Nuclear Power Plant Containment Research Articles

Seismic Fragility Analysis of Seismically Isolated Nuclear Power Plant Structures using Equivalent Linear- and Bilinear- Lead Rubber Bearing Model.

In order to increase seismic performance of nuclear power plant (NPP) in strong seismic zone, lead-rubber bearing (LRB) can be applied to seismic isolation system of NPP structures. Simple equivalent linear model as structural analysis model of LRB is more widely used in initial design process of LRB than a bilinear model. Seismic responses for seismically isolated NPP containment structures subjected to earthquakes categorized into 5 different soil-site classes are calculated by both of the equivalent linear- and bilinear- LRB models and compared each others. It can be observed that the maximum displacements of LRB and shear forces of containment in the case of the equivalent linear LRB model are larger than those in the case of bilinear LRB model. From the seismic fragility curves of NPP containment structures isolated by LRB, it can be observed that seismic fragility in the case of equivalent linear LRB model are about 5~30 % larger than those in the case of bilinear LRB model.

Influences of nuclear containment radius on the aircraft impact force based on the Riera function

The aircraft impact force directly influences the local failure and global response of the nuclear power plant (NPP) containment, while the existing theoretical models and the field tests were almost based on the flat target. In order to analyze the radius effect of the circular sectional containment on the impact force, a fine FE model of the commercial aircraft A320 was established and validated by the available limited full-scale F-4 Phantom impact experiment. In order to determine the force to crush the A320 FE model, the influences of aircraft longitudinal crushing strength on the impact process were analyzed based on the Riera function. Considering the containment decaying effect to aircraft impact velocity, the impact impulse was theoretically calculated, while the influences of the losses of mass and energy were not included. The numerical simulations of A320 aircrafts impacting on simplified NPP containments with different radii were conducted, which could well reproduce the airframe crushing and debris scattering. By comparison of the simulated impact impulses and the calculation values by the Riera function, the coefficients corresponding to different containment radii are derived and a fitting formula is obtained. Finally, an improved Riera function dependent on the dimensionless ratio of nuclear containment radius and aircraft wingspan is proposed.

Mechanical properties of two-way different configurations of prestressed concrete members subjected to axial loading

In order to analyze the mechanical properties of two-way different configurations of prestressed concrete members subjected to axial loading, a finite element model based on the nuclear power plant containments is demonstrated. This model takes into account the influences of different principal stress directions, the uniaxial or biaxial loading, and biaxial loading ratio. The displacement-controlled load is applied to obtain the stress estrain response. The simulated results indicate that the differences of principal stress axes have great effects on the stressestrain response under uniaxial loading. When the specimens are subjected to biaxial loading, the change trend of stress with the increase of loading ratio is obviously different along different layout directions. In addition, correlation experiments and finite element analyses were conducted to verify the validity and reliability of the analysis in this study. Copyright © 2015, Published by Elsevier Korea LLC on behalf of Korean Nuclear Society.

Development of CAP code for nuclear power plant containment: Lumped model

CAP (nuclear Containment Analysis Package) code has been developed in Korean nuclear society for the analysis of nuclear containment thermal hydraulic behaviors including pressure and temperature trends and hydrogen concentration. Lumped model of CAP code uses 2-phase, 3-field equations for fluid behaviors, and has appropriate constitutive equations, 1-dimensional heat conductor model, component models, trip and control models, and special process models. CAP can run in a standalone mode or a linked mode with a reactor coolant system analysis code. The linked mode enables the more realistic calculation of a containment response and is expected to be applicable to a more complicated advanced plant design calculation. CAP code assessments were carried out by gradual approaches: conceptual problems, fundamental phenomena, component and principal phenomena, experimental validation, and finally comparison with other code calculations on the base of important phenomena identifications. The assessments showed appropriate prediction capabilities of CAP.

