Effectiveness Of Hydrogen Water Chemistry Research Articles

Evaluation of Early Hydrogen Water Chemistry on Corrosion Mitigation in Boiling Water Reactors

Hydrogen water chemistry (HWC), aiming at coolant chemistry improvement, has been adopted worldwide for mitigating intergranular stress corrosion cracking in operating boiling water reactors (BWRs). However, a conventional hydrogen injection system employed in this technology was designed to operate only at power levels >30% of the rated power or at coolant temperatures >232°C. This system is usually in an idle and standby mode during a start-up operation. The coolant in a BWR during a cold shutdown normally contains a relatively high level of dissolved oxygen from intrusion of atmospheric air. Accordingly, the structural materials in the primary coolant circuit (PCC) of a BWR could be exposed to a strongly oxidizing environment for a short period of time during a subsequent start-up operation. In this study, the computer code DEMACE was used to investigate the variations in redox species concentration and in electrochemical corrosion potential (ECP) of structural components in the PCC of a domestic BWR during start-up operations with HWC. Simulations were carried out for power levels ranging from 3.8% to 11.3% during start-up operations. Our analyses indicated that for selected power levels with steam present in the core, a higher power level would tend to promote a more oxidizing coolant environment and therefore lead to less HWC effectiveness on ECP reduction. At even lower power levels in the absence of steam, the effectiveness of HWC was more prominent. At a feedwater hydrogen concentration of merely 0.1 parts per million, significant ECP reductions in the PCC of the BWR were observed.

The Effectiveness of Hydrogen Water Chemistry on Corrosion Mitigation in an Advanced Boiling Water Reactor

For further improvements on thermal efficiency and operation safety, reactor internal pumps, instead of conventional recirculation systems, are adopted in an advanced boiling water reactor (ABWR). With the novel design of internal circulation, the traveling path and pattern of the recirculated liquid coolant in an ABWR is actually different from that of the coolant in a conventional boiling water reactor. To ensure operation safety, optimization of the coolant chemistry in the primary coolant circuit (PCC) of a nuclear reactor is essential no matter what type or generation the reactor belongs to. For a better understanding of the water chemistry in an ABWR, such as the one being constructed in the northern part of Taiwan, and for safer operation of this ABWR, in this study we conducted a proactive, thorough water chemistry analysis prior to the completion of this reactor. A well-developed computer code was used to investigate the effectiveness of hydrogen water chemistry (HWC) on the redox species concentrations and electrochemical corrosion potential (ECP) behavior of components in the PCC of the Lungmen ABWR in Taiwan. Our analyses indicated that the effective oxidant concentrations at the top of the downcomer location would be expected to be >100 ppb at 0.5 ppm [H2]FW at the original rated power. While an effective ECP reduction at 0.4 ppm [H2]FW was observed at the downcomer outlet, a 2.0 ppm [H2]FW was not enough to reduce the ECP below the Ecrit at the upper plenum outlet. In summary, the effectiveness of HWC in the PCC of an ABWR is expected to vary from location to location and eventually from plant to plant due to different degrees of radiolysis and physical dimensions in different ABWRs.

Predicted impact of core flow rate on the corrosion mitigation effectiveness of hydrogen water chemistry for Kuosheng boiling water reactor

It is currently a common practice that a boiling water reactor (BWR) adopts hydrogen water chemistry (HWC) for mitigating corrosion in structural components in its primary coolant circuit. When the core flow rate (CFR) in a BWR is changed, the coolant residence time in the primary coolant circuit would be different. The concentrations of major redox species (i.e. hydrogen, oxygen, and hydrogen peroxide) in the coolant may accordingly vary due to different durations of radiolysis in the core and other near-core regions. A theoretical model by the name of DEMACE was used in the current study to investigate the impact of various CFRs (from 100% to 80.0%) on the effectiveness of HWC in a domestic BWR. Our analyses indicated that the HWC effectiveness at some locations could be downgraded due to a decrease in CFR. However, a lower CFR was instead beneficial to the corrosion mitigation efficiency of HWC at other locations. The impact of CFR on the HWC effectiveness could vary from location to location in a BWR and eventually from plant to plant.

The Impact of Core Flow Rate on the Hydrogen Water Chemistry Efficiency in Boiling Water Reactors

It is currently a common practice that a boiling water reactor (BWR) adopts hydrogen water chemistry (HWC) for mitigating corrosion in structural components in its primary coolant circuit (PCC). The optimal feedwater hydrogen concentration ([H2]FW) varies from plant to plant and is usually set at a constant value. When the core flow rate (CFR) in a BWR is changed, the coolant residence time in the PCC would be different. The concentrations of major redox species (i.e., hydrogen, oxygen, and hydrogen peroxide) in the coolant may accordingly vary because of different radiolysis durations in the core and other near-core regions. A theoretical code by the name of DEMACE was used in the current study to investigate the impact of various CFRs (from 100 to 80.6%) on the effectiveness of HWC in a domestic BWR. Our analyses indicated that the HWC effectiveness could be downgraded because of an increase in CFR at locations such as upper downcomer, recirculation system, and lower plenum. However, the HWC efficiency at the upper plenum area did not vary with either increasing or decreasing CFRs. The impact of CFR on the HWC effectiveness is therefore expected to vary from location to location in a BWR and eventually from plant to plant.

