Small modular reactor (SMR) concept has been developed as one of the key solutions for the growing demand of safe and clean energy. SMR designs can be applied extensively in areas such as sea water desalination and small-scale power generation etc. Unlike conventional light water reactors, most SMRs greatly simplify the structure of reactor pressure vessel, usually eliminate pumps and use natural circulation to cool down the core and transfer energy. However, flow instability may easily occur and affect the entire two phase natural circulation, which is of great importance for the start-up and normal operation process of BWR-type SMRs. For PWR-type SMRs, two-phase natural circulation could exist during accidents such as small break loss of coolant accident (SBLOCA) and loss of heat sink. Current research aims to experimentally investigate potential flow instabilities related to natural circulation for a PWR-type SMR during the accidents. For current research, the NuScale reactor design is selected as the research prototype.

In this paper, the design and scaling analysis of a scaled PWR-type experimental facility are provided. In order to experimentally study the natural circulation behavior of PWR-type SMR during accidental scenarios, detailed scaling analyses are necessary to ensure that the scaled phenomena could be obtained in a laboratory test facility. A three-level scaling method is used to get the scaling ratios derived from various non-dimensional numbers. An ideally scaled facility is first accomplished based on derived scaling ratios. RELAP5 simulations of both steady state and transient cases for the ideally scaled facility are performed and compared to the prototype to ensure the accuracy of the scaling analysis. Then the ideally scaled facility is modified under engineering considerations and an engineering scaled facility is designed. Similar RELAP5 analyses are performed on the engineering scaled facility and the results match well with those in the prototype and ideally scaled facility.

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