Near Infrared Spectroscopy, a Diverse Analytical Tool with Unlimited Potential for Discoveries!

sample and does not have the luxury to selectively remove or ignore any component from the whole. Over the last decade, we have experienced first-hand how versatile NIR spectroscopy has been as an analytical tool. Whether it was the application of NIR spectroscopy to the identification of electric cable insulation materials in nuclear power plant containment (which by some estimates resulted in millions of dollars of savings in replacement costs) or the determination of FA composition in fats and oils (which was recently approved by the AOCS as a Standard Procedure, Cd 14f-14, that will appear online soon), or even in tackling obesity in humans by accurately monitoring body composition, specifically the fat content. For the first time, this latter application was more recently extended to demonstrate that the body composition of pregnant women could be accurately monitored non-invasively and with no health risk to the mother to help monitor the health status of the expectant mother and her baby. When Karl Norris made the discovery that NIR spectroscopy could be used to measure the moisture, protein and oil content in grains and oilseeds from the same NIR data, he could not have imagined the extent of applications this powerful analytical tool has unleashed! We owe a great deal of appreciation to Karl Norris for leading the way to this discovery. We will describe the applications mentioned above which prove that new discoveries can be made using the same NIR spectral information with different chemometric approaches!

Investigation of the effect of aggregates' morphology on concrete creep properties by numerical simulations

Prestress losses due to creep of concrete is a matter of interest for long-term operations of nuclear power plants containment buildings. Experimental studies by Granger (1995) have shown that concretes with similar formulations have different creep behaviors. The aim of this paper is to numerically investigate the effect of size distribution and shape of elastic inclusions on the long-term creep of concrete. Several microstructures with prescribed size distribution and spherical or polyhedral shape of inclusions are generated. By using the 3D numerical homogenization procedure for viscoelastic microstructures proposed by Šmilauer and Bažant (2010), it is shown that the size distribution and shape of inclusions have no measurable influence on the overall creep behavior. Moreover, a mean-field estimate provides close predictions. An Interfacial Transition Zone was introduced according to the model of Nadeau (2003). It is shown that this feature of concrete's microstructure can explain differences between creep behaviors.

Influence of the Saturation Ratio on Concrete Behavior under Triaxial Compressive Loading

When a concrete structure is subjected to an impact, the material is subjected to high triaxial compressive stresses. Furthermore, the water saturation ratio in massive concrete structures may reach nearly 100% at the core, whereas the material dries quickly on the skin. The impact response of a massive concrete wall may thus depend on the state of water saturation in the material. This paper presents some triaxial tests performed at a maximum confining pressure of 600 MPa on concrete representative of a nuclear power plant containment building. Experimental results show the concrete constitutive behavior and its dependence on the water saturation ratio. It is observed that as the degree of saturation increases, a decrease in the volumetric strains as well as in the shear strength is observed. The coupled PRM constitutive model does not accurately reproduce the response of concrete specimens observed during the test. The differences between experimental and numerical results can be explained by both the influence of the saturation state of concrete and the effect of deviatoric stresses, which are not accurately taken into account. The PRM model was modified in order to improve the numerical prediction of concrete behavior under high stresses at various saturation states.

Radiation occupational health interventions offered to radiation workers in response to the complex catastrophic disaster at the Fukushima Daiichi Nuclear Power Plant.

