IEEE Power and Energy Society Kerala chapter conducted a meetup for its young professionals at India’s largest nuclear power plant at koodamkulam, Tamil Nadu on 08-12-2019 . The PES young professionals working at different industries from different parts of the state participated in the meetup. The number of participants were restricted to a maximum of eight, due to security issues.  The meetup aimed at improving practical knowledge of the young professionals who are working in different utility-related industries.  Mr. Sathish A V, Scientific officer, Koodamkulam Nuclear Power plant gave guidance to the program. The participants visited the entire plant and discussed different aspects of Nuclear Power Generation. 

During the visit the participants got a chance to see a nuclear reactor under construction which helped them to know the structural aspects of Nuclear reactor. The participants also discussed about different design aspects of Nuclear Power plant and accidents which happened in various parts of the world. The summary of the technical details of the visit is as follows:

Nuclear Power plants

A nuclear power plant is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a generator that produces Nuclear plants are usually considered to be base load stations since fuel is a small part of the cost of production and because they cannot be easily or quickly dispatched. Their operations and maintenance and fuel costs are, along with hydropower stations, at the low end of the spectrum and make them suitable as base-load power suppliers. The conversion to electrical energy takes place indirectly, as in conventional thermal power stations. The fission in a nuclear reactor heats the reactor coolant. The coolant may be water or gas, or even liquid metal, depending on the type of reactor. The reactor coolant then goes to a steam generator and heats water to produce steam. The pressurized steam is then usually fed to a multi-stage steam turbine. After the steam turbine has expanded and partially condensed the steam, the remaining vapour is condensed in a condenser. The condenser is a heat exchanger which is connected to a secondary side such as a river or a cooling tower. The water is then pumped back into the steam generator and the cycle begins again. The water-steam cycle corresponds to the Rankine cycle. The nuclear reactor is the heart of the station. In its central part, the reactor’s core produces heat due to nuclear fission. With this heat, a coolant is heated as it is pumped through the reactor and thereby removes the energy from the reactor. Heat from nuclear fission is used to raise steam, which runs through turbines, which in turn power the electrical generators. Nuclear reactors usually rely on uranium to fuel the chain reaction. Uranium is a very heavy metal that is abundant on Earth and is found in sea water as well as most rocks. Naturally occurring uranium is found in two different isotopes: uranium-238 (U-238), accounting for 99.3% and uranium-235 (U-235) accounting for about 0.7%. Isotopes are atoms of the same element with a different number of neutrons. Thus, U-238 has 146 neutrons and U-235 has 143 neutrons.

Koodamkulam Nuclear Power plant

Kudankulam Nuclear Power Plant (or Koodankulam NPP or KKNPP) is the largest nuclear power station in India, situated in Koodankulam in the Tirunelveli district of the southern Indian state of Tamil Nadu.Unit 1 was synchronised with the southern power grid on 22 October 2013 and since then, has been generating electricity at its warranted limit of 1,000 MW.The original cost of the two units was ₹ 13,171 crore, but it was later revised to ₹ 17,270 crore (US$2.6 billion). Russia advanced a credit of ₹ 6,416 crore (US$0.97 billion) for both the units.Unit 2 attained criticality on 10 July 2016 and was synchronised with the electricity grid on 29 August.In 2015, Nuclear Power Corporation Ltd (NPCIL) announced a price of ₹ 4.29/kW·h (6.4 ¢/kW·h) for energy delivered from Kudankulam nuclear power plant.The ground-breaking ceremony for construction of units 3 & 4 was performed on 17 February 2016. Due to operators and supplier’s requirement to insure the next two units at ₹39,747 crore (US$5.75 billion), the cost of units 3 & 4 amounted to twice the cost of units 1 & 2.

Design and specification of power plant

The reactors are pressurised water reactor of Russian design, model VVER-1000/V-412 referred also as AES-92. Thermal capacity is 3,000 MW, gross electrical capacity is 1,000 MW with a net capacity of 917 MW. Construction is by NPCIL and  Atomstroyexport. When completed the plant will become the largest nuclear power generation complex in India producing a cumulative 2 GW of electric power. Both units are water-cooled, water-moderated power reactors.

Allocation of power

Government of India announced the power allocation from the two units of the reactor on 29 August 2013

Cooling of plant

Russia’s Hydro project Institute has designed the service water intake for the Koodamkulam 1&2 secondary side once-through cooling system, a large complex of interconnected structures providing cooling water from the ocean, its treatment and supply to NPP structures, and discharge to Mannar Bay. The cooling water flow volume amounts to 80.8m3/second per unit, and it will amount to 98.8 m3/s considering the fish protection system, according to Ruslan Shakirov, chief design engineer of the Kudankulam NPP service water supply system. In addition, the system has been designed to raise the temperature of the seawater at the discharge point by not more than 7°C. The customer, Nuclear Power Corporation of India, determined the level based on local seawater chemistry and other site conditions. To meet these requirements, Hydro project has designed a unique water intake structure.

The main civil structure is a square enclosed dyke set 200 m offshore. Seawater at 31°C flows into it from a reinforced concrete intake pipe constructed 1200 m away from shore on the sea bed. The position of the dyke and its streamlined walls protects it from sediment blowing offshore into shallow water during windy weather. The near edge of the dyke forms an artificial canal, bounded on the other side by the seashore, which is spanned by a road bridge. The Mannar Bay’s fertile seawater hosts a great range of organisms and biomass; at peak times of year they could amount to nearly 1.5 ton per 100 m³, almost double the maximum rate of traditional filtration systems. Ingress of such a large amount of biomass would inevitably result in power station stoppages, and serious consequences for the station’s electrical output.

Water intake structures minimise the amount of biomass entering the system. First, the position of the intake pipe at the sea bottom minimises uptake of biomass floating on the water surface (and also maximises uptake of the coolest seawater, which sinks to the bottom). Second, the edges of the dyke are made up with precast concrete tetrapod structures that create an artificial reef, diverting fish from the water intake zone (large fish can swim against the current generated in the intake structure). Third, the water that enters the dyke is filtered through a trash rack filter with cells 80 mm wide and 7 m high.

Those organisms that make it through the first rack then move through a fish protection system. This is designed for drifting organisms (12-60 mm in size) that are unable to cope with the current flow. A compressor situated in a service building on the near side of the dyke pumps air to a grid of holes on the bottom of the dyke. The air comes out as bubbles, which lift floating biomass as they rise to the surface. They are directed back into the sea (into the channel between dyke and seashore) through a fish tailrace system measuring 2.5 m across at minimum. A water ejector in the tailrace system increases water velocity. The ejector pump station is also located in the service building. Meanwhile, the lower layer of water heads toward a supply pipeline. At this point, the bottom of the dyke incorporates chute structures that create underwater rapids, tending to slow down the flow of the lower layers of water. It is slower-moving water that enters a second intake pipe, again mounted at the bottom of the dyke.

The pipes cross underneath the channel to a forebay, where it is filtered again using a traditional water filter with rotating, self-cleaning grids. To save energy, the machine stops working if the incoming water is clean. The system is designed to have a kill rate of only 20% (by comparison, Russian regulations are 30%). This water is then used by a 22 MW pumping station for secondary side once-through cooling. The main reinforced concrete structural elements of the service water supply system are submerged in seawater, which has a slightly higher concentration of salt than typical. Salt tends to erode traditional waterproofing treatments for concrete and steelwork. Hydro project used titanium and steel with special polymer coatings. Two more water intakes are planned, one for the planned units 3-6, and one for the planned units 7-8