Utilização de exergia para o diagnóstico de centrais nucleares

Abstract

Nuclear power is a source with firm power, high capacity factor, greenhouse gas emissions similar to renewable plants, and its high implementation costs are compensated by low generation and maintenance costs. As such plants have high power and operate for long periods uninterruptedly, small fluctuations or malfunctioning of their equipment imply significant energy losses. Therefore, efficient operation plant is important to ensure maximum energy production. The use of monitoring and diagnostic techniques in nuclear power plants are fundamental in this process, in order to locate points of unplanned energy losses, allowing to understand its origin and seeking alternatives to mitigate or even eliminate these losses. This work makes use of exergy to evaluate three nuclear power plants with PWR reactors seeking to identify and quantify the equipment irreversibilities, when the plant operates in the design condition and in Valve Wide Open (VWO) condition. The analyses of high and low pressure turbines of nuclear power plants were evaluated according to ASME standards (ASME PTC 6, ASME 6A and ASME 6S). The use of ASME standards allowed us to obtain for the lowpressure turbine: corrected enthalpy in its exhaust, the steam expansion curve, its effectiveness and the quantification of the extracted water. The results allow us to conclude that the variation in mass flow in the nuclear power plant may contribute to increasing the irreversibility of some equipment, but it may favour the reduction of others, according to the operating condition of the secondary circuit. In general, it was observed that the equipment irreversibilities will follow a tendency of growth, or reduction, according to the different operating conditions of the plant, but this tendency of growth or reduction is not observed for the exergetic efficiencies of the equipment, which presented very distinct results between the conditions and the analyzed in the power plants. The analyses also allowed us to perceive that the low-pressure turbine in the condition of wide open valves (VWO) has a higher irreversibility than the one for the design condition, although its power gain is substantially higher, thus compensating the increase of its irreversibility in this condition.