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This paper presents both analytical thermodynamic analysis and experimental results of ethanol steam reforming in a thermal plasma reformer at various working conditions. Since our thermal plasma reformer can work well at atmospheric pressure, a thermodynamic equilibrium prediction is first performed at temperatures in the range from 500 to 1000°C and at mole flow ratios of ethanol to water from 1:1 to 1:6. And then the experiment for ethanol steam reforming of a fabricated thermal plasma reformer is performed and the reformate stream is immediately analyzed using GC/MS, GC/FID/TCD, and pre‐concentrator. Comparing predicted data with experimental data, an optimal working condition is determined at the temperature of 750°C and at mole flow ratio of ethanol to water of 1:3. In the future, an optimal temperature control system will be designed to maintain the thermal plasma reformer at the temperature of 750°C under the inlet mole flow ratio of ethanol to water of 1:3.

A complete scheme of scaling methods to design the reduced-height, reduced-pressure (RHRP) Institute of Nuclear Energy Research Integral System Test (IIST) facility and to specify test conditions for incident simulation was developed. In order to preserve core decay power history and coolant mass inventory during a transient, a unique power-to-mass scaling method is proposed and utilized for RHRP and full-height, full-pressure (FHFP) systems. To validate the current scaling method, three counterpart tests done at the IIST facility are compared with the FHFP tests in small-break loss-of-coolant, station blackout, and loss-of-feedwater accidents performed at the Large-Scale Test Facility (LSTF) and the BETHSY test facility. Although differences appeared in design, scaling, and operation conditions among the IIST, LSTF, and BETHSY test facilities, the important physical phenomena shown in the facilities are almost the same. The physics involved in incident transient phenomena are well measured and modeled by showing the common thermal-hydraulic behavior of key parameters and the general consistency of chronological events. The results also confirm the adequacy of power-to-mass scaling methodology.

A passive core cooling system (PCCS) has been installed at the Institute of Nuclear Energy Research Integral System Test facility. It includes three core makeup tanks (CMTs), three accumulators (ACCs), a four-stage automatic depressurization system (ADS), a passive residual heat removal (PRHR) heat exchanger submerged into an in-containment refueling water storage tank (IRWST). The purpose of this research is to study the performance of the PCCS with passive injection during either a pressure balance line (PBL) break or a direct vessel injection (DVI) line break. Five experiments were performed simulating break area ratios of 0.5 to 2.0% (1.88 to 3.77 mm) at either a PBL or a DVI line. The general system response and the interactions of CMT, ACC, PRHR, and IRWST to the effect of core heat removal are observed and discussed. The experimental results show long-term core cooling can be reached for the cases of the PBL break and the DVI-line break following the PCCS actuation procedures.

The thermal-hydraulic behavior of a postulated 1% cold-leg break loss-of-coolant accident (LOCA) in a pressurized water reactor system was investigated experimentally by the three-loop Institute of Nuclear Energy Research (INER) Integral System Test (IIST) facility with the passive core cooling system (PCCS) and numerically by the RELAP5/MOD3.2 computer code. The PCCS of the IIST facility includes three core makeup tanks (CMTs), three accumulators, and a four-stage automatic depressurization system. The aim of this research is to study the performance of the CMTs with the actuation of the ADS during a small-break LOCA. The experimental results show that the IIST PCCS has the capability to maintain long-term cooling under a postulated 1% cold-leg break LOCA. The comparison of the RELAP5/MOD3.2 simulation against the experimental data shows good agreement in major thermal-hydraulic phenomena in the reactor coolant system, but the prediction of the asymmetric behavior for the three CMTs during a gravity drain period is inadequate.

The current emergency operating procedures (EOPs) for a three-loop pressurized water reactor on steam generator tube rupture (SGTR) incident are experimentally evaluated at the Institute of Nuclear Energy Research Integral System Test Facility. The focus is on the adequacy of EOPs to limit primary-to-secondary leakage with particular emphasis on the number of ruptured U-tubes on the severity of an incident and the response time available for operator actions. By comparing test data with plant records of a Mihama-2 SGTR event, the key thermal-hydraulic phenomena during SGTR transients can be successfully simulated. The test results indicated that the current EOPs can function well in terminating the break flow and maintaining adequate core cooling. However, the effectiveness in minimizing the radioactive release demands an early and substantial operator involvement. To mitigate the consequences of such an event, the timing to isolate the faulted steam generator (SG) and to terminate safety injection flow will be critical. Furthermore, to avoid overfilling, the water level in the faulted SG needs to be drained prior to the implementation of the cooldown process.

The RELAP5/MOD3.2 code is used at the Institute of Nuclear Energy Research Integral System Test Facility to analyze a 2% cold-leg-break experiment that includes failure of the high-pressure injection system. The assessment code predictions include primary pressure, inventory distribution in the reactor coolant system (RCS), loop flow rate, break flow rate, and core thermal hydraulics. A comparison between the calculated results and the experimental data shows (a) a good match with the predictions of the RCS pressure and hot- and cold-leg fluid temperatures, (b) underprediction of the core and down-comer levels, (c) overprediction of the loop flow rates in single- and two-phase natural circulation, and (d) inadequate prediction of asymmetric coolant holdup in the three stean generators. Also presented are sensitivity studies of choked flow associated with the defaulted values of discharge coefficients in the simulation of the break flow, and of the core bypass area to evaluate the effect of core level depression.

