Results 1 - 10 of 1981
Results 1 - 10 of 1981. Search took: 0.028 seconds
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[en] A new series of subcritical measurements has been conducted at the zero-power Walthousen Reactor Critical Facility (RCF) at Rensselaer Polytechnic Institute (RPI) using a 3He neutron multiplicity detector. The Critical and Subcritical 0-Power Experiment at Rensselaer (CaSPER) campaign establishes a protocol for advanced subcritical neutron multiplication measurements involving research reactors for validation of neutron multiplication inference techniques, Monte Carlo codes, and associated nuclear data. There has been increased attention and expanded efforts related to subcritical measurements and analyses, and this work provides yet another data set at known reactivity states that can be used in the validation of state-of-the-art Monte Carlo computer simulation tools. The diverse (mass, spatial, spectral) subcritical measurement configurations have been analyzed to produce parameters of interest such as singles rates, doubles rates, and leakage multiplication. MCNP®6.2 was used to simulate the experiment and the resulting simulated data has been compared to the measured results. Comparison of the simulated and measured observables (singles rates, doubles rates, and leakage multiplication) show good agreement. This work builds upon the previous years of collaborative subcritical experiments and outlines a protocol for future subcritical neutron multiplication inference and subcriticality monitoring measurements on pool-type reactor systems.
[en] The development of a diagnosis system is one of the important aspects in application of noise analysis technique. A diagnosis system for a BWR plant has been developed in Japan, and is now in the feasibility study. The diagnosis objects of the system are reactor core, main control systems (recirculation flow control system, feedwater control system and pressure control system) and jet pumps. The system includes an on-line algorithm based on statistical decision theory for surveying noise data and diagnosing plant operating status. The system was installed on a BWR plant and the test operation has been performed. It is confirmed that this system performance is satisfactory and that this system will be of great use for surveillance of core and control system without artificial disturbances. (author)
[en] Reactor surveillance methods and systems based on noise analysis techniques have been developed in Germany during the last ten years. A survey is given of the present state of application in German LWRs, surveillance measures, operational experiences in sound and vibration monitoring and current research projects. After a brief description of existing guide lines and standards under preparation, the present situation in LWRs with respect to noise surveillance systems is discussed. Some practical examples are given. Experiences refer to: operational noise pattern variations, metal impact sound generation and propagation/attenuation, location of sound sources, variations of sensor characteristics. The relevance of noise surveillance systems for plant licensing is discussed. (author)
[en] Some results concerning noise analysis studies performed in French LMFBR are presented in support to the design of an on-line noise analysis system to be included in the core surveillance and protection system of SUPER-PHENIX. This computerized system is presented: signal processing, block diagram, operating modes. (author)
[en] Some possible applications of the multi-variate noise analysis technique of partial and multiple coherence for reactor noise are investigated. Definitions and theory are reviewed. Partial coherence is considered as the coherence of signals, where the contribution in common with another (''conditioning'') set has been removed. In multiple coherence the effects in common with each of the conditioning signals are enhanced. Numerical problems of computation are discussed; efficient and stable (presumably new) algorithm are described. The application to transfer function estimation in systems with correlated measurable inputs is not further discussed, but emphasis is given to the possibility to separate global and local noise components, and to suppress or enhance certain components if there are many detectors and only few unmeasurable noise sources. The detector noise may be a disturbing factor; further work is suggested on decomposition and factorization of noise spectrum matrices by complex factor analysis. Some examples of the applications are presented for measurements with several in-core and ex-core neutron detectors in a PWR (Borssele). (author)
[en] Highlights: •A 3-D 2-group neutron noise simulator is developed for hexagonal-structured reactor core. •Neutron noise induced by propagating perturbations is calculated in VVER-type reactor core. •Propagation noise is modeled via both the forward and adjoint approaches. •The space- and frequency-dependence of the propagation noise are investigated. -- Abstract: Neutron noise induced by propagating disturbances in VVER-type reactor core is addressed in this paper. The spatial discretization of the governing equations is based on the box-scheme finite difference method for triangular-z geometry. Using the derived equations, a 3-D 2-group neutron noise simulator (called TRIDYN-3) is developed for hexagonal-structured reactor core, by which the discrete form of both the forward and adjoint reactor dynamic transfer functions (in the frequency domain) can be calculated. In addition, both types of noise sources, namely point-like and traveling perturbations, can be modeled by TRIDYN-3. The results are then benchmarked in different cases. Considering the noise source as propagating perturbations of the macroscopic absorption cross sections, the induced neutron noise is calculated throughout the reactor core. For the first time, adjoint approach is applied and examined for modeling moving noise sources. Moreover, the space- and frequency-dependence of the propagation noise are investigated in this paper.
