|Fig. 1: The Rajasthan Atomic Power Station (Source: Wikimedia Commons) -|
After India built it's first nuclear reactor in 1957, Prime Minister Jawarlal Nehru stated that the atomic revolution was inevitable, and India had to either go ahead with it, or fall back and fall behind. The nuclear power program had the political and financial backing of leaders in India. Today, India has an expanding and largely indigenous nuclear power program and expects to have 14.6 GWe nuclear capacity by 2024 and supply 25% of electricity from nuclear power by 2050. 
The Indian nuclear program was developed to reprocess spent fuel to manage the back end of the fuel cycle.  Nuclear waste has been a contentious aspect of nuclear power programs around the world. In India, the nuclear fuel cycle begins with mining and milling uranium and processing uranium into U3O8. The resulting spent fuel is reprocessed to recover uranium and plutonium. At each end stage of each cycle, different kinds of nuclear waste are produced. While the management of nuclear waste depends on the properties of the waste—radioactivity and other physical and chemical compounds—the guidelines for managing these aspects categorizes waste into four categories. India’s categories include Low-Level Waste, Intermediate-Level Waste, and High-Level Waste. The only PHWRs operating prior to 1982 have been RAPS-I and RAPS-II, which produced 1,59,079 MWeD of electricity from 1978 to 1982, and therefore would have produced 75.6 tons of spent fuel. 
India started building nuclear power plants in the 1960s and continued to add more units progressively to meet the growing demand for electricity. Today, India has 14 operating nuclear power units with a total installed capacity of 2770 MWe. Starting the first unit in Tarapur in 1969, to commissioning of four units at Kaiga and Rajasthan in the year 2000, India has made significant advancements in this arena.  The Rajasthan Atomic Power Station, or RAPS, is located in the Northern grid and has the country's largest nuclear power plant. It has six nuclear power reactors at present with the total installed capacity of 1,180 MW.  Located in Rawatbhata, a remote village in the Chittorgarh district, RAPS I and RAPS I are the first two Indian Pressurized Heavy Water Reactors (PHWR). 
The common benefits of a PHWR include the use of natural uranium as fuel, which circumvents the need for developing fuel enrichment facilities. A country that has neutron rich economy by use of heavy water can benefit from building PHWR reactors due to low requirements of natural uranium both for initial core as well as for subsequent refueling. Additionally, in PHWRs, fissile plutonium production is higher than alternative reactors like Light Water Reactors. 
The pressurized heavy water reactor is a horizontal pressure tube reactor using natural uranium dioxide fuel. Heavy water is the moderator and coolant which is maintained at low-pressure and temperature. Heat energy is then extracted by the coolant from the fuel, and is transferred to the secondary side light water to produce steam. Utilizing margin in the fuel linear heat rating and further flux flattening enhances the power output of the reactor. Extraction of additional heat is achieved by allowing boiling of coolant near the channel exit. In fact, the same reactor assembly and primary coolant loop are capable of delivering thermal energy equivalent to 700 MWe. 
Safety and reliability of a nuclear power plant are of utmost importance requiring constant vigilance by all the concerned agencies. Most of the structures, systems and components of nuclear power plants in India are continuously under varying influence of material degradation due to neutron irradiation, dynamic stresses, thermal fatigue, creep, corrosion, erosion, wear, vibration, and more. The maintenance of these systems, structures and components in Rajasthan plays an important role in assuring their safe and reliable operation. In PHWRs, the liquid wastes originate mainly at the following points: personnel showers, active laundry; heavy water upgrading plant, reactor building sump, heavy water cleanup rooms (tritiated waste); laboratories and decontamination center as active chemical waste. Liquid waste generated at the plant is collected in tanks at the Liquid Effluent Segregation System, which is located in the service building. Subsequently, the waste is pumped to the Treatment and Disposal System of the Waste Treatment Plant, which is equipped with facilities for chemical treatment, purification by ion exchange, evaporation, and more. After treatment of liquid waste, sampling and monitoring is diluted with condenser cooling water/blow down water and discharged to the environment water body through a single point. 
RAPS I and II PHWRs have had various safety issues. Turbine blade has been one common issue. In 1981, RAPS I was shut down twice because of oil leakage in the turbine building. This leakage led to high levels of sparking in the generator exciters; after the initial shut down, it was later found that large amounts of oil had leaked form the turbine governing system. Later after reopening, it was discovered that there were high vibrations of the turbine bearings and the blades were failing; the ensuing shutdown and repair of the plant took another five months. In 1983 it was discovered that the temperatures were too high in the turbine bearing, and two plates in the second stage of the high-pressure rotor had sheered off at the root. RAPS I was further shut down in 1985, 1989, and 1990. In May 1998, titriated heavy water with levels of tritium above levels set by the AERB was released from RAPS II into the Rana Pratap Sagar Lake; the release was due to a leak in the moderator heat exchanger. However, the public did not know about this occurrence until December 1999.  Yet, some upgrades have occurred in recent years. As part of the replacement of the pressure tubes in RAPS II, significant upgrades were performed to bring the safety systems to current standards. These include changing the containment dousing system with a fixed dousing flow rate, an enhanced Emergency Core Cooling System, the addition of a supplementary control room, a modification to the air flow valve system to minimize instrument air in-leakage in containment, and improvements to the station electric power supplies with a third diesel generator. 
© Tanvi Jayaraman. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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