Kaiga on course

Print edition : July 31, 1999

The second unit of the Kaiga Atomic Power Project attains criticality in August.

THE rain had stopped and there was a nip in the air as we drove up the dirt track on a forested hill in the Sahyadri range of the Western Ghats in Karnataka. In the valley below, which was surrounded by densely forested hills, the domes of two massive re actor buildings rose amidst the clouds. The scene was one of remarkable coexistence of high technology and pristine nature.

This is Kaiga, where the second unit of the Kaiga Atomic Power Project will attain criticality in the second fortnight of August. The second unit will be commissioned first because the undersurface of a portion of the inner dome of the first unit's doubl e containment collapsed on May 13, 1994. Work on the modified dome is at an advanced stage. The first unit will be commissioned next year. The two units have a capacity of 220 megawatt (MW) each. Eventually, four more reactors with similar capacity will be built. (When a reactor in an atomic power project reaches criticality, the project becomes a station. When the second unit of the Kaiga Atomic Power Project reaches criticality, it will be called the Kaiga Atomic Power Station.)

V.K. Sharma, Project Director, told the visiting Frontline team: "The run-up to the attainment of criticality has been smooth. Hot commissioning has been completed."

A view of the Kaiga Atomic Power Project in Karnataka. The reactor plant, buildings and other facilities occupy 25 hectares of land.-SAGGERE RAMASWAMY

Station Director N. Rajasabai said: "We completed fuel loading today (July 15). We did it in a short span of seven days." Filling up of heavy water is planned for July 30. "We will add 70 tonnes of heavy water in the coolant system and another 140 tonnes in the moderator system... So far there has been no problem," he said.

Like the other Pressurised Heavy Water Reactors (PHWRs), the Kaiga project will use natural uranium as fuel and heavy water as both moderator and coolant. The second unit at Kaiga will be the ninth PHWR that will be operational in the country. There are two each at Rawatbhatta in Rajasthan, Kalpakkam in Tamil Nadu, Narora in Uttar Pradesh and Kakrapar in Gujarat. Two boiling water reactors, built by General Electric of the United States, are located at Tarapur in Maharashtra. All these units belong to t he Nuclear Power Corporation of India Limited (NPC).

THE plant is situated near Kaiga village on the left bank of the Kalinadi river, about 60 km from Karwar in Uttara Kannada district. The nearest airport is 150 km away at Dabolim in Goa. The drive on the smooth metalled road from Dabolim to Kaiga unfolds the beauty of the Sahyadri. The road from Mallapur village to Kaiga - a distance of about 18 km - winds through dense forests inhabited by the Kunabi tribal community.

Ashok Mohan, Technical Advisor to the Atomic Energy Commission Chairman.-SAGGERE RAMASWAMY

Recalling the tough task of acquiring the land for the project, which began in 1987, Jugal Kishore Singh, Manager (Public Relations), said: "There was only a pucca road from Karwar to Dewalmukki. A cart track led up to Mallapur, and there was no road to Kaiga from there. We had to clear the vegetation to make a track for our vehicles." It took a lot of persuasion to make people living in the vicinity to part with their land, a total of about 425 acres (170 hectares). The reactor plant, the buildings and other facilities of the project occupy about 25 hectares of a total of 120 hectares of forest land that was acquired.

Today, there is hectic activity at the second unit.

The reactor building is about 73 metres tall and 46 metres in diameter. Sophisticated machines, are all in place, and the control rooms are ready. The project took about 3,20,000 cubic metres of concreting. The deployment of a 650-tonne heavy duty crawle r crane with 105-metre boom length; the installation of two end-shields, each weighing 120 tonnes, in the reactor vault; the clamping in of the fuel channels; the readying of two state-of-the-art control rooms (where computerised information on 2,000 par ameters would be available every second) give an indication of the frontier technology that went into the construction of the two units. Kilometres of cables have been used in them.

Project Director V.K. Sharma.-SAGGERE RAMASWAMY

Sharma said: "The PHWR is one of the most advanced reactors in the world. It compares in safety at any level with any other type of reactor." He dismissed as "ridiculous" fears that a Chernobyl-type accident was possible. The dreaded scenario of a Loss o f Coolant Accident (LOCA) - when the fuel core loses its cooling, the fuel melts down and loses its shape and a fire breaks out - might be possible in the case of other types of reactors but not in the case of the Indian PHWRs, he said.

Three huge doors, called personal air locks, provide entry into the reactor building of the second unit. They are arranged in such a way that only one door can be opened at a time. The third door, made of three-foot-thick concrete and lined with steel, s lides on rails to lead into the calandria vault, the heart of the reactor. The calandria is a huge cylindrical vessel made of stainless steel. It is supported on either end by massive plates, the end-shields. The calandria consists of 306 pressure tubes, also called coolant tubes. These tubes house the natural uranium fuel bundles, about 50 cm long and 8.17 cm in diameter and in pellet form. Twelve such bundles are located in each pressure tube. In other words, these pressure tubes are the fuel channels . The coolant tubes are located inside the calandria tubes, both containing heavy water. The calandria tubes are rolled into the end-shields.

