Containment Vessel Research Articles

A comparative study of manipulator teleoperation methods for debris retrieval phase in nuclear power plant decommissioning

ABSTRACT This paper presents a comparative study of teleoperation methods of robotic manipulators aiming at application to the decommissioning operation of the primary containment vessel (PCV) of Fukushima Daiichi Nuclear Power Plant Unit 3. A detailed set of mockup is constructed from data collected by internal investigation of the damaged PCV, and a series of teleoperation experiments using a dual-arm robotic manipulator simulating the actual obstacle removal operation is conducted. Three teleoperation methods, manual, teaching-based, and planning-based, are compared in terms of multiple performance indices. The manual teleoperation resulted in low efficiency and safety, and high cognitive load. The method based on pre-recorded teaching data showed the highest safety score, but required large amount of time for preparation. The planning-based method achieved efficient teleoperation with small amount of preparation time, while it was found that it needs further improvement in terms of safety.

Large-eddy simulation on gas mixing induced by the high-buoyancy flow in the CIGMAfacility

The hydrogen behavior in a nuclear containment vessel is a significant issue when discussing the potential of hydrogen combustion during a severe accident. After the Fukushima-Daiichi accident in Japan, we have investigated in-depth the hydrogen transport mechanisms by utilizing experimental and numerical approaches. Computational fluid dynamics is a powerful tool for better understanding the transport behavior of gas mixtures, including hydrogen. This paper describes a Large-eddy simulation of gas mixing driven by a high-buoyancy flow. We focused on the interaction behavior of heat and mass transfers driven by the horizontal high-buoyant flow during density stratification. For validation, the experimental data of the Containment InteGral effects Measurement Apparatus (CIGMA) facility were used. With a high-power heater for the gas-injection line in the CIGMA facility, a high-temperature flow of approximately 390 °C was injected into the test vessel. By using the CIGMA facility, we can extend the experimental data to the high-temperature region. The phenomenological discussion in this paper helps understand the heat and mass transfer induced by the high-buoyancy flow in the containment vessel during a severe accident.

Performance of Structural Alloys in Bio-oil Production, Upgrading, and Storage Systems

Selection of corrosion-resistant, cost-effective structural materials for the process and containment vessels required for the production, upgrading, and storage of biomass-derived oils has been the subject of study in our laboratory for many years. The wide variety of biomass resources and the many liquefaction techniques and processing conditions result in products with a broad range of properties and compositions. This paper will address the materials issues in three distinct areas. In production, materials are exposed to temperatures that range from 350 to 550 °C depending upon the process. Generally, austenitic stainless steels have performed reasonably well, although thicker oxide scales and intergranular attack have sometimes been observed. For storage and transport of the bio-oil products, temperatures experienced by the containment materials are not expected to exceed 50 °C. Our studies have shown that most raw bio-oils contain significant concentrations of organic acids, and low-molecular-weight organic acids were quite corrosive to carbon and low alloy steels. For some applications, subsequent processing is required, which includes hydrotreating or co-processing with a petroleum-derived liquid. These processes utilize a catalyst that requires periodic retreatment with a sulfidizing gas, and the exposure to this gas at elevated temperatures can cause appreciable corrosion to the more common austenitic stainless steels. The materials considered most cost-effective and sufficiently corrosion-resistant for each of these environments were identified.

Method of Analyzing Criteria for Primary Containment Vessel Venting and Protective Measures for Public Risk Reduction

Method of Analyzing Criteria for Primary Containment Vessel Venting and Protective Measures for Public Risk Reduction

Evaluation of Blast Mitigation Effects of Cylindrical Explosion Containment Vessels Based on Foam

Evaluation of Blast Mitigation Effects of Cylindrical Explosion Containment Vessels Based on Foam

Quantitative damage evaluation of prestressed concrete containments with steel fiber strengthening under internal pressure

