Kudankulam N-plant has foolproof safety mechanisms

Denis Kolchinskiy, chief project engineer of SPbAEP, the developers of the AES 92 nuclear reactor installed at Kudankulam, said modern Russian designs have an optimised balance of active and passive safety systems that have been developed over a decade.

"Now we implement such projects in Russia and offer them our foreign partners," Kolchinskiy told IANS in an email interview.

According to Kolchinskiy, the Kudankulam plant is built with "active" and "passive" safety systems to provide two layers of protection. While the active layer requires an electrical actuator, or starter, the passive one uses natural force, like that of gravity.

Spurred by Japan's Fukushima disaster, activists of the People's Movement Against Nuclear Energy (PMANE) have been holding protests against the Kudankulam plant, citing safety and enviromnent concerns. The Supreme Court had last year rejected a plea against the project but asked the government to put in place stringent security measures.

The key to preventing an apocalypse in the event of a core meltdown, said Kolchinskiy, is the "molten-core catcher" - a mandatory safety system included in the Kudankulam project's basic supply package.

To remove heat from the reactor core which contains nuclear fuel, it is necessary to supply water by means of pumps. Should the reactor fail to be cooled down for some reason, the fuel inside would not melt down.

"The molten core would go to the 'catcher', which would ensure its cooling down and prevent release of hydrogen," Kolchinsky said.

"When the molten matter gets into the 'catcher', an endothermic reaction (reaction with thermal energy absorption) begins, which results in solidification of the melt. Besides, the material contains dysprosium, which absorbs neutrons, and this excludes the possibility of a chain reaction," the Russian engineer said.

In the Fukushima disaster, the impact of a tsunami wave damaged the nuclear plant's diesel generators and interrupted power supply to pumps. With the pumps shut down, heat removal discontinued, leading to a core meltdown.

"If such a system had been at Fukushima, no one would have ever known what Fukushima is," Kolchinskiy maintained.

Russia's concerns over the operator's responsibility in India's nuclear liability law have stalled agreement on Unit 3 and 4 of the Kudankulam project.

"The passive emergency protection system turns on without electricity and begins cooling by heat to heat exchanges owing to thrust. It directs heat to the atmosphere for an unlimited period of time," the Russian engineer said.

He explained that there is a vessel with water, while steam goes up by a pipe, condensates and returns to the steam generator so as to establish natural circulation.

"For the passive system to remove heat, no electricity is needed, no action by the personnel. As soon as temperature increases in the primary circuit, the system starts removing heat automatically," Kolchinskiy said.

"The reactor is designed so that the passive and active safety systems prevent the core from melting down. However, in the event of a hypothetical accident, our reactor provides for a special device, the molten-core catcher," he added.

The only other Generation III+ units with double-wall containment, combination of passive and active systems, and a "molten-core catcher" in the world in actual operation are the 1st and 2nd units of the Tianwan nuclear plant in China, Kolchinskiy said.

"When we were designing the catcher, a full-scale experimental facility was created, on which fuel was specially molten, and the molten matter flew out into the catcher at a temperature of 2,300 degrees Celsius," he said.

Pointing out that nuclear power is "most harmless", sans hazardous emissions into the environment, Kolchinskiy said construction at Kudankulam "was preceded by landscaping the surrounding areas, as a result of which all necessary conditions were created for birds, the pond in which they fish and trees where birds build nests."