity is suppressed during the burn-up cycle by the distribution of burnable poison in the fuel. The burnable poison is a set of gadolinium oxide particles (Gd 2 O 3 ) similar to microfuel ones. In this work, a neutronic study is performed to assess the pos- sibility of an extended life time assembly, and evaluate the fuel assembly parameters during the improvement of the fuel cycle characteristics. 2. Reactor design description and methodology used 2.1. Core design description The core design of BWR-PB reactor is shown in Fig. 1. Distinctive features of the present core are the following: • Internal reservoir for fresh microfuel particles in upper part of reactor vessel. • Internal repository for spent microfuel particles is mounted upon the vessel bottom. 0029-5493/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nucengdes.2009.02.001