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[en] The water chemistry control in Nuclear Power Plants (NPPs) is important at least for the next reasons: structural materials integrity, plant radiation levels, deposits build-up and safety. One of the most important NPP systems is Primary Heat Transport System (PHTS) having in view its role in active zone cooling and heat transfer to steam generators. In PHTS the chemical control is directed to keep chemical parameters within specified limits in order to mitigate the corrosion of the key equipment and related piping, to control the corrosion rate and impurities concentration, such as corrosion and fission products and to minimize activity transport and heat transfer surfaces fouling. By operation in aqueous environment at high temperature and pressure, the structural materials from PHTS are covered with protective oxide films, which maintain the corrosion rate in admissible limits. A lot of potential factors exist, which can degrade the protective films and consequently intensify the corrosion processes. In order to minimize these adverse effects, an optimal water chemistry control and corrosion monitoring program were established. The understanding of the corrosion degradation phenomena that result in failure of some components from PHTS of CANDU NPP necessitates investigation of the structural materials corrosion processes in different conditions of water chemistry and temperature. Water chemistry management in Nuclear Power Plants can then be applied to mitigate the corrosive environments inherent in plant operation. The basis of chemistry control process consists of operational experience, laboratory tests, structural materials corrosion behaviour and the transport and deposition of impurities and corrosion products under operating conditions. To investigate the corrosion process of some structural materials from PHTS (Zr alloys) of CANDU 6 reactor corrosion experiments were performed in autoclaves assembled in by-pass loops of CANDU 6 reactor PHTS Cernavoda Unit#1 This paper presents the results obtained by in-situ monitoring of PHWR water chemistry effect on fuel cladding corrosion, Zircaloy-4. The optical metallographic and scanning electron microscopies, as well as XRD analysis have been used to evaluate the corrosion behaviour of the fuel cladding material, Zircaloy-4 coupons exposed in PHTS autoclaves system. The obtained results allowed us to establish the contribution of the water chemistry on the Zircaloy-4 corrosion behaviour. (author)
[en] The out of core structural material in the primary heat transport system of Indian Pressurized Heavy Water Reactor is Carbon Steel (CS). Prolonged operation of these reactors at high temperature and high pressure leads to the formation of activated corrosion products which get deposited on out-of-core surfaces causing radiation field build up and man-rem problems. Though the corrosion rate of CS is reduced by passive magnetite (Fe3O4) film, the radioactivity transport problem necessitates further reduction in the metal ion release. Metal ion passivation method is used to modify the oxide films to control the base metal corrosion. In this context, experiments were carried out to know the extent of improvement in corrosion resistance of CS with the addition of external metal ions such as Ni2+, Zn2+ and Mg2+ compared to Fe3O4. In addition, the effect of Mg2+ on the surface oxide films formed on Zircaloy-2 and Incoloy-800 were also studied. For CS, all the experiments were carried out in a static autoclave with lithium hydroxide in presence of Ni2+, Zn2+ and Mg2+ ions respectively at 250°C exposed for 96 and 240 hours by hydrothermal method. For Incoloy-800 and Zircaloy-2, experiments were done in a dynamic loop for duration of 7, 21 and 42 days only with magnesium ion. The films were characterized both by surface analytical techniques like Raman and GI-XRD for compositional analysis and also by electrochemical techniques for evaluating corrosion resistance properties. On CS, the films grown in presence of metal ions exhibited a higher polarization resistance compared to its absence by impedance studies. Potentiodynamic anodic polarization studies showed a similarity in corrosion current densities for the films obtained in the absence and presence of metal ions. The calculated thickness of these modified films using Clarke’s method was lower in presence of Zn2+ and Mg2+ ions compared to Ni2+ ions and Fe3O4. From the results, it was inferred that the zinc and magnesium ferrites form a more adherent and compact film compared to Fe3O4 and nickel ferrite. On both Incoloy and Zircaloy, a restructuring of oxide was indicated as a function of time and the corrosion rates and defect densities were found to be significantly lower on Mg2+ incorporated oxides. (author)
