| 1. |
- Chen, Jiaxin, et al.
(författare)
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EELS and electron diffraction studies on possible bonaccordite crystals in pressurized water reactor fuel CRUD and in oxide films of alloy 600 material
- 2017
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Ingår i: Nuclear engineering and technology. - : Elsevier BV. - 1738-5733 .- 2234-358X. ; 49:4, s. 668-674
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Tidskriftsartikel (refereegranskat)abstract
- Experimental verification of boron species in fuel CRUD (Chalk River Unidentified Deposit) would provide essential and important information about the root cause of CRUD-induced power shifts (CIPS). To date, only bonaccordite and elemental boron were reported to exist in fuel CRUD in CIPS-troubled pressurized water reactor (PWR) cores and lithium tetraborate to exist in simulated PWR fuel CRUD from some autoclave tests. We have reevaluated previous analysis of similar threadlike crystals along with examining some similar threadlike crystals from CRUD samples collected from a PWR cycle that had no indications of CIPS. These threadlike crystals have a typical [Ni]/[Fe] atomic ratio of ∼2 and similar crystal morphology as the one (bonaccordite) reported previously. In addition to electron diffraction study, we have applied electron energy loss spectroscopy to determine boron content in such a crystal and found a good agreement with that of bonaccordite. Surprisingly, such crystals seem to appear also on corroded surfaces of Alloy 600 that was exposed to simulated PWR primary water with a dissolved hydrogen level of 5 mL H2/kg H2O, but absent when exposed under 75 mL H2/kg H2O condition. It remains to be verified as to what extent and in which chemical environment this phase would be formed in PWR primary systems.
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| 2. |
- Johansson, Cristina, et al.
(författare)
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How to use an Optimization-based Method Capable of Balancing Safety, Reliability, and Weight in an Aircraft Design Process
- 2017
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Ingår i: Nuclear engineering and technology. - : Elsevier. - 1738-5733 .- 2234-358X. ; 49, s. 404-410
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Tidskriftsartikel (refereegranskat)abstract
- In order to help decision-makers in the early design phase to improve and make more cost-efficient system safety and reliability baselines of aircraft design concepts, a method (Multi-objective Optimization for Safety and Reliability Trade-off) that is able to handle trade-offs such as system safety, system reliability, and other characteristics, for instance weight and cost, is used. Multi-objective Optimization for Safety and Reliability Trade-off has been developed and implemented at SAAB Aeronautics. The aim of this paper is to demonstrate how the implemented method might work to aid the selection of optimal design alternatives. The method is a three-step method: step 1 involves the modelling of each considered target, step 2 is optimization, and step 3 is the visualization and selection of results (results processing). The analysis is performed within Architecture Design and Preliminary Design steps, according to the company’s Product Development Process. The lessons learned regarding the use of the implemented trade-off method in the three cases are presented. The results are a handful of solutions, a basis to aid in the selection of a design alternative. While the implementation of the trade-off method is performed for companies, there is nothing to prevent adapting this method, with minimal modifications, for use in other industrial applications.
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| 3. |
- Liu, Zhenzhong, et al.
(författare)
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Geochemical and S isotopic studies of pollutant evolution in groundwater after acid in situ leaching in a uranium mine area in Xinjiang
- 2023
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Ingår i: Nuclear engineering and technology. - : Elsevier BV. - 1738-5733 .- 2234-358X. ; 55:4, s. 1476-1484
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Tidskriftsartikel (refereegranskat)abstract
- Laboratory experiments and point monitoring of reservoir sediments have proven that stable sulfate reduction (SSR) can lower the concentrations of toxic metals and sulfate in acidic groundwater for a long time. Here, we hypothesize that SSR occurred during in situ leaching after uranium mining, which can impact the fate of acid groundwater in an entire region. To test this, we applied a sulfur isotope fractionation method to analyze the mechanism for natural attenuation of contaminated groundwater produced by acid in situ leaching of uranium (Xinjiang, China). The results showed that delta S-34 increased over time after the cessation of uranium mining, and natural attenuation caused considerable, area-scale immobilization of sulfur corresponding to retention levels of 5.3%-48.3% while simultaneously decreasing the concentration of uranium. Isotopic evidence for SSR in the area, together with evidence for changes of pollutant concentrations, suggest that area-scale SSR is most likely also important at other acid mining sites for uranium, where retention of acid groundwater may be strengthened through natural attenuation. To recapitulate, the sulfur isotope fractionation method constitutes a relatively accurate tool for quantification of spatiotemporal trends for groundwater during migration and transformation resulting from acid in situ leaching of uranium in northern China.
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| 4. |
- Mishra, Vaibhav, Doktorand, 1989-, et al.
(författare)
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Material attractiveness of irradiated fuel salts from the Seaborg Compact Molten Salt Reactor
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Ingår i: Nuclear engineering and technology. - 1738-5733 .- 2234-358X.
