Bhabha Atomic Research Centre,

India

V — 1. DESCRIPTION OF THE AHWR DESIGN

The Advanced Heavy Water Reactor (AHWR) is a concept for a 300 MW(e), vertical pressure tube type reactor cooled by boiling light water and moderated by heavy water. The AHWR design is being developed by the Bhabha Atomic Research Centre (BARC, India). The reactor is designed to be fuelled with (U233-Th)O2, together with (Pu-Th)O2. In this, the AHWR would be nearly self-sustaining in U233. The design of the AHWR is fine tuned to derive most of its power from thorium based fuel, while achieving a negative void coefficient of reactivity. A detailed description of the AHWR concept and its design status can be found in [VI-1].

The general arrangement of the AHWR is shown in Fig. VI-1. Heat removal from the core is achieved by natural circulation of the coolant. The core consists of vertical fuel channels housed in a calandria containing the heavy water moderator.

The calandria is located in a water filled reactor cavity. The core is connected to four steam drums. A large water pool, called the gravity driven water pool (GDWP), is located near the top of the containment. Moderator heat is utilized for feedwater heating. As shown in Fig. VI-2, double containment is provided to prevent any release of radioactivity to the environment.

The fuel assembly is suspended from the top into the coolant channel of the reactor. The assembly consists of a single, long fuel cluster (see Fig. VI-2) and two shield sub-assemblies. The cluster has 54 fuel pins arranged in three concentric rings, 12 pins in the inner ring, 18 pins in the intermediate ring, and 24 pins in the outer ring

FIG. VI-1. General arrangement of AHWR [VI-1].

around a central rod containing the burnable absorber dysprosium as Dy2O3-ZrO2. The 24 fuel pins of the outer ring incorporate (Th-Pu)O2 fuel and the 30 fuel pins in the inner and intermediate rings are based on (Th-233U)O2 fuel. Like other pressurized heavy water reactor designs, the AHWR provides for on-line refuelling.

The AHWR incorporates several passive safety systems to facilitate the execution of safety functions related to normal reactor operation, residual heat removal, emergency core cooling, confinement of radioactivity, etc. Passive shutdown during a high pressure transient due to a failure of wired (sensors, signal carriers and actuators) shutdown systems and high temperature protection of the concrete by passive cooling are some of the additional features of the AHWR. A 6000 m3 capacity GDWP, located at higher elevation inside the containment, serves as a heat sink for the residual heat removal system and several other passive systems; in addition to this, it acts as a suppression pool.

Major design specifications of the AHWR are given in Table VI-1.