The earliest pressurized water
nuclear plants were developed by the Soviets between 1956 and 1970.
Six primary coolant loops
(providing multiple paths for cooling the reactor), each with a
horizontal steam generator (for better heat transfer), that together
provide a large volume of coolant. In some respects this design is more
forgiving than Western plant designs with two, three or four large
vertical steam generators.
Isolation valves that allow plant
operators to take one or more of the six coolant loops out of service for
repair while continuing to operate the plant. This feature is found in
only a few Western plants.
Ability to sustain a simultaneous
loss of coolant and off-site power, due to coolant pumps and two
internal power generators that "coast down" after a shutdown.
Plant worker radiation levels reportedly lower than many Western
plants, due to selection of materials, high-capacity primary
coolant-purification system, and water-chemistry control.
Ability to produce significant amounts of power despite design and I&C
Localization System--which serves as a reactor confinement--designed to
handle only one four-inch pipe rupture. If larger coolant pipes
rupture, this system vents directly to the atmosphere through nine
large vent valves. Western nuclear plants have containments designed for
rupture of the largest pipes. In addition, the confinement has very
small volume, very poor leak-tightness and poor hydrogen mitigation.
No emergency core-cooling systems or auxiliary feedwater systems
similar to those required in Western nuclear plants.
concern about embrittlement (gradual weakening) of the reactor pressure
vessel surrounding nuclear fuel, due to lack of internal stainless-steel
cladding and use of low-alloy steel with high levels of impurities.
Plant instrumentation and controls, safety systems, fire-protection
systems, and protection for control-room operators are below Western
Quality of materials, construction, operating
procedures and personnel training are below Western standards.