Development and testing of multicomponent fuel cladding with enhanced accidental performance

The structural characteristics of VO x films prepared by He-introduced reactive RF unbalanced magnetron sputtering

Traditional design of CPR1000 nuclear plants has a lot of studies on engineering safety facilities which are important for Design Basis Conditions (DBC). Based on more recent studies on safety, such as Defense in Depth (DID) concept, Probabilistic Safety Analysis (PSA), and especially after lessons from Fukushima Nuclear Accident, more and more attentions are paid to Design Extension Conditions (DEC). This paper has studied the abilities and requirements of CPR1000 Nuclear Plants for DEC accidents mitigation. Some important modifications on mechanical systems are introduced. DEC accidents are separated into DEC-A, and DEC-B. DEC-A accidents are caused by multiple failures. A main reason for a multiple failure is Common Cause Failure (CCF), such as CCF on Emergency Feed Water System (EFWS) pumps, Emergency Core Cooling System (ECCS) pumps, Emergency Diesel Generators or Cooling chain. Diverse design should be considered to deal with CCF. Several modifications are applied, such as enhancing EFWS turbine pumps, fast-backup between ECCS and Containment Spray System (CSS), mobile water makeup and mobile injection for primary and secondary side, etc. For DEC-B, which means severe accidents, several dedicated systems are added to CPR1000 design, such as hydrogen monitor and control, containment venting filter and In-Vessel Retention systems. Thanks to all the modifications, CPR1000 can sufficiently improve its defense for DEC accidents, which will help CPR1000 to reach a new safety level.

After the Fukushima Daiichi Accident, the safety features such as accident tolerant fuel (ATF) and diverse and flexible coping strategies (FLEX) for existing nuclear fleets are being investigated by the US Department of Energy under the Light Water Reactor Sustainability Program. This research is being conducted to quantify the risk-benefit of these safety features. Dynamic probabilistic risk assessment (DPRA)-based response-surface approach has been presented to quantify the FLEX and ATF benefits by estimating the risk associated with each option. ATFs with multilayered silicon carbide (SiC), iron-chromium-aluminum, and chromium-coated zirconium cladding were considered in this study. While these ATF candidates perform better than the current zirconium cladding (Zr), they may introduce additional failure modes in some operating conditions. The fuel failure analysis modules (FAMs) were developed to investigate ATF performance. The dynamic risk assessments were performed using RAVEN, a DPRA tool, coupled with RELAP5 and FAMs. A cumulative distribution function-based index provided a mean of comparing the benefits of safety enhancements. For medium break loss of coolant accidents, FLEX operational timing window for each fuel type was estimated. Among these ATF candidates, SiC-type ATF was the most beneficial candidate for an increased safety margin than Zr-based fuel and was found to complement FLEX strategies in terms of risk and coping time.

Zirconium-based cladding materials used in nuclear power plants have been shown to pose safety concerns due to their susceptibility to oxidation and hydrogen production during high-temperature conditions, such as loss-of-coolant accidents. In order to address these concerns, alternative cladding materials that are more resistant to these conditions are being explored. This study investigates the potential of using silicon carbide (SiC) and iron-chromium-aluminum (FeCrAl) cladding materials to improve the safety and efficiency of nuclear power plants, particularly in the context of accident tolerant fuel (ATF) technology concepts. The study utilized Serpent Monte Carlo 2.31 to conduct neutronics analyses on the APR-1400 reactor, assessing the impact of SiC and FeCrAl cladding materials on fuel reactivity, neutron spectrum, Pu-239 inventory, and pin power distribution. A sensitivity analysis was conducted by adjusting parameters such as fuel enrichment, cladding thickness, and pellet diameter to determine the effects of the new materials on design parameters. Results of the analysis revealed that, by adjusting design parameters, SiC and FeCrAl materials could be used to meet the cycle length of the original fuel-cladding (zircalloy). Furthermore, using SiC cladding resulted in a hardening of the neutron spectrum, which increased the production of actinides such as plutonium. By analyzing the effects of changing parameters, including fuel enrichment, fuel geometry, and cladding material, the study concludes that SiC is a feasible substitute for conventional zirconium cladding. The findings of this study have practical implications for the safety and efficiency of nuclear power plants. The use of SiC and FeCrAl cladding materials could significantly reduce the risks associated with loss-of-coolant accidents and other high-temperature conditions, thereby improving the safety and reliability of nuclear power plants.

