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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] Pressurized Heavy Water Reactor (PHWR), CANadian Deuterium-Uranium (CANDU), Operating Experience (OPEX) provides evidence that performing post-refurbishment Primary Heat Transport System (PHTS) Hot Conditioning (HC) with fuel in core presents a risk that the fuel bundles may become coated with iron-based, primarily magnetite and hematite, deposits during the evolution. This OPEX also provide evidence that these deposits remain on the fuel sheath for a period of approximately three to six months into the subsequent operation of the plant before the deposit material is redistributed into the PHTS coolant and removed from the system through the PHTS purification system. Such deposits, while present on the sheath, are thought to contribute to fuel sheath corrosion and impact fuel element heat transfer properties. OPG commissioned a series of laboratory testing to investigate the factors that contribute to the phenomena of fuel sheath deposit formation. These tests included comparative studies of HC evolutions, which emulated recent CANDU post-refurbishment OPEX in a laboratory setting. These investigations provided clarity on the parameters relevant to this adverse condition and on controls that can be implemented to minimize deposition on fuel bundle sheath surfaces. Sensitive parameters and associated controls include; (1) use of a “conventional” HC process as compared to a chelating-agent type HC, that use forms of Ethylenediaminetetraacetic Acid (e.g. Li2EDTA), (2) HC prior to reactor first approach-to-critical (i.e. no fuel heat), (3) maintenance of PHTS pH per current industry expert recommendations, and (4) careful control of other dissolved materials in the PHTS during PHT cold flush. OPEX observations suggest that the surface condition of fuel sheathing may also be a contributing factor related to the probability of deposition. This indicates that fuel sheaths that have been “polished” following tube production may be less susceptible to deposition of magnetite on sheath surfaces during HC. While OPG has considered this observation to be interesting, it was not further investigated, and thus requires validation. (author)
[en] In general, Primary Heat Transport System (PHTS) chemistry for pressurized heavy water reactors (PHWRs) is stable and believed to be well understood. The current narrow-band control to minimize feeder wall thinning and hydrogen addition to maintain reducing conditions are effective chemistry control strategies to maximize component lifetimes and minimize degradation and activity transport processes in the PHTS circuit. However, recent laboratory-scale investigations, ongoing evaluations of available reactor chemistry data and the increased availability of on-line analyses are providing more detailed insights into PHTS chemistry in operating plants that may allow future refinements to operating practices. This paper will provide an overview of recent work related to PHTS chemistry from CNL. (author)
[en] Heating and cooling are two important procedures in manufacturing as well as transportation industries.Rather than the conventional fluids, solutions of fluids with metal nanoparticles have higher thermal conductivity for effective cooling. Therefore, present paper is a comparative study of squeezing flow analysis of copper oxide–water and oil (kerosene)-based nanofluid between two parallel plates. Magnetohydrodynamic flow of kerosene-based nanofluid along with the dissipative heat energy may enhance the thermal properties of the fluid. Assuming self-similar variables, the governing equations get transformed into non-dimensional forms and approximate analytical techniques such as variation parameter method is employed for these transformed equations. With the well posed physical parameters, the computation is carried out using the mathematical package MATHEMATICA and displayed via graphs and numerical results are shown in tabular form. Favourable cases in comparison with earlier studies are also studied wherever possible. However, when the plates are away from each other, it is seen that the kerosene-based nanofluid velocity overrides the water-based nanofluid whereas the impact is reversed in the case of squeezing.(author)
[en] Summary - Introduction: ESFR SMART project is a four year project that began in September 2017.; It follows the Euratom CP ESFR project which was also a follow up of the European Fast Reactor (EFR) project.; Main purpose of the ESFR SMART project is to improve the reactor safety, and make a proposal for new safety options, based on both present and previous projects experience.; 1500MWe SFR pool type reactor with oxide fuel.; The deliverable giving the list of proposals for these new safety measures has been provided during the first year of the project with the drawings.; Several papers have been presented to explain these options in ICAPP 2018, ICONE 2018, ICAPP 2019, ICAPP 2020, Physor 2020; Reactivity control; Containment; Decay heat removal; Secondary loops and sodium fires detection; Conclusion: List of ESFR SMART simplifications - Dome (or polar table) suppression.; Safety vessel suppression, functions taken over by the reactor pit.; Primary sodium containment improvement with a massive metallic roof and other dispositions.; Natural convection cooling enhancement in the secondary side.; Optimized and simplified DHR dedicated circuits. (no DHX system in the primary vessel, no supplementary sodium circuits to manage).; Secondary loops with higher level of safety for sodium fires and sodium water reaction. Passive systems / Intrinsic safety - Passive control rods that stop the plant on physical parameters.; Low void effect in the core able to support severe transients (ULOF, etc.).; Passive decay heat removal by DHRS 2 and 1 (12 independent loops in natural convection) using only air, always available.; Thermal pumps totally passive to increase flow rate in natural convection and the decay heat removal systems capabilities,; Long delay before necessity of operator action, even in case of loss of water and loss of electricity supply.
