Periodic Reporting for period 1 - ELSMOR (Towards European Licencing of Small Modular Reactors)
Reporting period: 2019-09-01 to 2021-02-28
ELSMOR advances the understanding and technological solutions pertaining to light water SMRs on several fronts: Collection, analysis, and dissemination of the information on the potential and challenges of Small Modular Reactors to various stakeholders, including the public, decision makers and regulators; Development of the high level methods to assess the safety of LW-SMRs; Improvement of the European experimental research infrastructure to assist in the evaluation of the novel safety features of the future LW-SMRs, and; Improvement of the European nuclear safety analysis codes to demonstrate the capability to assess the safety of the future LW-SMRs.
The project will produce a state-of-the-art review of the proposed near term LW-SMRs and their proposed safety features. A methodology for safety analysis will be developed for the innovative LW-SMRs based on the experience in both large reactor analysis methodology as well as the experience in implementing such high-level methodology for Generation IV reactors. The work on passive safety functions of LW-SMRs in ELSMOR will consist of both experimental and analytical assessments of key safety features. The exact solutions differ between the LW-SMR concepts, but in general the verification of the operation of the passive safety functions and the validation of the analysis codes are vital. An application of the developed safety case methodologies and models with a chosen reference design will be performed in order to demonstrate their applicability for real cases. The approach will focus on the safety features of the global design, but with special attention and effort on safety systems that differ from large PWRs.
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.
The analysis of LW-SMR relevant topics e.g. control of the three fundamental safety functions (reactivity, decay heat removal capabilities, containment), fuel handling and transport, SA management. The analyses have been utilizing NUWARDTM data complemented by other SMR design (NuScale). The output of this second section will be a set of recommendations for the technical assessment of LW-SMRs. During the first 18 months period, the work was initiated on specific tasks.
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 18 months, 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”. For the experimental activity the pre-test analyses was started with the preparation of the RELAP model of the facility, in the configuration proposed by SIET, excluding the mock-up heat exchanger of which the necessary information was not obtained.
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.
LW-SMR specificities when it comes to safety considerations and licensing. ELSMOR proposes to
develop methodologies suited to LW-SMR specificities (such as an enhanced use of passive systems,
installation of several reactors within a same building) that provide guidance in the design orientation
from a safety point of view, in the safety assessment and further in the licensing process. Finally, the
project aims to share a common view with key stakeholders of how such methodologies can be used
in the LW-SMR development in Europe.