ALFRED: A revised concept to improve pool related thermal-hydraulics

Highlights: • Thermal-hydraulic challenges are addressed from a design stand-point. • Thermal stratification is avoided through an internal structure. • Mitigation of steam entrainment from SGTR prevents positive reactivity insertion. • Lead freezing in passive mode is avoided by self-regulation through non-condensable gases. • An experimental infrastructure aimed at the qualification of the design features is planned in Romania. - Abstract: ALFRED, namely the Advanced Lead-cooled Fast Reactor European Demonstrator, has been conceived to serve the industrial deployment of the Lead-cooled Fast Reactor (LFR) technology. ALFRED is a demonstrator reactor designed with the specific purpose to test and qualify innovative components and procedures to be used in commercial reactors. In its role of European Technology Demonstrator Reactor, it will offer a representative operational environment of interest for research organizations, industry and safety authorities. Initially developed as part of a collaborative effort funded through the European 7th Framework Programme, the project was taken over by an international consortium Fostering ALFRED Construction (abbreviated to FALCON). As one of the priorities of the consortium Expert Board, the ALFRED design underwent an in depth review, aimed at identifying and addressing vulnerabilities in terms of reliability and safety, investigating also scalability of the design, flexibility for maintenance and replacement, manufacturability of components, availability of codes and standards for nuclear components and materials. The reactor coolant system arrangement was found susceptible to two main thermal-hydraulic issues typical of Fast Reactor (FR) pool-type designs: (i) thermal stratification in the upper part of the pool and (ii) potential steam entrainment in case of Steam Generator Tube Rupture or leakage. Moreover, (iii) the risk of lead freezing, more specific to the use of high melting point metals as coolants, represented a third issue, of particular concern in conjunction with the passive residual heat removal function in accident conditions. Starting with a general description of the ALFRED Project framework, including the experimental facilities in support to the LFR Research, Development and Qualification plan, the paper will focus on the new system arrangement and Decay Heat Removal (DHR) system of the ALFRED concept design, aimed at improving the pool thermal-hydraulics against the above described issues and risks. Since the ALFRED revised configuration is considered to offer improved safety and robustness, the FALCON consortium is willing to share the outcome of private and national investments, with hope of stimulating new opportunities for further developments and investigations through advanced computational tools and experimental tests within the LFR research community.