Development of In-Situ Gas Analyzer for Hydrogen Isotopes in Fusion Fuel Gas Processing

To develop a real time and in-situ process gas analyzer for fusion fuel gas processing systems, application study of laser Raman spectroscopy was performed by measurement of hydrogen isotopes. Using an Ari on type laser of which wavelength 488 nm, power 0.7 W, and single pass irradiation method, Raman spectra of hydrogen isotopes were measured and intensities of the Stokes rotational lines and Q-branch were quantitatively analyzed. The Stokes rotational lines at 587, 443 and 415 cm¹ were selected as suitable ones for quantitative analysis of H₂, HD and D₂. Normalizing the Raman intensity of partial pressure H₂ as 100, relative Raman intensity ratio of H₂:HD:D₂ was obtained as 100:58:47. The detection limit for hydrogen was estimated as 0.05 kPa in partial pressure and 500 ppm in concentration. But multiple pass method further improved the detection limit to 100 ppm.     

Computer Analysis on Steady State Separation Characteristics of Hydrogen Isotope Separation System by Cryogenic Distillation

A computer code is developed for effective and exact simulation of cryogenic distillation columns. The simulation model incorporates the differences of latent heat of vaporization among the six molecular species, pressure drop, decay heat of tritium, heat transfer through the column wall, Raoult's law deviation of the solutions of hydrogen isotopes, multiple feeds and multiple sidestreams. The calculational procedure developed by Tomich for general equilibrium stage processes is further modified to match this complicated simulation model.

A computer simulation study is performed for the typical cryogenic distillation column cascade and separation characteristics of each column are clarified. The effects of pressure drop are found not significant. If the tritium concentration in the column is considerably high, the lower performance caused by decay heat effects cannot be neglected any longer. Increase of the reflux ratio or refrigeration of the stripping section, is required for improvement.

The present study provides a great help to development of exact simulation models and simulation procedures of cryogenic distillation columns.     

Estimation of the Tritium Behavior in the Pebble Type Gas Cooled Reactor for Hydrogen Production

In Korea, a nuclear hydrogen program has been established to develop and demonstrate mass production system for hydrogen generation. The objective of this study is to establish the evaluation procedure for predicting the tritium behavior in the 300 MWth Pebble type gas cooled reactor which is the one of the candidate reactors for nuclear hydrogen development and demonstration plant. The tritium generated by the fission reaction can be leaked to the helium coolant from the coated ceramic particles and fuel elements. The annual total release rate of the tritium is estimated as 0.47% from the fuel kernel to the helium coolant by the numerical method. Tritium attributed by ⁶Li existing as impurities in the reflector can be released to the helium coolant by the diffusion process and the total annual release rate of the tritium is estimated as 5.3% through the reflector to the helium coolant. Based on the Siverts' law, tritium permeation from the primary coolant to the hydrogen production system is also evaluated and the result is calculated as 76?0.23 Bq/g-H₂ with respect to the PRF (Permeation Reduction Factor= 10?1000) in case of the normal operation of the 300 MWth Pebble type reactor.     

Experimental and Analytical Studies on Chromatography of Hydrogen-Deuterium Mixtures with Vanadium Particle Fixed-Bed

The exchange chromatography of hydrogen and deuterium in a vanadium particle bed was experimentally and analytically studied for the isotope separation with small scale facilities. In the analysis, diffusion across a fluid film and in a solid phase, an apparent exchange reaction on surfaces including effects of impurities, and axial dispersion in a fixed-bed are taken into consideration. A simplified calculation method using a numerical technique of the inverse Laplace transform was also applied for the analysis of the chromatography with a pulse or step change of a deuterium concentration at the inlet of the bed. From the experiment, it was found that the apparent exchange reaction rate on surfaces controls the overall mass transfer and the tortuosity factor in the bed is about 2, The numerical effluent curves calculated by using the mass transfer coefficient and the tortuosity factor obtained from the first and second moments could be well fitted to the experimental results.     

