• Nuclear Engineering and Technology
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• v.54 no.5
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• pp.1804-1812
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• 2022

The aim of this paper is to assess the reliability and accuracy of the PSI standard method, used in many previous works, for the quantification of ND uncertainties in the SPERT-III RIA transient, by quantifying the discrepancy between the actual inserted reactivity and the original static reactivity worth and their associated uncertainties. The assessment has shown that the inherent S3K neutron source renormalization scheme, introduced before starting the transient, alters the original static reactivity worth of the transient CR and reduces the associated uncertainty due to the ND perturbation. In order to overcome these limitations, two additional methods have been developed based on CR adjustment. The comparative study performed between the three methods has showed clearly the high sensitivity of the obtained results to the selected approach and pointed out the importance of using the right procedure in order to simulate correctly the effect of ND uncertainties on the overall parameters in a RIA transient. This study has proven that the approach that allows matching the original static reactivity worth and starting the transient from criticality is the most reliable method since it conservatively preserves the effect of the ND uncertainties on the inserted reactivity during a RIA transient.

• Journal of ILASS-Korea
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• v.16 no.1
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• pp.51-57
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• 2011

An experimental study was performed to explore characteristics of combustion and exhaust emissions in the compression ignition engine of RCCI (reactivity controlled compression ignition) using diesel-gasoline dual fuel. A dual-fuel reactivity controlled compression ignition concepts is demonstrated as a promising method to achieve high thermal efficiency and low emissions. For investigating combustion characteristics, engine experiments were performed in a light-duty diesel engine over a range of SOIs (start of injection) and gasoline percents. The experimental results showed that cases of diesel-gasoline dual fuel combustion is capable of operating over a middle range of engine loads with lower levels of NOx and soot, acceptable pressure rise rate, low ISFC (indicated specific fuel consumption), and high indicated thermal efficiency.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.3175-3180
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• 2008

A metal-fueled pool-type liquid metal fast reactor (LMFR) provides large margins to sodium boiling and fuel damage under accident conditions. The favorable passive safety results are obtained by both a reactivity feedback mechanism in the core and a passive decay heat removal system. Among the various reactivity feedbacks, the ones by a thermal expansion of a radial dimension of the core and by the control rod drivelines are strongly dependent on the flow conditions in the core and the hot pool, respectively. The effects of multidimensional thermal hydraulic characteristics on these reactivity feedbacks are investigated by the system-wide safety analysis code SSC-K with advanced thermal hydraulics models. Particularly a detailed three dimensional thermal hydraulics reactor core model is integrated into SSC-K for use in a whole system analysis of the passive safety aspects of LMR designs. The model provides fuel and cladding temperatures for every fuel pin in a reactor and coolant temperatures for every coolant sub-channel in the reactor.

• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1110-1119
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• 2020

The Floating Absorber for Safety at Transient (FAST) is a safety device used in the innovative Sodium-cooled Fast Reactor (iSFR). The FAST insert negative reactivity under transient or accident conditions. However, behavior of the FAST is still unclear under transient conditions. Therefore, the existing Floating Absorber for Safety at Transient Analysis Code (FASTAC) is improved to analyze the FAST movement by considering the reactivity and temperature distribution within the reactor core. The current FAST system is simulated under a single control rod withdrawal accident condition. In this investigation, the reactor thermal power does not return to its initial thermal power even if the FAST inserts negative reactivity. Only a 9 K of coolant temperature margin, in the hottest fuel assembly at EOL, can lead to unnecessary insertion of the negative reactivity. On the other hand, the FASTs cannot contribute to controlling the reactivity when normalized radial power is less than 0.889 at BOL and 0.972 at EOL. These simulation results suggest that the current FAST design needs to be optimized depending on its installed location. Meanwhile, the FAST system keeps the fuel, cladding and coolant temperatures below their limit temperatures with given conditions.

• Composites Research
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• v.28 no.6
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• pp.395-401
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• 2015

This study investigated the thermal stability of Grubbs' catalyst and its reactivity with self-healing agents for self-healing damage repair. Four types of Grubbs' catalyst supplied by manufacturers were considered and each catalyst was tested in as-received and grinded conditions. Four types of self-healing agents were prepared by varying the mixing ratio of dicyclopentadiene (DCPD) and 5-ethylidene-2-norbonene (ENB). Heat flows as a function of temperature were measured through a differential scanning calorimetry (DSC) to determine the thermal stability of catalysts. Reaction heats of self-healing agents with the catalyst were measured to evaluate the reactivity of the catalyst. For this evaluation, Fluka Chemika Grubbs' catalyst was used based on the maximum temperature and the time to reach the maximum temperature. According to the results, catalysts had different shapes depending on the manufacturer and the results showed that the smaller the size of the catalyst the higher the reactivity with self-healing agents. As the ENB ratio in self-healing agents increased, the maximum temperature increased, and the time to reach the maximum temperature decreased. As the amount of the catalyst increased, the maximum temperature increased, and the time to reach the maximum temperature decreased. Considering the thermal stability of the catalyst and its reactivity with the self-healing agent, combination of 0.5 wt% catalyst and the D3E1 self-healing agent was optimal for self-healing damage repair. Finally, as the thermal decomposition may occur depending on the environmental temperature, the catalyst must not be exposed to temperature higher than that is necessary to maintain the thermal stability of the catalyst.

