• Nuclear Engineering and Technology
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• v.46 no.2
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• pp.183-194
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• 2014

Recently, a CANDU digital reactivity computer system (CDRCS) to measure the worth of the liquid zone controller in a CANDU-6 was developed and successfully applied to a physics test of refurbished Wolsong Unit 1. In advance of using the CDRCS, its measureable reactivity range should be investigated and confirmed. There are two reasons for this investigation. First, the CANDU-6 has a larger reactor and smaller excore detectors than a general PWR and consequently the measured reactivity is likely to reflect the peripheral power variation only, not the whole core. The second reason is photo neutrons generated from the interaction of the moderator and gamma-rays, which are never considered in a PWR. To evaluate the limitations of the CDRCS, several tens of three-dimensional steady and transient simulations were performed. The simulated detector signals were used to obtain the dynamic reactivity. The difference between the dynamic reactivity and the static worth increases in line with the water level changes. The maximum allowable reactivity was determined to be 1.4 mk in the case of CANDU-6 by confining the difference to less than 1%.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1775-1782
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• 2023

Several reactor physics commissioning experiments were conducted to obtain the neutronic parameters at the beginning of the G.A. Siwabessy Multi-purpose Reactor (RSG-GAS) operation. These parameters are essential for the reactor to safety operate. Leveraging the experimental data, this study evaluated the calculated core reactivity, control rod reactivity worth, integral control rod reactivity curve, and fuel reactivity. Calculations were carried out with Serpent 2 code using the latest neutron cross-section data ENDF/B-VIII.0. The criticality calculations were carried out for the RSG-GAS first core up to the third core configuration, which has been done experimentally during these commissioning periods. The excess reactivity for the second and third cores showed a difference of 510.97 pcm and 253.23 pcm to the experiment data. The calculated integral reactivity of the control rod has an error of less than 1.0% compared to the experimental data. The calculated fuel reactivity value is consistent with the measured data, with a maximum error of 2.12%. Therefore, it can be concluded that the RSG-GAS reactor core model is in good agreement to reproduce excess reactivity, control rod worth, and fuel element reactivity.

• Nuclear Engineering and Technology
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• v.50 no.5
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• pp.648-653
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• 2018

Elimination of soluble boron from reactor design eliminates boron-induced reactivity accidents and leads to a more negative moderator temperature coefficient. However, a large negative moderator temperature coefficient can lead to large reactivity feedback that could allow the reactor to return to power when it cools down from hot full power to cold zero power. In soluble boron-free small modular reactor (SMR) design, only control rods are available to control such rapid core transient. The purpose of this study is to investigate whether an SMR would have enough control rod worth to compensate for large reactivity feedback. The investigation begins with classification of reactivity and completes an analysis of the reactivity balance in each reactor state for the SMR model. The control rod worth requirement obtained from the reactivity balance is a minimum control rod worth to maintain the reactor critical during the whole cycle. The minimum available rod worth must be larger than the control rod worth requirement to manipulate the reactor safely in each reactor state. It is found that the SMR does have enough control rod worth available during rapid transient to maintain the SMR at subcritical below k-effectives of 0.99 for both hot zero power and cold zero power.

• Nuclear Engineering and Technology
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• v.45 no.5
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• pp.573-580
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• 2013

The combined effects of reactivity coefficients, along with other core nuclear characteristics, determine reactor core behavior in normal operation and accident conditions. The Power Coefficient of Reactivity (PCR) is an aggregate indicator representing the change in reactor core reactivity per unit change in reactor power. It is an integral quantity which captures the contributions of the fuel temperature, coolant void, and coolant temperature reactivity feedbacks. All nuclear reactor designs provide a balance between their inherent nuclear characteristics and the engineered reactivity control features, to ensure that changes in reactivity under all operating conditions are maintained within a safe range. The $CANDU^{(R)}$ reactor design takes advantage of its inherent nuclear characteristics, namely a small magnitude of reactivity coefficients, minimal excess reactivity, and very long prompt neutron lifetime, to mitigate the demand on the engineered systems for controlling reactivity and responding to accidents. In particular, CANDU reactors have always taken advantage of the small value of the PCR associated with their design characteristics, such that the overall design and safety characteristics of the reactor are not sensitive to the value of the PCR. For other reactor design concepts a PCR which is both large and negative is an important aspect in the design of their engineered systems for controlling reactivity. It will be demonstrated that during Loss of Regulation Control (LORC) and Large Break Loss of Coolant Accident (LBLOCA) events, the impact of variations in power coefficient, including a hypothesized larger than estimated PCR, has no safety-significance for CANDU reactor design. Since the CANDU 6 PCR is small, variations in the range of values for PCR on the performance or safety of the reactor are not significant.

