Martin Mareček

A custom low-chromium MoNiCr alloy produced by wire-fed laser directed energy deposition (W-DED) was exposed to eutectic LiF–BeF₂ (FLiBe) at 750 °C for 1000 h to assess corrosion of the retained deposition surface. A nominally 100 × 100 × 100 mm cube was divided into as-built (AB) and hot-isostatically pressed (HIP) portions. Two coupons were extracted from each of the X–Y, Z–X, and Z–Y surface layers of each portion, giving 12 coupons. Each coupon was fully immersed in a separate nominally equal salt charge within a graphite crucible enclosed in an individually sealed AISI 304 capsule. Characterization focused on the original W-DED face. Optical profilometry compared exposed coupons with adjacent unexposed reference regions. Cross-sectional scanning electron microscopy and energy-dispersive X-ray spectroscopy assessed microstructure and near-surface chemistry. The topography measurements showed substantial spatial variability and did not establish a consistent dependence on orientation or material condition. Backscattered-electron images and semiquantitative elemental profiles indicated a shallow near-surface region associated with Cr depletion, without establishing a quantitative penetration depth or corrosion rate. The results provide descriptive screening observations for retained W-DED surfaces under the specific static exposure conditions. Unmeasured salt redox potential and impurity concentrations, together with the limited replication, constrain their use in material qualification.

A Hastelloy N-like MoNiCr alloy produced by wire-laser directed energy deposition (W-DED) was exposed to eutectic LiF–BeF₂ (FLiBe) at 750 °C for 1000 h to assess the effects of manufacturing-generated surface states on corrosion response. Surface-skin coupons were extracted from as-built (AB) and hot-isostatically pressed (HIP) portions of a W-DED cube while preserving either the deposited surface or a wire electrical-discharge-machined (wire-EDM) surface. High-purity LiF and BeF₂ powders were mixed to the eutectic composition (66 mol% LiF–34 mol% BeF₂), melted at 700 °C under nitrogen, and the salt was subsequently remelted and poured over specimens in individual graphite crucibles before hermetic enclosure in laser-welded AISI 304 capsules. Optical profilometry compared exposed coupons with adjacent unexposed reference regions; metallography, SEM, and EDS evaluated microstructure and near-surface chemistry. Preserved deposited surfaces largely retained their orientation-dependent topography, whereas exposed wire-EDM surfaces had lower height-related roughness parameters than the unexposed references and developed a more uniform chromium-depleted region. HIP altered internal microstructure more strongly than macroscopic surface morphology. Because redox potential and a complete material balance were not measured, the results are interpreted as comparative static-screening data for MSR service. Mean chromium-depletion depth was approximately 8 ± 2 µm for preserved W-DED surfaces and 11 ± 1 µm for wire-EDM surfaces.

The Experimental Molten FLiBe Salt Loop (MSL), which was previously damaged during operation, is currently undergoing renovation using a risk-based design approach. An important part of this approach is to reliably define and explore normal and abnormal states of the MSL in order to avoid repeating such failures. A numerical model consisting of heated walls and working fluid volume was created for the ANSYS Fluent code. The quality of this model was checked, and sensitivity analysis for mesh quality was performed. Moreover, another sensitivity analysis was performed for the heat transfer coefficient between the insulation and the surrounding air. A number of different normal and abnormal states were identified, investigated, and described, including the loop filling process, regular operation with natural circulation or forced circulation, heating cutoff without draining, and insulation failure. The results of these investigations will be used for the risk-based design of the MSL renovation; for precise establishment of operation and safety limits, conditions, rules, and procedures before the MSL commissioning; and consequently, on a regular basis, for the risk-based operation, experiments, and maintenance of the MSL.

In this paper is described the concept of a 20 MW microreactor cooled by molten salts with the registered trademark of Energy Well. Energy Well reactor is designed to supply either electricity or heat, in remote areas or into populated areas. The description includes context, main design features, safety systems, thermohydraulic analysis in RELAPS 3D, logistic, and transport of the reactor.

This paper describes the measurement of 55Mn(n,2n) and 127I(n,2n) reaction rates in a well-defined reactor field in a special core of LR-0 reactor. The reaction rates were derived using gamma-spectrometry by measuring gamma activities of irradiated MnO2 and NaI samples at a high purity germanium (HPGe) detector. The spectral average cross section (SACS) in 235U prompt fission neutron spectrum (PFNS) was experimentally determined to be 0.2393 ± 0.015 × 10−3 b for 55Mn and 1.2087 ± 0.052 × 10−3 b for 127I. These obtained results were compared with calculations by MCNP6 code using ENDF/B VII.1, ENDF/B VII, JEFF-3.1, JEFF-3.2, JENDL-3.3, JENDL-4, ROSFOND- 2010, CENDL-3.1, and IRDFF nuclear data libraries. In a case of 55Mn, a good agreement with ENDF/B VII.1, JEFF 3.1, JENDL 3.3, JENDL 4, ROSFOND, and CENDL 3.1 nuclear data libraries was found, where C/E−1 is 0.1%, while IRDFF underestimated by about 15.8%. In the case of 127I, more significant discrepancies were found, where JENDL 3.3 and JENDL 4 overestimate the result by about 31.3%.

A new special structural nickel-based alloy for use in molten fluoride salt environments in molten salt reactors (MSR) began to be developed by the COMTES FHT Company in the Czech Republic as early as 2001. The outcome of this development was the MoNiCr alloy, an alternative to Hastelloy-N. The present study was carried out on two experimentally-manufactured nickel alloys: MoNiCr and HN80MTY. Its purpose was to activate recrystallization processes in the as-cast microstructure of these alloys. In addition, experiments were performed to find a temperature which produces complete recrystallization. Static and dynamic recrystallization was studied in both alloys as well. An important aspect was to determine the lowest amount of deformation which still ensures complete recrystallization and provides as uniform recrystallized grains as possible. Such microstructure is well-suited for subsequent forming operations. Specimen microstructures were characterized using light microscopy (LM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and electron backscatter diffraction (EBSD). Furthermore, corrosion tests of the MoNiCr alloy were conducted.