The initial fuel load for the unit is 56 tonnes of natural uranium. The uranium required for the PHWRs is mined by the Uranium Corporation of India at Jaduguda, Narvapahar and Bhatin in Bihar. It is sent to the Nuclear Fuel Complex in Hyderabad, where it is sintered and made into pellets. The heat produced due to fission in the natural uranium bundles is removed by the heavy water coolant, which transfers it to light water (ordinary water) contained in the secondary side of the steam generators to produ ce steam. The steam is led to turbines, which drive the generator to generate electricity. This electricity is wheeled into the Karnataka grid.

Station Director N. Rajasabai.-SAGGERE RAMASWAMY

Nuclear engineers completed the hot commissioning of the coolant system in March. This provided a protective layer of 0.7 micron thickness of magnetite to the coolant system. According to Dr. Ashok Mohan, Technical Advisor to Dr. R. Chidambaram, Chairman of the Atomic Energy Commission, hot commissioning entails depositing layers of iron oxide on the coolant system to produce a surface that slows down further oxidation and prevents corrosion.

In the first week of July, 3,672 (306x12) fuel bundles were loaded into coolant tubes manually as the fuel was new and entailed no radiation. But it was a tough job, which demanded accuracy in millimetres.

According to Rajasabai, only 3,637 uranium bundles were fed into the reactor; the remaining 35 were thorium bundles which reduce neutron flux. Neutron flux would be high in the fuel core and could lead to high fission. The heat output would also be high and the temperature would tend to rise. "In order to avoid that, we put thorium bundles. Thorium cannot (by itself) cause fission. So the rising trend in temperature will be controlled."

The dome of the first unit, which will attain criticality next year.-SAGGERE RAMASWAMY

Once the reactor becomes operational, manual loading of fresh fuel will not be possible because there would be intense radiation and the calandria vault would be inaccessible. (The fuel bundles last about a year.) Two robots or fuelling machines would re move the radioactive spent fuel bundles and load fresh bundles once the unit attains criticality. The fuelling machines are like cranes, with scores of thick cables flowing out of them. The PHWRs have the advantage of on-line fuelling; that is, machines feed fuel bundles into the reactor without having to shut down the reactor.

Although each fuelling machine weighs several tonnes, the machines would clamp the fuel bundles with an accuracy of a few millimetres. This operation would be done from the control room of the reactor, Ashok Mohan said. "Accuracy of the installation of f uel bundles is important. Any mismatch could cause leakage of heavy water. The subtlety of engineering is evident from the accurate performance of these machines."

Each fuelling machine has 12 chambers called magazines and each serves a purpose: storing new fuel, spent fuel, seal plugs (to make coolant channels water-tight), sealed plugs (to provide radiation shielding) and so forth.

Work in progress at the reactor building.-SAGGERE RAMASWAMY

One fuelling machine would be positioned near each end-shield. First, one machine would remove the seal and sealed plugs and keep them in their respective magazines. This would make the radioactive, spent fuel bundles in the fuel channels visible. Then i t would pick up two fuel bundles and clamp them inside the fuel channels by pushing out two spent fuel bundles. The other machine, in turn, would receive the bundles that are pushed out. In one day, four pairs or eight bundles would be fed into the react or. Rajasabai said: "By pushing in eight new bundles, eight old bundles will be pushed out. Then, the sealed plugs and the seal plugs will be put in place." Sharma calls it "a push-and-pull arrangement."

Sharma said that the spent fuel would be kept in a stainless steel tank, which has water up to a depth of 20 feet. This tank, lined with stainless steel, is located in the reactor building. "Ten years of spent fuel plus one calandria fuel unload in case of an emergency can be kept in this tank," he said.

Kaiga has two separate state-of-the-art control rooms for the two reactors. The reactor controls at Kaiga are more advanced than those available at the other PHWRs. They have several banks of computer consoles. The control panels provide full information to reactor operators on the status of the plant.

The personal air lock system, so called because it keeps the air out, leads into the reactor building.-SAGGERE RAMASWAMY

Rajasabai said that information on every one of the 2,000 parameters such as compressor, pressure, flow and temperature for every second was stored in the computer for 24 hours. In case of any disturbance, or for any review, control room engineers could retrieve the information for every second of the previous 24 hours. "We can find out the cause of the abnormality and its effects. This is called computerised operator information system (COIS)," he said.

Sharma said that there were two computers in the control room. "These controls are unique and they are used for the first time at Kaiga. This is in line with the system that is in vogue anywhere else in the world."

Inside the reactor plant. Multiple barriers have been created to prevent radioactivity from escaping into the environment.-SAGGERE RAMASWAMY

The testing of fire alarms was under way in the control room of the second unit when the Frontline team visited it. The fire alarm windows lit up. The panels would glow if anything went wrong with the emergency core cooling system, the primary shu t-down system, the steam generator or the turbine.

Thus, everything is on course at Kaiga.
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