Periodic Reporting for period 2 - SCORPION (SiC composite claddings: LWR performance optimization for nominal and accident conditions)
Berichtszeitraum: 2024-03-01 bis 2025-02-28
The Fukushima Daiichi event in 2011 demonstrated the need for enhanced nuclear energy safety, becoming a major driving force for global investments in accident-tolerant fuels (ATFs) over the past decade. Candidate ATF cladding material concepts that are being developed in replacement of the standard zirconium-based alloy (zircaloy) fuel cladding materials used in light water reactors (LWRs) must outperform commercial zircaloys under nominal operation, high-temperature transient (<1200°C) and accident (>1200°C) conditions. SiC/SiC composites are a rather ‘revolutionary’ ATF cladding material concept exhibiting inherent refractoriness, pseudo-ductility, and a lack of accelerated oxidation during a loss-of-coolant scenario. Due to their unique potential in meeting the stringent property requirements of the ATF cladding application, SiC/SiC composites have already claimed large global investments. Despite these investments, all state-of-the-art variants of the SiC/SiC composite cladding material concept must still overcome inherent shortcomings prior to their perspective deployment. Two important weaknesses are their inadequate compatibility with the coolant (water and steam) and the early (<2 dpa) saturation of radiation-induced swelling during nominal operation. SCORPION strives for a radical improvement in the performance of SiC/SiC composite fuel claddings by highly innovative material tailoring on the nanoscale to limit hydrothermal corrosion and radiation swelling, whilst also modifying the fibre/matrix interface for better stability under irradiation and in high-temperature oxidizing environments. SCORPION is an ATF application-driven international collaboration between Europe (including the UK and Switzerland), the USA and Japan, which combines multidisciplinary scientific excellence, stakeholder know-how, and cutting-edge manufacturing approaches to produce proof-of-concept (PoC) SiC/SiC composite fuel cladding materials with a radically optimized performance for Gen-II/III LWR service environments. If SCORPION succeeds in achieving its scientific & technical objectives, it will become an important stepping stone to the prospective deployment of SiC/SiC composite ATF claddings in Gen-II/III LWRs on a global scale.
SCORPION achievements in the 1st & 2nd reporting periods:
WP1 – Processing of bulk proof-of-concept (PoC) materials
• Grain boundary (GB) engineered & doped SiC were produced by SPS. SiC GB decoration by rare-earth (RE)-silicates/garnets and various oxides was successful.
• High-purity RE-silicates/garnets were produced by pressureless sintering; the samples were pulverised and densified via SPS.
• Porous SiC ceramics (uniform/gradient porosity) were produced & characterised.
• State-of-the-art CVD/CVI & LPS SiC/SiC composites were produced.
WP2 – Deposition of PoC coatings
• RE-silicate coatings were made by magnetron sputtering from compound & elemental targets.
• RE-garnet coatings were made by pulsed laser deposition from compound targets.
• The coatings were characterised with various techniques (XRD, ERDA, SEM/EDS).
WP3 – Joining of PoC materials & testing of joints
• Pressure-less joining of SiC/SiC composites was achieved with the help of localised laser heating; the candidate joining materials were RE-silicates/garnets.
• Joining SiC by fibre-reinforced preceramic polymers has been achieved.
• The joint quality was controlled by computed tomography (CT), SEM/EDS.
WP4 – Characterization of PoC materials & joints
• RE-silicates/garnets (bulk samples & coatings) & doped SiC were characterized by SEM/WDS, XRD, FIB, STEM/EELS.
WP5 – Cladding/coolant interaction tests
• The hydrothermal stability of RE-silicates/garnets was tested in autoclave (360°C, 187 bar, PWR water with 1000 ppm B & 2 ppm Li).
• All materials showed negligible weight changes; minor weight loss was observed in 2 samples with small fractions of residual SiO2.
• The steam oxidation resistance of RE-silicates/garnets was assessed:
o Isothermally at 1200°C for 1 h – negligible weight change.
o Isothermally at 1600°C for 1 h – negligible weight change except from 1 sample with residual SiO2.
• The steam oxidation resistance of GB engineered & doped SiC was assessed during slow transient heating to 1600°C – small weight change except from few samples that reacted with the sample holder.
WP6 – Ion/proton irradiation campaigns
• RE-silicates/garnets were in situ ion irradiated in the TEM (600 keV Kr+, 350-1000°C) – despite the harsh test conditions, all materials behaved well (@800°C, crystallinity was retained to >40 dpa).
• Porous SiC appeared stable under in situ ion irradiated in the TEM (600 keV Ar+, RT & 350-1000°C).
• Synergistic proton irradiation/aqueous corrosion tests (5.4 MeV p+, 320°C, 48 h, PWR water with 3 ppm H2) showed better performance for RE-silicates/garnets than CVD SiC.
WP7 – Advanced PIE of BR2-irradiated SiC-based ATF cladding materials
• Hot transport of BR2-irradiated SiC-based claddings from SCK CEN to JRC is ongoing.
