[en] High capacity blowdown concept is applied in steam generator design for Korea Standard Nuclear Power Plant (KSNP) to remove sludge on tubesheet before solidification. NSSS system design adopted the operation mode as one of performance related design basis events, and proved that no adverse results happen such as reactor trip during high capacity blowdown operation. But KEPCO don't want to perform the operation for fearing of power reduction and the possibility of reactor trip due to SG level fluctuation. This report presents the performance analysis results for KSNP and the operation data for PVNGS related with the operation, to confirm the necessity of high capacity blowdown operation. (author)

[en] The computer program SAFE has been used to size and analyze the performance of a steam generator which has two types of heat transfer regions in Korean Standard Nuclear Power Plants (KSNP) and Korean Next Generation Reactor (KNGR) design. The SAFE code calculates the analytical boiling heat transfer area using the modified form of the saturated nucleate pool boiling correlation suggested by Rohsenow. The predicted heat transfer area in the boiling region is multiplied by a constant to obtain a final analytical heat transfer area. The inclusion of the multiplier in the analytical calculation has some disadvantage of loss of complete correlation by the governing heat transfer equation. Several comparative analyses have been performed quantitatively to evaluate the possibility of removing the multiplier in the analytical calculation in the SAFE code. The evaluation shows that the boiling correlation and multiplier used in predicting the boiling region heat transfer area can be replaced with other correlations predicting nearly the same heat transfer area. The removal of multiplier included in the analytical calculation will facilitate a direct use of a set of concerned analytical sizing values that can be exactly correlated by the governing heat transfer equation. In addition this will provide more reasonable basis for the steam generator thermal sizing calculation and enhance the code usability without loss of any validity of the current sizing procedure. (author)

[en] After cutting and drilling the spent fuel, we made a scrapping crud from the surface on the cladding. To scrap crud on the cladding surface, we made a special apparatus which has a 1/1,000 mm accuracy, but we could not taken crud. Thus, we effort the most possible use equipment to take crud samples, but unfortunately failed to get crud. We assume the crud would be dissolved. Because of the two fuel cladding, 17ACE7 and Plus 7, which were storage in PIEF pool for few years, it would be chemical reaction between pool water and crud deposited on the cladding. But we could not know the reason clearly. Therefore, it was impossible to analysis the crud, after that this project had to be stopped

[en] In order to apply the Leak-Before-Break(LBB) concept to the reactor coolant system(RCS) main loop piping, the capability of RCS leak detection systems should be adequate in accordance with the regulatory requirements. In this paper, the RCS leak detection systems for Kori units 3 and 4 are evaluated to determine their compliance to the regulatory requirements as well as to improve the system

[en] The modified ring tensile test technique was proposed in order to evaluate mechanical properties of fuel cladding under hoop loading condition in hot cell. The hoop loading grip for the modified ring tensile test is designed such that a constant specimen curvature is maintained during deformation, and the diameter of half-cylinder is 8.08 mm. The interface between the outer surface of the die insert and the inner surface of the cladding specimen was lubricated by Teflon tape or graphite lubricant in order to minimize the friction between this contact surface. The ring specimen design for ring tensile test is conducted to limit deformation within the gauge section and to maximize uniformity of strain distribution. The dimensions of the ring specimen are 5 mm in the ring width, 3mm in gage length and 2 mm in width of the gage section. In order to confirm the applicability of the proposed ring tensile test technique, Westinghouse PWR 16x16 type Zircaloy-4 unirradiated cladding material (nominal OD=9.5 mm, ID=8.36 mm) was tested in hot cell. Based on the load-displacement curve obtained in this study, the ultimate tensile load, the uniform plastic elongation and the total plastic elongation were compared with the test results reported previously. And the fractured ring specimens were observed by using the stereo microscope