The Fukushima Daiichi Nuclear Power Plant (NPP) 1 was severely damaged from the chain reaction of the Great East Japan Earthquake and Tsunami on 11 March 2011, and the consequent meltdown and hydrogen gas explosions. This resulted in the worst nuclear accident since the Chernobyl accident of 1986. Just as in the case of Chernobyl, emergency workers were recruited to conduct a wide range of tasks, including disaster response, rescuing activities, NPP containment, and radiation decontamination. This paper describes the types and efficacy of the various occupational health interventions introduced to the Fukushima NPP radiation workers. Such interventions were implemented in order to prevent unnecessary radiation overexposure and associated adverse health effects and work injuries. Less than 1% of all emergency workers were exposed to external radiation of >100 mSv, and to date no deaths or health adversities from radiation have been reported for those workers. Several occupational health interventions were conducted, including setting of new regulatory exposure limits, improving workers' radiation dosimetry, administration of stable iodine, running an occupational health tracking system, and improving occupational medicine and preventative care. Those interventions were not only vital for preventing unnecessary radiation, but also for managing other general health issues such as mental health, heat illness and infectious diseases. Long-term administration of the aforementioned occupational health interventions is essential to ensure the ongoing support and care for these workers, who were put under one of the most severe occupational health risk conditions ever encountered.

납-고무받침에 의해 면진된 원전 격납구조물의 다중단계해석

In order to increase the seismic safety of nuclear power plant (NPP) structures in high seismicity regions, seismic isolation techniques can be adapted to NPP structures. In this paper, the applicability of multi-step analysis of seismically isolated NPP containment structures with lead-rubber bearings (LRB) is evaluated. The floor response spectrum of NPP containment structures with equivalent linear LRB and nonlinear LRB are compared. In addition, the force-displacement relationships for equivalent linear LRB and nonlinear LRB are compared.

상용 반도체 소자를 이용한 내방사선 원전 센서신호 공통회로 연구

In this study, we designed a signal processing module using a radiation hardened technology that can be applied to the all measurement sensors inside nuclear power plant containment. Also, for verification that it can be used for high-level radiation environment (Harsh environmental zone inside containment of NPP), we carried out evaluation tests for a designed module using a Co60 gamma-ray source up to 12 kGy(Si). And, we had checked radiation hardening level that it has been satisfied up to 12 kGy(Si).

Discussion and Application of Passive Hydrogen Recombiner in Qinshan Phase II Nuclear Power Plant

A large amount of hydrogen would be generated because of zirconium-water reaction during serious accidents in nuclear power plant (NPP). Hydrogen could be combusted or explode under certain conditions, resulting in damage of the containment integrity and releasing radioactive substances into surrounding environment. Therefore, hydrogen elimination inside the NPP containment is an important subject. According to the requirements of NNSA (National Nuclear Security Administration), enough passive hydrogen recombiners (PHR) had been installed in unit 3&4 of Qinshan phase II NPP to prevent the hydrogen explosion in a serious accident. Additionally, new PHRs for unit 1&2 were also added. This article introduces the practical experience for the PHR modification, the comparisons between unit 1&2 and unit 3&4.

Deployment Strategies for Wireless Sensor Networks in Nuclear Power Plants

Applications of wireless technologies in nuclear power plants (NPPs), in particular for monitoring purposes, have been gaining popularity recently. It has been shown that wireless technologies can offer several advantages over wired solutions. However, many challenges need to be overcome before widespread adoption of wireless systems in nuclear industries. This paper has extended the existing work in this area and has developed a systematic procedure to deploy a wireless sensor network within a NPP containment. The developed scheme deals with the following challenges explicitly: (a) restrictions on the peak transmission power of the wireless sensor modules, (b) workaround of large concrete and metal structures, and (c) avoidance of locations with high radiation levels. Starting from the sensor locations dictated by the variables to be measured, the scheme determines the positions of the wireless relaying modules in a three-dimensional containment space to ensure reliable data communication. The results from case studies under realistic NPP containment conditions demonstrate the practical value of the proposed solution.