Current investigations cannot quantitatively predict the overall damage performance of prestressed concrete containment vessels (PCCVs) under internal pressure and the effect of steel fiber strengthening on the damage performance improvement has not been investigated. A new parameter definition is proposed to characterize the entire damage performance of conventional and steel fiber-reinforced concrete (SFRC) PCCVs under internal pressure in this study. The prestress loss is precisely calculated considering 40 years of the service period of PCCV. To review the possibility of operating lifetime extension of PCCV, the subsequent 60 years are also considered. Firstly, elaborate three-dimensional numerical models of conventional and SFRC containments were established. Then, three parameters to represent the extent corresponding to concrete, steel liner, and prestressed tendons of containment under damage were proposed. Finally, damage performance of conventional and SFRC containments considering the impact of prestress loss was discussed in depth. The results show that by introducing the SFRC and considering the five-year prestress loss, the pressure capacities for containment concrete, steel liner, and prestressed tendons are increased by 22.16%, 18.99%, and 12.35%, respectively. What's more, the proposed parameters can reflect the changing trend of the damage extent of containments under internal pressure and inclusion of steel fibers can improve damage performance significantly. To examine the realistic damage performance under internal pressure, the five-year prestress loss requires to be specifically considered.

Blast resistance of RC tubular structure under internal ANFO explosion

The degree of structural damage is significantly more severe when a blast occurs inside than outside of a structure. However, existing designs for RC structures such as reinforced concrete containment vessels (RCCV) do not include design features to protect the structure for internal blast. Therefore, the internal blast resistance capacity of RC structures is evaluated by performing internal blast tests on RC tubular structures. The main objective of the study was to observe and document the basic structural behavior data obtained from internal detonation tests. ANFO explosive charge weights of 15.88, 20.41, 22.68 and 24.95 kg were selected for a charge detonating at a cross section center of the mid-span of the specimen, giving a standoff distance to the inner wall surface of 1000 mm. The data acquisitions include blast pressure, deflection, strain, and crack pattern. When the explosive charge weight increased from 15.88 to 24.95 kg, the peak incident pressure and time duration increased from 0.1718 to 0.3394 MPa and from 5.856 to 5.981 ms, respectively. Then, the test data were used to predict the internal charge weight required to fail a real scale RCCV using simple assumptions and the test data. The results of the study are discussed in detail in the paper.

Shock vibration and damage responses of nuclear island subjected to an aircraft crash

Although more attention has been given towards the analysis of large commercial aircraft impacts since the September 11 attacks, little work has been done on the vibration response of internal structures and equipment of nuclear power plants (NPPs) during an impact. With a focus on new NPPs, this paper develops a remeshing algorithm for contact surfaces, which utilizes the advantages of scaled boundary finite element (SBFE) polyhedral elements to fully realize the potential of Octree and structured grid discretization methods. The vibration response of nuclear island internal structures is examined. The influence of the interaction between the foundation and the structure on the overall dynamic response is analyzed. Meanwhile, different ranges of foundation size are investigated for balance between computational efficiency and accuracy. The vibration propagation mechanism is found by studying the influence of different artificial boundary types and damping conditions of foundation. The results show that the interaction has a significant influence on the vibration response, and that a foundation size of 1B (height of the steel containment vessel) on all sides provides the optimal balance between computational and accuracy requirements. Furthermore, the damping ratio of the foundation plays a key role in vibration propagation. Finally, the combined bonding method is highly flexible, and allows cross-scale integration of different mesh sizes.

Welding Numerical Simulation Analysis of AP 1000 Insert Plate and Penetration Sleeves Based on ABAQUS

Frequently, cracks are found in welded joints of the insert plate assembly of a nuclear reactor containment vessel. To study the residual stress state of the dissimilar steel welded joint of the insert plate assembly and ensure that there are no defects after welding, the ABAQUS finite element analysis software was used to simulate the temperature field and the post-weld residual stress field of the dissimilar steel inserted into the plate assembly in the containment of the nuclear reactor. The insert plate and sleeve material are SA738GR.B and A350, respectively; the heat treatment process after welding is simulated to predict the residual stress state of the welded joint after heat treatment. The simulation results show that the weld zone is the most sensitive to the circumferential cracks, and the maximum residual stress appears near the weld toe near the tube side.

