January/February 2000 - Highlight

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Highlight

A vacuum leak test and related repairs have improved the capacity factor of Rivne Unit 3. The improvement is beneficial to both safe steady- state operation of the plant and increased electricity production.

Vacuum leak test technique shows promise in improving plant output

Results of experimental tests conducted at Rivne nuclear power plant (NPP) indicate that a leak test technique may be an effective means of increasing the output, or capacity factor, of Ukraine's nuclear power plants. Increased output will enable the plants to run at steady-state power levels, well above the low vacuum turbine trip setting. During steady-state operation, conditions such as temperature, reaction rate, and neutron flux do not change appreciably with time. This operational state tends to be the safest for a nuclear power plant. Improved capacity factors also hold potential for increased electricity to sell, with attendant increase in revenues to a plant, raising the capability to pay for critical equipment maintenance and personnel salaries.

The tests were an outgrowth of a U.S.-supported project completed in June 1999, in which potential methods were identified for improving nuclear power plant capacity factor. A key recommendation emerging from that project was to reduce vacuum leaks in a plant's main condenser. Because those leaks reduce efficiency, their elimination can increase the amount of electricity a plant produces.

Air leakage into a vacuum is difficult to detect. In Ukraine, the primary technique used to discover these leaks is called a smoke test. The smoke test involves holding a candle near potential vacuum leaks and tracing the path of the smoke.

A more advanced technique involves mixing a phosphorescent dye with water. The mixture is sprayed with an atomizer bottle in the area surrounding equipment that is under vacuum. An ultraviolet light is used to locate the paths followed by the mixture. Dye is drawn toward the leakage point and concentrates there, making the leak visible under ultraviolet light. After the leaks are located, minor repairs are made immediately and major repairs occur during the subsequent outage.

Ukrainian nuclear specialists conducted three vacuum leak tests at Rivne Unit 3 over the past few months (September, December, and January) under various conditions (demonstration, cold equipment during start-up, and hot equipment during operation). After each test, major leaks were repaired, including leaks with an equivalent air in-leakage of 40 kilograms/hour. The method was especially valuable in detecting small leaks and leaks in areas difficult to inspect with older methods like the smoke test.

Test results were made available at the end of February following Rivne's annual outage. Although the results are preliminary, the capacity factor for the Rivne Unit 3 VVER-1000 reactor increased by approximately 5 megawatts electricity, a significant improvement. The excellent results suggest the value of applying this technique at all nuclear power plants in Ukraine with VVER-1000 reactors. (Rich Reister, DOE, 301-903-0234; Bob Talbert, PNNL, 509-372-4061)