• Nuclear Engineering and Technology
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• v.25 no.3
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• pp.361-370
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• 1993

Low power physics tests should be peformed for the domestic pressurized light water reactors (PWRs) after refueling. The tests are peformed to ensure that operating characteristics of the core are consistent with predictions and that the core can be operated as designed. But in some low power physics tests, slow but steady reactivity increasing phenomena were noticed after step reactivity insertion by the control rod movement. These reactivity increasing phenomena are due to the low flux level and the gamma background because an uncompensated ion chamber (UIC) is used as the ex-core neutron detector. The gamma background may affect the results or the lour power physics tests. The aims or this paper are to analyze the grounds of such phenomena, to simulate a reference bank worth measurement test and to present a resolution quantitatively. In this study, the gamma background level was estimated by numerically solving the point kinetics equations accounting the gamma background effect. The reactivity computer check test was simulated to verify the model. Also, an appropriate neutron flux level was determined by simulating the reference bank worth measurement test. The determined neutron flux level is approximately 0.3 of the nuclear heating flux. This level is about 3 times as high as the current test upper limit specified in the test procedure. Then, the findings from this work were successfully applied to Kori unit 4 cycle 7 and Yonggwang unit 1 cycle 7 physics tests.

• The korean journal of orthodontics
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• v.30 no.2 s.79
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• pp.235-243
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• 2000

Magnetic resonance imaging(MRI) of the temporomandibular joint(TMJ) is very useful method to diagnose internal derangement of the TMJ because of its high specificity foy identification of condyle-disc relationships. The purpose of this study was to evaluate the existence, incidence and severity o』 internal derangement o』 the TMJ by the MRI of Patients who are suspected to have TMJ disorder. MRI sample was composed of 50 subjects(10 males, 40 females) and the mean age was 22.9 years. 43 subjects of the sample were found to have positive findings. $56\%$ of the subjects with positive findings had ADD(anterior disc displacement) without reduction, and $65\%$ had internal derangement of bilateral joints. Distributions in the types of malocclusion in patients with positive findings, the Angle's classification had shown : the largest $41.9\%$ for Cl II ($39.6\%$ for Cl II div 1 and $2.3\%$ for Cl II div 2), $37.2\%$ for Cl I, $18.6\%$ for Cl III, and $2.3\%$ for the unidentified. $8.6\%$ of the subjects with positive findings had facial asymmetry and $55.8\%$ had openbite. We can conclude that the percentage of Cl II is the highest in patients with internal derangement of the TMJ. Openbite or facial asymmetry is considered to be uncompensated or compensated deformity which results from facial skeleton remodeling in the process of degenerative joint disease(DJD) due to TMJ degeneration. Therefore it is recommended to screen the patients with facial asymmetry or openbite by MRI before the beginning of orthodontic treatment. Differential diagnosis is essential because the tendency of relapse is high after the orthodontic treatment and continuous observation of TMJ is needed in patients with TMJ disorder.