ADVANCED HEAVY WATER REACTOR

ADVANCED HEAVY WATER REACTOR

ABSTRACT

The Bhabha Atomic Research Centre (BARC), Mumbai, has developed an advanced heavy water reactor (AHWR) to expedite transition to thorium-based systems. A rigorous evaluation of the feasibility of AHWR design concept was completed in 1997.The reactor physics design of AHWR is timed to generate about 65 percent power from thorium.

The design incorporates several safety features to enhance its operational efficiency. Being a thorium system, the wastage from it is expected to be minimal. thorium utilisation is very crucial to meet the increasing energy demands in the country. A small beginning has already been made by introducing thorium in a limited way in research reactors and in the pressurised heavy water reactors (PHWRS). With sustained efforts over the years India has gained experience over the entire thorium fuel cycle. A research reactor called Kamini is operating in Kalpakkam, Tamil Nadu, based on Uranium 233 fuel which is derived from thorium. This fuel was bred, reprocessed and fabricated indigenously.

Most advanced water reactor development programmes have the dual aim of improving safety and reducing environmental impacts while at the same time providing further reductions In the cost of generating electricity. Environmental and public health benefits are to be achieved through improvements in reactor design and operation to further reduce the already low probability and potential consequences of accidents -the so-called "residual risk" of reactor operations.

INTRODUCTION

The heavy water reactor uses a molecular variation of ordinary water comprised of two atoms of deuterium for every atom of oxygen, instead of the usual two atoms of hydrogen for every atom of oxygen. A deuterium atom is twice as heavy as an ordinary hydrogen atom. Heavy water has different nuclear properties than ordinary light water, although its appearance and chemical behaviour are the same.

The Advanced Heavy Water Reactor (AHWR) now being designed in Bhabha Atomic Research Centre (BARC) aims to meet the objectives of utilisation of thorium for commercial power generation, demonstration of thorium based fuel technologies, sustenance of technologies and expertise developed for PHWRs, and incorporation of advanced salty and economy enhancing features that are now being internationally stipulated for next generation of nuclear power plants.

The AHWR is a vertical pressure tube type reactor cooled by boiling light water under natural circulation. The reactor is mainly heavy water moderated. The general arrangement of AHWR building is shown in Fig-1. Near the top of primary containment a large pool of water, called Gravity Driven Water Pool (GDWP), is located. This is designed to perform several passive safety functions.

The reactor design incorporates advanced technologies, together with several proven positive features of Indian Pressurised Heavy Water Reactors (PHWRs). These features include pressure tube type design, low pressure moderator, on-power refueling, diverse fast acting shut-down systems, and availability of a large low temperature heat sink around the reactor core. One of the drawbacks with the use of heavy water as coolant, as done in PHWRs, relates to an increased potential for leaks from the high pressure high temperature system resulting in economic penalty due to irrecoverable losses, and incorporation of sophisticated leakage recovery and heavy water upgradation systems, and incorporation of extreme leak tightness in all seals and valves, and the constraints imposed by the need to minimise personnel radiation exposure due to tritium activity. In view of these factors, the AHWR design has adopted boiling light water in a direct cycle as the main cooling system.

Download full seminar papers At
http://www.enjineer.com/forum