Seungmin Oh

Analysis Model for Sulfur-Iodine and Hybrid Sulfur Thermochemical Cycles

Abstract This paper presents a transient control volume modeling scheme for both the sulfur-iodine (SI) and Westinghouse hybrid sulfur (HyS) thermochemical cycles. These cycles are very important candidates for the large-scale production of hydrogen in the 21st century. In this study, transient control volume models of the SI and HyS cycles are presented, along with a methodology for coupling these models to codes that describe the transient behavior of a high-temperature nuclear reactor. The transient SI and HyS cycle models presented here are based on a previous model with a significant improvement, namely, pressure variation capability in the chemical reaction chambers. This pressure variation capability is obtained using the ideal gas law, which is differentiated with respect to time. The HyS model is based on a time-dependent application of the Nernst equation. Investigation of the new pressure assumption yields a peak pressure rate of change of 5.877 kPa/s for a temperature-driven transient test matrix and 2.993 kPa/s for a mass flow rate–driven transient test matrix. These high rates of pressure change suggest that an accurate model of the SI and/or HyS cycle must include some method of accounting for pressure variation. The HyS model suggests that the hydrogen production rate is directly proportional to the SO2 production rate.

SIMULATION OF SULFUR-IODINE THERMOCHEMICAL HYDROGEN PRODUCTION PLANT COUPLED TO HIGH-TEMPERATURE HEAT SOURCE

Abstract The sulfur-iodine (SI) cycle is one of the leading candidates in thermochemical processes for hydrogen production. In this paper a simplified model for the SI cycle is developed with chemical kinetics models of the three main SI reactions: the Bunsen reaction, sulfuric acid decomposition, and hydriodic acid decomposition. Each reaction was modeled with a single control volume reaction chamber. The simplified model uses basic heat and mass balance for each of the main three reactions. For sulfuric acid decomposition and hydriodic acid decomposition, reaction heat, latent heat, and sensible heat were considered. Since the Bunsen reaction is exothermic and its overall energy contribution is small, its heat energy is neglected. However, the input and output streams from the Bunsen reaction are accounted for in balancing the total stream mass flow rates from the SI cycle. The heat transfer between the reactor coolant (in this case helium) and the chemical reaction chamber was modeled with transient energy balance equations. The steady-state and transient behavior of the coupled system is studied with the model, and the results of the study are presented. It was determined from the study that the hydriodic acid decomposition step is the rate-limiting step of the entire SI cycle.

Investigation of a Passive Condenser System of an Advanced Boiling Water Reactor

An experimental study and best-estimate thermal-hydraulic code model assessment is performed to investigate the characteristics of the filmwise condensation with and without noncondensable gas in a passive condenser system. A vertical condenser tube is submerged in a water pool, where the heat from the condenser tube is removed through boiling heat transfer. Data are obtained for various inlet steam flow rates and noncondensable gas mass fractions at various system pressure conditions for two tube inner diameters: 26.6 and 52.5 mm. Experimental data are compared with analysis for complete condensation and flow-through conditions. Degradation of the condensation with noncondensable gas is investigated, where the condensation heat transfer coefficient decreases with the noncondensable gas. Experimental results are simulated with the RELAP5 code using two different condensation models. Code predictions are compared with experimental data, and the results indicate that there is a need for improved condensation models in RELAP5.

Investigation of the noncondensable effect and the operational modes of the passive condenser system

Abstract An experimental study is performed to investigate the effect of noncondensable gas in a passive condenser system. A vertical condenser tube is submerged in a water pool where the heat transferred from the condenser tube is removed through boiling. Data are obtained for three operational modes of the passive condenser. Degradation of the condensation with noncondensable gas is investigated. The condensation heat transfer rate is enhanced by increasing the inlet steam flow rate and the system pressure. For the condenser submerged in a saturated water pool, strong primary pressure dependency is observed. A boundary layer–based condensation model and a simple condensation model with the interfacial friction factor correlation are developed. The model predictions are compared with the pure steam data, and the agreement is satisfactory.