[en] Facilitating the dissociation of water and desorption of hydrogen are both crucial challenges for improving the hydrogen evolution reaction (HER) in alkaline media. Herein, we report the synthesis of heterostructure of RuP/WO@NPC (N, P co-doped carbon) by a simple hydrothermal reaction using ruthenium and tungsten salts as precursors, followed by pyrolyzing under an Ar atmosphere. The RuP/WO@NPC electrocatalyst exhibits an outstanding HER activity with an overpotential of 15 mV at a current density of 10 mA cm and excellent durability in a 1.0 M KOH solution, outperforming state-of-the-art Pt/C and most reported electrocatalysts. Experimental results combined with density functional calculations reveal that the electron density redistribution in RuP/WO@NPC is achieved by electron transfer from NPC to RuP/WO and from RuP to WO, which directly promotes the dissociation of water on W sites in WO and desorption of hydrogen on Ru sites in RuP. (© 2020 Wiley‐VCH GmbH)
[en] In this work, La2Mo2O9 (LMO) powder was synthesized via the molten salt procedure. The coatings of NiCrAlY/LMO, NiCrAlY/YSZ and NiCrAlY/YSZ/LMO were developed by the plasma-spray process. The NiCrAlY/ LMO coating demonstrated higher oxidation and hot corrosion rates than those of NiCrAlY/YSZ and NiCrAlY/YSZ/LMO coatings. The higher oxidation and hot corrosion rates are attributed to higher ionic conductivity of LMO in the NiCrAlY/ LMO coating. The NiCrAlY/YSZ/LMO coating demonstrated the lowest oxidation and hot corrosion rates, while NiCrAlY/YSZ coating exhibited an intermediate behaviour. Further, the coating also showed higher thermal gradient performance. The high oxidation, hot corrosion resistance and thermal gradient performance achieved due to the suppression of ionic conductivity by YSZ buffer layer in the multi-layer coating. The present work paves new pathways for the development of plasma spray coatings with low thermal conductivity oxides for the rapid heating application of thermal barrier coatings. (author)
[en] Single-atom-layer catalysts with fully activated basal-atoms will provide a solution to the low loading-density bottleneck of single-atom catalysts. Herein, we activate the majority of the basal sites of monolayer MoS, by doping Co ions to induce long-range ferromagnetic order. This strategy, as revealed by in situ synchrotron radiation microscopic infrared spectroscopy and electrochemical measurements, could activate more than 50 % of the originally inert basal-plane S atoms in the ferromagnetic monolayer for the hydrogen evolution reaction (HER). Consequently, on a single monolayer of ferromagnetic MoS measured by on-chip micro-cell, a current density of 10 mA cm could be achieved at the overpotential of 137 mV, corresponding to a mass activity of 28, 571 Ag, which is two orders of magnitude higher than the multilayer counterpart. Its exchange current density of 75 µA cm also surpasses most other MoS-based catalysts. Experimental results and theoretical calculations show the activation of basal plane S atoms arises from an increase of electronic density around the Fermi level, promoting the H adsorption ability of basal-plane S atoms. (© 2021 Wiley‐VCH GmbH)
[en] Herein, we present a new strategy for the synthesis of 2D porous MoP/MoN heterojunction nanosheets based on the pyrolysis of 2D [PMoO]-melamine (PMo-MA) nanosheet precursor from a polyethylene glycol (PEG)-mediated assembly route. The heterostructure nanosheets are ca. 20 nm thick and have plentiful pores (<5 nm). These structure features offer advantages to promote the HER activity, including the favorable water dissociation kinetics around heterojunction as confirmed by theoretical calculations, large accessible surface of 2D nanosheets, and enhanced mass-transport ability by pores. Consequently, the 2D porous MoP/MoN heterojunction nanosheets exhibit excellent HER activity with low overpotentials of 89, 91 and 89 mV to achieve a current density of 10 mA cm in alkaline, neutral and acidic electrolytes, respectively. The HER performance is superior to the commercial Pt/C at a current density >55 mA cm in neutral medium and >190 mA cm in alkaline medium. (© 2021 Wiley‐VCH GmbH)
[en] A chemical methodology has been selected to isolate and concentrate select trace fission product (FP) elements from separated Pu for nuclear forensics. The methodology employs several different resins and eluents to chromatographically separate U and the FP elements of interest into their own fractions. The U, rare-earth element, Cs, and Ba fractions were isolated with relative yields of ≥ 73.8%, ≥ 80.7%, ≥ 98.5%, and ≥ 98.0%, respectively. The methodology was able to successively isolate select FP elements on the order of 10-10 g out of much larger samples of Pu. (author)
[en] Cs-137 is one of the most intensively studied Isotopes used when investigating fission product transport behavior, and much experimental data are available. For LEU fuel, the main sources of information are the measurements of Brown and Faircloth (1976) of the United Kingdom Atomic Energy Authority (UKAEA), Harwell, on 80% dense UO2 prepared using the powder agglomeration technique. The kernel release was determined by cracking irradiated, intact, TRISO coated particles and measuring the Cs-137 content in the kernel and the coating.
