3. VVER reactor safety

VVERs are pressurized water reactors whose main functional characteristics are similar to those of Western reactors. However, there are some notable differences:

• materials (steel grades used) ;

• the design of steam generators, which are horizontal in the case of VVER ;

• the fuel, with uranium oxide pellets with a central hole and rods distributed according to a triangular pitch;

• two different levels for hot branch outlets and cold branch inlets;

• the absence of penetrations at the bottom of the tank.

Three successive VVER families were mass-produced in the 1960s (VVER 440/V230), 1970s (VVER440/213) and 1980s (VVER 1000/320). The two VVER 440 models (both with 440 MWe electrical...