미사일-타깃해석법에 의한 콘크리트돔의 항공기 충돌해석에 관한 연구

In this paper, the authors performed the missile-target interaction analysis for B747 airplane against prestressed concrete dome structure. The aircraft model was developed and verified from the previous researches that were done by the authors. Therefore, the FE aircraft model can be used for the aircraft impact loading case. The development of aircraft FE model is theoretically based on the Riera function which was proposed by Riera derived from the rigid wall impact hypothesis. When the aircraft impact to the freeform or circular section shaped structure, the resulting impact force and it's integral impulse force may be different from the theoretical values. In this paper, the authors developed the artificial prestress concrete dome structure which has circular section shape and usually using for the nuclear power plant containment building structure. And the aircraft impact analyses were performed using missile-target interaction method. The commercial Hydrocode AUTODYN was used for FE modelling and simulations. From the comprehensive numerical studies, the shape of target structure significantly affects the aircraft impact load and decreases it compared to the Riera function and rigid wall impact simulation.

Thermal-pressure loading effect on containment structure

Because the elevated temperature degrades the mechanical properties of materials used in containments, the global behavior of containments subjected to the internal pressure under high temperature is remarkably different from that subjected to the internal pressure only. This paper concentrates on the nonlinear finite element analyses of the nuclear power plant containment structures, and the importance for the consideration of the elevated temperature effect has been emphasized because severe accident usually accompanies internal high pressure together with a high temperature increase. In addition to the consideration of nonlinear effects in the containment structure such as the tension stiffening and bond-slip effects, the change in material properties under elevated temperature is also taken into account. This paper, accordingly, focuses on the three-dimensional nonlinear analyses with thermal effects. Upon the comparison of experiment data with numerical results for the SNL 1/4 PCCV tested by internal pressure only, three-dimensional analyses for the same structure have been performed by considering internal pressure and temperature loadings designed for two kinds of severe accidents of Saturated Station Condition (SSC) and Station Black-out Scenario (SBO). Through the difference in the structural behavior of containment structures according to the addition of temperature loading, the importance of elevated temperature effect on the ultimate resisting capacity of PCCV has been emphasized.

One-dimensional model for containment in AP1000 nuclear power plant based on thermal stratification

Passive containment cooling system operating based on natural circulation is innovatively used in AP1000 nuclear power plant to improve safety. However, the overall heat and mass transfer will decrease and the heat transfer through the containment shell will be slow due to stable stratification which will occur if the forced convection mixing is not sufficiently strong enough to disrupt the stable fluid layers, so it is important for system design and accident analysis to evaluate whether the circulation can establish or not in the containment accurately and efficiently. Many researches indicate that the gradients of such parameters in horizontal direction are so small that can be ignored, in this paper, one-dimensional model is developed for AP1000 containment based on thermal stratification theory, natural circulations in and outside the containment are both included. Based on the results, the thermal stratification and circulation exist simultaneously, the pressure in the containment can be kept at the safe level, and positive pressure gradient in the vertical direction affords the force of circulation. The steam and air with higher temperature concentrating at the top will strengthen the heat and mass transfer because the cooling capacity of top head is higher than of other parts.

Advanced aircraft analysis of an F-4 Phantom on a reinforced concrete building

The nonlinear dynamic fracture and collapse characteristics of an F-4 Phantom aircraft under an extreme load caused by the impact of an F-4 Phantom are investigated. Three types of FE models considering the fuel mass effect are developed to investigate the superiority of the developed model. A rigid wall impact test is conducted to determine the material properties and the eroding failure criteria. The impact forces exerted by the aircraft against mounted thick concrete walls are then verified by comparing the results here with earlier experimental data obtained from an actual-scale F-4 Phantom aircraft impact test conducted by Sandia National Laboratory. Validation of the methodology is further investigated by extending the comparative studies to a constrained thin concrete wall similar to the type used in nuclear power plant containment buildings. The experimental and simulation results are also analyzed and discussed.