WP8 – Predictive modelling activities
• The thermodynamic stability of coating materials was assessed by:
o screening of the entire periodic table, and
o development of CALPHAD databases for 2 ternary systems comprising RE-oxides, Al2O3 and SiO2.
• In-service damage evolution in SiC/SiC composites was simulated by a phase field model with cohesive voxels.
• Stress generation in SiC/SiC composites due to radiation swelling was simulated.
WP9 – Dissemination, communication & training
Four Workshops were organised:
• Workshop on application-driven coating methodologies
• Workshop on multiscale engineering of advanced materials
• Workshop on advanced manufacturing methods for materials frontiers
• Workshop on modelling-enabled material development
WP1 – Processing of bulk proof-of-concept (PoC) materials
• Grain boundary (GB) engineered & doped SiC were produced by SPS. SiC GB decoration by rare-earth (RE)-silicates/garnets and various oxides was successful.
• High-purity RE-silicates/garnets were produced by pressureless sintering; the samples were pulverised and densified via SPS.
• Porous SiC ceramics (uniform/gradient porosity) were produced & characterised.
• State-of-the-art CVD/CVI & LPS SiC/SiC composites were produced.
WP2 – Deposition of PoC coatings
• RE-silicate coatings were made by magnetron sputtering from compound & elemental targets.
• RE-garnet coatings were made by pulsed laser deposition from compound targets.
• The coatings were characterised with various techniques (XRD, ERDA, SEM/EDS).
WP3 – Joining of PoC materials & testing of joints
• Pressure-less joining of SiC/SiC composites was achieved with the help of localised laser heating; the candidate joining materials were RE-silicates/garnets.
• Joining SiC by fibre-reinforced preceramic polymers has been achieved.
• The joint quality was controlled by computed tomography (CT), SEM/EDS.
WP4 – Characterization of PoC materials & joints
• RE-silicates/garnets (bulk samples & coatings) & doped SiC were characterized by SEM/WDS, XRD, FIB, STEM/EELS.
WP5 – Cladding/coolant interaction tests
• The hydrothermal stability of RE-silicates/garnets was tested in autoclave (360°C, 187 bar, PWR water with 1000 ppm B & 2 ppm Li).
• All materials showed negligible weight changes; minor weight loss was observed in 2 samples with small fractions of residual SiO2.
• The steam oxidation resistance of RE-silicates/garnets was assessed:
o Isothermally at 1200°C for 1 h – negligible weight change.
o Isothermally at 1600°C for 1 h – negligible weight change except from 1 sample with residual SiO2.
• The steam oxidation resistance of GB engineered & doped SiC was assessed during slow transient heating to 1600°C – small weight change except from few samples that reacted with the sample holder.
WP6 – Ion/proton irradiation campaigns
• RE-silicates/garnets were in situ ion irradiated in the TEM (600 keV Kr+, 350-1000°C) – despite the harsh test conditions, all materials behaved well (@800°C, crystallinity was retained to >40 dpa).
• Porous SiC appeared stable under in situ ion irradiated in the TEM (600 keV Ar+, RT & 350-1000°C).
• Synergistic proton irradiation/aqueous corrosion tests (5.4 MeV p+, 320°C, 48 h, PWR water with 3 ppm H2) showed better performance for RE-silicates/garnets than CVD SiC.
WP7 – Advanced PIE of BR2-irradiated SiC-based ATF cladding materials
• Hot transport of BR2-irradiated SiC-based claddings from SCK CEN to JRC is ongoing.
WP8 – Predictive modelling activities
• The thermodynamic stability of coating materials was assessed by:
o screening of the entire periodic table, and
o development of CALPHAD databases for 2 ternary systems comprising RE-oxides, Al2O3 and SiO2.
• In-service damage evolution in SiC/SiC composites was simulated by a phase field model with cohesive voxels.
• Stress generation in SiC/SiC composites due to radiation swelling was simulated.
WP9 – Dissemination, communication & training
Four Workshops were organised:
• Workshop on application-driven coating methodologies
• Workshop on multiscale engineering of advanced materials
• Workshop on advanced manufacturing methods for materials frontiers
• Workshop on modelling-enabled material development
In the 1st & 2nd reporting periods, SCORPION made significant progress with respect to the state-of-the-art (i.e. CVD/CVI & LPS) SiC/SiC composite fuel cladding materials. SiC is susceptible to radiation-assisted hydrothermal attack, as confirmed by synergistic proton irradiation/aqueous corrosion tests on CVD SiC. Moreover, LPS SiC/SiC composites are very susceptible to radiation-accelerated dissolution due to the high solubility of standard sintering additives (Al2O3, Y2O3) in warm PWR water. SiC losses in water (nominal operation) is the reason why many technology drivers try to protect SiC/SiC composites with metallic coatings (Cr or Ti/Cr). SCORPION produced two different types of PoC materials to improve the LWR coolant compatibility of SiC-based ATF claddings: (a) RE-silicates/garnets to be used as protective coatings, and (b) GB engineered & doped SiC to ‘seal’ SiC GBs. Both types of PoC materials are more resistant to hydrothermal ageing under irradiation as compared to pure SiC tested under identical test conditions.