Results 1 - 10 of 2620
Results 1 - 10 of 2620. Search took: 0.036 seconds
|Sort by: date | relevance|
[en] Absolute measurements of neutron fluence are an essential prerequisite of neutron-induced cross section measurements, dosimetric investigations and neutron beam lines characterisation. Independent and precise neutron flux measurements can be performed with respect to the H(n,p) elastic cross section. However, the use of silicon proton recoil detectors is not straightforward below incident neutron energy of 1 MeV, due to a high background in the detected proton spectrum. A new gaseous proton-recoil detector based on a double ionisation chamber, has been designed to answer the challenge. The detector is constituted by a H-rich deposit (polypropylene, mylar foil or tristearin deposit), and a segmented ΔE-E ionization chamber (4*4*12 cm3), read by a 64 pads Micromegas-based detection plane. The chamber is filled with gas (CF4 or N2-CO2) at an adjustable pressure, from few tens of mbar to few tens of 100 mbar, to reduce as much as possible the detector sensitivity to Compton electrons. Tests have confirmed the low electron sensitivity of the detector, making it well suited for neutron energies down to 200 keV in a gammas and electrons dense environment. The ΔE-E coincidences, coupled to a 3D proton track analysis, enables the disentanglement between direct and scattered neutrons
[en] There are different types of off gases generated during various operations of reprocessing of spent nuclear fuels. These off gases also carries significant amount of particulate activity which are treated at various steps in clean-up systems before being discharged to environment through tall stack. At final stage of every off gas clean-up system there is a dedicated deep bed and HEPA filters which remove the particulate activity. Therefore filtration efficiency of deep bed and HEPA filters play important role in controlling the discharges of particulate activity into environment. There are various method for efficiency test of off gas filters such as DOP (Di-octyl Phthalate) test, Methylene blue test, Sodium flame test, Uraniane test, radioactivity measurement etc. For efficiency test of newly installed off gas filters, DOP test is considered as standard method at nuclear industry. However during active operation DOP test is not used because of interference of radioactive contamination. To overcome these difficulties a compact efficiency test module designed and developed inhouse at reprocessing plant Tarapur. The efficiency of off gas filters (Deep bed and HEPA) can be determined by this module with error less than 1 % provided the inlet beta count rate is more than 100 cps, hence it is a replacement of DOP efficiency test method
[en] In this study, we designed, constructed, and operated an experimental facility to realize the inlet conditions to evaluate a turbine exhaust heat exchanger of a space launch vehicle. The entire facility consists of a steam generator for high-temperature fluid simulation and a flow stabilizer to ensure uniform flow. The inlet conditions at the target heat exchanger are a pressure of 0.22 MPa and a temperature of 773 K. For a 10-s combustion test at a pressure of 0.22 MPa, the resulting temperature was 850 K. The pressure was measured with 7 % error, and the temperature was uniformly realized at about 10 % higher than the target temperature. Based on this, it is expected that performance tests of the pressurized heat exchanger will be conducted in the future.
[en] We study the optimal performance of Feynman’s ratchet and pawl system operating as a heat engine (refrigerator), by optimizing the product of efficiency (coefficient of performance) and power output (cooling power), which is known as the efficient power (-criterion) in the literature. The analysis is performed by recourse to two different methods: the first employs an exact optimization over the internal energy scales of the device, and the second method is based on the use of prior information to estimate the optimal performance of the device. From the two-parameter optimization, universal features of the efficiency at maximum efficient power (EMEP) are shown. Then, an exact one-parameter optimization is carried out for the linear model of the engine in high temperature regime, by constraining one of the energy scales, and well-known forms of efficiency are obtained. Further, using the prior information approach, the obtained efficiency concurs with the EMEP of an endoreversible heat engine. An analogous analysis is carried out for the Feynman’s ratchet as a refrigerator. From the estimated behavior of the device under limited information, we are able to highlight universal features of its performance that remain robust under an inference analysis. (paper: classical statistical mechanics, equilibrium and non-equilibrium)
[en] Low-speed path following and high-speed lateral stability are vital performance for safety driving of truck–trailer combinations (TTCs). These two performance can be effectively improved by active trailer steering (ATS) system. This paper investigates low-speed path following and high-speed lateral stability for TTCs with ATS system. First of all, the driver model and yaw plane model of TTC are proposed to capture the optimal control performance index. Next, a method based on shift register operation is proposed to deduce the path-following off-tracking (PFOT) of TTC. Then, two controllers of path following and lateral stability are designed, respectively. Finally, numerical experiments on the directional performance of TTC are carried out under the low-speed intersection turn and roundabout maneuvre, and the high-speed single lane-change maneuvre. The numerical results demonstrate that the TTC with ATS system improves both low-speed path following and high-speed lateral stability compared with the baseline TTC without ATS system, and the designed controllers have good performance on reducing PFOT and RWA in any maneuvre conditions.
[en] In this paper, a model of irreversible three-electron-reservoir energy selective electron (ESE) cooling device with heat leakage is established. By utilizing the finite time thermodynamics, the optimal performance of the cooling device is studied and the influences of chemical potential differences of electron reservoirs, center energy level of energy filters and heat leakage on the optimal performances are discussed. On the basis of cooling rate and coefficient of performance (COP) analyses, the exergy-based ecological function and figure of merit are proposed as objective functions. The operation properties of ESE cooling device with different objective functions are investigated and the optimal performance region is obtained. Higher cooling rate and COP can both be attained for the ESE cooling device when it is working in the optimal performance region.
[en] Multi-model frameworks are widely used to identify the appropriate model structure for the study catchment. However, most frameworks mainly consider the process complexity of the model, and few of them consider the spatial complexity. In this paper, we investigated the appropriate model structure for a karst catchment from the aspect of spatial complexity. The purpose is twofold: (1) to investigate whether the spatial complexity is needed to simulate the spring discharge of this karst catchment and (2) to investigate whether the increase of model’s spatial complexity can make up its deficiency on the process complexity. Three simple lumped models with different process complexities were chosen to gradually increase the spatial heterogeneity of their parameters to investigate the appropriate model structure for simulating the discharge of a karst spring. The results show that the performances of three lumped models highly improve when adding the routing function to them. However, further considering the spatial parameter heterogeneity, only one model shows obvious performance improvement and other two models show limited improvement. Moreover, this model with relatively complex spatial parameter heterogeneity still shows worse performance than another lumped model. This indicates an increase of models’ spatial complexity cannot always make up their process deficiencies. The final comparison results indicated that the lumped model or their semi-lumped version with flexible process complexity is enough to simulate the discharge of this karst spring and no extra spatial complexity is needed. Our studies also indicated that the increase in spatial complexity of the model cannot always fully compensate its deficiency in process complexity.
[en] This paper presents the drop performance test of the control rod assembly which is one of the main components strongly related to the safety of the prototype generation IV sodium-cooled fast reactor. To investigate the drop performance, a real-sized control rod assembly that was recently modified based on the drop analysis results was newly fabricated, and several free drop tests under different flow rate conditions were carried out. Then the results were compared with those obtained from the previous tests conducted on the conceptually designed control rod assembly to demonstrate the improvement in performance. Moreover, the drop performance tests under several types and magnitudes of seismic loadings were also conducted to investigate the effect of the seismic loading on the drop performance of the modified control rod assembly. The results showed that the effects of the type and magnitude of the seismic loading on the drop performance of the modified control rod assembly were not significant. Also, the drop time requirement was successfully satisfied, even under the seismic loading conditions