Uncertainty analysis of ATF Cr-coated-Zircaloy on BWR in-vessel accident progression during a station blackout

Substructure in the columnar crystals of the Ti0.45O0.20N0.35 oxynitride thin film

The electrical and optical properties of carbon-nitride CNx films (0⩽x⩽0.25) deposited by unbalanced reactive magnetron sputtering from a graphite target in mixed Ar/N2 discharges at a substrate temperature of 350 °C have been investigated. Pure C films exhibit a dark conductivity at room temperature of 25 Ω−1 cm−1, which grows up to 250 Ω−1 cm−1 for CNx films with N content of 20%. For CNx films, temperature-dependent conductivity measurements suggest that two electron conduction processes exist in the investigated temperature range 130<T<300 K. Under white-light illumination, photoconductivity is observed. The film optical properties obtained from spectroscopic ellipsometry measurements between 1.24 and 5 eV indicate a semimetallic behavior with a large amount of sp2 bonds in the material. The measured electrical and optical properties of the films are related to the apparent film microstructure and bonding nature. Electron microscopy show that the addition of N2 in an Ar discharge leads to a transformation from amorphous to a fullerene-like microstructure consisting of curved, frequently intersecting, and highly in-plane oriented basal lattice planes.

Superhard nanocomposite coatings of TiN/Si 3N 4 prepared by reactive direct current unbalanced magnetron sputtering

The coating of engineering components with electroplated hard chromium is a widely used practice. These coatings are reasonably hard (~1000 HV) and are deposited in thicknesses of ~20 μm, having a fine microcracked structure. Physical vapour deposition (PVD) is an alternative technique, replacing the limited performance and environmentally unfriendly electroplating process (hexavalent chromium). CrNx is the most promising PVD coating to replace electroplated hard chromium. In contrast to other PVD hard coatings, it can be deposited in thicknesses up to 50 μm and at deposition temperatures below 250°C. The unbalanced magnetron sputtering technique allows reasonably high growth rates, typically several micrometers per hour. In contrast to cathodic arc evaporation, unbalanced magnetron sputtered coatings are smooth, without the arc typical droplets. The deposition equipment used in the present study allowed a wide range of deposition parameters leading to insights in the growth of bcc Cr–N, hcp Cr2N, and fcc CrN coatings. The following modifications were observed: a fine grained solid solution bcc Cr–N (1800 HV at 18 at.-%N) with a Young's modulus similar to that of steel; an under stoichiometric hcp Cr2N phase (2200 HV at 24 at.-%N); a soft single phase stoichiometric hcp Cr2N phase (1600 HV at 33 at.-%N); the established {110} textured fcc CrN phase (1800–2000 HV) and finally, a new hard fcc CrN phase (2700–3100 HV) obtained with high bias voltages ( >- 200 V) and nitrogen flow rates in excess of the argon flow. The latter coating promises excellent properties with respect to wear, friction and corrosion.

After the Fukushima nuclear disaster, the nuclear materials community has been vastly investing in accident tolerant fuel (ATF) concepts to modify/replace Zircaloy cladding material. Iron–chromium–aluminum (FeCrAl) alloys are one of the leading contenders in this race. In this study, we investigated FA-SMT (or APMT-2), PM-C26M, and Fe17Cr5.5Al over a time period of 6 months in simulated BWR environments and compared their performance with standard Zirc-2 and SS316 materials. Our results implied that water chemistry along with alloy chemistry has a profound effect on the corrosion rate of FeCrAl alloys. Apart from SS316 and Zirc-2 tube specimens, all FeCrAl alloys showed a mass loss in hydrogen water chemistry (HWC). FA-SMT displayed minimal mass loss compared to PM-C26M and Fe17Cr5.5Al because of its higher Cr content. The mass gain of FeCrAl alloys in normal water chemistry (NWC) is significantly less when compared to Zirc-2.