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Tidskriftsartikel (refereegranskat)abstract
- To deter possible state and non-state actors from misusing nuclear material and technology, accurate knowledge of material attractiveness and weapons usability of uranium and plutonium in Spent Nuclear Fuel (SNF) is crucial. Equipped with this knowledge, nuclear safeguards inspectors can ensure adequate safeguarding of such material at the requisite points in the nuclear fuel cycle. Such assessments are also valuable in the design phase of Nuclear Energy Systems (NES) where they can be incorporated as a part of the Safeguards by Design (SBD) features thereby reducing the burden on operators and the International Atomic Energy Agency (IAEA) by easing future safeguards inspections. Organizations that have accrued significant experiencing in safeguarding the fuel cycle such as the IAEA can use this information to craft effective nuclear safeguards verification frameworks to strengthen the non-proliferation regime by eliminating the possible diversion pathways in the fuel cycle. Over the years, numerous such evaluations of material attractiveness have been performed for Light Water Reactor (LWR) fuel to better understand the nature of the SNF material and its weapons usability at different points in the nuclear fuel cycle. However, availability of such assessments for newer, generation IV reactors such as Molten Salt Reactors (MSR) is severely limited.In the present study we address the gap in knowledge of material attractiveness for such advanced systems and describe the nature of irradiated fuel salts which the nuclear safeguards community might be faced with in the near future as more and more such reactors are anticipated to reach commission and operation. Within the scope of the paper, we use a large database of simulated irradiated fuel salt isotopics (and other derived quantities such as gamma activity, decay heat, and spontaneous fission rates) developed specifically for a MSR concept in order to shed some light on possible weapons usability of uranium and plutonium present in the irradiated fuel salts. This is achieved by using a suitably defined attractiveness metric in a manner similar to what has been implemented for uranium and plutonium separated from LWR spent fuel at different stages in the fuel cycle for a model MSR. The database used in the study has been created by simulating the irradiation of molten fuel salt in a MSR core over a wide range of operational parameters (burnup, initial enrichment, and cooling time, or collectively known as BIC) using the Monte-Carlo particle transport code, Serpent. With the help of this attractiveness metric, the findings from this study have shown that spent fuel from the MSR concept selected in this study is more attractive than that from a conventional LWR. The findings also underscore the need for strengthened safeguards measures for such SNF. These results are expected to be useful in the future for regulatory authorities as well as for nuclear safeguards inspectors for designing a functional safeguards verification routine for irradiated fuel of such unique nature.
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| 5. |
- Olsen, Börge, et al.
(författare)
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Stabilization effect of fission source in coupled Monte Carlo simulations
- 2017
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Ingår i: Nuclear engineering and technology. - : Korean Nuclear Society. - 1738-5733 .- 2234-358X. ; 49:5, s. 1095-1099
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Tidskriftsartikel (refereegranskat)abstract
- A fission source can act as a stabilization element in coupled Monte Carlo simulations. We have observed this while studying numerical instabilities in nonlinear steady-state simulations performed by a Monte Carlo criticality solver that is coupled to a xenon feedback solver via fixed-point iteration. While fixedpoint iteration is known to be numerically unstable for some problems, resulting in large spatial oscillations of the neutron flux distribution, we show that it is possible to stabilize it by reducing the number of Monte Carlo criticality cycles simulated within each iteration step. While global convergence is ensured, development of any possible numerical instability is prevented by not allowing the fission source to converge fully within a single iteration step, which is achieved by setting a small number of criticality cycles per iteration step. Moreover, under these conditions, the fission source may converge even faster than in criticality calculations with no feedback, as we demonstrate in our numerical test simulations.
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| 6. |
- Pan, Qingquan, et al.
(författare)
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Acceleration method of fission source convergence based on RMC code
- 2020
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Ingår i: Nuclear engineering and technology. - : Elsevier BV. - 1738-5733 .- 2234-358X. ; 52:7, s. 1347-1354
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Tidskriftsartikel (refereegranskat)abstract
- To improve the efficiency of MC criticality calculation, an acceleration method of fission source convergence which gives an improved initial fission source is proposed. In this method, the MC global homogenization is carried out to obtain the macroscopic cross section of each material mesh, and then the nonlinear iterative solution of the SP3 equations is used to determine the fission source distribution. The calculated fission source is very close to the real fission source, which describes its space and energy distribution. This method is an automatic computation process and is tested by the C5G7 benchmark, the results show that this acceleration method is helpful to reduce the inactive cycles and overall running time.
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| 7. |
- Parsaei, S., et al.
