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[en] The purpose of this project is to propose a causality analyzer for maintenance/test tasks in nuclear power plants in terms of fault tree analysis and turbine cycle simulation for a secondary side. In nuclear power plants, a lot of efforts to reduce unanticipated trips caused by maintenance or tests have been conducted, so many of trip causalities in a primary side were eliminated. However, it is still difficult to effectively recognize the causalities for the tasks of maintenance/tests in a secondary side. This study, therefore, attempted to propose a methodology based on fault tree analysis and derate simulation, which is particularly applicable for a secondary side. Ultimately, it is possible to develop the guidelines to warn the vulnerability in the tasks by proactively providing the human errors from maintenance or tests. The products of this study is able to predict the enhancement of plant availability by correlating the human errors resulting from maintenance/tests with a various type of plant losses
[en] The Fukushima accident has started a new era in nuclear industry and now the industry is looking forward for the methodologies to mitigate the Beyond Design Basis Accidents (BDBA). BDBA's marked by loss of residual heat removal, and coupled events such as loss of electric power and loss or degradation of critical instrumentation are difficult to mitigate due to the loss of information on critical parameters. It has been suggested that the severe accident management guidelines (SAMGs) could only be much more useful if the monitoring of critical parameters is somehow made available to the operator. A desired capability of the monitoring system is to predict the gross behavior of the essential NPP subsystems under BDBA conditions, especially before substantial core damage occurs. International Nuclear Energy Research Initiative (INERI) project has been started to address this area of nuclear safety with the intention to develop an accident monitoring and diagnostics tool which could guide the emergency procedures at plant to limit the accident progression in a prolonged Station blackout (SBO). It is therefore, necessary that while giving a signal regarding plant safety (Safety Index: SI) the processing unit should also be able to diagnose the pattern of accident progression. As a part of INERI team, we have started our research to identify the requirements, methodologies and resources for the development of a Safety Index Monitoring during Severe Accidents (SIMSA) system. In this paper, we are going to present the preliminary concepts regarding the SIMSA system
[en] We present a scheme for the optomechanical entanglement between a micro-mechanical mirror and the field inside a bimodal cavity system using a non-degenerate optical parametric amplifier (NOPA). Our results show that the introduction of NOPA makes the entanglement stronger or more robust against the mean number of average thermal phonons and cavity decay. Interestingly, macroscopic entanglement depends upon the choice of the phase associated with classical field driving NOPA. We also consider the effects of input laser power on optomechanical entanglement. (paper)
[en] We present a comparative study of the collinear and orthogonal pre-ablation dual pulse configurations of laser induced breakdown spectroscopy (LIBS) of silver using Nd:YAG lasers. The effect of the inter-pulse delay and the ratio of the laser pulse energies on the signal intensity enhancement for both the dual pulse configurations have been investigated. Using the first laser at 532 nm and second laser at 1064 nm delayed by 5 μs, we achieved nearly 2 times signal enhancement in the collinear double-pulsed configuration and nearly 12 times in the pre-ablation orthogonal configuration as compared to SP LIBS. It is ascertained that at the optimized value of the inter-pulse delay between the two lasers, the intensity ratio of the neutral silver lines follows the local thermo dynamical equilibrium (LTE) condition and it is also in excellent agreement with that of the relative transitions probabilities ratio listed in the NIST data base.
[en] We present an efficient and inexpensive method for calculating the time resolved emission spectrum from the time integrated spectrum by monitoring the time evolution of neutral and singly ionized species in the laser produced plasma. To validate our assertion of extracting time resolved information from the time integrated spectrum, the time evolution data of the Cu II line at 481.29 nm and the molecular bands of AlO in the wavelength region (450–550 nm) have been studied. The plasma parameters were also estimated from the time resolved and time integrated spectra. A comparison of the results clearly reveals that the time resolved information about the plasma parameters can be extracted from the spectra registered with a time integrated spectrograph. Our proposed method will make the laser induced plasma spectroscopy robust and a low cost technique which is attractive for industry and environmental monitoring.
