ELSMOR has been organized in several work packages that have started in parallel.
In the first phase of the project, a review of the European nuclear safety directives as well as IAEA and WENRA guidance and national rules and regulations was done. A list of about 21 different SMRs have been investigated with regards to specific and innovative design decisions used to fulfill the regulatory requirements. Finally, potential challenges for safety demonstration have been identified for the following points: Reactivity control; Decay heat removal; Containment integrity; Decommissioning; Refuelling, spent fuel management, transport and disposal; Multi-unit site and sharing of systems issues; Severe accident management and; Operation and human factors.
Review of the general safety requirements regarding the implementation of defense in depth and subsequent plant conditions to be analysed in the design, mainly based on WENRA requirements, and identification of possible adaptations due to LWR SMR specificities was performed. Then, a review of the methodologies recommended for the design and preliminary safety assessment of Gen4 plants and recommendations for their applicability to LWR SMRs was finalized. In parallel to this review work, a systematic methodology of deriving the high level requirement into more detailed requirements was created.
One of the project focuses is the core cooling safety functions of integral light-water small modular reactors (LW-SMRs). The work to be performed is associated with safety analysis, development and assessment of codes and models, specification of scaling or other requirements for tests and experiments to characterize the most promising passive systems to accomplish the relevant safety function in SMR designs. During the first phases, the first tasks have been accomplished, with the completion of “Simplified PIRT on passive safety systems of integrated PW-SMRs for decay heat removal” and “State-of-the-art of the relevant experiments for SMR safety”. The focus for the second phase has been in the preparation of experimental work. For the experimental activity the test heat exchanger has been ordered and pre-test analyses have been started with the preparation of the RELAP model of the facility.
For the containment studies there has been performed the elaboration of a reduced PIRT, with focus on thermal hydraulic phenomena regarding the containment safety functions and focusing on containment heat removal issues. Two designs were selected as being of major interest. In compliance with the ELSMOR project, the French NUWARDTM (formerly F-SMR) concept was the obvious choice. In addition, the NuScale concept was chosen since it is in an advanced state and recently received design certification approval from the U.S. NRC. An important outcome is the identification and assessment of phenomena or physical processes, their mathematical modelling, as well as the experimental data needed to evaluate the safety function behavior and gaps still existing and necessary to be closed in whatever field. This is done relative to a specific objective, so called Figure Of Merit (FOM) that is in this case the assurance of containment integrity by keeping its pressure well below plant specific design limits. The main result of this PIRT process is a matrix containing relevant phenomena necessarily to be considered to provide a better understanding of the safety functions in the containment, water pools within and outside of the containment and the heat transfer from and to the containment shell.
Database on "E-SMR" has been prepared, with the intent on creating a SMR dataset for future academic exercises using publicly available information. Summer School has been held in Lecco, Italy on 5.-9.7.2022.
ELSMOR has produced studies on safety concepts and challenges of SMRs, produced experimental data on plate type heat exchangers; studied heat transfer across a water wall of submerged containment; produced an academic free to use database of light water SMR for scientific studies and training; and produced open educational material on SMRs.
