High Efficiency Combined Aggregate – Submerged Combustion Melter–Electric Furnace for Vitrification of High-Level Radioactive Wastes

It is well known that high-level radioactive wastes (HLRAW) are usually vitrified inside electric furnaces. Disadvantages of electric furnaces are their low melting capacity and restrictions on charge preparation. Therefore, a new concept for a high efficiency combined aggregate – submerged combustion melter (SCM)–electric furnace was developed for vitrification of HLRAW. The main idea of this concept is to use the SCM as the primary high-capacity melting unit with direct melt drainage into an electric furnace. The SCM employs a single-stage method for vitrification of HLRAW. The method includes concentration (evaporation), calcination, and vitrification of HLRAW in a single-stage process inside a melting chamber of the SCM. Specific to the melting process is the use of a gas-air or gas-oxygen-air mixture with direct combustion inside a melt. Located inside the melt are high-temperature zones with increased reactivity of the gas phase, the existence of a developed interface surface, and intensive mixing, leading to intensification of the charge melting and vitrification process. The electric furnace clarifies molten glass, thus preparing the high-quality melt for subsequent melt pouring into containers for final storage.

Integral Solutions of Phase Change With Internal Heat Generation

This paper presents solutions to a one-dimensional solid-liquid phase change problem using the integral method for a semi-infinite material that generates internal heat. The analysis assumed a quadratic temperature profile and a constant temperature boundary condition on the exposed surface. We derived a differential equation for the solidification thickness as a function of the internal heat generation (IHG) and the Stefan number, which includes the temperature of the boundary. Plots of the numerical solutions for various values of the IHG and Stefan number show the time-dependant behavior of both the melting and solidification distances and rates. The IHG of the material opposes solidification and enhances melting. The differential equation shows that in steady-state, the thickness of the solidification band is inversely related to the square root of the IHG. The model also shows that the melting rate initially decreases and reaches a local minimum, then increases to an asymptotic value.

Transition Risk Method and Example

Paragraph (a)(4) of the Maintenance Rule (re 10CFR§50.65) states that before performing maintenance activities, the licensees shall assess and manage the increase in risk that may result from the maintenance activities. The rule is explicitly applicable to all operating modes. Currently, most plants use a qualitative tool for assessing and controlling the risk of the various plant conditions during an outage. Fewer plants have any means of performing a quantitative or qualitative assessment of the associated risks of transitioning the plant in each configuration from power to “cold shutdown.” Typically, only the end-state of shutdown is considered. The transition-period includes short-duration configurations when the available set of equipment is not what it was during power operations, e.g., having only one main feedwater train in-service. Given the concern that the NRC may require quantitative risk assessments of plant transitions and plant configurations during shutdown operations, Omaha Public Power District (OPPD) pro-actively authorized Westinghouse Engineering Services to develop a method for assessing risk associated with a transition from all power to shutdown and back to full power. An outage schedule is highly plant specific, with plant-to-plant and outage-to-outage variations in system configurations, and maintenance practices. Accordingly, the duration of the transition largely depends on equipment maintenance activities driving the decision to shutdown and repair. The time spent in various parts of the transition is a strong determinant in the associated risk of the transition. A transition takes the plant through a series of Plant Operational States (POSs). The features important to the characterization of each of the POSs include decay-heat level, plant activities involved, available equipment, as well as RCS temperature and pressure. The risk of the entire transition comes from calculating a figure-of-merit of each POS which can be loosely thought of as a per-hour core-damage frequency (CDF). This number gets multiplied by the associated duration of the POS. The sum is the transition risk. The effective CDF associated with the transition comes from dividing the POS-specific CDF sum by the total transition time, and converting that result to an annual frequency. Our paper describes decomposing OPPD operating procedures into periods for which we quantified sequences. In particular, the method considers the dominant shutdown failure modes: loss of shutdown cooling, loss of inventory, and loss of offsite power (including both plant centered and grid-related events). The transition example presented herein covers a simple shutdown and restart stemming from an indeterminate-quality problem. That is, all equipment is functional and available to the plant operators.

