• Nuclear Engineering and Technology
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• v.53 no.12
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• pp.3910-3917
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• 2021

Reactor fuel's power distribution plays a vital role in designing the new generation thermionic Space Reactor Power Systems (SRPS). In this paper, the 1/12th SPACE-R's full reactor core was numerically analyzed with two kinds of different axial power distribution, to identify their impacts on thermal-hydraulic and thermoelectric characteristics. In the benchmark study, the maximum error between numerical results and existing data or design values ranged from 0.2 to 2.2%. Four main conclusions were obtained in the numerical analysis: a) The axial power distribution has less impact on coolant temperature. b) Axial power distribution influenced the emitter temperature distribution a lot, when the core power was cosine distributed, the maximum temperature of the emitter was 194 K higher than that of the uniform power distribution. c) Comparing to the cosine axial power distribution, the uniform axial power distribution would make the maximum temperature in each component of the reactor core much lower, reducing the requirements for core fuel material. d) Voltage and current distribution were similar to the axial electrode temperature distribution, and the axial power distribution has little effect on the output power.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05a
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• pp.459-464
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• 1996

The 3-D power distribution synthesis scheme was implemented in Totally Integrated Core Operation Monitoring System (TICOMS), which is under development as the next generation core monitoring system. The on-line 3-D core power distribution obtained from the measured fixed incore detector readings is used to construct the hot pin power as well as the core average axial power distribution. The core average axial power distribution and the hot pin power of TICOMS were compared with those of the current digital on-line core monitoring system, COLSS, which construct the core average axial power distribution and the pseudo hot pin power. The comparison shows that TICOMS results in the slightly more accurate core average axial power distribution and the less conservative hot pin power. Therefore, these results increased the core operating margins. In addition, the on-line 3-D power distribution is expected to be very useful for the core operation in the future.

• Nuclear Engineering and Technology
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• v.21 no.4
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• pp.294-301
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• 1989

The Axial Power Distribution Monitoring System(APDMS) program was developed to calculate a detailed axial power distribution using two-level excore detector, cold leg temperature and control rod position signals. The unnormalized two-level excore detector signals were corrected for the rod shadowing factor determined by control rod position and for the temperature shadowing factor calculated based on cold leg temperature. A shape annealing matrix was then applied to the corrected excore detector response to yield peripheral power. After the core average power was obtained using linear relationship bet-ween core average and peripheral power, the boundary point power correction coefficient was applied to core average power in order to obtain boundary power for both upper and lower core axial boundaries. Then, the axial power distribution was synthesized by spline approximation. In spite of burnup, power level, control rod postion and axial offset changes, the comparisons of axial power distributions between BOXER simulation program and APDMS results showed good agreements within 5% root mean square error for Kori Unit 3 Cycle 4.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.58-63
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• 1997

This paper is concerned with an algorithm based on neural networks to calculate the axial power distribution using excore defector signals in the nuclear reactor core. The fundamental basis of the algorithm is that the detector response can be fairly accurately estimated using computational codes. In other words, the training set, which represents relationship between detector signals and axial power distributions, for the neural network can be obtained through calculations instead of measurements. Application of the new method to the Yonggwang nuclear power plant unit 3 (YGN-3) shows that it is superior to the current algorithm in place.

• Nuclear Engineering and Technology
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• v.23 no.3
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• pp.316-320
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• 1991

The Core Operating Limit Supervisory System (COLSS) is digital computer based on-line monitoring system that is designed to assist the operator in monitoring of the Limiting Conditions for Operation. A current COLSS calculates axial power distribution based on in-core detector signals using 5th order Fourier series method. It was found that the 5th elder Fourier series method was not accurate for certain axial power shapes, especially saddle power shapes, resulting in thermal margin decrease. A cubic spline synthesis was applied to the COLSS in order to improve the axial power distribution monitoring for the various axial power shapes. The results showed that the cubic spline synthesis simulated more accurately the axial power shapes, up to 5% in RMS errors, compared to those of the Fourier series.