[en] We present new studies on the effects of laser wavelengths, pulse energy ratio and interpulse delay between two laser pulses in the collinear dual pulse configuration of laser-induced breakdown spectroscopy (LIBS) on an iron sample in air using the fundamental (1064 nm) and the second harmonics (532 nm) of Nd:YAG lasers. In the dual pulse LIBS, an optimum value of interpulse delay with an appropriate combination of laser wavelengths, and laser pulse energy ratio, yields a 30 times signal intensity enhancement in the neutral iron lines as compared with single pulse LIBS. A comparison in the spatial variations of electron temperature along the axis of the plume expansion in single and double pulse LIBS has also been studied. (letter)
[en] Reactor core components and structural materials for nuclear power plants to be decommissioned have been irradiated by neutrons of various intensities and spectrum. This long term irradiation results in the production of large number of radioactive isotopes that serve as a source of radioactivity for thousands of years for future. Decommissioning of a nuclear reactor is a costly program comprising of dismantling, demolishing of structures and waste classification for disposal applications. The estimate of radio-nuclides and radiation levels forms the essential part of the whole decommissioning program. It can help establishing guidelines for the waste classification, dismantling and demolishing activities. ORIGEN2 code has long been in use for computing radionuclide concentrations in reactor cores and near core materials for various burn-up-decay cycles, using one-group collapsed cross sections. Since ORIGEN2 assumes a constant flux and nuclide capture cross-sections in all regions of the core, uncertainty in its results could increase as region of interest goes away from the core. This uncertainty can be removed by using a Monte Carlo Code, like MCNP, for the correct calculations of flux and capture cross-sections inside the reactor core and in far core regions. MCNP has greater capability to model the reactor problems in much realistic way that is to incorporate geometrical, compositional and spectrum information. In this paper the classification of radioactive waste from the side structural components of a CANDU reactor is presented. MCNP model of full core was established because of asymmetric structure of the reactor. Side structural components of total length 240 cm and radius 16.122 cm were modeled as twelve(12) homogenized cells of 20 cm length each along the axial direction. The neutron flux and one-group collapsed cross-sections were calculated by MCNP simulation for each cell, and then those results were applied to ORIGEN2 simulation to estimate nuclide inventory in the wastes. After retrieving the radiation level of side structural components of in- and ex-core, the radioactive wastes were classified according to the international standards of waste classification. The wastes from first and second cell of the side structural components were found to exhibit characteristics of class C and Class B wastes respectively. However, the rest of the waste was found to have activity levels as that of Class A radio-active waste. The waste is therefore suitable for land disposal in accordance with the international standards of waste classification and disposal. (author)
[en] A dual-pulse laser-induced breakdown spectroscopic (DP-LIBS) technique for emission intensity enhancement is presented, using a Nd:YAG laser pulse to generate the plasma and a nitrogen laser pulse to enhance the degree of ionization in the laser-generated plasma plume. The higher degree of ionization with the nitrogen laser (337 nm) reveals significant enhancement of the signal intensity of several lead spectral lines. Besides the other advantages, the use of a nitrogen laser significantly reduces the experimental cost of DP-LIBS. The mechanism for the re-ionization of the laser-generated plasma plume by nitrogen laser has been discussed, and a comparison is presented of the plasma parameters in single-pulse and dual-pulse LIBS. (paper)
[en] Radwaste inventory from a nuclear reactor to be decommissioned comprises of neutron-activated materials and contaminated materials. The amount produced by activation is quite large as compared to the contamination products. Computer codes have been developed to estimate the radionuclide inventory attributed to neutron activation with reasonable accuracy. These computer codes use their own build-in cross-section and decay data libraries for the calculation of buildup and decay of a radionuclide in irradiated material. The built-in cross-section libraries generally contain spectrum-averaged one-group cross-sections for various nuclear reactions computed at certain reactor condition and therefore seem inappropriate for inventory calculations in far-core regions where the neutron spectrum is significantly different from that of in-core region. In this paper, we have analyzed the influence of spectrum-averaged capture cross-sections on estimated source terms for side structural components of a CANDU reactor, using MCNP/ORIGEN2 system which is a candidate computer code for radionuclide inventory calculations
[en] Reactor grade (RG) plutonium, accumulated as nuclear waste of commercial reactors can be re-utilized in CANDU reactors. TRISO type fuel can withstand very high fuel burn ups. On the other hand, carbide fuel would have higher neutronic and thermal performance than oxide fuel. In the present work, RG-PuC/ThC TRISO fuels particles are imbedded body-centered cubic (BCC) in a graphite matrix with a volume fraction of 60%. The fuel compacts conform to the dimensions of sintered CANDU fuel compacts are inserted in 37 zircolay rods to build the fuel zone of a bundle. Investigations have been conducted on a conventional CANDU reactor based on GENTILLYII design with 380 fuel bundles in the core. Three mixed fuel composition have been selected for numerical calculation; (1) 10% RG-PuC + 90% ThC; (2) 30% RG-PuC + 70% ThC; (3) 50% RG-PuC + 50% ThC. Initial reactor criticality values for the modes (1), (2) and (3) are calculated as k∞,0 = 1.4848, 1.5756 and 1.627, respectively. Corresponding operation lifetimes are ∝ 2.7, 8.4, and 15 years and with burn ups of ∝ 72 000, 222 000 and 366 000 MW.d/tonne, respectively. Higher initial plutonium charge leads to higher burn ups and longer operation periods. In the course of reactor operation, most of the plutonium will be incinerated. At the end of life, remnants of plutonium isotopes would survive; and few amounts of uranium, americium and curium isotopes would be produced. (orig.)