A new mechanistic critical heat flux (CHF) model has been developed for flow boiling CHF data of low-pressure (i.e., 0.2 to 4.0 MPa), low-mass-flux (i.e., 189 to 789 kg/m 2 .s), and high-quality conditions. In general, CHF at these conditions associates with the flow regime of annular flow. This model assumes that the Helmholtz instability at the liquid-vapor interface of annular flow triggers the onset of CHF. CHF is the energy required to dryout the liquid film isolated by flow instability With five empirical constants to properly correlate the liquid-vapor configurations of annular flow in the steam-water systems, the model successfully achieves a mean deviation error of 0.2% over a CHF data set consisting of 733 CHF data. The prediction of this model is more accurate than those of Biasi and Bowring correlations at the aforementioned low-pressure and low-mass-flux conditions.

Thermal-hydraulic responses in the station blackout experiment conducted at the IIST facility are simulated through the use of the advanced system code RELAP5/MOD3. Typical behaviors occurring in the IIST station blackout transient are characterized by secondary boiloff, primary saturation and pressurization, and subsequent core uncovery and heatup. As the coolant inventory within the steam generator secondary system boils dry, the primary system pressure increases as a result of degradation of the heat removal ability of the steam generator secondary side. This pressurization phenomenon causes the pressurizer safety valve to open and the primary coolant to deplete through the valve, causing the core to eventually become uncovered. The same response can be exactly simulated by the current model. The current calculated results show fairly good agreement with the experimental data, but the timing of the events occurring in the station blackout transient is calculated earlier than the measured value. The overall comparison of key parameters between the calculated results and IIST test data, however, reveals that the current RELAP5/MOD3 model can provide rear sonable station blackout modeling for simulating longterm system behavior.

The simulation capabilities of RELAP5/MOD3 are analyzed and assessed in comparison with the IIST experiments conducted to investigate the system response to the loss of the residual heat removal (RHR) system during midloop operation. Two IIST experiments are simulated; a one-loop test under closed system conditions and a three-loop test with a vent at the top of the pressurizer. Once the RHR cooling system is lost and if alternate heat sinks are not established in time, the primary system will be heated up by the decay power, causing core boiling, system pressurization, and potential core uncovery and fuel heatup. The predicted responses of system parameters by the current model show reasonable agreement with the experimental data. These key parameters consist of the system pressure transient, temperature histories, and variation in the active heat transfer length within the steam generator. The liquid flooding in the pressurizer and the steam generator can also be captured in the current simulation. A periodic fill-and-down cycle developed in the steam generator U-tubes has been observed in the IIST measured data of oscillatory differential pressure across the steam generator. This phenomenon is not simulated in the calculation. However, the calculated differential pressure will follow the experimentalmore » trend and agree qualitatively with the measured data averaged over one fill-and-down cycle. As shown in the comparison of the calculated and experimental data, the overall system responses to the loss-of-RHR system event during midloop operation can be appropriately simulated by the current RELAP5/MOD3 model.« less

A series of experiments dealing with variable secondary-side cooling conditions have been conducted at the IIST facility, including the natural circulation experiments under the secondary-side conditions of normal feedwater, loss of feedwater, and full of air. Different cooling conditions at the secondary side directly affect the primary-to-secondary heat transfer and then may influence the heat removal capability of natural circulation in the primary system. The corresponding analytical work is performed using the RELAP5/MOD3 code. Good agreement is reached both qualitatively and quantitatively between the experimental data and calculated results, demonstrating the satisfactory assessment of RELAP5/MOD3 code compared with the IIST natural circulation experiments. The cooling conditions at the secondary side have no significant effect on the heat removal capability of natural circulation as long as sufficient coolant exists on the steam generator secondary side, based on current IIST data and analytical results. Continuous increase of the core temperature and system pressure is also demonstrated experimentally and analytically in the test with the secondary side dry for the sake of deficient heat transfer capability at the steam generator secondary system.

In this paper a new approach to bundle critical power predictions is presented. In addition to a very accurate critical heat flux (CHF) model, correction factors that account for the effects of grid spacers, heat flux non-uniformities, and cold walls, which are needed for critical power predictions for practical fuel bundles, are developed. By using the subchannel analysis code COBRA IIIC/MIT-1, local flow conditions needed as input to CHF correlations are obtained. Critical power is therefore obtained iteratively to ensure that the bundle power value from the subchannel analysis will cause CHF at only one point in the bundle. Good agreement with the experimental data is obtained. The accuracy is higher than that of the W-3 and EPRI-1 correlations for the limited data base used in this study. The effects of three types of fuel abnormalities, namely, local heat flux spikes, local flow blockages, and rod bowing, on bundle critical power are also analyzed. The local heat flux spikes and flow blockages have no significant influence on critical power. However, rod bowing phenomena have some effect, the severity of which depends on system pressure, the gap closure between adjacent rods, and the presence or absence of thimble tubes (cold walls).more » A correlation for the influence of various rod bowing phenomena on bundle critical power is developed. Good agreement with experimental data is shown.« less

A theoretical critical heat flux (CHF) model based on microlayer dryout and Helmholtz instability for subcooled tube flow under pressurized water reactor operation conditions is first extended to t...

Based on the Helmholtz instability at the microlayer/vapor interface as a trigger condition for microlayer dryout, Lee and Mudawwar developed a mechanistic critical heat flux (CHF) model for subcoo...