[en] A novel high-speed photodiode (PD) with an InGaAs/Si structure fabricated by atomic-diffusion bonding (ADB) is proposed with the aim of improving the heat transfer. The fabricated PD shows a responsivity of 0.42 A W and a 3 dB bandwidth of over 50 GHz. The maximum damage-threshold photocurrent, or high-power tolerance, is higher than that of a conventional PD on an InP substrate, thanks to the high thermal conductivity of Si used as the collector in the PD. (© 2020 Wiley‐VCH GmbH)
[en] We demonstrate a simple, low-cost, and passive radiative cooler based on a monolithic design consisting of thin nanoporous anodic alumina (NAA) films grown on aluminium sheets. The NAA/Al structure maintains a high broadband reflectivity close to 98% within the solar spectrum (0.4–2.2μm) and simultaneously exhibits a high average emissivity of 88% within the atmospheric infrared (IR) transmission window of 8–13μm with the peak IR emission approaching 99% at a wavelength of 10μm. Optical modelling of the system using optical parameters of the materials confirms that the high solar reflectance arises due to the transparent nature of NAA and high reflectivity of bottom Al, while the large thermal IR emissivity arises from the interference effects of the NAA film and the high absorption of IR light due to phonon resonances in alumina at wavelength larger than 10μm. Further, we estimate the average cooling power of NAA/Al to be about 136 W m−2 at ambient temperature even after including the contribution to heat input from external non-radiative processes. This robust and light weight NAA/Al can be projected as an excellent alternative to optical solar reflectors used in spacecraft for thermal heat management and rooftop cooling green technologies. (author)
[en] Radon-222 (Rn) is a short-lived radioactive gas naturally emitted from land surfaces and has long been used to assess convective transport in atmospheric models. In this study, we simulate Rn using the GEOS-Chem chemical transport model to improve our understanding of Rn emissions and surface concentration seasonality and characterize convective transport associated with two Goddard Earth Observing System (GEOS) meteorological products, the Modern-Era Retrospective analysis for Research and Applications (MERRA) and GEOS Forward Processing (GEOS-FP). We evaluate four global Rn emission scenarios by comparing model results with observations at 51 surface sites. The default emission scenario in GEOS-Chem yields a moderate agreement with surface observations globally (68.9 % of data within a factor of 2) and a large underestimate of winter surface Rn concentrations at Northern Hemisphere midlatitudes and high latitudes due to an oversimplified formulation of Rn emission fluxes (1 atom cm s over land with a reduction by a factor of 3 under freezing conditions). We compose a new global Rn emission scenario based on Zhang et al. (2011) and demonstrate its potential to improve simulated surface Rn concentrations and seasonality. The regional components of this scenario include spatially and temporally varying emission fluxes derived from previous measurements of soil radium content and soil exhalation models, which are key factors in determining Rn emission flux rates. However, large model underestimates of surface Rn concentrations still exist in Asia, suggesting unusually high regional Rn emissions. We therefore propose a conservative upscaling factor of 1.2 for Rn emission fluxes in China, which was also constrained by observed deposition fluxes of Pb (a progeny of Rn). With this modification, the model shows better agreement with observations in Europe and North America (> 80 % of data within a factor of 2) and reasonable agreement in Asia (close to 70 %). Further constraints on Rn emissions would require additional concentration and emission flux observations in the central United States, Canada, Africa, and Asia. We also compare and assess convective transport in model simulations driven by MERRA and GEOS-FP using observed Rn vertical profiles in northern midlatitude summer and from three short-term airborne campaigns. While simulations with both GEOS products are able to capture the observed vertical gradient of Rn concentrations in the lower troposphere (0–4 km), neither correctly represents the level of convective detrainment, resulting in biases in the middle and upper troposphere. Compared with GEOS-FP, MERRA leads to stronger convective transport of Rn, which is partially compensated for by its weaker large-scale vertical advection, resulting in similar global vertical distributions of Rn concentrations between the two simulations. This has important implications for using chemical transport models to interpret the transport of other trace species when these GEOS products are used as driving meteorology.
[en] Fuel pool cooling is an essential task in the scope of nuclear power applications. During the first years of commercial nuclear power implementation robust fuel pool cooling systems have been developed and used for several decades. Two decades ago the development of a new cooling technology/concept was initiated to ensure prevention of accidents, including fuel damage. The so-called advanced cooling technology offers a modular design system which enables tailor-made robust and cost efficient cooling solutions. However, all the advanced cooling systems feature an indispensable and distinctive fall back option of a passive heat removal in case of a station blackout as most important feature. In contradiction to conventional cooling systems the advanced cooling solutions use immersed heat exchangers to establish an additional safety barrier inside the heat removal chain. This results in the necessity of a free convective heat transfer on pool water side. This in turn requires a special design approach and methodology. Because of the huge nominal heat load and the size of the heat removal systems itself full size test are under economical aspects nearly impossible. In this paper a purpose-built simulation and design methodology is presented, which has been developed and proved in the scope of several first-of-a-kind projects during the last years.