All four hydraulic tanks of the emergency core cooling system (ECCS) have been installed in the design position at unit 2 of Russia’s Kursk-II NPP two months ahead of schedule, according to Rosatom. They form the first of three stages of the ECCS. In case of a loss of coolant, the hydraulic tanks of each stage are sequentially activated as part of the passive safety system.

“Each tank of the emergency core cooling system is a thick-walled pressure vessel with a volume of 60,000 litres,” explained Andrey Osharin, First Deputy Director for the Construction of New Units of the Kursk NPP. “During NPP operation, these tanks store an aqueous solution of boric acid (neutron absorber). When the pressure in the primary circuit drops below a certain level, the liquid is automatically supplied to the reactor and cools the core. This prevents damage to the fuel rods and melting of the fuel.”

Hydraulic tanks weighing about 75 tons are installed in the reactor building in a vertical position at around 14.5 metres. Each tank will be connected by a pipeline to the reactor vessel. If necessary, the solution will be supplied from two tanks to the space above the core, and from two tanks – under the reactor core.

“The hydraulic reservoirs were installed using a heavy crane using the open-top method – through the open top of the building. The installation of one tank in the design position on average took about 2-3 hours,” said Oleg Shperle, Vice President and Director of the project for the construction of the Kursk NPP. Work will be completed soon on installation of the main circulation pumps and the concreting of the steam generator supports at unit 2.

Rosatom has also completed installation of the third tier of the internal containment (VZO) at unit 2. “The third tier was mounted in separate elements – 11 armoured blocks were enlarged into a ring on the mounting horizon. This is the heaviest tier of all: the weight of assembled structures is more than 800 tons. This completes installation of the cylindrical part of the VZO. Next, the metal structures of the domed part of the building will be mounted,” explained Alexander Uvakin, director of the Kursk NPP.

The design of the third tier includes individual sections of embedded parts for locks: transport, main operational and backup. Because of this, some armoured blocks have a displaced centre of gravity, making installation particularly difficult and requiring accuracy with a tolerance of 5mm.

Image: Installation of the hydraulic tanks of the emergency core cooling system at Kursk NPP (photo courtesy of Kursk NPP)