Condensation Correlation for a Vertical Passive Condenser System

A condensation correlation was developed for vapor and air mixture condensation in a vertical tube based on experimental data and a mechanistic model based on heat and mass analogy model. Parametric computations were performed using a heat and mass analogy model for various operating parameters of the passive condenser system. The parameters investigated were noncondensable gas mass fraction Wbulk, mixture gas Reynolds number ReG, and Jacob number JaG. An alternating conditional expectation (ACE) regression algorithm was used to develop the condensation heat transfer correlation for the passive condenser. A total of 102600 data points was used as input to the ACE. Local condensation heat transfer correlations in terms of Nusselt number (Nucond) obtained were: Nucond = 0.08Wbulk–0.9ReG1.1·exp(-42.5JaG) for turbulent flow and Nucond = 160Wbulk–0.9·exp(-42.5JaG) for laminar flow. The correlations are valid for 0 ≤ Wbulk ≤ 0.5, 0 ≤ ReG ≤ 4 × 104, 0.002 ≤ JaG ≤ 0.05. The prediction of the developed correlation agreed well with the available experimental data. The correlations are useful in predicting the heat transfer characteristics of a passive containment cooling system (PCCS) in an economic simplified boiling water reactor. These correlations apply to the three modes of PCCS operation, namely through-flow mode, complete condensation mode, and cyclic condensation and venting mode.

Transient modelling of sulphur-iodine cycle thermochemical hydrogen generation coupled to pebble bed modular reactor

A transient control volume model of the sulphur iodine (S-I) and Westinghouse hybrid sulphur (HyS) cycles is presented. These cycles are some of the leading candidates for hydrogen generation using a high temperature heat source. The control volume models presented here are based on a heat and mass balance in each reaction chamber coupled to the relevant reaction kinetics. The chemical kinetics expressions are extracted from a relevant literature review.

Development of Efficient Flowsheet and Transient Modeling for Nuclear Heat Coupled Sulfur Iodine Cyclefor Hydrogen Production

The realization of the hydrogen as an energy carrier for future power sources relies on a practical method of producing hydrogen in large scale with no emission of green house gases. Hydrogen is an energy carrier which can be produced by a thermochemical water splitting process. The Sulfur-Iodine (SI) process is an example of a water splitting method using iodine and sulfur as recycling agents.

Scaling of Passive Condenser System Separate Effect Facility

The Passive Containment Cooling System (PCCS) of the Simplified Boiling Water Reactor (SBWR) is a passive condenser system designed to remove energy from the containment for long term cooling period after a postulated reactor accident. Depending on pressure condition and noncondensable (NC) gas fraction in drywell (DW) and suppression pool (SP), three different modes are possible in the PCCS operation namely the forced flow, cyclic venting and complete condensation modes. The prototype SBWR has total of six condenser units with each units consist of hundreds of condenser tubes. Simulation of such prototype system is very expensive and complex Hence a scaling analysis is used in designing an experimental model for the prototype PCCS condenser system. The motive for scaling is to achieve a homologous relationship between an experiment and the prototype which it represents. A scaling method for separate effect test facility is first presented. The design of the scaled test facility for PCCS condenser is then given. Data from the test facility are presented and scaling approach to relate the scaled test facility data to prototype is discussed.Copyright

Simulation of Heat Exchanger Transients in Sulfuric-Acid and Hydrogen-Iodide Decomposition

In the Sulfur-Iodine (SI) water splitting cycle hydrogen is produced via the decomposition of Hydrogen-Iodide (HI) and sulfuric acid (H2 SO4 ). These reactions proceed at around 400 °C and 850 °C respectively. A high temperature heat source, such as nuclear reactor heat, is required for the SI cycle. Since both the nuclear plant and the SI cycle plant are coupled through heat exchangers, any transients for either plant will affect the entire system. For a nuclear reactor system, it is especially important to understand the transient behavior of the SI cycle during a reactor startup or an emergency shutdown. A simplified transient model of the SI cycle, which can be coupled to heat from a nuclear plant, has been developed. Preliminary results from both steady state and transient calculations are presented in this paper.Copyright

Steam Condensation in a Vertical Passive Condenser

A set of steam condensation experiments is conducted to evaluate the heat removal capacity of a vertical passive condenser. A condensing tube is submerged in a water pool where condensation heat is transferred by secondary boiling heat transfer. Condensation heat transfer coefficients (HTC) are obtained under various test conditions, such as different primary pressure (150 - 450 kPa), inlet steam flow rate (1 - 5 g/s), air mass fraction (0 - 20%) and tube size (26.6 mm and 52.5 mm ID). The effects of these parameters to condensation performance are evaluated in this paper. Experimental data are compared with code predictions from RELAP5 with 2 condensation models. The comparison result shows that an improved condensation model is needed in RELAP5.Copyright