Radiolysis Of Coolant Research Articles

Hysteresis in Coolant Radiolysis in a Pressurized-Water Reactor and its Effect on the Critical Hydrogen Concentration

Mathematical modeling is used to investigate the effect of the thermophysical non-uniformity of the core in a reactor on the behavior of radiation-chemical processes in the first-loop water coolant of pressurizedwater power reactors. The problem of determining the critical hydrogen concentration in coolant that is sufficient to maintain the concentration of oxidizers in the coolant at a corrosion safe level is used as an example. It is shown that in a reactor the critical hydrogen concentration may not have a definite value but rather a range of values dependent on the radiation-chemical process and the reactor’s thermo- and neutron-physical parameters. Calculations also showed that the conditions under which oxidizer formation is suppressed can be determined accurately only with detailed three-dimensional modeling of thermophysical phenomena and radiation-chemical transformations in the entire core volume.

An improved method for modelling coolant radiolysis in ITER

Predicting the effects of coolant water radiolysis induced by neutron and gamma radiation in the International Thermonuclear Experimental Reactor (ITER) is important, as oxidizing species like O2 and H2O2 will corrode structural materials, increasing maintenance costs and potentially compromising safety. In this work, a new model has been developed, by modifying existing models, to evaluate the water radiolysis behaviors in different Primary Heat Transfer Systems (PHTSs) in ITER. The new model takes the circulation of coolant, and the combined gamma and 14 MeV neutron radiation into consideration. We recommend injection of about 5 cc H2 under standard temperature and pressure (STP) per kilogram of H2O into the First Wall/Blanket (FW/BLKT) PHTS to both efficiently suppress water radiolysis and avoid problems caused by addition of excessive H2.

Hydrogenation behavior of Ti-implanted Zr-1Nb alloy with TiN films deposited using filtered vacuum arc and magnetron sputtering

More than 60 years of operation of water-cooled reactors have shown that local or general critical hydrogen concentration is one of the basic limiting criteria of zirconium-based fuel element claddings. During the coolant radiolysis, released hydrogen penetrates and accumulates in zirconium alloys. Hydrogenation of zirconium alloys leads to degradation of their mechanical properties, hydride cracking and stress corrosion cracking. In this research the effect of titanium nitride (TiN) deposition on hydrogenation behavior of Ti-implanted Zr-1Nb alloy was described. Ti-implanted interlayer was fabricated by plasma immersion ion implantation (PIII) at the pulsed bias voltage of 1500V to improve the adhesion of TiN and reduce hydrogen penetration into Zr-1Nb alloy. We conducted the comparative analysis on hydrogenation behavior of the Ti-implanted alloy with sputtered and evaporated TiN films by reactive dc magnetron sputtering (dcMS) and filtered cathodic vacuum arc deposition (FVAD), respectively. The crystalline structure and surface morphology were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The elemental distribution was analyzed using glow-discharge optical emission spectroscopy (GD-OES). Hydrogenation was performed from gas atmosphere at 350°C and 2atm hydrogen pressure. The results revealed that TiN films as well as Ti implantation significantly reduce hydrogen absorption rate of Zr-1Nb alloy. The best performance to reduce the rate of hydrogen absorption is Ti-implanted layer with evaporated TiN film. Morphology of the films impacted hydrogen permeation through TiN films: the denser film the lower hydrogen permeation. The Ti-implanted interface plays an important role of hydrogen accumulation layer for trapping the penetrated hydrogen. No deterioration of adhesive properties of TiN films on Zr-1Nb alloy with Ti-implanted interface occurs under high-temperature hydrogen exposure. Thus, the fabrication of Ti-implanted layer with dense TiN films can be an effective way to protect Zr-1Nb alloy from hydrogen embrittlement.

Numerical Simulation on Effect of Methanol Addition on Coolant Radiolysis in Pressurized Water Reactor

The addition of alcohol into the primary coolant of pressurized water reactors (PWRs) was proposed as an alternative of hydrogen addition. The radiolysis of the coolant in the presence of methanol was simulated, assuming a batch system and changing dose rate. At 300°C, the addition of 4.0 ppm methanol shows an equivalent scavenging capacity toward the OH radical to a typical dissolved hydrogen concentration in Japanese PWR plants. At low dose rate, the addition of 1.0 ppm methanol suppresses considerably the radiolysis of the coolant. At high dose rate, the addition of at least 10 ppm methanol is necessary to lower concentrations of the radiolytic oxidizing products. Concentrations of the radiolytic oxidizing products are determined not only by the scavenging of the OH radical but also by secondary reactions. In the presence of fast neutron irradiation, methanol acts to decompose the radiolytic oxidizing products. The fact that steady-state concentrations of the final organic products depend on dose rate means that complicated secondary reactions contribute to the decomposition of methanol. The major final organic product is formed through a reaction of ethylene glycol with OH. Methanol addition may have the same effect as ethylene glycol addition, and radiation chemical reactions of ethylene glycol systems should be elucidated in future.

