Analyses have been performed on various experiments conducted using the Semi-Homogeneous Experimental Assembly (SHE) to examine the accuracy of computer codes employed in the neutronic design of experimental Very High Temperature Reactor (VHTR). The neutronic design codes are DELIGHT-6 to obtain the neutron spectrum of a fuel cell and to produce group constants with burnup utilizing the nuclear data from ENDF-B/IV, CITDEGA to calculate the three-dimensional core performance considering the coupling effect between neutronic and thermohydraulic characteristics, and ANISN-JR and TWOTRAN-II for transport calculation. These codes are examined by the analysis on the integral quantities of effective multiplication factor, neutron flux distribution, burnable poison rod worth and control rod worth. The maximum degrees of disagreement with the relevant experiments are 0.57, 5, 7 and 5%, respectively.
Click to increase image sizeClick to decrease image sizeKEYWORDS: Monte Carlo methodshielding analysiscomputer networksparallel computingNetwork File Systemmessage passinglockingspeedupparallel efficiency
The clinical and neuroimaging characteristics of 22 consecutive patients with Chiari type I malformations were evaluated to investigate the pathogenesis of syrinx formation. All patients underwent magnetic resonance imaging and x-ray tomography before surgery. The electric manometric Queckenstedt test was performed on 16 patients pre- and postoperatively. Syringomyelia was present in 17 patients and absent in five patients. All patients without syringomyelia suffered from foramen magnum compression syndrome, with a wider basal angle, more acute clivo-axial angle, shorter clivus, and more prominent tonsillar ectopia than patients with syringomyelia. Low brain stem position, basilar impression, and beaking of the cervicomedullary junction were also more prominent in patients without syringomyelia. Marked to complete block with the neck in flexed position by Queckenstedt test was present in all patients except one. Patients with Chiari malformation not associated with syringomyelia have more pronounced compression of the brain stem at the foramen magnum. Therefore, despite a block of the cerebrospinal fluid pathway at the foramen magnum, syrinx formation may be prevented by severe compression.
Many nuclear reactor systems have transport lag elements in their control loops. In such systems, the examination of stability using lag time as a continuously variable parameter will be found useful to the preliminary design of control systems or to evaluate the effectiveness of control systems when a lag time changes from a designed value in normal or abnormal condition. In this paper, the stability of a reactor system with multiple transport lags and a nonlinear control element is analyzed by using the parameter plane method in which variables are transformed into a logarithmic function. Taking lag time as the continuously variable parameter, stability analyses have been conducted for both simplified and realistic reactor models. From the former, many interesting phenomena are observed. For example, under some conditions, the system repeats the periodic sequence of stability and instability with the increment of lag time, while the frequency of a limit cycle changes discontinuously at specific lag time. In the latter model, similar phenomena are observed.
Abstract After the collapse of the Soviet Union and consequently the termination of the Cold War and the disarmament agreements, many nuclear warheads are in a queue for dismantling. As a result, substantial number of nuclear submarines equipped with ballistic missiles will be also withdrawn from service. However, Russian nuclear submarines have suffered from reactivity accidents five times. In the paper, a reactivity accident on a nuclear submarine that happened at Chazhma Bay located between Vladivostok and Nakhodka on August 10, 1985, has been described. In addition, the characteristics of submarine nuclear reactors, procedures of refueling, and the possibility of a similar accident are given. Further, the radiological risk to Japan and neighboring countries has been assessed by using an atmospheric pollutant transport code, WSPEEDI, developed by Japan Atomic Energy Research Institute. The radiological risk has been evaluated for the Chazhma Bay accident and for a hypothetical reactivity accident of a retired submarine during defueling, assuming winter meteorological conditions. The analyses have shown that the radioactive material might be transported in the atmosphere to Japan in one to several days and might contaminate wide areas of Japan. Under the assumptions taken in the paper, however, the radiological dose to population in the area might be not significant. KEYWORDS: nuclear submarinesreactor accidentsreactivity accidentpollutantsatmospheric transportVladivostokRussiaradioactive contaminationWSPEEDIChazhma Bayanalysis
The clinical efficacy and safety of MK-0787/MK-0791 were compared with piperacillin (PIPC) in respiratory tract infections by a well controlled study. Drugs were administered by intravenous drip infusion twice a day for 14 days, at a daily of 1 g/1 g of MK-0787/MK-0791 or 4 g of PIPC.The following results were obtained.1. Out of 367 patients (183 administered MK-0787/MK-0791, 184 PIPC) included in this trial, the clinical efficacy of 301 patients (155 received MK-0787/MK-0791, 146 PIPC) was evaluated by the committee members.2. The clinical efficacy rates in all cases evaluated by the committee members were 80.0% in MK-0787/MK-0791 and 71.7% in PIPC, respectively, and no significant difference was observed between the two drugs. Wheras, the clinical efficacy rates evaluated by the attending physicians were 82.0% in MK-07871/MK-0791 and 72.0% in PIPC, and significant difference was observed between the two drugs.3. No significant difference was observed between the clinical efficacy of the two drugs evaluated by the committee members in patients with pneumonia or pulmonary suppuration. But in patients with chronic respiratory tract infections, the clinical efficacy rates were 83.5% in MK-0787/MK-0791 and 63.0% in PIPC, respectively, therefore MK-0787/MK-0791 was significantly superior to PIPC. The clinical efficacy evaluated by both the attending physicians and the committee members in those patients were observed to be similar.4. The clinical and bacteriological efficacy against causative organisms in all cases were observed to have no significant difference between the two drugs, but MK-0787/MK-0791 was significantly superior to PIPC in single infections by P. aeruginosa.5. No significant difference was observed between the two drugs in regard to side effects or abnormality in laboratory findings.6. The usefulness of MK-0787/MK-0791 was superior to PIPC in all cases and in patients with chronic respiratory tract infections judged by committee members, and in patients with chronic respiratory tract infections judged by attending physicians.From these results it was concluded that MK-0787/MK-0791 is an extremely useful drug in the treatment of respiratory tract infections.
The applicability of Monte Carlo codes to a parallel computer is studied. Two Monte Carlo codes-a radiation shielding analysis code MCACE and a criticality analysis code KENO-IV-are examined and modified in order to execute on an experimental highly parallel computer, AP-1000. Despite simple modifications without changing the original program flow, the MCACE code has achieved a speedup of 52 times on the AP-1000 equipped with 64 cell processors. In the case of the KENO-IV code, it is less suitable for parallel computers than the MCACE code, but a speedup of 13 times has been achieved by using 32 cell processors.Two main causes of performance deterioration have been found; one is nonparallelizable part of the codes which affects more significantly with the increment of cell processors, and the other is idle times of cell processors which deteriorate the performance when the number of particles processed at each cell is small.
