Conversion Cycles with Supercritical Fluids for Nuclear Plants

by Petr Hajek
Quality Assurance Institute ltd.

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The supercritical power cycles are taking advantage of real gas behavior in order to achieve high thermal efficiency. The two most common supercritical cycles perform with water and carbon dioxide. The supercritical water cycle enhances thermal efficiency with rising turbine inlet temperature, while the supercritical carbon dioxide (S-CO2) cycle takes advantage of reduction of compressor input power (in comparison with classic Brayton cycle) due to changing properties close to the critical point (30.98°C, 7.38MPa).

The other effort was directed to analyze the real properties of conversion cycles. It is possible to divide this effort into two areas, theoretical studies and experimental verification.

The theoretical studies include mainly analysis of different architectures’ of cycles, in comparison with simple Brayton cycle. Preliminary calculation shows the advantages of recompression cycle.

The second important part of theoretical studies, are analysis and optimization of key components of the cycle that are heat exchangers, compressors and turbo machineries.

Also specific aspects, mainly cycle stability, transient modeling and safety analysis (full power/part load performance, start up, heat up, cooling down, Loss Of Load, Loss Of Coolant Accident, Loss Of Cooling, etc.) are analyzed. The problem of flow oscillations is very important. Safety of all system can be affected with very strong pulsation, which can rise due to relatively high density of S-CO2.

The low temperature cycles with special intermediate heat exchanger and with flow acceleration were partially analyzed.

Two large experimental devices will be realized in Research Centre Rez. The first one, “small” loop, has 500kW electrical power input, the second “large” loop 10 MW.

An “small” experimental S-CO2 loop was built in 1999 in the Czech Republic. The main objective was to obtain experimental data for comparison with previous theoretical studies. This facility was the first of its kind in the world. Its operation and performed measurements have provided many interesting data and thus brought valuable operational experience as well as new objectives for future research and development of S-CO2 cycles. The design and production of the “small” loop is finishing in these days. First operation is planned in 2011.

“Large” 10MW loop will be constructed in Centre Plzen. The goal of the “Large” loop is to check the properties of compete cycles at different architectures. The scale 10MW was found as minimal realistic conversion cycle with turbo machineries, allowing the real comparison with real power plants. The operation is supposed at 2014.