2.1. SESSION I: HLM COMPATIBILITY WITH STRUCTURAL MATERIALS:
PHENOMENA, MODELLING AND OPERATIONAL EXPERIENCE K. Tucek (European Commission, Joint Research Centre),
Session I discussed aspects related to the structural material compatibility with HLM, specifically what concerns the involved phenomena, performed modelling and experimental activities, as well as acquired out-of-pile operational experience. The Session included six presentations from four IAEA Member States and one International Organisation (European Commission, Joint Research Centre/JRC).
The first presentation of A. Hojná (CVR, Czech Republic) provided a very comprehensive overview of experimental assessments of the structural material compatibility of T91 ferritic martensitic steel and 15-15Ti austenitic steel with lead and lead-bismuth eutectic (LBE), forming also an important contribution to the discussion on the involved degradation phenomenology (in particular, the mechanism of crack initiation). The crack initiation tests verified the immunity of 15-15Ti to liquid metal embrittlement (LME) and environmentally assisted cracking (EAC),) and showed the sensitivity of T91 steel to LME/EAC with tendency to crack initiation in contact with liquid lead at 350-400 °C and liquid LBE at 300°C at stresses above ultimate tensile strength (UTS) and high plastic deformation. Based on the new and past research experience is stated that the T91 steel can be sensitive to LME/EAC in low flow HLM, but only beyond design loads of operation of Gen IV systems’ components.
Two presentations were further given by RATEN ICN (Romania), reporting on R&D activities in support of the FALCON (Fostering ALfred CONstruction) Consortium and the deployment of the European demonstrator of the LFR technology (the Advanced Lead Fast Reactor European Demonstrator - ALFRED). The first presentation delivered by D. Gugiu (a neutronic study of refractory metals –Vanadium and Molybdenum alloys) envisaged to be used as alternative fuel cladding materials for the ALFRED reactor. The key observations are that the molibden alloys, especially Mo-Re alloys can significantly affect the neutron economy of the reactor when used as fuel pins cladding. Due to the microstructural changes that were observed the use Mo-Re alloys with high rhenium concentrations in neutron environments is not recommended. The use of vanadium results in an increase of the reactivity, but this effect could be managed by control rods or through changing the fissile enrichment during the design phase.
The proposal for further studies of formation of gaseous elements with irradiation and increase of chromium was made.) In the second presentation, A. Nitu reported on the development of experimental capabilities for mechanical testing in molten lead at RATEN ICN, including the discussion of results of preliminary tensile tests conducted in-situ on 316L-grade austenitic steel.
The fourth presentation of V. Slugeň (Slovak University of Technology) explained benefits and challenges related to the use of positron annihilation spectroscopy (PAS) to study vacancy type defects induced by irradiation. The corrosion behaviour of steam generator tubes and related experimental activities supporting the ongoing construction licensing of the BREST-OD-300 LFR demonstrator in the Russian Federation were then comprehensively discussed by K. Shutko (NIKIET). The main conclusion here is that the material of heat exchanger tubes (EP302M stainless steel) demonstrates adoptable corrosion and corrosion-mechanical behavior for providing reliable stem generator (SG) designed service life of 30 years. In this context, the dual/combined aspects of steam corrosion and lead corrosion were addressed in relation to the
advanced austenitic steel (EP302M) considered for BREST-OD-300. Lastly, the sixth presentation of K. Tuček (EC/JRC) described development and acceptance testing of a new experimental facility for performing mechanical tests in molten lead in oxy gen-controlled environment at temperatures up to 650 °C, and reported on outcomes of the first campaign of slowstrain rate tensile (SSRT) tests of T91 in oxygen-depleted lead environment. It shows that the ductility of T91 does not decrease compared to the reference tests in argon, meaning no LME effect occurred under these conditions. Further tests are recommended to make a conclusion about T91 susceptibility to LME in liquid lead.
