3 power units are operated at SU NPP. The Unit include: WWER-1000 reactor, K-1000-60 turbine, TVV-1000 generator, PGV-1000 steam generators, main circulation pumps, pressurizers, main circulation circuit pipes, emergency cooling system tanks, refueling machine, spent fuel and refueling ponds, other process equipment.
Fig. Circuit heat flow diagram of NPP
- reactor control and protection system
- reactor coolant pump
- reactor vessel
- steam generator
- reactor core with a fuel
- feed pump
- circulating pump
- cooling pond
Plant heat flow diagram – double circuit.
Primary circuit is radioactive. It consists of a reactor of WWER-1000 type and four circulation cooling loops. Each loop contains reactor coolant pump (2), steam generator (4), main circulation pipelines. Pressurizer is linked to one of the primary circulation loop that helps to maintain the specified water pressure in circuit.
WWER-1000 reactor is PWR of vessel type. The term “WW” means that the demineralized borated water is used as the neutron moderator and coolant.
The reactor vessel (3) accommodates the core (5), structural elements for organization of the coolant flow and reactivity control components (1). The fuel is low-enriched uranium dioxide.
The circulation loop pipes are connected to the reactor vessel (3) inlet and outlet pipes. Through the inlet pipes the water flows between the reactor well and vessel downward to the reactor bottom, then in upward direction through the core removing the heat from the fuel elements (FE), and via the outlet pipes is supplied to the steam generators (4). The water temperature at the reactor inlet 288 ºС, outlet 320 ºС, the water pressure in the primary circuit is 160 kgf/sm2. The water is pumped through the core by the main circulation pumps (2), at flow rate of 80 000 m3/h, the water inventory in the primary circuit is 380 m3. The basic structural material of the primary circuit components is stainless steel.
The reactor core is arranged of 163 hexagonal fuel assemblies (FA). Each working fuel has 312 fuel rods (FR) cladded with zirconium alloy (non-fissile material). Fuel kernel consists of the stacks of sintered uranium dioxide (UO2) pellets. Fuel assembly containment provides storage of its geometrical shape and mechanical strength prevents contamination of the coolant with fission products and prevents corrosion. The fuel rod diameter is 9.1 mm.
The refueling operations are accomplished with the reactor shut down, remotely under a water layer by the special refueling machine. The spent fuel assemblies are removed from the core and inserted into the fuel pond for 3-5 years to remove the decay heat and FA radioactivity reduction. Annually partial discharge (about 1/3) of the working fuel assemblies and charge of the same number of fresh ones are accomplished.
The primary circuit equipment is enclosed into the air-tight shell made of prestressed concrete. In sudden emergency depressurization of the reactor equipment and pipes all radioactive materials are localized inside the air-tight shell, which prevents their release to the environment.
The secondary circuit is non-radioactive. It includes four steam generators (4), steam pipelines, steam turbine (6), generator (7), moisture separator-reheaters, feed pumps (8), pipelines, deaerators and regenerative heaters. Steam generators are common equipment for the primary and secondary circuits. Heat energy generated in the reactor transfers to the secondary circuit through the heat exchange tubes. Saturated steam (temperature 274ºC, pressure 60 kgf/cm2), produced in the steam generators goes along the pipeline into the turbine (6), which makes the generator rotor (7) producing electric current rotate.
Circulation water, supplied by the pumps (10) installed at the unit pump station linked with Tashlyk cooling pond (11) through the headrace canal, cools down the turbine condensers. After the condenser circulating water is discharged back into the cooling pond. Condensate (cooled steam) with a help of feeding pump (8) supplied into steam generators (4). And further the process is repeated in the closed cycle.