Numerical Simulation on Effect of Methanol Addition on Coolant Radiolysis in Pressurized Water Reactor

The addition of alcohol into the primary coolant of pressurized water reactors (PWRs) was proposed as an alternative of hydrogen addition. The radiolysis of the coolant in the presence of methanol was simulated, assuming a batch system and changing dose rate. At 300°C, the addition of 4.0 ppm methanol shows an equivalent scavenging capacity toward the OH radical to a typical dissolved hydrogen concentration in Japanese PWR plants. At low dose rate, the addition of 1.0 ppm methanol suppresses considerably the radiolysis of the coolant. At high dose rate, the addition of at least 10 ppm methanol is necessary to lower concentrations of the radiolytic oxidizing products. Concentrations of the radiolytic oxidizing products are determined not only by the scavenging of the OH radical but also by secondary reactions. In the presence of fast neutron irradiation, methanol acts to decompose the radiolytic oxidizing products. The fact that steady-state concentrations of the final organic products depend on dose rate means that complicated secondary reactions contribute to the decomposition of methanol. The major final organic product is formed through a reaction of ethylene glycol with OH. Methanol addition may have the same effect as ethylene glycol addition, and radiation chemical reactions of ethylene glycol systems should be elucidated in future.

Optimization of Dissolved Hydrogen Concentration for Control of Primary Coolant Radiolysis in Pressurized Water Reactors

Optimization of the dissolved hydrogen concentration in primary coolant of pressurized water reactors has several potential advantages in material integrity and dose reduction. To assess the threshold value of dissolved hydrogen for reducing condition, in-pile loop experiments and radiolysis model calculations were performed. Both experiments and model calculations indicate that the threshold value of dissolved hydrogen for radiolysis is much less than the present control level in pressurized water reactors, and the in-core region is more easily affected by reduced dissolved hydrogen level than the out-of-core region. The measurement of electrochemical corrosion potential of structural material, while varying dissolved hydrogen levels, is desirable in the future to compensate for the uncertainty of the model calculation. For this purpose, electrochemical corrosion potential of stainless steel at the top-of-core, in which the reference electrode could be inserted, was estimated based on the correlation between the experiments and the modeling for the loop.

Optimization of Dissolved Hydrogen Concentration for Control of Primary Coolant Radiolysis in Pressurized Water Reactors

Optimization of the dissolved hydrogen concentration in primary coolant of pressurized water reactors has several potential advantages in material integrity and dose reduction. To assess the threshold value of dissolved hydrogen for reducing condition, in-pile loop experiments and radiolysis model calculations were performed. Both experiments and model calculations indicate that the threshold value of dissolved hydrogen for radiolysis is much less than the present control level in pressurized water reactors, and the in-core region is more easily affected by reduced dissolved hydrogen level than the out-of-core region. The measurement of electrochemical corrosion potential of structural material, while varying dissolved hydrogen levels, is desirable in the future to compensate for the uncertainty of the model calculation. For this purpose, electrochemical corrosion potential of stainless steel at the top-of-core, in which the reference electrode could be inserted, was estimated based on the correlation between the experiments and the modeling for the loop.

Modelling of radiolysis of reactor cooling water—A comparative study

Computations of the coolant radiolysis in the primary heat transport (PHT) system of the CANDU (Canadian Deuterium Uranium) PWRs by using two reaction mechanisms—hot water radiolysis and supercritical water radiolysis, are presented. The radiolytic product concentrations formed under the conditions of both radiolytic mechanisms in the presence of different amounts of hydrogen in the coolant are compared. The results suggest that the PHT system should react in a more sensitive way to changes in the hydrogen concentration when the mechanism of the supercritical water radiolysis is applied. The consequences of using either mechanism in modelling of the coolant radiolysis are briefly discussed.

Modelling of coolant radiolysis in the primary heat transport system of candu reactors — E ffect of coolant boiling

A modelling of radiolysis of coolant water and the effect of deuterium variation in the primary heat transport (PHT) system of the Bruce-A reactor is presented. The radiolytic products' concentration profiles along a fuel channel were calculated by using the MAKSIMA-CHEMIST computer program and radiolysis of supercritical water. Deuterium stripping into the steam due to coolant boiling at the outlet end of fuel channel was modelled with help of a modified Henry's law. According to these models, coolant boiling in the Bruce reactor may lead to nearly complete recovery of the original degree of the coolant radiolysis prior to deuterium injection into the PHT system with concomitant establishment of oxidizing water chemistry. Consequences of the homogeneous character of the models are discussed.

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