Two special presentations were also made during this session, one presentation on the status of the IAEA CRP on fuel materials for fast reactors and other on IAEA publication rules and guidelines.
2.2.SESSION II: CORROSION MITIGATION MEASURES: COATING, NEW STRUCTURAL MATERIALS, ENVIRONMENTAL CONDITIONING
P. Szakalos (KTH), A. Weisenburger (KIT)
Eight presentations have been provided in the session highlighting different aspects of corrosion and corrosion mitigation strategies. Two presentations focused on corrosion of conventional ferritic/ martensitic and austenitic steels at different conditions. One of these presented the innovative steam generator design concept for the micro-modular LFR. The newly designed double walled layer functionally graded cellular (FGC) tubes were introduced and it was determined that the 316L austenitic steel is suitable for the lead-bismuth side. While the other proposed the addition of silicon for corrosion mitigation(Si-containing stainless steel and oxide dispersion strengthened-China low activation martensitic (ODS-CLAM) steel proposed by The Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences - INEST, CAS).
The results revealed that the corrosion resistance with the addition of silicon gained a considerable improvement. Three presentations addressed the development of alumina-forming austenitic (AFA) steels; the first presented the results of corrosion resistance of AFA alloy. It was proven that the AFA alloy has promising corrosion behavior and mechanical properties compared with the AISI316L reference material. Thus, AFA steels could be suitable cladding materials used in in liquid lead at elevated temperatures. Other two presentations addressed high- entropy alloys (HEA) The use of Cr-Fe-Mn-Ni high entropy alloys with the lead melts can be recommended to a temperature of 500 ºC. By optimizing the HEA’s composition and by adding additional alloys the operating temperature can be increased. The second presentation showed that elements like niobium or yttrium act either as a principal element (Nb in HEA) or as a minor additions (AFA) and can have a positive effect on the alumina scale formation in molten lead at elevated temperatures. The application of surface alloying was part of a combined presentation. One presentation highlights the use of nano-ceramic coatings in lead environment, proving that the coating guarantees the suppression of the permeation of tritium through the structural steel. Also, the chemical stability was verified, no delamination and no reduction of the thickness of the coating were observed. The other discussed the corrosion mitigation strategies induced by the impurities in the fuel. It was shown that the carbon impurities presented in the composition of the fuel can affect the condition of the steel cladding, mostly in the low temperature part of the temperature range. The possible way to reduce this effect is to block carbon penetration into the shell by adding into its composition an effective carbide former. This can suppress intergranular corrosion of steel cladding.
2.3.SESSION III: QUALIFICATION PROGRAMMES OF STRUCTURAL MATERIALS FOR HLM FAST REACTORS
B. Long (CIAE), E. Stergar (SCK•CEN)
In Session III, five presentations reviewed materials and their selection during the design stage in heavy liquid metal cooled nuclear systems such as MYRRHA, CiADS, ALFRED and SVBR-100. R&D on the application of structural and functional materials as well as possible co ating technologies has been discussed. Contributions came from Belgium (MYRRHA), Italy (ALFRED), Russia (SVBR-100) and China (CiADS).
In the first presentation, Z.G. Wang presented the R&D efforts around the silicon containing ferritic martensitic SIMP steel. This presentation was followed by an overview of the MYRRHA materials research program by E. Stergar and a presentation of S. Bassini about the materials qualification program for the ALFRED reactor. Their research shows that during the short-term exposure of AFA steels in liquid lead the corrosion resistance is very high. The long-term corrosion tests are yet to be done. A. Dedul gave some insights in the materials R&D and licensing processes of SVBR-100. The session was concluded with a presentation by B. Long about the status of the heavy liquid metal corrosion research in the China Institute of Atomic Energy (CIAE). The results show that austenitic stainless steel exhibits a good corrosion resistance under 400 ºC in liquid LBE, while ferritic/martensitic (FM) T91 steel has a slightly better corrosion resistance. And that FM T91 has excellent resistance to lead and bismuth corrosion below 550 ºC.