• Journal of the Korean Society of Systems Engineering
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• v.19 no.2
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• pp.46-58
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• 2023

Deterministic safety analysis is a crucial part of safety assessment, particularly when it comes to demonstrating the safety of nuclear power plant designs. The traditional approach to deterministic safety analysis models is to model the nuclear core using point kinetics. However, this simplified approach does not fully reflect the real core behavior with proper moderator and fuel reactivity feedbacks during the transient. The use of Multi-Physics approach allows more precise simulation reflecting the inherent three-dimensionality (3D) of the problem by representing the detailed 3D core, with instantaneous updates of feedback mechanisms due to changes of important reactivity parameters like fuel temperature coefficient (FTC) and moderator temperature coefficient (MTC). This paper addresses a CEA ejection accident at hot full power (HFP), in which the underlying strong and un-symmetric feedback between thermal-hydraulics and reactor kinetics exist. For this purpose, a multi-physics analysis tool has been selected with the nodal kinetics code, 3DKIN, implicitly coupled to the thermal-hydraulic code, RELAP5, for real-time communication and data exchange. This coupled approach enables high fidelity three-dimensional simulation and is therefore especially relevant to reactivity initiated accident (RIA) scenarios and power distribution anomalies with strong feedback mechanisms and/or un-symmetrical characteristics as in the CEA ejection accident. The Systems Engineering approach is employed to provide guidance in developing the work in a systematic and efficient fashion.

• Polymer(Korea)
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• v.39 no.1
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• pp.13-22
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• 2015

A new methacrylate copolymer that includes chalcone as a side group, poly(4-methacryloyloxyphenyl-4'-methoxystyryl ketone-co-styrene) was synthesized by free radical copolymerization. FTIR and $^1H$ NMR spectroscopic techniques were used to characterize the homopolymers and copolymers. The copolymerizations were carried out to high conversions. Copolymer compositions were established by $^1H$ NMR spectra analysis. The monomer reactivity ratios for copolymer system were determined by the linearized Kelen $T{\ddot{u}}d{\ddot{o}}s$, and Extended Kelen $T{\ddot{u}}d{\ddot{o}}s$ methods and a non-linear least squares method. The molecular weights and polydispersity index of copolymers were measured by using the gel permeation chromatography (GPC). The effect of copolymer compositions on their thermal behavior were studied by differential scanning calorimetry and thermogravimetric analysis methods. The optical properties of the resulting copolymer were also investigated.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.459-459
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• 2011

Graphene has many fascinating material properties such as high electron mobility, high optical transparency, excellent thermal conductivity, superior Young's modulus, etc. Several studies have recently found that single-layer graphene is chemically more reactive than few-layer graphene when supported on silicon dioxide substrates with sub-nm roughness. In this study, we have investigated the influence of substrates on chemical reactivity of graphene. Morphology and thermal oxidation behavior of graphene on atomically flat mica substrates were studied by atomic force microscopy (AFM) and Raman spectroscopy compared to graphene on SiO2/Si substrates. Notably, oxidation of single-layer graphene proceeds more slowly on mica than SiO2/Si. Detailed analysis led to a conclusion that deformation along the out-of-plane direction enhances reactivity of graphene.

• Nuclear Engineering and Technology
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• v.54 no.1
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• pp.1-10
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• 2022

This study discusses the effect of using ²³²Th instead of ²³⁸U on the neutronic characteristics and the main operating parameters of the pressurized water reactor (PWR). MCNPX version 2.7 was used to compare the neutronic characteristics of UO₂ with (Th, ²³⁵U)O₂ and (Th, ²³³U) O₂. Firstly, the infinity multiplication factor (K_inf), thermal neutron flux, and power distribution have been studied for the investigated fuel types. Secondly, the effect of Gd₂O₃ and Er₂O₃ on the K_inf and on the radial thermal neutron flux and thermal power has been investigated to distinguish which of them is more suitable than the other in reactivity management. Thirdly, to illustrate the effectiveness of ²³²Th in decreasing the inventory of both the actinides and non-actinides, the concentration of plutonium (Pu) isotopes and minor actinides (MAs) has been simulated with the fuel burnup. Besides, due to their large thermal neutron absorption cross-section, the concentrations of ¹³⁵Xe, ¹⁴⁹Sm, and ¹⁵¹Sm with the fuel burnup have been investigated. Finally, the main safety parameters such as the reactivity worth of the control rods (ρ_CR), the effective delayed neutron fraction β_eff, and the Doppler reactivity coefficient (DRC) were calculated to determine to which extent these fuel types achieve the acceptable limits.

• Nuclear Engineering and Technology
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• v.54 no.8
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• pp.3106-3116
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• 2022

The present work presents analysis results of the core design optimizations for an annular, prismatic High Temperature Gas-cooled Reactor (HTGR) with passive decay-heat removal features. Its thermal power is 100 MW_t and the operating temperature is 850 ℃ (1123 K). The neutronic calculations are done for the core with heterogeneous distribution of fuel and burnable poison particles (BPPs) to flatten the reactivity swing and power peaking factor (PPF) during the reactor operation as well as for control rod (CR) insertion into the core to restrain a small excess reactivity less than 1$. The next step of the study is done for evaluation of core reactivity coefficient of temperature.