[en] There is a system was developed to detect the ultra fine particles (> 4 nm). For conventional system, working fluid is filtered using various cleaning system. Even though the working fluid was filtered, there are many ultra fine particles. If a fluid flows out from a crack, the particles, which are in the working fluid, also flow out and are spread into the air. Therefore, the crack can be detected by particle detection. In present study, preliminary experiments were performed for a micro crack detection technique using an ultra fine particle sensor. Preliminary experimental test for a micro crack detection technique using an ultra fine particle sensor were performed. Micro crack detection technique using ultra fine particle detecting system was validated for 0.6 ~ 0.7 MPa with several size cracks (hydraulic diameter 15 ~ 100 μm).

[en] The injected coolant decreases temperature of the heated fuel rods for 40 - 200 second (reflood). After core vessel is filled by coolant, it is long-term cooling. During the single-phase steam flow in the early phase of the reflood, the cladding temperature may increase and have a peak value due to low heat transfer from the fuel to the steam. The increased temperature can make a ballooned fuel rods. As a result, the flow passage area of sub-channel is reduced and it leads the redistribution of flow and heat transfer in sub-channels. The flow rate through the sub-channel between ballooned fuel rods is decreased while the flow rate through the sub-channel between intact fuel rods is increased. The reduction of flow reduces the capacity of coolability and ballooned fuel rods have higher temperature than non-deformed fuel rods. If a LBLOCA condition and ballooned fuel rods are occurred, the effect of reduced flow passage on the convective heat transfer by single-phase steam flow is important phenomena to analyze the safety of a reactor. During the LOCA condition, accumulation of fuel debris in the ballooned region of the bust cladding, which resulted from fuel fragments slumping from upper regions, can be occurred.. This fuel relocation makes different thermal hydraulic behavior. The present experiments were performed in various Reynolds numbers (about 2600 - 13000) and Heater power (0.14 - 1.12 kW/m) to investigate the effect of the Fuel-relocation on heat transfer phenomena by single-phase steam flow. The experiments were performed in three rod bundles in KAERI reflood ATHER test facility. One is a non-deformed 6 x 6 rod bundle, which consists of 36 non-deformed heater rods. Experimental study of heat transfer phenomena by single-phase steam flow using three type heater bundles (intact bundle, ballooned bundle, fuel-relocated bundle) were performed to investigate the effect of fuel-relocation on single-phase steam flow. Fuel-relocated bundle showed its own characteristics

[en] To improve safety analysis technology for a nuclear reactor containment considering an interaction between a reactor coolant system (RCS) and containment, this study aims at an experimental investigation on the integrated simulation of the RCS and containment, with an integral effect test facility, ATLAS-CUBE. For a realistic simulation of a pressure and temperature (P/T) transient, the containment simulation vessel was designed to preserve a volumetric scale equivalently to the RCS volume scale of ATLAS. Three test cases for a steam line break (SLB) transient were conducted with variation of the initial condition of the passive heat sink or the steam flow direction. The test results indicated a stratified behavior of the steam-gas mixture in the containment following a high-temperature steam injection in prior to the spray injection. The test case with a reduced heat transfer on the passive heat sink showed a faster increase of the P/T inside the containment. The effect of the steam flow direction was also investigated with respect to a multi-dimensional distribution of the local heat transfer on the passive heat sink. The integral effect test data obtained in this study will contribute to validating the evaluation methodology for mass and energy (M/E) and P/T transient of the containment

[en] The purpose of the assessment process of large thermal-hydraulic system codes is verifying their quality by comparing the code predictions against the experimental data. The Fast Fourier Transform Based Method (FFTBM) has been used widely for quantification of the prediction accuracy regardless of its limitation that it does not provide any time resolution for a local event. This limitation can be overcome by a wavelet transform because the resolution of the wavelet transform effectively varies in the time-frequency plane depending on the choice of basic functions. A wavelet transform is applied to an assessment of thermal-hydraulic system code with several parameter data of the ISP-50. To compare code prediction and experimental data, the cross-wavelet-transform and wavelet-coherence, which are methods to present similarity of two 1-D data, were also applied. Additional method that a pattern analysis using the cross-wavelet-transform and wavelet-coherence is conducted for a representative value to verify a similarity between the two data. (author)

