Things are getting set for the commissioning of the first unit of 1000 MWe of the Kudankulam Nuclear Power Project (KKNPP) in Tamil Nadu by the end of September or in October this year. Preparations are under way for the hot run of the reactor, an important activity that will take place before the reactor is loaded with the real fuel assemblies made of enriched uranium.

Pre-commissioning activities of the second reactor at the KKNPP, also of 1000 MWe capacity, have already started. It will reach criticality about nine months after the first reactor does so.

The two reactors are Russian ones that belong to the advanced design of VVER family but have been built by the Nuclear Power Corporation of India Limited (NPCIL). These are the biggest reactors to be built in India. They use enriched uranium as fuel, and light water as both coolant and moderator.

“The clearance for starting the hot run of the first unit is expected shortly. The hot run itself will start in some days,” said M. Kasinath Balaji, Site Director, KKNPP. The hot run will continuously last about three weeks and it will be completed by the end of June. It will entail heating the primary coolant water to the reactor's operating temperature of 280 degrees Celsius. “We will be operating the reactor systems at the temperature at which the reactor will operate when it has real fuel bundles,” he said.

Dummy fuel assemblies

The process of hot run will take place with the dummy fuel assemblies, which were loaded into the reactor several months ago. The dummy fuel assemblies have the same configuration as the real fuel assemblies but have no enriched uranium inside. The reactor vessel houses the 163 fuel assemblies inside.

Right now, the KKNPP engineers are preparing the reactor (the first unit) with the dummy fuel inside and the control rod drives installed, for conducting hydro tests at a pressure of 180 kg per sq. cm. as per the standard operating procedure. A hydro test done in December 2010 at 250 kg per sq. cm validated the strength of the reactor vessel and the primary coolant circuits. The control rod drives, which shut down the reactor in an emergency, were installed subsequently. The test at a pressure of 180 kg per sq. cm. will be done in a few days. After these tests are done, clearance for the hot run is expected.

“Hot run means taking the temperature of the primary coolant water to the operating temperature of 280 degrees Celsius with the help of energy from the primary coolant pumps,” Mr. Balaji said. There are four primary coolant pumps, each requiring 6.3 MWe. During the hot run, three primary coolant pumps will be running and they will circulate the water through the dummy fuel assemblies. All safety systems will be tested.

Robotic inspection

After completion of the hot run, Mr. Balaji said, the reactor would be disassembled and the control rod drives removed. The cover of the reactor would be opened up and the dummy fuel assemblies inside the reactor vessel removed. Then the reactor vessel, the main coolant pipelines and all associated systems would be inspected for their integrity using highly sophisticated robotic machines. “These robotic machines have been tested in a mock-up facility and they are ready to carry out inspection operations inside the reactor once the hot run is completed. These inspection operations will last about a month,” said Mr. Balaji.

The results of the hot run and inspection by the robotic machines will be reviewed by the Indian specialists along with their Russian counterparts.

After further review by the regulatory authorities, the KKNPP officials will make a request to the regulatory authorities for loading the real fuel assemblies into the reactor. The first fuel assemblies will be loaded in the beginning of September and after all the 163 fuel assemblies are loaded, the approach to its criticality will begin. The reactor will reach criticality by the end of September or the beginning of October. After a few weeks of low power experiments, electricity will be wheeled into the grid. Nine months later, the second unit will be started up.

From the two units with a total capacity of 2,000 MWe, Tamil Nadu's allocation will be 925 MWe, Karnataka 442 MWe, Kerala 266 MWe, Puducherry 67 MWe and the unallocated is 300 MWe.

Safety features

The Kudankulam reactors have state-of-the-art safety features in terms of the various passive safety systems backing the active safety systems. Twelve huge water tanks are installed inside the reactor building to ensure that the reactor is filled with water with boron in case of loss of water from the reactor fuel core. In addition, the reactor is cooled by way of natural circulation of air in the event of loss of electricity supply. Each reactor at Kudankulam is provided with four diesel generators of 6.3 MWe capacity each. Of the four diesel generators, only one is required to keep the reactor in a cool state under shutdown condition. The diesel generators were installed at a height of nine metres above the mean sea level, isolated from tsunami-like floods, Mr. Balaji said.