Level swell analysis of stagnant water pool in filtered containment venting systems

A filtered containment venting system (FCVS) prevents over pressurization of containment vessel and releasing of radioactive materials during the severe accidents in nuclear power plants. During the venting process, it has been reported that the two-phase mixture level in a wet FCVS tends to swell and fluctuate. The behaviors depend on inlet/boundary conditions and physical properties of the injected gas, which vary as the accident progresses. Proper controlling and monitoring of the FCVS pool water level is crucial because it affects filtration performance including scrubbing process and thermal-hydraulic stability. In order to investigate this phenomenon, the current study proposes a set of nitrogen and steam injection experiments using a vertical pipe with a diameter of 105 mm to evaluate the effects of flow conditions and physical properties of gases. Drift flux analysis was carried out to predict the two-phase mixture water level and its fluctuations. The experimental two-phase mixture level was consistent with the values predicted by the drift flux model for nitrogen and steam injection, and the model's capability was confirmed for the system pressure ranging from atmospheric to 0.20 MPa and initial water level ranging from 0.6 to 2.6 m for both small and large diameter pipe configurations. The fluctuation amplitudes in the current experiment were smaller than those observed in experiments conducted on small-diameter pipes. The mean two-phase mixture water level increased upon pressurization of the scrubbing pool. However, it was found that the effect of pressurization on the two-phase mixture level fluctuation amplitude was negligibly small.

Electrodeposited NiMo Alloy Coatings for Improved Molten Salt Compatibility

The use of molten halide salts as a primary coolant within next generation molten salt nuclear reactors (MSRs) has the potential to improve efficiency and nuclear reactor safety by operating at low pressures and high temperatures without boiling. However, these coolants will require the development of new corrosion resistant material systems that will have to meet or supersede existing standard codes for these systems. Therefore, new MSRs will require validation and testing of new material systems that can produce robust component structures and enable them to withstand these corrosive environments. Furthermore, any next generation process to apply protective coatings must allow for a conformal, thick, dense, and bonded material to be formed onto an ASME code approved material (e.g. type 316H stainless steel) that will comprise the structure of heat exchanger and containment vessel components.Within this context, Faraday Technology Inc. in collaboration with Oak Ridge National Lab and Quintus Technologies is working to develop and demonstrate the effectiveness of a low cost and high value corrosion-resistant alloy coating for next generation molten salt reactors. The manufacturing process involves the application of a functionally graded NiMo coating by electrodeposition onto 316H alloy substrates and their subsequent high temperature corrosion evaluation in molten fluoride salt at 700°C. After application the components were hot isostatically pressed (HIPped; at Quintus) to create a diffusion bond between the coating and alloy substrate. Initially, 316H alloy coupons were coated for evaluation (Figure 1 Left) in Mo capsules with static FLiNaK salt known to be corrosive due to metallic impurities. The next stage of testing involved evaluating coatings on the inner diameter of 316H tubes (25mm outer diameter; Figure 1 Middle). Coated tubes (75mm long) had coated endcaps welded to either end and were filled with the same FLiNaK salt and tested for 500 h at 700°C and 1000 h at 750°C. In addition, the microstructure and salt performance of butt welds were evaluated for joints between coated 316H tubes and joints between coated and uncoated 316H tubes. Results from the static capsule testing will be presented including the effect of coating composition and heat treating conditions on the depth of attack in the molten salt as feedback for the coating development process. The final phase of testing will include 200 mm long coated 316H tube sections in the hot and cold legs of a flowing FLiNaK thermal convection loop experiment which is currently being fabricated (Figure 1 R). Acknowledgements: The financial support of DOE Contract No. DE-SC0019602 is acknowledged. Figure 1: Corrosion characterization test plan. (Left) static coupon studies, (Middle) static pipe studies, and (Right) continuous flow loop pipe studies. Figure 1

CFD analysis on stratification dissolution and breakup of the air-helium gas mixture by natural convection in a large-scale enclosed vessel

