Tetsushi Hino, Masaya Ohtsuka, Renzo Takeda, Junichi Miwa, and Kumiaki Moriya

Abstract The RBWR (resource-renewable boiling water reactor) is an innovative BWR that has a capability to breed and burn trans-uranium elements (TRUs) using a multi-recycling process. The RBWR can be used as a long-term energy supply, and it reduces the negative environmental impact that TRUs cause as they are otherwise long-lived radioactive wastes. Various design concepts of the RBWR core have been proposed. The RBWR-AC is a break-even reactor and the RBWR — TB and RBWR-TB2 are TRU burners. The RBWR-TB is designed to burn TRUs from the RBWR-TB itself and to burn almost all the TRUs by repeating their recycling. The RBWR-TB is assumed to be applied for a nuclear power phase-out scenario. The RBWR-TB2 is intended to burn TRUs from LWR spent fuels. The RBWR-TB2 is assumed to be applied for reducing the amount of TRUs to be managed in storage facilities. The RBWR cores achieve their TRU multi-recycling capability under the constraint that the void reactivity coefficient must be negative by introducing the parfait core concept. This chapter reviews details of the specific design and core characteristics of the RBWR.

Keywords Break-even • Burner • BWR • Multi-recycle • TRU • Void reactivity coefficient

14.1 Introduction

Nuclear-generated electrical power is one irreplaceable candidate energy source that responds to the needs for energy security and for reduction of greenhouse-gas emissions. However, there has also been growing concern that significant amounts

T. Hino (*) • M. Ohtsuka • R. Takeda • J. Miwa

Hitachi, Ltd., Hitachi Research Laboratory, 7-1-1, Omika-cho, Hitachi-shi Ibaraki-ken 319-1292, Japan e-mail: tetsushi. hino. kd@hitachi. com

K. Moriya

Hitachi-GE Nuclear Energy, Ltd., 3-1-1, Saiwai-cho, Hitachi-shi, Ibaraki-ken 317-0073, Japan © The Author(s) 2015

K. Nakajima (ed.), Nuclear Back-end and Transmutation Technology for Waste Disposal, DOI 10.1007/978-4-431-55111-9_14

of trans-uranium elements (TRUs) are becoming long-lived radioactive wastes. If TRUs could be recycled as nuclear fuel, the benefits attained from nuclear power would increase as a long-term energy supply and the negative environmental impact of TRUs as radioactive wastes could be greatly reduced. For these purposes many types of innovative reactors, including the sodium-cooled fast reactor (SFR), have been proposed. The resource-renewable BWR (RBWR) has been proposed to achieve the same purposes using concepts based on proven BWR technologies and the BWR capability to control the neutron energy spectrum flexibly [1—3]. A major characteristic of the BWR is “boiling” in the core, which includes water that functions as both a moderator and a coolant. The neutron energy spectrum can be hardened by reducing the hydrogen-to-uranium ratio (H/U) using the two-phase flow and using the hexagonal tight fuel lattice, so that the transmutation of 238U to fissile plutonium is promoted with increasing resonance absorption: this enables the multi-recycling process of both breeding and consuming TRUs. On the other hand, there is a tendency that the harder the neutron spectrum becomes in the TRU-loaded core, the more positive the void reactivity coefficient becomes. The void reactivity coefficient is one of the main safety parameters for light water reactors (LWRs) and must be negative. The RBWR achieves the TRU multi-recycling capability under the constraint of the negative void reactivity coefficient by introducing the parfait core concept [4].

This chapter reviews details of the specific design and core characteristics of the RBWR.