Reactor Types:	|	RBMK	|	VVER 440/213	|	VVER 440/230	|	VVER 1000

VVER-440 Model 230

The earliest pressurized water nuclear plants were developed by the Soviets between 1956 and 1970.

Principal Strengths:

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 deficiencies.

Principal Deficiencies:

Accident 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.

Major 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 standards.

Quality of materials, construction, operating procedures and personnel training are below Western standards.