[en] After having evoked the context (commitments related to the Paris Agreement, ecological transition, objective of carbon neutrality, reduction of the dependence of industry on fossil energies, use of decarbonized inputs to produce heat, and necessary development and deployment of new processes and also new technologies for CO2 capture, storage and valorization); this contribution proposes a critical discussion of the exploitation of hydrogen combustion, of its strengths and weaknesses, of its scientific and technological locks. Then, it discusses the exploitation of the combustion of hydrogen-natural gas mixtures (Hythane): production, strengths and weaknesses, benefits of such a combustion (due to energy properties of natural gas, to energy storage and transport, to CO2 emission reduction). It addresses the case of ammoniac combustion: NH3 production, use as fuel or energy vector, scientific and technological locks.
[en] In recent years, annual electricity consumption in France amounted to around 470 TWh, 90% being decarbonized; at the same time, oil and natural gas consumption has been around 900 TWh and 450 TWh respectively. At present, electricity accounts for only a quarter of energy consumption. Energy savings alone will not be enough to move away from oil and natural gas: as equally anticipated for Germany and Great Britain, French reliance on electricity will have to increase significantly to replace oil and gas consumption. Various recent projections underestimate this growth. However, erroneous assumptions would affect the security of our energy supply and the daily life of the French people; the impacts on the cost of electricity and energy in general, and on the competitiveness of our economy would be considerable. In this position paper, the National Academy of Technologies of France (NATF) proposes a reasonable assessment of electricity demand in 2050. It points out that the European electricity system will be more vulnerable in coming years. It proposes some principles for the choice of economic data to be used in optimisation models. On the basis of these elements, it highlights some key points for managing change in the electricity system.
[fr]La consommation annuelle d'electricite en France a ete d'environ 470 TWh, decarbonee a plus de 90%; dans le meme temps, les consommations de petrole et de gaz naturel ont ete respectivement d'environ 900 TWh et 450 TWh. L'electricite ne represente aujourd'hui que le quart de la consommation d'energie. Les seules economies d'energie ne suffiront pas a sortir du petrole et du gaz naturel: comme le prevoient egalement l'Allemagne et la Grande-Bretagne, le recours a l'electricite en France devra croitre significativement pour se substituer aux consommations de petrole et de gaz. Diverses estimations recentes sous-estiment cette croissance. Or des anticipations erronees affecteraient la securite de notre approvisionnement energetique et la vie quotidienne des francais; les impacts sur le cout de l'electricite et des energies en general, et sur la competitivite de notre economie seraient majeurs. Dans cet avis, l'Academie des technologies propose une evaluation raisonnable de la demande d'electricite en 2050. Elle rappelle que le systeme electrique europeen sera plus fragile dans les prochaines annees. Elle propose quelques principes pour le choix des donnees economiques a retenir dans les optimisations. A partir de ces elements, elle souligne quelques points clefs de la conduite du changement du systeme electrique.