P. G. BOCZAR, IndependentConsultant(formerlyDirector, Reactor Core Technology Division, Chalk River Laboratories, AECL), Canada

Abstract: This chapter begins with a description of the CANDU reactor, describing the main plant features, its fuel and fuel cycle and the control and safety aspects of the reactor. The chapter then summarizes evolutionary trends in the reactor design, followed by a discussion of the advanced fuel cycles that could be employed in existing or future CANDU reactors, including LEU, recovered uranium, DUPIC, MOX, actinides and thorium.

Key words: CANDU, EC6, ACR-1000, advanced CANDU reactor, SCWR, supercritical water reactor, advanced fuel cycles, recovered uranium, MOX, thorium, actinide burning.

11.1 Introduction

A distinguishing feature of the CANDU®[19] power reactor is its use of natural uranium fuel. This fuel has many advantages, including simplicity, low fuel cycle cost, high uranium utilization and ease of fuel manufacturing localization. In the back-end of the fuel cycle, the higher volume of used nuclear fuel is offset by lower decay heat and radiotoxicity compared to used LWR fuel (Boczar et al, 2010). The Advanced CANDU Reactor™ (ACR-1000™[20]) and the heavy-water moderated, pressure-tube supercritical-water-cooled reactor (PT-SCWR) represent evolutions of the traditional CANDU design. The features of the CANDU reactor that enable the use of natural uranium fuel also facilitate the use of a wide variety of fuels and fuel cycles, including recovered uranium (RU) from reprocessed light water reactor (LWR) fuel, low enriched uranium (LEU), MOX, minor-actinide bearing fuels and thorium. Fuel cycle flexibility is hence another hallmark of the CANDU design. While there are several variants of the CANDU reactor design, this chapter will use the 700 MWe-class CANDU 6 reactor for illustration (AECL, 2005) with the 37-element fuel bundle. (In terminology, a CANDU fuel element is equivalent to an LWR fuel rod; a CANDU fuel bundle is equivalent to an LWR fuel assembly, although much smaller.)