(författare)
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Effect of test-caused degradation on the unavailability of standby safety components
- 2024
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Ingår i: Nuclear engineering and technology. - : Elsevier. - 1738-5733 .- 2234-358X. ; 56:2, s. 526-535
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a safety-critical standby component unavailability model that contains aging effects caused by the elapsed time from installation, component degradation due to surveillance tests, and imperfect maintenance actions. An application of the model to a Motor-Operated Valve and a Motor-Driven Pump involved in the HPIS of a VVER/1000-V446 nuclear power plant is demonstrated and compared with other existing models at component and system levels. In addition, the effects of different unavailability models are reflected in the NPP's risk criterion, i.e., core damage frequency, over five maintenance periods. The results show that, compared with other models that do not simultaneously consider the full effects of degradation and maintenance impacts, the proposed model realistically evaluates the unavailabilities of the safety-related components and the involved systems as a plant age function. Therefore, it can effectively reflect the age-dependent CDF impact of a given testing and maintenance policy in a specified time horizon.
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| 8. |
- Pazsit, Imre, 1948, et al.
(författare)
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The extinction probability in systems randomly varying in time
- 2017
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Ingår i: Nuclear Engineering and Technology. - : Elsevier BV. - 2234-358X .- 1738-5733. ; 49:6, s. 1301-1309
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Tidskriftsartikel (refereegranskat)abstract
- The extinction probability of a branching process (a neutron chain in a multiplying medium) is calculated for a system randomly varying in time. The evolution of the first two moments of such a process was calculated previously by the authors in a system randomly shifting between two states of different multiplication properties. The same model is used here for the investigation of the extinction probability. It is seen that the determination of the extinction probability is significantly more complicated than that of the moments, and it can only be achieved by pure numerical methods. The numerical results indicate that for systems fluctuating between two subcritical or two supercritical states, the extinction probability behaves as expected, but for systems fluctuating between a supercritical and a subcritical state, there is a crucial and unexpected deviation from the predicted behaviour. The results bear some significance not only for neutron chains in a multiplying medium, but also for the evolution of biological populations in a time-varying environment.
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| 9. |
- Tran, Chi-Thanh, et al.
(författare)
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Simulation of core melt pool formation in a reactor pressure vessel lower head using an effective convectivity model
- 2009
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Ingår i: Nuclear engineering and technology. - 1738-5733 .- 2234-358X. ; 41:7, s. 929-944
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Tidskriftsartikel (refereegranskat)abstract
- The present study is concerned with the extension of the Effective Convectivity Model (ECM) to the phase-change problem to simulate the dynamics of the melt pool formation in a Light Water Reactor (LWR) lower plenum during hypothetical severe accident progression. The ECM uses heat transfer characteristic velocities to describe turbulent natural convection of a melt pool. The simple approach of the ECM method allows implementing different models of the characteristic velocity in a Mushy Zone for non-eutectic mixtures. The Phase-change ECM (PECM) was examined using three models of the characteristic velocities in a mushy zone and its performance was compared. The PECM was validated using a dual-tier approach, namely validations against existing experimental data (the SIMECO experiment) and validations against results obtained from Computational Fluid Dynamics (CFD) simulations. The results predicted by the PECM implementing the linear dependency of mushy-zone characteristic velocity On fluid fraction are well agreed with the experimental correlation and CFD simulation results. The PECM was applied to simulation of melt pool formation heat transfer in a Pressurized Water Reactor (PWR) and Boiling Water Reactor (BWR) lower plenum. The Study suggests that the PECM is an adequate and effective tool to compute the dynamics of core melt pool formation.
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| 10. |
- Wang, Xicheng, Phd candidate, 1995-, et al.
(författare)
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Development of scaling approach based on experimental and CFD data for thermal stratification and mixing induced by steam injection through spargers
- 2024
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Ingår i: Nuclear engineering and technology. - : Elsevier BV. - 1738-5733 .- 2234-358X. ; 56:3, s. 1052-1065
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Tidskriftsartikel (refereegranskat)abstract
- Advanced Pressurized Water Reactors (APWRs) and Boiling Water Reactors (BWRs) employ a suppression pool as a heat sink to prevent containment overpressure. Steam can be discharged into the pool through multi-hole spargers or blowdown pipes in both normal and accident conditions. Direct Contact Condensation (DCC) creates sources of momentum and heat. The competition between these two sources determines the development of thermal stratification or mixing of the pool. Thermal stratification is of safety concern as it reduces the cooling capability compared to a completely mixed pool condition. In this work we develop a scaling approach to prediction of the thermal stratification in a water pool induced by steam injection through spargers. Experimental data obtained from large-scale pool tests conducted in the PPOOLEX and PANDA facilities, as well as simulation results obtained using validated codes are used to develop the scaling. Two injection orientations, namely radial injection through multi-hole Sparger Head (SH) and vertical injection through Load Reduction Ring (LRR), are considered. We show that the erosion rate of the cold layer can be estimated using the Richardson number. In this work, scaling laws are proposed to estimate both the (i) transient erosion velocity and (ii) the stable position of the thermocline. These scaling laws are then implemented into a 1D model to simulate the thermal behavior of the pool during steam injection through the sparger.
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