Passion for safety

"SAFETY has no holiday", announces a board at the entrance to the gigantic reactor building under construction at the Kudankulam Nuclear Power Project (KKNPP). At the turbine building the slogan goes, "Job of any kind, plan with safety in mind". At the massive pump house, too, where huge motors will pump thousands of gallons of sea water for cooling the condenser, there are posters on safety aspects. In fact, the magnificent obsession with safety won for KKNPP the Industrial Safety Award of NPCIL in 2002, its inaugural year. It is given for nuclear projects under construction and the assessment is done on the basis of fewer numbers of accidents, efforts aimed at training in safety and safety promotion activities. Among the contenders were projects being built at Rawatbhatta in Rajasthan, Kaiga in Karnataka, Tarapur in Maharashtra, and Kalpakkam in Tamil Nadu. Project Director S.K. Agrawal received the award on September 27, 2003.

The motivation of the thousands of workers toiling at the site is at the root of this passion for safety. Competitions on safety are held for NPCIL employees and civil work contractors and their workers. They are encouraged to dream up skits, plays and songs highlighting safety.

Safety is embedded in the reactor systems themselves. The VVER-1000 type Russians reactors, which will be erected at Kudankulam, are among the safest in the world. Said A.I. Siddiqui, Senior Manager, Corporate Communications, NPCIL, and editor of Nu Power, a quarterly published by NPCIL: "The Kudankulam reactor has one of the safest new-generation designs. It has several inherent and engineered, both active and passive, safety features to meet abnormal conditions." The latest innovation is the addition of a core-catcher - a huge vessel weighing 101 tonnes, which will hold the highly radioactive molten uranium fuel core in the case of a serious accident such as the loss of coolant. The core-catcher will be surrounded by several lakh gallons of water. The Kudankulam reactors will also have the double-containment feature, which is a massive dome with two very thick concrete walls so as to prevent radioactivity from escaping into the environment. It is said this dome can withstand even the impact of an aircraft crashing onto it.

The wall of the inner containment has carbon steel liner (plates) and is designed to withstand extreme internal pressure and high temperatures. The space between the two containments and the space inside the reactor building are kept below the atmospheric pressure to prevent radioactivity leaking into the atmosphere. The International Atomic Energy Agency (IAEA) has listed VVER-1000 among the world's best reactors. It uses light water (ordinary water) as both coolant and moderator, unlike the RBMK-type reactor, which uses graphite as moderator and boiling water as coolant. The reactor that suffered a meltdown at Chernobyl in April 1986 was of the RBMK type.

Michael Kvasha, technical director, Atomstroyexport, who works at Kudankulam, said that from unit to unit, VVER-1000 had additional safety features and systems. For instance, VVER-1000 built 15 years ago had three "channels" (barriers, the philosophy of safety-in-depth) for safety. "Now four channels are an obligatory requirement." The VVER-1000 reactors at Kudankulam would have "the most advanced safety devices", he said. One of these is the core-catcher, which NPCIL has started erecting at the first unit in Kudankulam. Said Kvasha: "It is a new feature. The core-catcher has been installed in very few power plants that we have constructed in the last few years." As the name implies, it is a huge vessel of steel, into which the highly radioactive molten fuel will fall in the case of an accident and fuel meltdown. The molten fuel will stay in the "catcher" forever, surrounded by water.

The VVERs also have passive safety systems, which would operate without human intervention, on the principles of gravitation, conduction and so on. No mechanical parts are involved in these passive safety systems. In any emergency, they would shut down the malfunctioning reactor and cool it by dumping thousands of gallons of water on it. VVER-1000 has evolved from variants such as V-187, V-338, V-320, V-413, V-392, and V-428. Of these, V-392 has the most advanced design features and it is this design that has been adopted into VVER-1000.

According to S.K. Jain, Chairman and Managing Director of NPCIL, the V-392 (that is, VVER-1000) has a "negative power coefficient. It means that any abnormal increase in reactor power that could affect the safety of the reactor is self-terminating."

The Kudankulam reactors have adopted the design philosophy of "defence in depth" and have successive levels of safety so that failure of one does not impair the overall safety of the reactor. Said Siddiqui: "The reactor protective systems are 100 per cent quadruplicated, that is, four independent channels exist for such systems although one is sufficient for the protection of the reactor."

An unlikely scenario is the loss of coolant accident (LOCA). This means of loss of water, which is both coolant and moderator. A loss of coolant will hamper the removal of fission heat from the enriched uranium fuel core, which, in the absence of safety systems, can melt the core. In the absence of containment in such a situation, radioactivity can escape into the environment. The core-catcher is designed to "catch" the molten fuel in the event of a LOCA. The catcher is filled with bricks of ferrous oxide and aluminium oxide, which absorb the heat from the uranium (melting point 2,800Celsius) and melt in the process. Over a period of time, the molten fuel and the bricks form a lump.

Said Siddiqui: "The composition of these bricks and the design of the `melt fuel catcher' were decided after extensive research in one of the largest experimental facilities in the world, at the Kurchatov Institute in the Russian Federation. Millions of dollars are spent to carry out such experiments by a group of countries at this site."

Safety extends to training the operators who man the reactors. The operators are graduates in engineering. They undergo periodic training to sharpen their reflexes and responses in a crisis. They write tests and appear for interviews, conducted by the Atomic Energy Regulatory Board, at regular intervals to renew their licences for running the reactors. They are members of the World Association of Nuclear Operators (WANO), which came into being after the Chernobyl accident. In WANO, they exchange information about the safety practices of various reactors, the upgrading of their skills, innovations in reactors and so on.