Results 1 - 10 of 347
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[en] An assessment is made of recent test data from France, Japan, and Russia, and of earlier test data from the U.S., in relation to the safety analysis performed for power reactors in the U.S. Considerations include mode of cladding failure, oxidation, hydriding, and pulse-width effects. From the data trend and from these considerations, it is concluded that the cladding failure threshold for fuel rods with moderate-to-high burnup is roughly 100 cal/g for BWRs and PWRs. Realistic plant calculations suggest that cladding failure would not occur for rod-ejection or rod-drop accidents and, therefore, that pellet fragmentation and enhanced fission product release from fuel pellets should not have to be considered in the safety analysis for these accidents. However, the data base is sparse and contains a lot of uncertainty
[en] Several anomalies of important slowing or incomplete insertion of rod cluster control assemblies occurred on EDF 1300 MWe power plants since 1995. Different investigations have permitted to accuse the excessive distortions of fuel assemblies. Distortion measurements have been performed on an important number of fuel assemblies, in particular for reactors concerned by this phenomenon. New techniques of dimensional measurement have been developed. At this time, lateral distortion has been measured on several hundred of fuel assemblies. Studies achieved by FRAMATOME on the behavior under irradiation of the fuel assembly structure have permitted to understand phenomena at the origin of these distortions. The conception of the new products integrates the results of these studies in order to improve their performance and eliminate RCCAs drop time anomalies. (authors)
[en] The present status of safety studies on the light-water type atomic power reactor was described. First, over all changes of the studies were described. Secondly, the studies on each field (safety studies on the atomic reactor fuel, experimental studies on the loss of coolant, experimental studies on accidents of reactivity, and the arrangement and development of safety codes) were explained briefly. (Tsukamoto, Y.)
[en] Highlights: • Ensemble learning methods are proposed to improve performance of abnormal detectability. • Methods of PEM, TPS, WCM and ANN are used as base learners. • Boosting and bagging reduce errors for unstable learners; otherwise may increase them. • Stacking performs much better than bagging and boosting. - Abstract: Several ensemble learning methodologies have been presented to improve the performance of the core power distribution reconstruction, such as boosting technology, bagging technology and stacking technology. Four commonly used core power reconstruction methods, including PEM, TPS, WCM and ANN are adopted as base learners or meta-learners. The power distribution of the control rod drop accident and quadrant power tilt accident, which combine with detectors measurement noise, is reconstructed. The numerical simulation shows that the results of the stacking methodology can be better than any single one of these base learners under large sample spatial variation of power distribution and large measurement uncertainty. Otherwise results that close to the best one of these base learner results could be generated in stacking methods. In bagging and boosting methodologies, for the unstable learner such as TPS and ANN methods with large measurement uncertainty, both methodologies will help to reduce the reconstruction errors. The boosting methodology could even get better results than bagging. While for the stable learner (such as PEM learner, WCM learner) or unstable learner (e.g. the TPS or ANN method) but under small spatial variation (or small measurement uncertainty) that is not sensitive to the change of sample data, the bagging or boosting method even will reduce the reconstruction performance. Generally, ensemble learning methodologies have capability to improve the core abnormal detectability in most operation scene. Usually stacking methodology performs much better than bagging and boosting methodologies.
[en] The 9m free drop accident presented in 10CFR 71 is considered as the most critical scenario of hypothetical accident conditions during transport. In this paper, the 9m free drop for OASIS-32D using the LS-DYNA program was evaluated. The results of the analyses confirm that the structural integrity of OASIS-32D is maintained. The 9m free drop analyses of OASIS-32D were carried out for typical conditions. The results of the analyses show that the structural integrity of OASIS- 32D is maintained for the 9 m free drop analyses of horizontal and vertical drop conditions.
[en] Purpose: To enable to attain stabilized buffering performance upon control rod drop irrespective of conditions such as the reactor core temperature and the height of the dropping position. Constitution: Molded bellows buffers having different rigidities are arranged serially to the lower end of a control rod element to be vertically moved within the reactor core along the axial direction of a control rod main body. In the case where the control rod main body drops under a high temperature atmosphere during power operation, that is, where the yielding stress of the bellows is reduced and thus the energy absorbing performance is reduced, or in the case where the control rod main body drops from a higher position even under a low temperature atmosphere, the first bellows is at first yielded to deform plastically and, thereafter, the secondary bellows with a higher rigidity also deforms plastically to absorb dropping energy. (Kawakami, Y.)
[en] To stabilize electric power supplies, it is imperative to develop methods for raising the operation ratio of nuclear-power plants. The article describes the structure and features of a rod-drop detection system employing control-rod drop-order analysis to assist in locating faults when a rod-drop phenomenon occurs. The system is aimed at improving the efficiency of rod-drop time-measurement testing to reduce the time required for preventive maintenance. (author)
[en] This paper presents the qualification efforts performed by TPC and INER for the 3-D spatial kinetics code ARROTTA for LWR core transient analysis. TPC and INER started a joint 5 year project in 1989 to establish independent capabilities to perform reload design and transient analysis utilizing state-of-the-art computer programs. As part of the effort, the ARROTTA code was chosen to perform multi-dimensional kinetics calculations such as rod ejection for PWR and rod drop for BWR. To qualify ARROTTA for analysis of FSAR licensing basis core transients, ARROTTA has been benchmarked for the static core analysis against plant measured data and SIMULATE-3 predictions, and for the kinetic analysis against available benchmark problems. The static calculations compared include critical boron concentration, core power distribution, and control rod worth. The results indicated that ARROTTA predictions match very well with plant measured data and SIMULATE-3 predictions. The kinetic benchmark problems validated include NEACRP rod ejection problem, 3-D LMW LWR rod withdrawal/insertion problem, and 3-D LRA BWR transient benchmark problem. The results indicate that ARROTTA's accuracy and stability are excellent as compared to other space-time kinetics codes. It is therefore concluded that ARROTTA provides accurate predictions for multi-dimensional core transient for LWRs. (author)
[en] Purpose: To enable reactor power controlling, upon occurrence of abnormality in one control rod position indication system, while not inhibiting the control operation for all of the control rod but allowing the operation for the control rods in other normal control rod position indication systems, in the case where the reactor safety can be secured. Constitution: A control rod operation judging section is provided and, in a case where the position for a control rod becomes unclear, it is judged as to whether the reactor safety can be insured or not by the operation for the control rod intended to be operated based on the normal position data prior to the missing state and the present reactor core status. (Ikeda, J.)
[en] The paper describes an analysis of a postulated reactor head drop incident during refueling. The equations governing the head motion, the fluid, and the interaction between them are derived and used to calculate two limiting situations: a plant solid with water, and a plant with an air bubble. It is found that the dominant effect of the fluid stiffness in the solid system case yields much lower head/vessel impact velocities, but significantly higher vessel pressure loads than does the air bubble case. The inclusion of the fluidstructure interaction effects is found to be beneficial in both cases because of the difference in time between the peak pressure load and the final impact load. (author)