Detailed Investigation of Thermal-Hydraulic Aspects During the Reflood Phase in QUENCH Experiments

The QUENCH program, performed at Forschungszentrum Karlsruhe, Germany, is dedicated to out-of-pile studies of the initiation and progression of damage during core reflood of a degraded commercial nuclear reactor. Main work in this program is spent on the investigation of the material behavior of the solid structures. However, for the deeper understanding of the integral tests, especially of the quench phase, as well as for computational support of the tests and for the validation of severe accident codes, a sufficient knowledge of thermal-hydraulics in the bundle during the quench phase is also mandatory. Though much instrumentation is available in the test section, information to interpret thermal-hydraulics is scare due to principal and technical reasons. The main objective of the present paper is to get a better idea of the reflood process, based on all available experimental data. For this purpose, the test QUENCH-06 is used because of the amount of available qualified experimental data and because of its special importance for code validation, this test being selected as OECD International Standard Problem (ISP) no. 45. At reflood initiation of QUENCH-06, some irregularity of water injection occurred due to the malfunction of a check valve. A thorough inspection and comparison of experimental data is presented in this paper to clarify details of the start of the quench phase. It is complemented by still more detailed computations with the in-house version of SCDAP/RELAP5 mod 3.2 than at the time of ISP-45. Apart from its relevance for this special test and for ISP-45, this work sheds light on the consistency of the involved experimental data. Besides to this investigation, the transition from two- to single-phase flow is examined in more detail than before, giving indications for the axial extension of the two-phase flow region with large droplets or a sensible fluid fraction and for the duration of two-phase flow near saturation temperature. Again, the consistency of data of various instrumentations is assessed. Despite of this success, a better instrumentation for thermal-hydraulics, mainly of void sensors in the lower part of the bundle, is desirable to facilitate interpretation of thermal-hydraulic aspects of the tests.

Insights From Plant Specific Common Cause Failure Analysis

Insights from three plant specific common cause failure (CCF) analyses, which used CCF Data Base and Analysis System software by US NRC, were presented in this paper. It was found that detailed guidelines/criteria were needed for performing a plant specific CCF analysis, especially for more systematic and consistent determination of the impacts of historical CCF events on a specific target system. Information collection task, impact of using unscreened independent events, and insights from specific components CCF analyses were also discussed. Finally, the following recommendations were made: (1) Develop procedures and criteria, like those developed for the plant specific CCF analyses, for more systematic and consistent plant specific CCF analysis. In developing criteria, it should be considered to credit existing plants for the enhanced defenses against CCFs based on their accumulated operating experiences. (2) Use of generic CCF data is strongly discouraged. Instead, perform plant specific CCF analysis, at least initial screening of the original events as a minimum, in order to avoid potential over-conservatism. (3) Enhance the current internet based information data bases and develop a communication network among CCF analysts in order to facilitate the information collection task.

Study on Entrainment From High-Viscosity Falling Liquid Film of Counter-Current Two-Phase Flow in a Vertical Pipe

Behavior of a falling liquid film of highly viscous fluid in the counter-current flow condition was examined. In experiments, water and silicon oils of 500, 1000 and 3000 cSt were used as the liquid phase and air was adopted as the gas phase. A test section vertically oriented was a circular pipe of 30 mm in inner diameter and 5.4 m in length. Flooding velocities of the air-water system were well correlated with traditional correlations such as the Wallis correlation and the Kamei correlation. However, the flooding velocities of silicon films were greatly lower than the expected. When the effect of the viscosity was incorporated into the Wallis correlation, it predicted the experimental results well. The flooding in the air-silicon system was initiated by sudden growth of a wave on the film as in the air-water system although the film Reynolds number of the falling silicon film was considerably low; 0.02 ∼ 4. A considerable amount of droplets were detected a long time before the initiation of flooding in the air–silicon oil experiments as well as in the air–water experiments. The correlations tested for the onset condition of entrainment gave much higher gas velocities than the measured. Predicted velocities were rather close to the flooding velocities. The falling film thickness was predicted well by applying the universal velocity profile to the film flow over a wide range of a film Reynolds number; ranging from a water film to a 3000 cSt silicon oil film.

Simulations of Thermal Performance for One- and Two-Dimensional Insulation and Aluminum Foil Fire Barriers

Nonbearing walls made of concrete frequently include one or two-dimensional gaps between sections to allow the concrete exert expansion or contraction due to temperature transients. These section gaps require the use of a thermal fire barrier to stop a fire from spreading during a period of time. In some applications, such as seismic structures, fire barriers are large and form substructures and partial enclosures. These type of fire barriers are often manufactured by layering alternating blankets of ceramic fiber insulation with bounding thin metallic foil sheets. In this case, the barrier must meet the specifications and effectiveness given by the ASTM standard E-119. This effectiveness is determined by the requirement of maintaining structural integrity by allowing some heat release while not permitting the fire flame to pass through. Little data is available on the thermal interaction of 2-D corners and splicing the layers for large barriers. It is expected that spatial and angular effects might either degrade performance or even cause “hot spots” in a barrier wall. Therefore, a numerical simulation of the barrier is accomplished by utilizing the spectral/gray and directional/modeled data of each one of the components and by taking into account two common geometrical building shapes. This simulation analysis is done by coupling of the discrete ordinates method in radiation heat transfer and the energy equation to previously published thermophysical experimental data used as a validation of the properties for fire barrier materials. Some of the effects of directional and surface properties and radiative heat transfer in fire barrier materials have been included in the numerical model. The Fluent®-based numerical model is able to match thermal performance of previous test systems. Initial calculations suggest that a fire barrier consisting of a 2D corner geometry exposed to a fire from either side would be thermally less robust than a slab of the same characteristic aspect ratio. This approximation has shown a preferential orientation for the barrier to be positioned when a fire or other high energy source is postulated.

