[en] A deposition of corrosion products on fuel rods from the coolant circulated in a nuclear power plant (NPP) is commonly known as CRUD (Chalk River Unidentified Deposit). With the high temperatures reached in the reactor core, there is a high probability of the reactor reacting a sub-cooled nuclear boiling state. As CRUD formation is the function of reactor power and coolant temperature, it is predominantly formed around micro-bubbles that occur alongside the sub-cooled nucleate boiling. CRUD causes several reactor integrity problems. The first is B accumulation in CRUD, which creates an axial offset anomaly in the reactor core by absorbing neutrons. Another problem is radioactivity increasing on the inner surfaces of primary systems. After Co and Ni, which are dissolved in primary systems are deposited on fuel cladding, they are irradiated by neutrons and become radioactive isotopes, such as Co-60 and Co-58. These isotopes escape from fuel cladding and replace CRUD in the primary system's inner face. However, there have been many technologies applied for the mitigation of CRUD such as high operation, the use of enriched boric acid, H injection, chemical purification, magnetic filtering, and injection of metal ions such as Zn. In this study, we checked the effect of Zn on the formation of CRUD by SEM.

[en] In Fukushima Daiichi Nuclear Power Plant accident, No.4 plant was exploded by hydrogen explosion. There was a strong speculation about the possibility of the reaction between the overheated fuels and the steam-air mixture in the storage pool. Later, it turned out to be due to the hydrogen leaked from No.3 plant. However, the reaction of the hot fuels with the steam-air mixture became an important issue. There have been a lot of data accumulated about Zr-alloy interaction with steam. However, Zr-alloy interactions with air and steam-air mixtures have not been studied relatively much. In this study, we measured the oxidation kinetics of Zry-4 and Zirlo claddings in air, and steam-air mixtures, and analyzed the kinetics

[en] Human reliability analysis (HRA) is a method for evaluating human errors and providing human error probabilities (HEPs) for the application of probabilistic safety assessment (PSA). The main purpose of HRA in the context of the PSA is to identify, analyze and quantify all human failure events (HFEs) represented in the logic structure of the PSA, before and during the accident, which contributes to plant risk as defined in the PSA. HRA has been performed in a variety of complex systems such as nuclear power plants (NPPs), military systems, aircraft and chemical plants. This study aims to compare human reliability analysis methods, in terms of quantification process. First, four HRA methods, i.e., EPRI (Electric Power Research Institute) method, ASEP (Accident Sequence Evaluation Program), SPAR-H (Standard Plant Analysis Risk HRA), and K-HRA (Korean standard HRA), are selected for the comparison. These HRA methods are typically used, or based on the widely used one. Second, 7 post-initiators which have representative HRA conditions for OPR1000 type of NPPs in Korea are considered and analyzed in this study. Post-initiator means a HFE that includes operator’s errors in response to a disturbance after the initiating event. In addition, recovery factors and dependencies between HFEs are not included in this study. Lastly, an investigation of HRA results was carried out to verify the differences of HRA methods. The result of this study could be used as reference data to compare the human error probabilities from four HRA methods. It is expected to contribute to overcoming the uncertainties and limitations of HRA by deriving acceptable values for the HRA results.

[en] A deposition of corrosion products on fuel rods from the coolant circulated in a nuclear power plant (NPP) is commonly known as CRUD (Chalk River Unidentified Deposit).It has been an issue for NPP as increasing the level of radioactivity in reactor coolant system (RCS) and generating reactor imbalance of power distribution due to boron (AOA) and carrying on excess burden to the coolant purification system for a few decades. However there have been many technologies applied for the mitigation of CRUD such as high pH operation, the use of enriched boric acid, H injection, chemical purification, magnetic filtering, and injection of metal ions such as Zn. In this study, we checked the effect of Zn on the formation of CRUD, especially the composition change to see the effect of Zn (50 ppm)

[en] It is very important to analyze fuel cladding mechanical properties. Polycarbosilane(PCS) is a special ceramic whose protection films inhibit oxidation chemical resistance and strength at high temperatures. The PCS coating was carried out under various reaction conditions. The results showed that the supercritical process tries to moderate oxidation conditions such as temperature, time, and solution amount. In this study, we used specimens of the types currently used in nuclear reactors(zry-4, zirlo), as well as their corresponding coating specimens (PCS, CrN and CrN + Tungsten), to conduct an oxidation analysis four type of conditions(water, LiOH, LiOH + Boron, and steam) over the course of a month. CrN coating layers were successfully formed with good protection on metal surface and without any defect. CrN coated specimen formed protective coating layers, inhibiting oxidized layers. However, both Zry-4 and Zirlo PCS coated specimens experience suddenly high oxidation rates in all kinds of conditions. As a result, the specimens supported the acceleration of oxidation by PCS

