Overview of CONNECT-NM's sub-task 6.4.5.1 - Roadmap proposal for establishing design rules for ceramic fiber composite

This project has received funding from the Euratom Research and Training Programme under Grant Agreement No. 101165375 Maxime ZABIEGO (CEA-France) –CONNECT-NM’s sub-task 6.4.5.1 leader CEN WS064 PG2 meeting –April 14th 2025 Overview of CONNECT-NM’s sub-task 6.4.5.1 Roadmap proposal for establishing design rules for ceramic fiber composites Table of contents •Brief introduction •Background information •Context: development of a mixed (CMC-metal) cladding for PWR fuel rods •History: development of a mixed (CMC-metal) cladding for nuclear fuels •Motivation: mixed (CMC-metal) claddings open perspective for extended operation •CONNECT-NM sub-task 6.4.5.1 •Standard criteria for fully-ceramic claddings: ASME BPVC –Section III –Division 5 •Objective: search for relevant design criteria & related testing •Proposed extension of “standard” criteria •Current basis for codification & composite claddings •Conclusion & perspectives April 14th 2025 CEN WS064 PG2 meeting 1 Brief introduction April 14th 2025 CEN WS064 PG2 meeting Brief introduction –About me Maxime ZABIEGO –CEA Cadarache –Nuclear Fuel Studies Involved in design studies for innovative nuclear fuels •GFR: Ceramic core elements 2008-2012 •SFR: Reactivity Control Systems for ASTRID (2014-2018) •RTG: NP-SAFE (2013), PULSAR (2022-2024), GAIA (2022-2025) •PWR: Accident Tolerant Fuels (2011-2025) Not a specialist of codification: mostly an occasionnal user (RCC-MRx, RAMSES-II) Special interest in ceramic composite claddings (SiCf/SiC) Ongoing partnership with Framatome on mixed (CMC-metal) cladding for PWRs April 14th 2025 CEN WS064 PG2 meeting Brief introduction –About CONNECT-NM sub-task 6.4.5 CONNECT-NM sub-task 6.4.5 is dedicated to “design rules and material characterization for ceramics and ceramic fiber composites” Focus on SiCf/SiC claddings for LWR fuels, with multi-layer / multi-material design Three sub-tasks •6.4.5.1: Design rules •6.4.5.2: Modelling (homogenization) •6.4.5.3: Mechanical characterization & pre-normative activity Regarding sub-task 6.4.5.1, the underlying idea is to investigate the possibilities of adapting existing codes to the European products of interest •Review existing approaches •Propose a roadmap for adaptation, with focus on mixed (CMC-metal) claddings Anticipating codification appears interesting, even though it’s not presently required / necessary 2 Background information April 14th 2025 CEN WS064 PG2 meeting Context: development of a mixed (CMC-metal) cladding for PWR fuel rods In the context of Accident Tolerant Fuel (ATF) developments, Ceramic Matrix Composites (CMC) based claddings are envisionned as a long-term solution US option: fully ceramic French option: mixed « CMC-metal » April 14th 2025 CEN WS064 PG2 meeting History: development of a mixed (CMC-metal) cladding for nuclear fuels CEA has been involved in R&D on nuclear applications of CMCs for over 20 years •GFR: 2005-2012 •SFR: 2010-2014 •ATF (PWR): since 2011 Active partnership with Framatome Exploratory codification studies (RAMSES-II code) The present SiCf/SiC cladding design (mixed CMC-metal) is at TRL 4 The activity covers •Design: patents & dimensioning studies •Modelling: thermal/mechanical properties & fuel element simulations (FEM) •Fabrication: multi-layer/multi-material tubes & closure (end-cap joining) •Characterization: large variety of testing protocols & normative activity •Irradiation: cladding samples irradiated in Gösgen & rodlets irradiated in ATR April 14th 2025 CEN WS064 PG2 meeting Motivation: Mixed (CMC-metal) claddings open perspective for extended operation Complementary to the SiCf/SiC cladding reinforcement a metallic liner can ensure leak-tightness beyond PLS Fully ceramic option Mixed (CMC-metal) option Previous studies identified the need for specific design criteria to define usage limits associated with these mixed (CMC-metal) claddings April 14th 2025 CEN WS064 PG2 meeting Conclusion & perspectives Previous CEA-Framatome studies pointed at the lack of relevant criteria for dimensionning mixed claddings with outer CMC reinforcement & inner metallic liner There’s aclear need, for SiCf/SiC-based ATF cladding, to coordinate efforts on characterization, modelling and their integration with design activities Codification strategies can help guiding this task Beyond reviewing codification literature to establish a roadmap, our primary objective is to identify both criteria & testing protocols,in order to characterize the ability of a damaged cladding (nominal thermal stress) to ensure proper nominal behaviour and resistance to “ultimate”loads (high-BU PCMI, accidental transients…) What interaction could this task have with CEN WS064 PG2? •Codes & standards expertise is more than welcome •Possibility of applications beyond the reference product (PWR fuel rod) could be investigated, so as to allow for broader collaboration on applications of mutual interests (if any) •Cécile Pétesch proposed that we investigate the possibility of amulti-code (RCC-C & RCC-MRx) guide Thank you! This project has received funding from the Euratom Research and Training Programme under Grant Agreement No. 101165375 [email protected] Who wants to ask the first question ?  