Assessment of MELCOR 1.8.5 Versus Different Versions of SCDAP/RELAP5 MOD 3.3 With Lower Head Creep Rupture Analysis of Alternative Accident Sequences of the Three Mile Island Unit 2

The objective of this analysis is to assess MELCOR 1.8.5-RG against SCDAP/RELAP5 MOD 3.3kz (SR5m33kz), and SCDAP/RELAP5 MOD 3.3bf (SR5m33bf). This lower head creep rupture analysis considers: (1) Three Mile Island Unit 2 (TMI-2) alternative accident sequence-1, and (2) TMI-2 alternative accident sequence-2. SCDAP/RELAP5 model of TMI-2 alternative accident sequence-1 includes the continuation of the base case of the TMI-2 accident with the reactor coolant pumps (RCP) tripped, and the High Pressure Injection System (HPIS) throttled after approximately 6000 s accident time, SCDAP/RELAP5 model of TMI-2 alternative accident sequence-2 is derived from the TMI-2 base case accident by tripping the RCP after 6000 s, and the HPIS is reactivated after 12,012 s. MELCOR model of TMI-2 alternative accident sequence-1 is based on MELCOR TMI-2 phase-2 model by tripping the RCP and throttling back the makeup flows to zero from 6000 s onward. In MELCOR model of TMI-2 alternative accident sequence-2, the RCP are tripped from 6000 s and the constant makeup flow rate of 3.75 kg/s — including pump seal flow rate, but without HPIS flow rate — is activated from 6000 s and beyond 10440 s. The simulation is run until the lower head wall ruptures. In addition, the lower head penetration failure is also calculated with MELCOR for both TMI-2 alternative accident sequences. Lower head temperature contours calculated with SCDAP/RELAP5 are visualized and animated with open source visualization freeware ‘OpenDX’. Significant findings of the analysis include: (1) the TMI-2 lower head wall fails by creep rupture with either deactivations or activations of the HPIS; (2) for the TMI-2 alternative accident sequence-1 the time to creep rupture calculated with MELCOR 1.8.5-RG, SR5m33kz, and SR5m33bf agrees reasonably; (3) the calculation with MELCOR for the TMI-2 alternative accident sequence-1 predicts that the lower head wall failure occurred earlier than penetration failure, while MELCOR predicts the opposite for the TMI-2 alternative accident sequence-2; (4) calculation with MELCOR for TMI-2 alternative accident sequence-2 shows that when the lower head wall fails the temperature calculated with MELCOR is 1810.9 K, which exceeds the melting temperature of 1789 K for carbon steel; (5) calculations with both SR5m33kz and SR5m33bf for both TMI-2 alternative accident sequences indicate that different lower head wall locations fail rapidly one after another by a delay of a few seconds, while this is not the case for MELCOR.

Flow Analyses Using RELAP/MOD3.3 Code for the Simulant Melt Experiments (LAVA-ERVC) Under the External Reactor Vessel Cooling

Flow analyses using RELAP5/ MOD3.3 code have been performed to investigate the occurrence and the effects of steam binding for the LAVA-ERVC experiments. The main objectives of the LAVA-ERVC experiments are investigations of coolability through external reactor vessel cooling according to RPV insulation design. It could be found from the sensitivity studies for the flow path in the annulus of insulation that steam binding could occur in case of the limited steam venting capacity, which is definitely coincident with the LAVA-ERVC experimental results. In case of sufficient flow path for the steam venting, the vessel experienced effective cooling by nucleate boiling heat transfer. And existence of the upper free volume had little effect on occurrence of steam binding in the LAVA-ERVC experiments.

Effects of Contact Line Condition on Excitation of Internal Waves Confined by a Cylindrical Wall

Standing internal waves can be excited when fluids overlaid in a stationary enclosure are subjected to harmonic, vertical oscillations. The oscillatory deformation of the fluid-fluid interface near the wall, due to the limited mobility of the fluid-fluid-wall contact line, can play an important role in the excitation of waves. The contact line may or may not move depending on the amplitude of fluid excitation. When it moves, it may do so only in a limited portion of each cycle. We analyze numerically the wave excitation associated with such nonlinear, intermittent motions of the contact line. The analytical results consistently reproduce the experimental results, and give insight into the interactions between the contact line motions and the waves on the interface.