[en] Fuel-clad interaction and the formation of fuel-clad bonding layers with specified chemical, physical and mechanical properties are of importance with regard to the evolution of thermal conductivity as well as in the context of a Pellet-Clad Mechanical Interaction (PCMI). It is also important in the framework of the long-term storage of spent fuel where the phases formed at the fuel-clad boundary are considered to be the first to be leached in the case of a cladding failure. The small volume of material analyzed and the easy of quantification made EPMA the ideal analytical tool with which to study the nuclear industry by providing fundamental information about the behavior Nof nuclear fuel under extreme irradiation conditions and about the performance of new fuel designed for the in-pile incineration of nuclear waste. The concentration of fission product shows a rapid increase in the concentration until the oxide film. In particular, the concentrations of Cs and Ce are as high as 0.5wt%. The zirconium concentration was 42wt% at the oxide layer part, and oxygen was 58wt% on 53,000 MWd/tU sample. It is represented through the formula of ZrO8x. It was confirmed that the concentration of oxygen was more than twice that of the zirconium dioxide. The formation of such an oxide layer causes a fatal defect in the integrity of the cladding tube, which can be considered as a fear of damage in the past. On the other hand, it was confirmed that the oxygen concentration of the oxidized layer of normal high burn-up spent fuel was about 15-18wt%

[en] To investigate the morphology and composition of the pure metallic material composing the crud, we tried to remove coolant impurities. We tried to increase the EPMA current to an abnormal intensity until the impurities contained in the crud were melted. The technique was applied by opening an adjustable aperture device for a gun alignment adjustment. As a result, it was confirmed that the impurities contained in the crud material disappeared and only the pure metal material remained. The shape and composition of the remained crud metal elements were analyzed, and the results are shown in this paper. The ratio of pure metal, compared to the volume of impurities and other water-soluble amorphous materials, is absolutely low in the entire volume of the crud. Fuel crud is generally composed of NiFe₂O₄, NiO, Ni⁰ etc. We tried to quantitative analyses the remaining metallic crud precipitate No1~4. We found NiFe₂O₄ at No1 specimen, and boll type pure Ni/Fe material at No3, also we can see Fe/Ni/O = 1/1/1 at No4 specimen. The results from this experiment may be different from the composition of crud.

[en] The post-irradiated examinations such as impact test, tensile test, composition analysis and etc. were conducted to monitor and to evaluate the radiation-induced changes, so called radiation embrittlement, in the mechanical properties of ferritic materials. Those data should be applied to confirm safety as well as reliability of reactor pressure vessel. The scopes and contents of hot cell examination on the surveillance capsule are as follows; - Capsule transportation, cutting, dismantling and classification - Shim block and Dosimeter cutting and dismantling - Impact test - Tensile test - Composition analysis by EPMA - SEM observation on the fractured surface - Hardness test - Radwaste treatment

[en] An in-situ scanning electron microscope (SEM) fatigue testing is proposed to investigate the fatigue crack the crack closure phenomenon within one cyclic loading under plane stress conditions. During the testing, the loading cycle is divided into a certain number of levels. At each level, high resolution images are taken around the crack tip region by SEM. Following this, imaging analysis is used to process these images in order to quantify the crack tip behavior at any time instant. Using an in-situ SEM fatigue testing, crack closure phenomenon is directly observed and measured on SEM image screen phenomenon. The proposed experimental methodology provides a new method for the comprehensive understanding of the fatigue damage accumulation. Survey on whether SEMTester can be installed in SEM and EPMA equipment in KAERI IMEF facility If this equipment could be install in IMEF facility, it may be a very good option because it can have various advantages such as storing image in real time in a small tensile specimen or performing quantitative analysis test for each part of tensile specimens.

[en] The mechanical testing data are required for the assessment of dry storage of the spent nuclear fuel. Laser cutting system could be useful tools for material processing such as cutting in radioactive environment due to non-contact nature, ease in handling and the laser cutting process is most advantageous, offering the narrow kerf width and heat affected zone by using small beam spot diameter. The feasibility of the laser cutting system was demonstrated for the fabrication of various types of the unirradiated cladding with and without oxide layer on the specimens. In the present study, the dimensional measurement and tensile test were conducted to investigate the mechanical behavior of the axial tensile test specimens depending on the material processing methods in a hot cell at IMEF (Irradiated Materials Examination Facility) of KAERI. Laser cutting system was used to fabricate the tensile test specimens, and the mechanical behavior was investigated using the dimensional measurement and tensile test. It was shown that the laser beam machining could be a useful tool to fabricate the specimens and this technique will be developed for the fabrication of various types of irradiated specimens in a hotcell