Narrow Results

Accurate seismic risk assessment of structures necessitates precise fragility analysis. This study focuses on the seismic fragility assessment of equipment in nuclear power plant structures, particularly emphasizing the influence of nonlinear hysteretic behavior exhibited by squat walls. By developing and comparing linear and nonlinear models of reactor containment and auxiliary buildings within a nuclear power plant, this research elucidates the significant impact of nonlinear behaviors on the seismic response and subsequent fragility curves of associated equipment and systems. Utilizing a lumped-mass stick model, the study efficiently captures the characteristics of squat shear walls, facilitating the calculation of floor response spectra and fragility for nuclear facility structures. The impacts of pinching and degradation, inherent characteristics of a squat wall’s hysteresis under cyclic loading, were identified as significant. These include the shift and change in amplitude of the floor response’s peak, along with amplification in high-frequency domains. Fragility assessments, informed by seismic response analysis, indicate significant variations in fragility curve parameters based on equipment location and frequency. The findings question the effectiveness of traditional response factor methods and general regression techniques in accurately addressing the complex probabilistic seismic demands of equipment, thus highlighting the importance of using direct analysis for calculating fragility in situations with significant nonlinearity.

While a large literature exists on the siting of controversial facilities, few theories about spatial location have been tested on large samples. Using a new dataset from Japan, this paper demonstrates that state agencies choose localities judged weakest in local civil society as host communities for controversial projects. In some cases, powerful politicians deliberately seek to have facilities such as nuclear power plants, dams and airports placed in their home constituency. This paper then explores new territory: how demographic, political and civil society factors impact the outcomes of siting attempts. It finds that the strength of local civil society impacts the probability that a proposed project will come to fruition; the greater the concentration of local civil society, the less likely state-planned projects will be completed.

In a nuclear power plant, impact force due to loose part is related to the structural damage in the plant. In general, the steam generator of the nuclear power plant is structured by thick plate. The paper presents a novel approach to locate an impact load in a thick plate. The approach is based on the analysis of the acoustic waveforms measured by a sensor array located on the plate surface. For accurate estimation of the location of the impact source, the time differences in the arrival times of the waves at the sensors and their propagation velocities are determined. The dispersion curves for multi modes of Lamb wave are calculated by using exact plate theory and SDPT. It is difficult to measure directly the group velocity for Lamb mode of acoustic waveform in the thick plate because they are dispersive wave. However, most of the energy in the wave is carried by the flexural waves (A0 mode), the group velocity of this mode is extracted using the CHOTF technique for estimating the impact source location. The estimates are shown to be in excellent agreement with the actual locations and it is applied to the damage analysis due to the loose part in a nuclear power plant.

The corrosion products formed on the internal surfaces of the primary system are the major factor that generates radioactive contaminants such as oxide films and cruds during decommissioning, causing radiation exposure to workers. Thus, decontamination of nuclear facility surfaces is crucial to ensure the safe completion of decommissioning work. This study applied laser decontamination, which enables precise work while minimizing the deformation of the material surface through the control of process parameters, and investigated the characteristics of the decontaminated area. Specimens coated with Ni-ferrite on an aluminum alloy (A6061) substrate were fabricated and used in this experiment. Laser decontamination was performed using a low-power Q’switching fiber laser while varying the laser beam overlap rate and number of scans. The results of laser decontamination differed by the process parameters and material characteristics. It is determined that high decontamination efficiency can be achieved if appropriate conditions are applied.

In a typical pressurized water reactor nuclear power plant, the condensate pumps contribute to the majority of the feedwater flow to the steam generators, which is converted into steam that spins the turbine generator to produce electricity. Adequate monitoring of the condensate pump feedwater flow is essential not only for the pump’s reliability but also for efficient plant operations overall. This study applies the functional principal component analysis in characterizing the vibration signals generated under six different levels of flow rates of the pump, an environmental factor. The functional design of experiments is then applied to obtain an optimal flow rate according to the target vibration curve. The obtained flow rate is found comparable to the theoretical pump curve’s best efficiency point and is recommended to be used for optimal pump performance and reliability.

The seismic analysis of a structure using continuum mechanics approach may yield good results. However, this approach is difficult to apply for complex geometrical problems such as nuclear reactor containment building. To incorporate the entire structural behaviour, a full 3D model is best suited. However, a large number of modes are required to achieve at least 90% mass participation or frequency content up to 33 Hz. This consumes a large computational time due to large number of local modes present. Therefore, an equivalent lumped mass beam model, which as compared to 3D model, is much simpler and produces conservative global responses, has been considered in analysis. The lumped mass equivalent beam model of the system can be prepared after carrying out static analysis of 3D model using static energy equivalence approach. Forces and moments obtained by the seismic analysis of this beam model can be applied on the 3D model in order to obtain stresses in each element. It was found that the results obtained by this approach gives higher results because of higher mass participation. Experimental investigation is also performed on one of the case study to support the analysis. Hence it is concluded that analysis using beam model based on strain energy equivalence, in combination with 3D model is much simpler, economic and gives conservative results.

