Atommash, AEM-Technologies, JSC Branch in Volgodonsk (part of Rosatom machine-building division - Atomenergomash) has started welding the upper semi-vessel of VVER-1000 nuclear reactor for Power Unit No.5 of “Kudankulam” NPP under construction in India.

After vertical assembly of two shells and flange, the 170-tonne upper semi-vessel was moved by crane to the turner and then to the welding station, where specialists started welding of two circumferential welds. Welding is performed under heating at a temperature of 150-300 degrees for 22 days.

After the operation is completed, weld areas of the semi-vessel will be heated to 300 degrees. Then the semi-vessel is transferred to a heat treatment furnace to obtain the required mechanical properties of the metal. The heating and holding process takes place at a maximum temperature of 620 degrees for three days.

Specialists will carry out a number of necessary inspections of welded joints after heat treatment. The semi-vessel will then be prepared for internal corrosion-resistant overlaying in the welded areas.

The reactor is a vertical cylindrical vessel with an elliptical bottom, inside of which the core and internals are located. The top of the reactor is hermetically sealed with a cover with drives of mechanisms and controls and protection elements of reactors installed on it and nozzles for outputting cables of in-reactor control sensors. In the upper part of the vessel, there are nozzles for supplying and removing of the coolant, as well as nozzles for emergency supply of the coolant when the circuit is depressurized.

"Kudankulam" NPP is a nuclear power plant with VVER-1000 power units located in the south of India, in the state of Tamil Nadu. The first power unit of “Kudankulam” NPP has been operating steadily at the design power level of 1000 MW since February 2016. The second power unit was included in the national power grid of India on August 29, 2016. The general framework agreement with ASE, JSC (part of “Rosatom” Engineering Division) on the construction of the third and fourth units was signed in spring of 2014.  In June 2017, ASE, JSC and the Nuclear Power Corporation of India signed an agreement on the construction of the third stage (Power Units No. 5 and No.6) of “Kudankulam” NPP.