This paper describes the computational fluid dynamics (CFD) analysis and validation works from the previous experimental study on the natural convection driven by outer surface cooling in the presence of density stratification consisting of air and helium (as a mimic gas of hydrogen). The experiment was conducted in the Containment InteGral effects Measurement Apparatus (CIGMA) facility at Japan Atomic Energy Agency (JAEA). CIGMA vessel is a large cylindrical stainless steel with an inner diameter of the main cylindrical part 2.5 m and an overall height of 11 m. The mass fraction proportion of helium in the whole vessel was 11% and the helium molar fraction at the top vessel was 48%. Two experiments were performed and the numerical simulation was carried out to analyze the detailed effect of the cooling region on the erosion of the helium stratification layer. First test was named CCLP30 or case 1 and second test was named CCPL34 or case 2. The main difference between case 1 and case 2 was the cooling area of case 1 was narrower than case 2. In case 1, cooling area was only located at the one-fourth of outer vessel. Whereas, in case 2, cooling area was located at one-half of outer vessel. The temporal and spatial evolution of the helium concentration and the gas temperature inside the containment vessel was predicted and validated against the experimental data. The results indicated that the numerical predictions fairly agreed with the experimental data. However, the predicted erosion rate showed discrepancies compare with the experimental data. The relative errors time required for the complete dissolution of the helium gas were within 15%. In addition, two stratification behaviors that depend on the cooling location were presented and discussed. The CFD simulation confirmed that an upper head cooling caused two counter-rotating vortexes in the helium-rich zone. Meanwhile, the upper half body cooling caused two counter-rotating vortexes in the helium-poor zone. These findings are important to understand the mechanism of the density stratification process driven by natural convection in the containment vessel.

Aerosol retention within submerged Containment-Type iPWRs: Experiments and modeling

Integral pressurized water reactor (iPWR) designs employing submerged, high-pressure steel containment vessels rely on water in the outer operating pool as the primary heat sink during an accident. This drives very strong steam condensation, and along with it, strong diffusiophoretic deposition rates for fission product aerosols. In this study, a loss-of-containment isolation accident is proposed and simulated with MELCOR, where the strong condensation/diffusiophoresis is the last barrier preventing direct radionuclide releases to the environment. This is supported by experiments that measured the thermal stratification, steam condensation rates, and aerosol deposition rates that would be experienced in a prototypic, iPWR-like geometry. The development of the steam layer, whose thickness was proportional to steam injection rates, impacted the aerosol deposition by limiting the area over which condensation-driven diffusiophoresis could occur. Diffusiophoresis was still confirmed to be the primary mechanism for aerosol deposition, with observed rates that were in line with established theory.

Thermodynamic analysis for solidification path of simulated ex-vessel corium

Molten corium is considered to form in a severe accident at the Fukushima Daiichi Nuclear Power Station (FDNPS). Investigation of the primary containment vessel (PCV) inside the FDNPS showed that a significant amount of the molten corium reached the bottom of the pedestal region. The molten corium and concrete likely caused a complex interaction called Molten Corium Concrete Interaction (MCCI). Then, ex-vessel debris was formed after the solidification of the MCCI products and accumulated in the pedestal region. The solidification hysteresis of ex-vessel debris significantly influences its properties. We performed a thermodynamic analysis using the TAF-ID database to infer the solidification path of U–Zr–Al–Ca–Si–O molten corium, which was chosen for a prototypic system of ex-vessel debris. The solidification path for the CaO-rich sim-corium showed the following sequence: (i) melting as a single liquid phase at temperatures higher than 2430 K, (ii) selective solidification of the oxide-rich corium mainly consisted of fuel materials, and (iii) solidification of the remaining materials as a silicate matrix. In contrast, the solidification path for the SiO2-rich corium indicated that (i) formation of liquid miscibility gap above 2200 K between U-rich and Zr-rich oxidic melts, (ii) individual precipitation of solid phases in each liquid phase. Identified features of these solidification paths were in good agreement with the experimental data for the solidified sim-corium.