Measurement of HETP of SUS Dixon Ring and Porcelain Packing in Small-Scale Water Distillation Column for H2O-HTO Isotope Separation

Series of water distillations in a total reflux mode have been performed in a 100cm height column of 1.6cm I. D. in order to measure values of HETP for various packings, that is, one brass or three SUS Dixon rings and three porcelain packings. The HETP were measured by changing the vapor flow rate within the column. The SUS Dixon ring of 1.5 mm diameter and the porcelain packing of 1.2 mm O. D. had a small HETP (～5cm), but could not meet a large vapor flow rate because of a large pressure drop. The SUS Dixon ring of 6.0 mm diameter had a small HETP (～6cm) in the vapor flow rate under 2g/min, but the HETP value increased with increasing the vapor flow rate. The pressure drop for the ring, however, was almost constant in the range of these measurements.     

Deactivation of Hydrophobic Pt/SDBC Catalyst in the WTRF LPCE Column for Tritium Separation

The styrene divinylbenzene copolymer (SDBC) supported platinum catalyst and the liquid phase catalytic exchange (LPCE) column have been developed to be applicable to the Wolsong tritium removal facility (WTRF) in Korea. The catalyst deactivation subject to both reversible uniform poisoning and permanent loss by impurity poisoning was investigated using a time-on-stream theory and a simplified shell progressive poisoning scenario in special case of higher internal diffusion resistance. Experimental data from fixed bed reactors with the Pt/SDBC catalysts have been used to establish the deactivation model and to estimate key parameters to be used in the WTRF LPCE column design. It was found that an impurity control in the streams would be critical to the WTRF LPCE column operation since the impurity poisoning played a very important role in the overall catalytic exchange reaction. Except for the case of the severe impurity poisoning of the whole catalysts, the LPCE column can be in operation over 10 years without any regeneration of the catalysts.     

Room-Temperature Reactor Packed with Hydrophobic Catalysts for the Oxidation of Hydrogen Isotopes Released in a Nuclear Facility

A room-temperature reactor packed with hydrophobic catalysts for the oxidation of hydrogen isotopes released in a nuclear facility will contribute to nuclear safety. The inorganic-based hydrophobic Pt catalyst named H1P has been developed especially for efficient oxidation over a wide concentration range of hydrogen isotopes at room temperature, even in the presence of saturated water vapor. The overall reaction rate constant for hydrogen oxidation with the H1P catalyst in a flow-through system using a tritium tracer was determined as a function of space velocity, hydrogen concentration in carriers, temperature of the catalyst, and water vapor concentration in carriers. The overall reaction rate constant for the H1P catalyst in the range near room temperature was considerably larger than that for the traditionally applied Pt/Al₂O₃ catalyst. Moreover, the decrease in reaction rate for H1P in the presence of saturated water vapor was slight compared with the reaction rate in the absence of water vapor due to the excellent hydrophobic performance of H1P. Oxidation reaction on the catalyst surface is the rate-controlling step in the range near room temperature and the rate-controlling step is shifted to diffusion in a catalyst substratum above 313K due to its fine porosity. The overall reaction rate constant in the range near room temperature was dependent on the space velocity and hydrogen concentration in carriers. The overall reaction rate constants in the range of 1;000=T greater than 3.2 correlated to k _overall[s^?1] = 5.59 × 10⁷ × SV[h^?1] × exp (?67.7 [kJ/mol]/R_gT), where the space velocity range was from 600 to 7,200 h^?1.     

Parameter Setting Method for Control System of Cryogenic Distillation Column

A computer code is developed for analysis of dynamic behavior of a single cryogenic distillation column. A dynamic simulation study is performed for the lead column in a typical column cascade which consists of four columns and two catalytic equilibrators.

The atom fraction of protium in the bottom product and the reflux ratio are regarded as the controlled variable and the manipulated variable, respectively. Fluctuation or change of the feed composition is considered as the disturbance and the PI control scheme is introduced for a constant value control.

The criteria are derived, which can be used in setting the choice of the two PI controller parameters. Investigated are the effects of the controller parameters on the response of the controlled variable to a step change in the feed composition, and the validity of the criteria is verified. The parameter setting method proposed in the present study has two advantages: it accounts for the strong nonlinearity of the column and it predicts the unstable region which must be avoided in the actual operation.