Rapid industrialization and urbanization in the last 30 years in China have caused severe air pollution. In order to meet the new challenges on the energy and environment, a new conceptual design of nuclear heating reactor (HAPPY200) is developed. HAPPY200 is a two-loop low pressure water reactor with low thermal parameters and passive safety systems. It can be used for heating, cooling, desalination and other process heat applications. Based on large volume pool completely passive technologies, HAPPY200 safety system can provide an inherent technical guarantee for the safety of the reactor.

The thermal-hydraulic behavior analysis is necessary for the safety and economy of the design. Subchannel analysis is the basic thermal-hydraulic analysis method used to predict the coolant enthalpy, quality, density, mass velocity rate, liquid temperature, vapor void fraction, pressure distribution, and the resulting DNBR distributions.

In this study, the analysis of thermal-hydraulic behavior for low pressure reactor is worked. Some problems are discussed for low pressure reactor, and the subchannel object model is established by subchannel code. Some low pressure CHF correlations developed for other fuel assemblies are analyzed. The thermal diffusion coefficient for reduced-height rod bundle is obtained compared with full-height rod bundle using CFD code. The value of reduced-height rod bundle can be used in the preliminary analysis of HAPPY200. According to the subchannel results, all the values satisfy conceptual design criteria.