[en] Since the Fukushima Daiichi accident, there has been an emphasis on the risk resulting from multi-unit accidents. Human reliability analysis (HRA) is one of the important issues in multi-unit probabilistic safety assessment (MUPSA). Hence, there is a need to properly identify all the human and organizational factors relevant to a multi-unit incident scenario in a nuclear power plant (NPP). This study identifies and categorizes the human and organizational factors relevant to a multi-unit incident scenario of NPPs based on a review of relevant literature. These factors are then analyzed to ascertain all possible unit-to-unit interactions that need to be considered in the multi-unit HRA and the pattern of interactions. The human and organizational factors are classified into five categories: organization, work device, task, performance shaping factors, and environmental factors. The identification and classification of these factors will significantly contribute to the development of adequate strategies and guidelines for managing multi-unit accidents. This study is a necessary initial step in developing an effective HRA method for multiple NPP units in a site

[en] In Korea, OPR1000 and Westinghouse type nuclear power plant reactor fuel rods oxide thickness has been evaluated by imported code A. Because of this, there have been multiple constraints in operation and maintenance of fuel rod design system. For this reason, there has been a growing demand to establish an independent fuel rod design system. To meet this goal, KNF has recently developed its own code B for fuel rod design. The objective of this study is to compare oxide thickness prediction performance between code A and code B and to check the validity of predicting corrosion behaviors of newly developed code B. This study is based on Pool Side Examination (PSE) data for the performance confirmation. For the examination procedures, the oxide thickness measurement methods and equipment of PSE are described in detail. In this study, code B is confirmed conservatism and validity on evaluating cladding oxide thickness through the comparison with code A. Code prediction values show higher value than measured data from PSE. Throughout this study, the values by code B are evaluated and proved to be valid in a view point of the oxide thickness evaluation. However, the code B input for prediction has been made by designer's judgment with complex handwork that might be lead to excessive conservative result and ineffective design process with some possibility of errors

[en] Performance shaping factors (PSFs) in the human reliability analysis (HRA) refer to any factor that influences human performance. To perform an HRA, it is necessary to identify PSFs that are most relevant and influential in the task analyzed. Generally, those PSFs are used to adjust basic human error probabilities (HEPs) in the nominal condition to calculate the final HEP in the condition of analyzed task. Many PSFs, such as training, procedure, stress, and complexity of task, have been suggested by HRA methodologies up to date. However, the selection of PSFs and the estimation of influence of PSFs in most HRA methodologies rely on expert judgments rather than the knowledge from actual experiments and observations. Therefore, it is not an easy work for HRA practitioners to decide whether a PSF really influences operator's performance or how much it contributes to the occurrence of error. This study conducted an experiment to investigate the relationship between operator's performance and PSFs. Actual operators and NPP simulator are applied in the experiment. The result indicates that the step completion time differed statistically depending on the procedure types and operator's experience. This study is an on-going research that is collecting the data on the effects on the operator's performances by different PSFs

[en] It is essential to input patients external contour in 3D treatment plan. We would like to see changes in depth and dose when 3D RTP is operating auto contouring when windows value (Width/Level) differs in this process. We have analyzed the results with 3D RTP after CT Scanning with round CT Phantom. We have compared and analyzed MU values according to depth changes to Isocenter changing external contour and inputting random Window value. We have watched change values according to dose optimization in 4 directions(LAO, LPO, RAO, RPO), We plan 100 case for exact analyzation. We have results changing window value random to each beam in 100 cans. It showed change between minimum and maximum value in 4 beam is Depth 0.26 mm, MU 1.2% in LAO. It showed LPO-Depth 0.13 mm, MU 0.9%, RAO-Depth 0.2 mm MU 0.8%, RPO-Depth 0.27 mm, MU 1.1%. Maximum change in depth 0.27 mm, MU error rate is according to Window change. As we can see in these results, it seems Window value change doesn't effect in treatment. However, it seems there needs to select appropriate Window value in precise treatment.

[en] Electron diagnostics based on electron–neutral atom (e–a) bremsstrahlung in the UV and visible range emitted from atmospheric pressure plasmas is presented. Since the spectral emissivity of the e–a bremsstrahlung is determined by electron density (n_e) and mean electron temperature (T_e) representing the Maxwellian electron energy distribution, their diagnostics is possible. As an example, emission spectra measured from capacitive discharges are presented, which show good agreement with the theoretically calculated emissivity of the e–a bremsstrahlung. For a single pin electrode nanosecond-pulsed plasma jet (n-PPJ) in argon, we investigate the electron properties and the temporal behavior of the positive streamers. Streamers with many branches are clearly observed inside the dielectric tube, while a few main streamers propagate outside the tube along the jet axis. A two-dimensional (2D) measurement of the time-averaged T_e distribution was developed using a commercial digital camera and optical band pass filters based on the emissivity ratio of two wavelengths of the e–a bremsstrahlung. The viable measurement range of T_e is 0.5–7 eV for the choice of two wavelengths of 300s and 900s nm and 0.5–4 eV for two wavelengths of 400s and 900s nm, which are uncontaminated by the atomic and/or molecular spectra. The 2D T_e distribution obtained using 514.5 and 632.8 nm emissions helps to reveal the role of electrons in streamer characteristics in the argon n-PPJ. Time-averaged T_e of 2.0 eV and 1.0 eV inside and outside the tube, respectively, were measured. The streamer dynamics of the n-PPJ is shown to be dependent on T_e. (paper)