[en] Real slug and bubbly flows were measured using a three ring impedance meter that can efficiently measure the void fraction of two phase flows in a tube. First, the fitting curves between the signal from the impedance meters and the void fraction were found. The impedance meter had different fitting curves for slug and bubbly flows that had the same void fraction. An impedance meter should choose one of the two fitting curves according to the flow pattern, and the flow patterns can be recognized using the measured void fraction. The velocities and sizes of the bubbles were calculated using the void fraction curves measured by two impedance meters

[en] Mid-loop operation tests were conducted at ATLAS facility to investigate the scaled down APR1400 model’s behavior under various pressures and noncondensable gas presence. Experimental results were compared to MARS-KS system code results to evaluate software capabilities predicting such phenomena as peak cladding temperature (PCT) and reflux condensation. The MARS-KS system code capabilities were tested against mid-loop operation experimental data. The negative non-condensable gas effect on condensation was prevailed by hydraulical issues corrupting proper reflux condensation simulation. Inappropriate method of the flow regime map implementation was found under various boundary conditions. Condensation model development in high pressure and temperature conditions with various non-condensable agents (air, N₂, He, H₂).

[en] The quantitative neutron imaging technique requires an exact relation between the measured neutron attenuation and the real macroscopic attenuation coefficient for every point of the sample. In this way quantitative information about the material composition or the sample thickness can be obtained. In the real case these conditions are not fulfilled and in dependence on the sample material we have more or less deviation from the exponential attenuation law. Because of the high scattering cross-sections of hydrogen for thermal neutrons, the problem with the scattered neutrons at quantitative investigations of hydrogenous materials (as PE, PMMA, oil, H₂O, etc.) is not trivial

[en] ATLAS has been recognized as one of the important IET facilities worldwide since the Isp-50 was successfully completed in 2011. A scaling of IET is one of the important issues to validate the experimental data from IET. Previous research discussed some of the problems involved when scaling similar phenomena measured in differently scaled facilities to the actual PWRs using Natural Circulation (NC). The NC scenarios occurring at different values of the primary system mass inventory were taken as a reference. NC in a PWR occurs due to the presence of a heat source (core) and sinks (steam generators), which in a gravity environment, create driving forces leading to flow rates in the loops and core cooling. The ATLAS NC characteristics were compared with the previous experimental data and discussed in the present study. A NCFM, which is one of the analysis tools for the scaling of IET, was performed for the ATLAS facility. In the case of 4.98% power, the NCFM of ATLAS is similar to previous researches. In the case of 1.82% power, however, the G/P value at the initial point was the upper side of the previous data. In spite of the different initial point, the peak and decreasing rate were similar to the envelope of curves. Therefore, the overall transient-trend of ATLAS for NC is suitable

[en] The quantitative neutron imaging technique requires an exact relation between the measured neutron attenuation and the real macroscopic attenuation coefficient for every point of the sample. In this way quantitative information about the material composition or the sample thickness can be obtained. Where I is the attenuated neutron flux, I_o is incident neutron flux, μ is attenuation coefficient, it is thickness of material. Equation is valid only in an ideal case, where a monochromatic beam, non-scattering sample and nonbackground contribution are assumed

[en] For a large break loss-of-coolant accident (LBLOCA) conditions in a pressurized-water reactor, the cladding temperature increases until the reflood phase and the increased temperature can make a ballooned fuel rods. As a result, the flow passage area of sub-channel is reduced and it leads the redistribution of flow and heat transfer in sub-channels. During the single-phase steam flow in the early phase of the reflood, the cladding temperature may increase and have a peak value due to low heat transfer from the fuel to the steam. If a LBLOCA condition and ballooned fuel rods are occurred, the effect of reduced flow passage on the convective heat transfer by single-phase steam flow is important phenomena to analyze the safety of a reactor. The present experiments were performed in various Reynolds numbers (about 2600∼13000) to investigate the effect of the Ballooned fuel rods on heat transfer phenomena by single-phase steam flow. The experiments were performed in two rod bundles in KAERI reflood ATHER test facility. One is a non-deformed 6x6 rod bundle, which consists of 36 non-deformed heater rods. The other is a deformed 5x5 rod bundle that consists of 9 deformed heater rods and 16 non-deformed heater rods. The cladding temperature and convective heat transfer for two rod bundles are compared for each flow conditions and the effects of experimental parameters are analyzed. (author)