Advanced Technologies for safer and cleaner Nuclear Energy

Nuclear energy for industrial civilization while protecting the environment Today over 400 nuclear reactors provide base-load electric power in 30 countries. Nuclear is a mature technology with the assurance of great improvement through Technology in the next generation. Well designed, well constructed, well operated and well maintained nuclear energy is not only clean, but it is also safe, reliable, durable and competitive. From Indian prospective, it is renewable too In the famous “factor of a million” terms, nuclear waste is about a million times smaller than fossil fuel waste. Recent WHO study reported 92% of world population breath polluted air. A frightening health hazard. Today the environmental reasons are in favor of nuclear energy as a 24X7 source of energy, every day.

Choice of PHWR and way ahead The choice of PHWR in the first stage, driven by the fact that, on account of use of heavy water as moderator and on power fueling, more number of neutrons are available to convert U238 to PU than in the case of LWRs. In the second stage, on account of unique characteristics of PU, it was logical to use PU in the Fast breeder Reactors. In the long run, the FBR will be based on metallic fuel that gives higher breeding ratio. Studies indicate that Thorium, the fuel in waiting, would be introduced in the third decade after launch of metallic fuel in FBR. As a window to third stage, AHWR is designed to demonstrate large scale use of Thorium for power generation and the involved technology.

Technological challenges in PHWR Coolant channel : Irradiation induced life limiting sag. Thus, the channel need replacement at least twice in the life of the reactor Solution: Concept of Long Life Coolant Channel using Yttria Stabilised Zirconia (YSZ) for insulating pressure tube from the hot coolant. Heat transfer studies show that Pressure tube outside surface temperature is maintained closer to moderator temperature.

Technological challenges in PHWR Residual stress: Tensile stresses in rolled joints has lead to many failures in the channel. Solution: Residual stress free rolled joined by Laser shock peening Residual tensile stress due to rolling Outcome: Tensile stress free region near the rolled joint Increased the service life of component Decreased susceptibility to failure by a service induced flaw.

Technological challenges in PHWR Fabrication: Complicated End-fitting to pressure tube joint Solution: Laser Rapid Manufacturing (LRM) Zr alloy SS Rolled Joint Pressure tube end End fitting end Functionally graded transition piece being developed by LRM Modified End fitting to Pressure tube joint Outcome Lower thickness of Endfitting and therefore lower outside diameter Shop assembly possible Easy replacement and installation, no Hydrogen embrittlement. Transition Piece End fitting Pressure tube

Facility for testing safety programs for 700 MWe PHWR In 700 MWe PHWR design during the Station Black out (SBO) scenario i.e. upon failure of Class-III and Class-IV power supply the heat from the reactor is removed by the Passive Decay Heat Removal System (PDHRS). It is connected with the secondary system i.e. steam generators as shown. The flow inside the tubes of PDHRS is buoyancy driven. The heat is rejected in the boiling pool in the tank and the inventory/water level in the tank is maintained using a filling line. PDHR Tank SG -1 SG -2 SG to PDHR Tank PDHR Tank to SG Down comer

Advance fuel cycles for PHWRs Full core & partial core loading MOX-7 fuel to improve burn-up Central 7 pins contain 0.4% Pu in (NU,Pu) MOX and remaining 12 pins contain NU; Burn-up increased 10.0 GWd/Te 50 bundles have been irradiated in 220 MWe PHWRs MOX-97 fuel to improve burn-up Central 7 pins contain 0.9% Pu in (DU*,Pu)MOX and remaining 12 pins contain 0.7% Pu in (DU, Pu) MOXNU; Burn-up increased 10.0 GWd/Te MOX-888 fuel to improve burn-up All 19 pins contain 0.8% Pu in (DU*,Pu)MOX; Burn-up increased 10.0 GWd/Te SEU in PHWRs Various studies were carried out for using SEU fuel containing 0.8, 0.9, 1.0 and 1.1% 235U 50 bundles have been irradiated in PHWRs

The Indian Advanced Heavy Water Reactor (AHWR) An innovative configuration with low risk nuclear energy using available technologies. Has advantages of both PHWR and BWR technology Significant fraction of Energy from Thorium Several passive features 3 days grace period No radiological impact Passive shutdown system to address insider threat scenarios. Design life of 100 years. Easily replaceable coolant channels. AHWR can be configured to accept a range of fuel types including LEU, U-Pu , Th-Pu , LEU-Th and 233U-Th in full core

Indigenous Development of 300 MWe Nuclear Turbine Island for AHWR The indigenous nuclear reactor will be supplied with indigenous turbine under development at BHEL. The turbine operating at near saturated steam at 70 bar pressure will be the first of its kind for BHEL. The question of once through/cooling tower based cooling system is being discussed to meet the new MoEF norms. A cross functional team from BHEL and DAE is monitoring the development of this first technological venture by BHEL

Thorium Utilization On account of large reserves of Thorium in India, due its peculiarity, it has to wait for the build up fast reactors envisaged in the 2nd stage under closed loop fuel cycle programme. The 3rd stage envisages use of reprocessed U233 from irradiated Thorium in 2nd stage reactors in Thorium based reactors. One of the potential option for Thorium based reactor is Molten salt-fuelled reactors (MSR). MSR is one of the six Generation-IV designs chosen in 2002 Main features The fuel is in molten form, basically mixture of (FLiBe) salts with dissolved low-enriched uranium fluorides (UF4) and Thorium. The molten salts circuit is not pressurization and temperatures range from about 500°C up to about 1400°C The hot molten salt exchange heat with secondary salt circuit or secondary helium coolant and generate power via the Brayton cycle. Fission products in the fuel salt can be ideally removed continuously Has significant load-following capability. When the molten salt is removed from the core, the reactor shuts down

Concept of MSBR

Loop-in-Tank type concept All highly active systems containing U, Th, Fission Products and MAs contained within a nickel lined safety vessel Active materials are retained within the safety vessel Conceptual design of 5MWth demonstration facility is in progress

Advantages of Technologies in nuclear plants Nuclear waste that remains radioactive for a few centuries instead of millennia 100-300 times more energy yield from the same amount of nuclear fuel Broader range of fuels. Ability to consume existing nuclear waste in the production of electricity. Improved operating safety features. Automatic passive reactor shutdown. Avoidance of water cooling and the associated risks of loss of water Avoidance of hydrogen generation/explosion Avoidance of contamination of coolant water.

How fear of nuclear power is hurting the environment

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