Probabilistic safety assessment of nuclear containment vessel under internal pressure considering spatial variability of material properties

It is well known that ensuring the safety of the nuclear containment vessels (NCVs) is very important. The assessment should be performed in a probability method considering various uncertainties. However, most of investigations focus on the deterministic analysis or only regard the uncertainty as random variables. The widely existing spatial uncertainty is ignored for nearly all studies on the NCV. In this paper, we conducted a probabilistic safety assessment of a typical NCV considering the spatial uncertainty of material properties. The spatial variability is modeled with the random field generated by the geodesic-based decomposition method. Accompanied with a high-fidelity finite element (FE) procedure and Monte Carlo simulation, 800 FE models considering spatial varying concrete properties are analyzed to investigate the stochastic performance of the NCV. It is demonstrated that when the spatial variability of concrete properties is considered, the results are very different from the deterministic and the random variables-based results, including the deformation curves, the failure point distributions, the internal pressure capacity distribution, and the failure probability. Moreover, the common variables-based analysis will overestimate the actual reliability of the NCV. Consequently, it is necessary to consider the spatial variability in the safety assessment of the pressured NCVs, and this type of safety assessment can be conducted by the procedure proposed in the paper.

Inadvertent Radiation Exposures in Combat Zones: Risk of Contamination and Radiobiologic Consequences.

On February 24, 2022, Russia began a military invasion of Ukraine. Missile and air strikes were reported throughout the country, shortly followed by a large ground invasion from multiple directions. Four major theaters developed: the Kyiv offensive, the Northeastern Ukraine offensive, the Eastern Ukraine offensive, and the Southern Ukraine offensive, with continued missile and air strikes far into Western Ukraine. Advancing Russian military units launched an attack and captured the Chernobyl nuclear station. Russian troops dug trenches into the area commonly known as the "Red Forest," violating the established radiation safety measures and threatening security within the Chernobyl Exclusion Zone. The placement of military units in such close proximity to the station also sparked concerns of possible damage occurring to the containment vessel constructed around the station's wrecked fourth reactor. There are 15 operating nuclear reactors in Ukraine. Each is vulnerable to an attack or sabotage that could precipitate a malfunction and possible release of radioactive isotopes. In this short commentary, we will discuss radiobiologic data obtained after the analysis of historical nuclear power plant (NPP) accidents and emphasize new challenges for nuclear security when NPPs are found and are possible targets within a conflict zone.

Estimation of Flow Field in Natural Convection with Density Stratification by Local Ensemble Transform Kalman Filter

For estimating thermal flow in a nuclear reactor during an accident accurately, it is important to improve the accuracy of computational fluid dynamics simulations. The temperature and flow velocity are not homogeneous and have large variations in a reactor containment vessel because of its very large volume. In addition, Kelm’s work pointed out that the influence of variations of initial and boundary conditions was important. Therefore, it is necessary to set the initial and boundary conditions taking into account the variations of these physical quantities. However, it is a difficult subject to set such complicated initial and boundary conditions. Then, we can obtain realistic initial and boundary conditions and an accurate flow field by data assimilation, and we can improve the accuracy of the simulation result. In this study, we applied data assimilation by a local ensemble transform Kalman filter to a simulation of natural convection behavior in density stratification, and we performed a twin model experiment. We succeeded in estimating the flow fields and improving the simulation accuracy by the data assimilation, even if we applied the boundary condition with error for the true condition.

Improved theory of the elastic-plastic response of spherical containment vessels subjected to internal blast loading and its application

Baker built the displacement equations of motion for a thin spherical shell to spherically symmetric internal blast loading, and further provided the analytical solution of the elastic-plastic response under a triangular decaying pressure, neglecting shell thinning and radius variation [1], which was widely used in the fields of analysis and design of explosion containment vessels. However, it appears that some improvements and corrections are needed when we revisit this classic problem. In this paper, the elastic-plastic response of thin spherical shells is investigated mathematically. The complete equations of motion for three models are developed. Then the main ideas of the analytical and numerical methods are presented, as well as some important procedures and results by using Laplace transform techniques, which are convenient to use and generalize. Three typical examples are solved to exhibit differences between our improved theory and Baker’s [1]. Furthermore, our models are employed to gain some insights into response regularities, including the effect of various degrees of strain-hardening on maximum displacements under impulsive loading, and the effect of loading duration on the shell displacement for a perfectly plastic material.