Chromium nitride and chromium oxynitride thin films were successfully deposited onto carbon, silicon and low carbon steel substrates by DC reactive magnetron sputtering using a chromium metallic target. Argon-nitrogen and argon-air mixtures were used as reactive gases to deposit CrN and Cr<sub>x</sub>N<sub>y</sub>O<sub>z</sub> films, respectively. The total flow (argon + reactive gas) was kept constant during all deposition processes. Relative humidity of air (water vapour pressure) was systematically changed from 0 to 90 % RH. Behaviour of the cathode was studied as a function of reactive gas flow and water vapour pressure. Evolution of the deposition rate and composition of the deposited films with increasing of reactive gas flow and amount of water vapour injected into the process was studied by Rutherford Backscattering Spectroscopy (RBS) and Resonant Nuclear Reaction Analysis (RNRA). The chemical bond was determined by Energy Electron Induced X-ray Spectroscopy (LEEIXS) and X-ray Photoemission spectroscopy (XPS). Hydrogen and nitrogen profiles were determined by RNRA. RBS and LEEIXS results have shown that in metallic mode, the composition can be fitted by CrN and Cr<sub>2</sub>O<sub>3</sub> stoichiometries, but in compound mode the CrO<sub>2</sub> stoichiometry predominates. XPS results have shown the coexistence of another phase with (CrO<sub>2</sub>)<sub>3</sub>N stoichiometry. Its proportion depends on the N content in thin films.

Effect of N content on phase configuration, nanostructure and mechanical behaviors in Ti–C x–N y thin films

In this work, nonstoicheometric titanium oxide film on silicon matrix was prepared by unbalanced reactive pulsed magnetron sputtering /hydrogen plasma reduction method. The film chemical composition was analyzed by X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The XRD patterns of the prepared films showed that titanium oxide films possess the single phase rutile structure . the XPS spectra of the film displayed that the valence state of Ti is Ti4+, Ti3+ and Ti2+ respectively and the films were nonstoichiomeric Ti-O film. The evidence showed that isolated oxygen exist in films. Ti/O ratio of Ti-O film from the XPS data vary with depth under different reduction temperature and time. And it corresponded with platelet adhesion tests of Ti-O film in vitro. Antithrombotic property of reduced titanium oxide thin films was examined by platelet adhesion tests. The results showed that the Ti-O films with lower non-stoicheometrical extent posses the better anticoagulation property than stoichiomeric TiO2 film and the Ti-O films with higher non-stoicheometrical extent. Hence hydrogen introducing is an effective way to improve the bloodcompatibility of titanium oxide film.

Canadian licensing framework of CANDU reactors and safety analysis challenges in the allocation of Emergency Mitigating Equipment

Substitutional solid solution (Ti1−xAlx)N films with different Al contents (0⩽x⩽0.41) were deposited onto unheated Si(100) substrates by reactive unbalanced close-field magnetron sputtering in an Ar–N2 gas mixture. The effect of Al atomic concentration on the sizes of crystal grains during deposition was investigated. X-ray diffraction analysis revealed that the incorporated Al atoms had an obvious impact on the grain growth of (Ti1−xAlx)N films and the average crystal grain size showed an exponential decay with Al atomic concentration. A phenomenological model was proposed to analyze this solute-drag effect occurring during film deposition. It was found that the presence of solute drag in normal grain growth resulted in a low kinetic growth exponent, and the exponential decay in average grain size with solute atomic concentration could be reproduced in our calculations.