Fault tree analysis for nuclear power plant probabilistic safety assessment is an intricate process. Personal computer-based software systems have therefore been developed to conduct this analysis. However, all existing fault tree analysis software systems only accept quantitative data to characterized basic event reliabilities. In real-world applications, basic event reliabilities may not be represented by quantitative data but by qualitative justifications. The motivation of this work is to develop an intelligent system by fuzzy reliability algorithm in fault tree analysis, which can accept not only quantitative data but also qualitative information to characterized reliabilities of basic events. In this paper, a newly-developed system called InFaTAS-NuSA is presented and its main features and capabilities are discussed. To benchmark the applicability of the intelligent concept implemented in InFaTAS-NuSA, a case study is performed and the analysis results are compared to the results obtained from a well-known fault tree analysis software package. The results confirm that the intelligent concept implemented in InFaTAS-NuSA can be very useful to complement conventional fault tree analysis software systems.

In this paper, we proposed a model for selection of the most suitable city for a new nuclear power plant in Turkey by using fuzzy analytical hierarchy process and fuzzy analytical network process due to linguistic terms. The implementation of the system is demonstrated by a problem having four stages of hierarchy which contains four criteria and twenty attributes. The study compares the fuzzy analytic hierarchy process and fuzzy analytic network process results.

Solubilization, precipitation, sorption, and uptake of metal cations by microorganisms justifies the use of fungi in the removal of superficial radionuclide deposits from brickwork and (corroded) metal elements of dismantled nuclear power facilities and accidental spills on a dry way. The citrate and oxalate releasing ascomycete, Aspergillus niger, the oxalate producing brown-rot basidiomycete, Fomitopsis pinicola and several wood- and soil-inhabiting basidiomycetes were tested for their ability to acquire, and translocate uranium and to reduce the weight of metal plates by the expected production of carboxylic acids. Metals and plates of Portland cement were also exposed to solutions of carboxylic and mineral acids to substantiate the results. The nature of the watersoluble and -insoluble reaction products was not determined. The recalcitrant uranium was taken up and translocated through 100-mm long hyphal systems. In addition, all fungal mycelia were able to reduce the weight of the pure or alloyed metals, Fe > Zn > Cu, CuZn > AlMgSi > Cr significantly when added as plates to liquid and solid fungal substrates for 50 to 180 d. The dominating fungal carboxylic acids, malonic > citric, malic > oxalic in realistic solutions of 1 g L⁻¹ were able to reduce the weight of Fe > Ni > Zn > Cu > Al disks upon the formation of soluble and insoluble compounds. The mineral acids, H₂SO₄ > HNO₃ > HCl in solutions with a comparable initial pH transformed Fe > Ni >> Al primarily to insoluble precipitates. Plates of Portland cement increased their dry weight in the solutions of carboxylic acids apparently by the incorporation of the acids’ carbon whereas the mineral acids reduced the dry weight of the samples. Calcium was solubilized by all acids but oxalate. It is concluded that trace metals such as U spread in entire fungal networks which can thus serve as repositories of critical nuclides. In addition, fungal carboxylic acids dissolve (potentially contaminated and corroded) metal surface layers in the μm range by the formation of soluble and insoluble compounds most of the latter can be brushed off. Further tests comprise the placement of plastic-net stabilized lignocellulose mats overgrown with trace metal accumulator fungi on dry structured surfaces contaminated by critical nuclides and the subsequent ashing of the mats by air filtering. Respective in-situ tests with contaminated construction elements are inevitable to confirm economy and efficacy of microbial versus acid- and surfactant-based cleaning procedures.

For implementation of advance passive safety features in future nuclear power plant design, a passive safety system has been proposed and its response has been observed for Loss of Coolant Accident (LOCA) in the cold leg of a reactor coolant system. In a transient simulation the performance of proposed system is validated against existing safety injection system for a reference power plant of 325 MWe. The existing safety injection system is a huge system and consists of many active components including pumps, valves, piping and Instrumentation and Control (I&C). A good running of the active components of this system is necessary for its functionality as high head safety injection system under design basis accidents. Using reactor simulation technique, the proposed passive safety injection system and existing safety injection system are simulated and tested for their performance under large break LOCA for the same boundary conditions. Critical thermal hydraulic parameters of both the systems are presented graphically and discussed. The results obtained are approximately the same in both the cases. However, the proposed passive safety injection system is a better choice for such type of reactors due to reduction in components with improved safety.