• Bulletin of the Korean Chemical Society
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• v.15 no.10
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• pp.860-864
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• 1994

2nd-order rate constants have been measured spectrophotometrically for the reactions of 4-nitrophenyl benzoate (1), S-4-nitrophenyl thiobenzoate (2) and 4-nitrophenyl thionbenzoate (3) with alkoxides, aryloxides and thioaryloxides in absolute ethanol at 25.0 ${\pm}0.1$${\circ}C$. The substitution of O by polarizable S in the leaving group has little affected the reactivity of 2 toward the charge localized species (eg. $EtO^-$ and $CF_3CH_2O^-$), while the effect of the similar replacement in the carbonyl group has led to a decrease in reactivity by a factor of 10. However, the reactivity of these esters toward charge delocalized aryloxides has been found to be in the order $1<3{\le}2$. The effect of replaced sulfur atom on reactivity becomes more significant for the reaction with polarizable thioaryloxides, i.e. the reactivity increases in the order $1<2{\ll}3$. The difference in reactivity for the present system is attributed to a polarizability effect.

• Nuclear Engineering and Technology
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• v.49 no.1
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• pp.6-16
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• 2017

This study presents a coolant void reactivity analysis of Canada Deuterium Uranium (CANDU)-6 and Advanced Canada Deuterium Uranium Reactor-700 (ACR-700) fuel lattices using a Monte Carlo code. The reactivity changes when the coolant was voided were assessed in terms of the contributions of four factors and spectrum shifts. In the case of single bundle coolant voiding, the contribution of each of the four factors in the ACR-700 lattice is large in magnitude with opposite signs, and their summation becomes a negative reactivity effect in contrast to that of the CANDU-6 lattice. Unlike the coolant voiding in a single fuel bundle, the $2{\times}2$ checkerboard coolant voiding in the ACR-700 lattice shows a positive reactivity effect. The neutron current between the no-void and voided bundles, and the four factors of each bundle were analyzed to figure out the mechanism of the positive coolant void reactivity of the checkerboard voiding case. Through a sensitivity study of fuel enrichment, type of burnable absorber, and moderator to fuel volume ratio, a design strategy for the CANDU reactor was suggested in order to achieve a negative coolant void reactivity even for the checkerboard voiding case.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.6
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• pp.86-92
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• 2003

To analyze the characteristics of ozone formation, measurements of the concentrations of individual exhaust hydrocarbon species have been made under various engine operating parameters in a 2-liter 4-cylinder engine for natural gas and LPG. Tests were performed at constant engine speed, 1800 rpm for two compression ratios of 8.6 and 10.6, with various operating parameters, such as excess air ratio of 1.0~1.6, bmep of 250~800 na and spark timing of BTDC 10~$55^{\circ}$. It was found that the natural gas gave the less ozone formation than LPG in various operating conditions. This was accomplished by reducing the emissions of propylene($C_3H_6$), which has relatively high maximum incremental reactivity factor, and propane($C_3H_8$) that originally has large portion of LPG. In addition, the natural gas show lower values in the specific reactivity and brake specific reactivity. Higher compression ratio of the test engine showed higher non methane HC emissions. However, specific reactivity value decreased since fuel species of HC emissions increase. brake specific reactivity showed almost same values under high bmep, over 500kPa for both fuels. This means that the increase of non methane HC emissions and the decrease of specific reactivity with higher bmep affect each other simultaneously. With advanced spark timing, brake specific reactivity values of LPG were increased while those of natural gas showed almost constant values.

• Nuclear Engineering and Technology
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• v.38 no.7
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• pp.657-664
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• 2006

The problem of reactivity oscillations for a point reactor constitutes an interesting aspect of nuclear reactor physics and its solution may give important information for dynamic and safety assessments. The present paper considers the problem of a reactivity oscillation for a source-driven system which involves some specific aspects that introduce significant differences with respect to the source-free situation. Assuming a square-wave shape for the reactivity insertion, the solution is derived by a fully analytical approach. The conditions for stability and instability can be identified in a straightforward way by directly studying the stationarity of the power response. Numerical results presented allow to discuss the role of the system kinetic parameters and of the time-shape of the reactivity wave.

• Journal of the Korean Institute of Gas
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• v.20 no.4
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• pp.15-24
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• 2016

In the semiconductor industry, the risk of chemical accidents due to miscibility between the many types of chemicals and leakage of toxic chemicals has increased. In order to evaluate the reactivity with miscibility of chemicals, experimental method is the most reliable, but there is a time and cost limitations to be evaluated through experiment all the chemicals. In the study, the reactivity of process gases in the semiconductor industry was considered by the CRW (Chemical Reactivity Worksheets) 3.0 program developed by US NOAA (National Oceanic and Atmospheric Administration) and EPA. The reactivity informations with the miscibility of process gases for semiconductor industry provided, and also a KOSHA guide for the storage/separation of gas cylinders in dispensing cabinets in the semiconductor industry was proposed.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.305-307
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• 2012

This study was computationally explored how the fuel autoignition reactivity was affected by operating parameters such as fuel, pressure, intake temperatures, engine speed and EGR compositions for HCCI combustion. This is done for DME and CHEMKIN-PRO was used as a solver. At first, influence of the operating parameters and EGR compositions were showed. And then, in order to clarify the mechanism of them on autoignition reactivity, data-sets of kinetic were analyzed to investigate the elementary reaction path for heat release at transient tempeatures by using contribution matrix.