CFD analysis of water vapor condensation in large containments: Numerical model, verification and validation

In the event of a loss of coolant accident (LOCA) in a Pressurized Water Reactor (PWR), large quantities of water vapor and hydrogen might be released into the containment building. Increasing pressure and the risk of hydrogen deflagration can threaten the containment integrity. Water vapor condensation on cold containment structures modifies the pressure load on the containment structures. On the one hand, the total pressure reduces due to the decrease of the water vapor content of the containment atmosphere. On the other hand, the concentration of hydrogen increases, which can reach locally the threshold of deflagration or detonation. A Computational Fluid Dynamics (CFD) model is developed and tested in order to predict transients of the pressure and the concentrations of gaseous species in reactor containments after a LOCA. Since the free volume of the containment of typical French PWRs is between 50,000 m3 and 80,000 m3, the CFD model requires significant simplifications.The physical model and its simplifications as well the implementation in the CEA OpenSource CFD code TrioCFD are described. Model tests are presented in two steps. In a first step, verification tests are discussed to show that the condensation model is implemented correctly in the CFD code. In a second step, the model is validated against experimental data of the International Standard Problem ISP47. In this benchmark, steady state conditions between vapor injection and condensation were reached experimentally in the MISTRA test containment of the CEA. In phase A of the benchmark, an equilibrium was achieved between water vapor injection and water vapor condensation on temperature controlled cold walls. One incondensable gas, namely air, was present in the test vessel. In phase B, a second incondensable gas was added to the containment atmosphere, namely helium. Both steady state situations were analyzed with the CFD model. The calculations represent well the experiment when the predominant condensation paths are modelled. It is shown that the pressure in the containment vessel as well as the mean mass fractions of water vapor and air, as well as of helium in phase B, are calculated in accordance to the experiment. The temperature in the containment is overestimated. Measured vertical profiles of the species concentrations are reproduced correctly.

Performance of SI Engine under the Effect of Magnetic Field by using CNG, Petrol and Ethanol

Abstract: The invention resides within the field of treatment of hydrocarbon fuels in liquid or gaseous form, to extend the fuelburning efficiency, by exposing the fuel in containment vessels or conduits to a shaped uniform field of force with a relentless directional flux. Hydrocarbon fuels have long branched geometric chains of carbon atoms which tend to fold over onto themselves and on adjoining molecules because of inter molecular electromagnetic attraction existing between like molecules or atoms. It is vital to grasp that in a very fluid that's subjected to an external field the electron excitation (magnetic moment) occurring, affects molecular orientation. because the axis of the electrons become aligned with the external magnetic flux, the momentum of the molecule not averages intent on zero, as within the normal case in molecules not possessing permanent dipole moments. This accommodation is attributed to the very fact that on the molecular level, a spinning electron subjected to an accurate amount of electromagnetic energy will captivate that energy and "spinflip" into an aligned state. When a magnetism is applied, the instant as seen by the electron excitation, causes the molecule to tend to align with the direction of the field of force. The momentum of the molecule not averages dead set zero because the axis of the electrons aligns with the external magnetic flux, because it does in molecules without permanent dipole moments. The fluctuating dipole moments under the influence of the external flux acquire a net attraction, which produces a stronger bonding with an oxygen ion. As a result of the complex fuel, molecules tend to uncluster, straighten and produce higher combustion efficiencies. the rise in combustion efficiency is because of the unfolding of the hydrocarbon molecules which produce an increased extent for more complete oxidation of the fuel. The unfolding of the fuel molecules is that the major effect of the dipole being off from its neutral state by the applied field of force. Increased combustion yields increased fuel efficiency, with lower hydrocarbon emissions from hydrocarbon-based fuelburning apparatus. However, certain problems remain to be overcome, like whether to focus the force field con or directional alignment, determine flux strength, select appropriate magnetic materials and determine mounting arrangements for the best efficiency. The effect is to stop scaling from occurring on the inner walls of the conduit from the liquid flowing there through by forcing the molecules which might attach themselves to the inner walls of the conduit toward the middle of the conduit. Keywords: The magnetic effect, Combustion, Emissions, paramagnetic, diamagnetic, aligns & orientation, efficiency