5 Complementary slides April 14th 2025 CEN WS064 PG2 meeting CONNECT-NM sub-task 6.4.5.1 statement The ambition of deploying new materials at the industrial scale necessitates the availability of consolidated design rules, such as featured in the RCC-MRx, for instance. It can be anticipated that design rules will be a requirement for the deployment of ceramic structural materials, such as C and/or SiC based monolithic or composite materials, for nuclear applications. Through the extended program driven by the development of Accident Tolerant Fuels, in the United-States, the American Society of Mechanical Engineers (ASME) issued a Boiler and Pressure Vessel Code (BPVC), dedicated to Rules for Construction of Nuclear Facility Components, for High Temperature Reactors, in 2019 (subsequently updated in 2021 and 2023), with a section dedicated to composite materials. A similar approach appears necessary in Europe. This sub-task would consist in writing a roadmap for such a document, which would need to be adapted to the structural materials targeted for priority applications. Indeed, the code developed in the US is specific to domestic material options which are not necessarily similar to those adopted by European partners. For instance, while General Atomics considers fully ceramic options for ATF claddings, CEA and Framatome rather aim at developing mixed (metal and ceramic) cladding options, which are considered more robust for ensuring cladding leak-tightness. This undoubtedly affects design rules and requires specific approaches. The objective of this sub-task would be to identify the type of products (ceramic-based structural materials and their targeted applications) prioritized by European partners, as well as their specificities, in order to propose relevant design rules, relying on modelling and characterization studies developed in the other two sub-tasks. Sub-task 6.4.5.2 = modelling / Sub-task 6.4.5.3 = mechanical characterization & pre-normative activity April 14th 2025 CEN WS064 PG2 meeting About ASME’s BPVC-III-5 semi-probabilistic approach ASME’s BPVC-III-5 relies on asemi-probabilistic approach that is based on aWeibull law. This applies to monolithic ceramics but not necessarily to (pseudo-ductile) SiCf/SiC composites. It is consistent with US claddings relying on monolithic layers to ensure leak-tightness. Composites with long fibers have been shown to exhibit reproductible (quasi-deterministic) behaviours,as long as their dimension is large enough relative to the elementary pattern of the fibrous preform. Except for details (porosity, defects…)which only account for minor deviations from mean behaviour, SiCf/SiC claddings do not rely on Weibull law. ASME’s semi-probabilistic approach might make sense for the US fully-ceramic design, but not necessarily for the French mixed design April 14th 2025 CEN WS064 PG2 meeting Experience from previous studies Fully-ceramic cladding : Mechanical behaviour A. Elastic response: PLS associated with leak-tightness loss B. Cracking initiation: softening of the response (Young modulus evolution) C. Cracking saturation: load transfer to fibers (Permanent deformation) D. Ultimate failure: UTS April 14th 2025 CEN WS064 PG2 meeting CEA’s normative activity on ceramic composites April 14th 2025 CEN WS064 PG2 meeting Characterization protocols: mechanical properties & damageable behaviour •Uniaxial tensile test [ISO-20323 & ISO/DIS-4255]: primary & membrane •Burst (pressure [ISO-21971] / expanding kernel) test: primary & membrane •C/O-ring compression test: secondary & bending (albeit azimuthally localized) Primary &membrane loading mode Secondary &(localized) bending loading mode April 14th 2025 CEN WS064 PG2 meeting Characterization protocols: cracking damage « Rabbit » capsule irradiation is the most representative testing protocol, to date The missing part : what’s the residual resistance of such a damaged cladding ? Secondary &(distributed) bending loading mode Not a through crack ! Tensile stress on the inside (compressive on the outside) maximum at shutdown April 14th 2025 CEN WS064 PG2 meeting In-reactor behavior of a mixed (CMC-metal) PWR cladding Mixed cladding implement materials that behave differently under reactor operation Hence, differential behaviours, potentially leading to interactions, must be anticipated •Initial gaps, closed in the course of irradiation Fast opening then closure for liner-reinforcement gap (swelling &creep-out) Slow closing for pellet-clad gap (swelling &no creep-down) •CMC-reinforcement can prevent failure of the thin metallic liner •Metallic liner distributes potentially concentrated loads on CMC-reinforcement •Acceptability of operating with a cracked reinforcement (but leak-tight liner) must be assessed Residual resistance of cracked reinforcement Corrosion issues, particularly if through-cracks occur