II — l. Introduction

The Indian nuclear power program consists of three stages. The first stage envisaged setting up of pressurized heavy water reactors (PHWRs) and the necessary fuel cycle facilities. Comprehensive capability in the design, construction, and operation of PHWR has been achieved. The second stage envisages development of fast breeder reactors using Plutonium and Depleted Uranium obtained from the first stage. Fast breeder test reactor (FBTR) has been operated successfully for 21 years and the construction of 500 Mw(e) prototype fast breeder reactor (PFBR) has started. The third stage aims at the development of reactors based on Uranium-233 obtained from irradiated thorium. The Kamini reactor uses Uranium-233 as a fuel and has operated since 1995. To transition to thorium based systems, an advanced heavy water reactor (AHWR) is being developed at Bhabha Atomic Research Centre.

The Bhabha Atomic Research Centre (BARC), located in Mumbai, is the premier multidisciplinary nuclear research centre of India having excellent infrastructure for advanced research and development. It has expertise covering the entire spectrum of nuclear science, engineering, and related areas. Detailed design, research, and development work on AHWR is being conducted in BARC.

The AHWR is a 300 MW(e) boiling light water cooled, heavy water moderated, vertical pressure tube type reactor designed to produce most of its power from thorium with an associated 500 m3/day capacity desalination plant. The core consists of (Th-U233) O2 and (Th-Pu)O2 fuel. A simplified sketch of the reactor is depicted in Fig. III-1. Some important features of the reactor are given below.

• Thorium based fuel with a negative void coefficient of reactivity,

• Advanced coolant channel design with easily replaceable pressure tubes,

• Passive systems for core heat removal (under both normal operating and shutdown condition), containment cooling and containment isolation,

• Direct injection of ECCS water into fuel bundle,

• Accumulator for high pressure ECC,

• Gravity driven water pool (GDWP) at high elevation,

• No emergency planning in public domain,

• Design life of 100 years,

• Associated desalination plant.

A number of passive systems that utilize natural circulation have been incorporated in AHWR. Some of them are briefly described below.