[en] Highlights: •Lightweight Concrete samples were produced with pumice aggregate and colemanite addition in different rates. •Linear and mass attenuation coefficient of the samples increased with colemanite addition. •Photon attenuation coefficients depend on density of samples. •Experimental results were compared with theoretical results obtained from WinXCom computer program. •In later cure ages, the values of and linear attenuation coefficients were raised very conspicuously. -- Abstract: Radiation shielding properties of lightweight concrete produced with pumice aggregate and colemanite addition in different rates and effect of cure ages to the radiation shielding were investigated by using 60Co (1250 keV) radioactive source. Gamma rays were counted by 0.6 cc, Farmer type PTW™ Ion chamber. Experimental results were compared with the theoretical values calculated by WinXCom program. Consequently, colemanite addition make enhancement in the radiation shielding of the lightweight concrete, however there is no directly proportional relation between colemanite rate (0.4–2%) and attenuation properties of the lightweight concrete and cure age especially long timed, raises the linear attenuation coefficient and decreases the mean free path values. The theoretical values were obtained as nearby the experimental results, especially in the later cure ages (360 day).
[en] Highlights: •Ex-vessel release of fission products in severe accidents for 600 MW PWR is analyzed. •Mitigation effect of RCS depressurization on ex-vessel release is studied. •Mitigation effect of wet cavity on ex-vessel release is studied. -- Abstract: In severe accidents of pressurized water reactor (PWR), after reactor pressure vessel (RPV) failure, ex-vessel release of fission products is occurred. In order to reduce radiological consequence, ex-vessel release of fission products should be mitigated. According to character of ex-vessel release, reactor cooling system (RCS) depressurization and wet cavity are studied. For RCS depressurization, the mitigation effect of typical severe accidents sequences on ex-vessel release is studied, and negative effect of RCS depressurization is also studied. For wet cavity, the mitigation effect of initial water in cavity and finite cavity injection are studied, in respectively.
[en] Highlights: •Pressure drop components in rolling motion are investigated. •Effects of rolling on mean frictional and local coefficients are studied. •Transient fluctuations of pressure drops under rolling condition are studied. •Effects of rolling on transient resistance characteristics are investigated. •New correlation for calculating transient frictional coefficient is developed. -- Abstract: Experimental investigations on resistance characteristics of single-phase water flow in a 3 × 3 rod bundle subjected to the rolling motion were performed. The mean Reynolds number ranged from 174 to 15,137, and the rolling period and amplitude ranged from 8 s to 16 s and from 5° to 15°, respectively. The results show that the rolling motion has no significant influence on mean frictional coefficient and local resistance coefficient. The growth rate of local pressure drop with flow rate is much higher than that of frictional pressure drop. The frictional and local pressure drops fluctuate significantly on the whole range of flow regime, and their fluctuation amplitudes gradually increase as the mean Reynolds number increases. The amplitude of relative frictional pressure drop increases with increasing the rolling amplitude, while it is nearly invariable with rolling period. However, the rolling motion nearly has no effect on the amplitude of relative local pressure drop and only changes its fluctuation period in such a limited variation of rolling conditions. New correlation for predicting transient frictional coefficient is developed by multiple regression by considering the influences of rolling motion as well as flow conditions.
[en] Highlights: •The capture cross sections of 107Pd were measured with an NaI(Tl) spectrometer. •Measurements were performed at J-PARC/MLF/ANNRI. •The accelerator was run in a special operational mode called “single bunch” mode. •The capture cross sections of 107Pd were derived from the thermal to keV energies. -- Abstract: Measurements of the neutron capture cross sections of 107Pd were carried out at the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). Gamma-rays were detected with an NaI(Tl) spectrometer of the Accurate Neutron–Nucleus Reaction Measurement Instrument (ANNRI). The neutron capture cross sections were determined by the time-of-flight method in the neutron energy region from the thermal to keV energies.