Short-term and long-term analysis of WWER-1000 containment parameters in a large break LOCA

Nuclear safety has been one of the major issues to be studied since the inception of the nuclear industry. Establishing and maintaining core cooling and ensuring containment integrity are the two main goals that nuclear safety must guarantee. The specific type of large LOCA is DECL (Double Ended Cold Leg) break which means a total guillotine type of break in cold leg pipe and is one of the most dangerous accidents in the reactor containment. In this paper, thermal-hydraulic parameters (Temperature and Pressure) of WWER-1000 (Bushehr Nuclear Power Plant) containment in a DECL accident have been simulated by CONTAIN2.0 code and a single cell model. The Containment has been divided to 23 cells in CONTAIN code but for simplicity only one cell has been considered in modeling. The model has been programmed by MATLAB. The accident has been simulated for Short-term (0 < time<200 s) and long-term (200 < time<100,000 s) and all of the results have been compared with Bushehr's Nuclear Power Plant FSAR.

Simulation of soil–foundation–structure interaction of Hualien large-scale seismic test using dynamic centrifuge test

Understanding the soil–structure interaction (SSI) mechanism is crucial in the seismic design of nuclear power plant (NPP) containment systems. Although the numerical analysis method is generally used in seismic design, there is a need for experimental verification for the reliable estimation of SSI behavior. In this study a dynamic centrifuge test was performed to simulate the SSI behavior of a Hualien large-scale seismic test (LSST) during the Chi-Chi earthquake. To simulate the soil profile and dynamic soil properties of the Hualien site, a series of resonant column (RC) tests was performed to determine the model soil preparation conditions, such as the compaction density and the ratio of soil–gravel contents. The variations in the shear wave velocity (VS) profiles of the sand, gravel, and backfill layers in the model were estimated using the RC test results. During the centrifuge test, the VS profiles of the model were evaluated using in-flight bender element tests and compared with the in-situ VS profile at Hualien. The containment building model was modeled using aluminum and the proper scaling laws. A series of dynamic centrifuge tests was performed with a 1/50 scale model using the base motion recorded during the Chi-Chi-earthquake. In the soil layer and foundation level, the centrifuge test results were similar to the LSST data in both the time and frequency domains, but there were differences in the structure owing to the complex structural response as well as the material damping difference between the concrete in the prototype and aluminum in the model. In addition, as the input base motion amplitude was increased to a maximum value of 0.4g (prototype scale), the responses of the soil and containment model were measured. This study shows the potential of utilizing dynamic centrifuge tests as an experimental modeling tool for site specific SSI analyses of soil–foundation–NPP containment system.

Analysis of thermal–hydraulic parameters of WWER-1000 containment in a large break LOCA

The consequences of sever reactor accident depend greatly on containment safety features and containment performance in retaining radioactive material. The specific type of large LOCA is DECL (Double Ended Cold Leg) break which means a total guillotine type of break in cold leg pipe and is one of the most dangerous accidents in the reactor containment. In this paper, thermal–hydraulic parameters (temperature and pressure) of WWER-1000 (Bushehr Nuclear Power Plant) containment in a DECL accident have been simulated by CONTAIN 2.0 code and a single cell model. The containment has been divided to 23 cells in CONTAIN code but for simplicity only one cell has been considered in modeling. The model has been programmed by MATLAB. The accident has been simulated for a short time (initial 200s) and all of the results have been compared with Bushehr’s Nuclear Power Plant FSAR.

Analysis of impact of large commercial aircraft on a prestressed containment building

In this paper, the results of nonlinear dynamic analyses of a concrete containment building under extreme loads are presented. The impact of a large commercial B747 airliner is investigated as the extreme load, and a rigid wall impact test is performed using commercial nonlinear finite element codes. The impact forces exerted by the aircraft are verified compared with the time-dependent impact force provided by OECD/NEA (2002), which was calculated based on the so-called Riera method. The rigid wall impact analysis shows that the finite element model of a B747 is appropriate for the purpose of the aircraft crash analysis exposed to the external hazard of “Beyond Design-Basis Events” defined by U.S. Nuclear Regulatory Commission. Finally, the applicability of this methodology is further studied and verified by conducting parametric studies on the critical infrastructures of nuclear power plant containment structures.