[en] A Z₂ orbifold compactification of the heterotic string is considered. The resulting 6D GUT groups can be SO(16) or E₇xSU(2) plus some hidden sector groups. The N=4 supersymmetry is reduced to N=2. In particular, the SO(16) 6D model with one spinor representation 128 can reduce to the previous 5D SO(16) or SO(14) family unification models after compactifying the sixth dimension. To obtain one spinor, we have to take into account the left-over center of SO(16). We also comment on the E₇xSU(2) model

[en] Inspection and repair of tower structure and lift, instrument calibration have been done in the scope of 'Environmental Radiation Monitoring Around the Nuclear Facilities' project. Wind direction, wind speed, temperature, humidity at 67m, 27m, and 10m height and temperature, humidity, atmospheric pressure, solar radiation, precipitation, and visibility at surface have been measured and analyzed with statistical methods. At the site, the prevailing wind directions were E in spring and summer, NNW in winter season. The calm distributed 27.3% at 67m, 37.4% at 27m, 52.2% at 10m height. Wireless data transmission to MIPS(Meteorological Information Processing System) has been done after collection in the DAS where environmental assessment can be done by the developed simulation programs in both cases of normal operation and emergency

[en] Electrochemical Corrosion Potential (ECP) measurement in circulating loop circuit has been performed as a basic test for accomplishing the ECP monitoring test in the feedwater train of nuclear power plants. ECP of steam generator tube material-Alloy 600, platinum and carbon steel piping material-A 106Gr.B was measured at the same condition as pure water temperature 230 .deg. C, cold pH 9.5. The behaviors of three different test specimen was observed while the DO concentration was varied from 0.1ppb to 30ppb, reversely to 0.3ppb. It is concluded that the ECP values of three kinds test specimen are sharply changed at the 3ppb ∼10ppb DO concentration

[en] In the authors' previous study an Internet survey had been conducted for employees in nuclear related industries and institutes in Korea and the monetary value placed on reductions in risks from occupational radiation exposure and car accidents had been estimated. This paper presents the results of the follow-up study using the same methodology for the general public. The double bounded dichotomous choice (DBDC) approach was used and willingness-to-pay (WTP) values for predefined 20% reductions of the car accidents and radiation exposure risks were elicited. WTP for the reductions of the risk were estimated and values of a statistical life were calculated from the mean WTPs. For the general public, the mean value of statistical life was 2.67 billion Won for car accidents and 2.28 billion Won for radiation exposure. Discussions on the use of Contingent Valuation Method (CVM) for determining the monetary value of risk reductions and recommendations for further study were given

[en] Environmental radiation monitoring was carried out with measurement of environmental radiation and environmental radioactivity analysis around KAERI nuclear facilities and Seoul Research Reactor are the follows: The average level of environmental radiation dose measured by NaI scintillation counter and accumulated radiation dose by TLD was almost same level compared with the past years. Gross α, β radioactivity in environmental samples showed a environmental level. γ-radionuclides in water samples were not detected. But only radionuclide K-40, which is natural radionuclide, was detected in the all samples and Cs-137 was detected in the surface soil and discharge sediment. The average level of environmental radiation dose around Seoul Research Reactor was almost same level compared with the past years, and Be-7 and Cs-137 were detected in some surface soil and discharge sediment by γ-spectrometry. (author). 37 refs., 67 tabs., 23 figs

[en] How to measure nuclear safety is the common subject of utility and regulator. This paper reviews the basic concept and definition of safety, hazard and risk and examines the reason why people pursue safety. Based on these general understanding, the meaning and characteristics of nuclear safety are discussed and methods to assure nuclear safety are addressed. International activities to develop safety performance indicators are analyzed and operational safety performance indicators, safety culture indicators developed by IAEA are explained and their relations are examined. Performance indicators in Korea are also explained with improvement plan and areas for future studies are suggested

[en] In this study, a sensitivity analysis on shear failure of a discontinuity adjacent to a circular opening has been performed based on a series system reliability analysis. To realize the failure surface of the system, Mohr-Coulomb yield criteria and other empirical models suggested by Jaeger, Ladanyi and Archambault, and Barton and Bandis have been adopted. Discontinuity direction, initial stress, pore water pressure and various physical properties obtainable from site investigation and Lab. test in discontinuous rock mass before the design stage are selected as multi-random variables, all of which could be simulated in terms of normal distribution, log-normal distribution, or beta distribution. In order to obtain generalized reliability index and failure probability, FORM(First-order reliability method) and PNET method have been adopted with modified HL-RF method as for an optimization scheme. A computer program has been developed and verified by comparing the analysis results by Monte Carlo simulation. The effect on probability of failure of cavern size, distance between a cavern and a discontinuity, and correlation coefficients have been reviewed through reliability analysis. The most sensitive parameter on system failure has been obtained through sensitivity study

[en] This study investigated geometrical arrangement of RI gauge using backscattered radiation. Calculations of important parameters such as distance between the source and detectors, the number of detectors and the position of the detectors were carried out using a Monte Carlo computer code MCNP4A. Depth of soil that is meaningful in determining wet and dry density was also calculated by MCNP4A. Cf-252 neutron source and He-3 detectors were adopted for wet density measurement and Co-60 gamma source and G· M detectors were used for dry density measurement. It was shown that calculate curve of backscatter type RI gauge were well agree with experiment result. As a experimental results, designed backscatter type RI gauge is superior to transmission type RI gauge in wet density, but additional study for precision measurement in dry density were need

[en] The ECP measurement technique was applied to one of Younggwang nuclear power plants unit 3(YGN 3) in order to define the extent of oxidizing and reducing environment quantitatively in the final feed water during start up and normal operation, and then to define optimum hydrazine concentration in the feed water. Ag/AgCl external reference electrode was used for the measurement program. The salt bridge was filled with pure water rather than KCI solution. Very stable reference potential could be maintained in high temperature test condition by filling pure water. The absolute reference potential value was determined by a separate qualification test. The hydragine concentration of YGN 3 in normal operation is maintained about 140ppb. ECP of platinum, Alloy 600 and carbon steel electrodes was monitored while the hydrazine concentration was varied between 50 and 200 ppb. It was found that ECP of the three different electrodes was not affected by the hydrazine concentration, and that % magnetite was maintained above 96% in the sludge sampled in the blow down line from hto leg side. The dissolved oxygen content was around 3 ppb in condensate and 0.1 ∼ 0.4 ppb in final feed water. It is concluded in this study that the reducing environment can be guaranteed when the hydrazine concentration maintained above 50 ppb. Firm evidences are available currently from both plant experience and laboratory test data that high hydrazine concentration causes accelerated FAC (flow accelerated corrosion) of carbon steel components in high temperature above 200 .deg. C. It is suggested that the optimum hydrazine concentration in the feed water be defined as the possible lowest range where reducing atmosphere can be guaranteed

[en] Inductively coupled plasma atomic emission spectrometry(ICP/AES) was used for the determination of uranium and thorium in geological materials. Samples were predecomposed by mixed acid digestion technique. The separation of the uranium and thorium was achieved by systematic solvent extraction with TTA(thenoyltrifluoroacetone) and TOA(tri-n-octylamine) and back extraction into HCl. The results for standard rock sample, NIST SRM 278, showed a good agreement with those certified from NIST as well as found values by other non-destructive techniques. Additional purification for extracted portions was carried out by anion exchange chromatography for measurement of several natural radioisotopes of uranium and thorium by alpha spectrometry. (author)