Maharashtra | Advanced Heavy Water Reactor, Maharashtra

Source : Bhabha Atomic Research Center

It is generally agreed that, in the long term, nuclear power, employing closed fuel cycle, is the only sustainable option for meeting a major part of the world energy demand. World resources of thorium are several times higher than those of uranium. Thorium is, therefore, widely viewed as the `fuel of the future'. Thorium based nuclear fuel cycle, however, possesses a large number of well-known characteristics which make it attractive for consideration in the near term as well. The Indian Advanced Heavy Water Reactor (AHWR) is being designed and developed to achieve large-scale use of thorium for the generation of commercial nuclear power. This reactor will produce most of its power from thorium, with no significant external input of uranium-233, in the equilibrium cycle. AHWR is a 300 MWe, vertical, pressure tube type, boiling light water cooled, and heavy water moderated reactor. The reactor incorporates a number of passive safety features, and it is associated with a fuel cycle having reduced environmental impact. At the same time, the reactor possesses several features, which are likely to reduce its capital and operating costs. The AHWR fuel contains three rows of fuel pins surrounding a central displacer rod. The inner two rows contain thirty (Th-U233)O2 fuel pins and the outer row contains twenty four (Th-Pu)O2 fuel pins. The central rod contains dysprosia in zirconia matrix. The central rod of fuel also incorporates a water tube for the injection of Emergency Core Coolant System (ECCS) water directly on fuel pins during a postulated Loss of Coolant Accident (LOCA). AHWR fuel is currently designed for an average burn-up of 24 GWd/Te. Its design makes it amenable for reconstitution, if desired to facilitate a further extension of burn-up in the (Th-U233)O2 fuel pins in future. AHWR employs natural circulation for cooling of the reactor core under all conditions. All event scenarios initiating from non-availability of main pumps are therefore excluded. During incidents leading to increase in void, the negative void coefficient of reactivity brings down the reactor power without necessitating any external control or operator action. The ECCS is designed to remove the core heat by passive means in case of a postulated LOCA. In the event of a rupture in the primary coolant pressure boundary, the cooling is initially achieved by a large flow of borated water from advanced accumulators, and later cooling of the core is achieved by the injection of cold water from a large Gravity Driven Water Pool (GDWP) located near the top of the reactor building and later submerging the core. In AHWR, subsequent to energy absorption by Gravity Driven Water Pool (GDWP), the Passive Containment Cooling System (PCCS) provides long term containment cooling following a postulated LOCA. The principle of double containment has been adopted in designing the containment for AHWR. For containment isolation, a passive system has been provided in the AHWR. The reactor building air supply and exhaust ducts are shaped in the form of U bends of sufficient height. In the event of LOCA, the containment pressure acts on the water pool surface and pours water by swift establishment of syphon into the U-bends of the duct. Water in the U-bends acts as a seal between the containment and the external environment, providing necessary isolation between the two. The AHWR fuel cycle will be self�sufficient in U233 after initial loading. The spent fuel streams will be reprocessed and thorium and U233 will then be recycled and reused. There are also plans to recycle the actinides back into the reactor. Incidentally, the thorium fuel cycle also presents low proliferation risks, a factor considered significant by several nuclear supplier nations for export of nuclear technology. A quantitative analysis of the AHWR fuel cycle substantiates this feature. VADODARA: India needs to fully exploit its potential to deve .


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