• Journal of Power System Engineering
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• v.20 no.6
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• pp.64-70
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• 2016

The unsteady-state, incompressible and three-dimensional large-eddy simulation(LES) was carried out to evaluate the vorticity distribution of a small-size axial fan(SSAF). The X-component vorticity profiles developed around blade tips turn from axial to radial, and diminish the density of distribution according to the increase of static pressure. Otherwise, the Z-component vorticity profiles evenly develop at the region larger than the half radial distance of blade at the operating points of A and B, partly at the trailing-edge region of blade and radially over bellmouth according to the increase of static pressure.

• Nuclear Engineering and Technology
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• v.29 no.5
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• pp.375-384
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• 1997

Relative power density distributions of the Kori Unit 1 pressurized water reactor are calculated by Monte Carlo modeling with the MCNP code. The Kori Unit 1 core is modeled on a three-dimensional representation of the one-eighth of the reactor in-vessel component with reflective boundaries at 0 and 45 degrees. The axial core model is based on half core symmetry and is divided into four axial segments. Fission reaction density in each rod is calculated by following 100 cycles with 5,000 test neutrons in each cycle after starling with a localized neutron source and ten noncontributing settle cycles. Relative assembly power distributions are calculated from fission reaction densities of rods in assembly. After 100 cycle calculations, the system converges to a k value of 1.00039 $\geq$ 0.00084. Relative assembly power distribution is nearly the same with that of the Kori Unit 1 FSAR. Applicability of the full-scope Monte Carlo simulation in the power distribution calculation is examined by the relative root moan square error of 2.159%.

• Structural Engineering and Mechanics
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• v.55 no.3
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• pp.473-494
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• 2015

A graded harmonic finite element formulation based on three-dimensional elasticity theory is developed for the structural analysis of 2D functionally graded axisymmetric structures. The mechanical properties of the axisymmetric solid structures composed of two different metals and ceramics are assumed to vary in radial and axial directions according to power law variations as a function of the volume fractions of the constituents. The material properties of the graded element are calculated at the integration points. Effects of material distribution profile on the static deformation, natural frequency and dynamic response analyses of particular axisymmetric solid structures are investigated by changing the power law exponents. It is observed that the displacements, stresses and natural frequencies are severely affected by the variation of axial and radial power law exponents. Good accuracy is obtained with fewer elements in the present study since Fourier series expansion eliminates the need of finite element mesh in circumferential direction and continuous material property distribution within the elements improves accuracy without refining the mesh size in axial and radial directions.

• International Journal of Fluid Machinery and Systems
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• v.10 no.1
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• pp.86-98
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• 2017

In order to obtain high efficiency and low resistance droplet separation apparatus, axial vane type gas-liquid separators with different guide vanes were designed, and the RNG $k-{\varepsilon}$ model as well as discrete phase model (DPM) were used to investigate the flow pattern inside the separators. It was shown that the tangential velocity distribution under different guide vanes have Rankine vortex characteristics, pressure distribution exhibits a high similarity which value becomes big as the increase of the blade outlet angle and the decrease of the guide vane numbers. The increase of the guide vane numbers and the decrease of the blade outlet angle could make separation improve significantly. The separation efficiency is almost 100% when the droplet diameter is bigger than $40{\mu}m$.

• Journal of Mechanical Science and Technology
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• v.17 no.8
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• pp.1171-1184
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• 2003

An experimental study on critical heat flux (CHF) has been performed in an internally heated vertical annulus with non-uniform heating. The CHF data for the chopped cosine heat flux have been compared with those for uniform heat flux obtained from the previous study of the authors, in order to investigate the effect of axial heat flux distribution on CHF. The local CHF with the parameters such as mass flux and critical quality shows an irregular behavior. However, the total critical power with mass flux and the average CHF with critical quality are represented by a unique curve without the irregularity. The effect of the heat flux distribution on CHF is large at low pressure conditions but becomes rapidly smaller as the pressure increases. The relationship between the critical quality and the boiling length is represented by a single curve, independent of the axial heat flux distribution. For non-uniform axial heat flux distribution, the prediction results from Doerffer et al.'s and Bowling's CHF correlations have considerably large errors, compared to the prediction for uniform heat flux distribution.