The Impact of Power Uprate on the Corrosion Mitigation Effectiveness of Hydrogen Water Chemistry in Boiling Water Reactors

In order to increase the power generation efficiency of nuclear reactors, the utilities of light water reactors have opted for power uprates in the past decades. Upon a power uprate, the power density and coolant flow rate of a nuclear reactor would change immediately, followed by water chemistry variations due to enhanced radiolysis of water and shortened coolant residence times. If the boiling water reactor (BWR) has adopted hydrogen water chemistry (HWC) for corrosion mitigation, the optimal hydrogen injection rate may thus require a proper adjustment. Because of limited measurable water chemistry data, a well-developed computer code DEMACE was used in the current study to investigate the impact of various power levels (ranging from 100 to 120%) on the redox species concentrations and electrochemical corrosion potential (ECP) behavior of components in the primary coolant circuit of a domestic BWR operating under either normal water chemistry or HWC. Our analyses indicated that the chemical species concentrations and the ECP did not vary monotonically with increases in reactor power level at a fixed feedwater hydrogen concentration. In particular, the upper plenum and the upper downcomer regions exhibited uniquely higher ECPs at 104 and 114% power levels than those at the other evaluated power levels. Accordingly, the impact of power uprate on the HWC effectiveness in a BWR is expected to vary from location to location and eventually from plant to plant because of different degrees of radiolysis and physical dimensions.

The Influence of Various Treating Parameters on the Corrosion of ZrO2-Treated Type 304 Stainless Steels in High-Temperature Water

Corrosion mitigation techniques specifically developed for the vessel internals of boiling water reactors (BWRs) such as hydrogen water chemistry (HWC), catalytic coatings, and inhibitive coatings have been studied and/or adopted worldwide in the past decade. The common goal of these techniques is to mitigate intergranular stress corrosion cracking in the vessel internal components of BWRs. For enhancing the effectiveness of HWC through a more effective reduction in electrochemical corrosion potential accompanied by a lower hydrogen consumption rate or even without any added hydrogen, the technique of inhibitive treatment on structural component surfaces was brought into consideration. In the current study, surfaces of preoxidized square-disk specimens made of Type 304 stainless steel (SS) were treated with zirconium oxide (ZrO2) (particle sizes of 0.7 μm and 0.1 μm) via hydrothermal deposition at either 90 or 150°C for 7 or 14 d, while some preoxidized specimens remained untreated. The concentration of the treating solution was maintained at either 10 parts per million (ppm) or 122 ppm (1mM) during the ZrO2 deposition processes. Electrochemical polarization analyses at 288°C were conducted to characterize the electrochemical properties of the treated and untreated SS specimens in pure water with either dissolved oxygen or dissolved hydrogen. It was found that a smaller particle size, a longer treating time, a lower treating temperature, as well as a higher treating solution concentration seemed to improve the corrosion resistance of the treated specimens in oxygenated environments and to moderately deter the hydrogen oxidation rate on the specimens.

The Influence of Various Treating Parameters on the Corrosion of ZrO2-Treated Type 304 Stainless Steels in High-Temperature Water

Corrosion mitigation techniques specifically developed for the vessel internals of boiling water reactors (BWRs) such as hydrogen water chemistry (HWC), catalytic coatings, and inhibitive coatings have been studied and/or adopted worldwide in the past decade. The common goal of these techniques is to mitigate intergranular stress corrosion cracking in the vessel internal components of BWRs. For enhancing the effectiveness of HWC through a more effective reduction in electrochemical corrosion potential accompanied by a lower hydrogen consumption rate or even without any added hydrogen, the technique of inhibitive treatment on structural component surfaces was brought into consideration. In the current study, surfaces of preoxidized square-disk specimens made of Type 304 stainless steel (SS) were treated with zirconium oxide (ZrO2) (particle sizes of 0.7 μm and 0.1 μm) via hydrothermal deposition at either 90 or 150°C for 7 or 14 d, while some preoxidized specimens remained untreated. The concentration of the treating solution was maintained at either 10 parts per million (ppm) or 122 ppm (1mM) during the ZrO2 deposition processes. Electrochemical polarization analyses at 288°C were conducted to characterize the electrochemical properties of the treated and untreated SS specimens in pure water with either dissolved oxygen or dissolved hydrogen. It was found that a smaller particle size, a longer treating time, a lower treating temperature, as well as a higher treating solution concentration seemed to improve the corrosion resistance of the treated specimens in oxygenated environments and to moderately deter the hydrogen oxidation rate on the specimens.

Evaluation of the mitigation effect of hydrogen water chemistry in BWRs on the low-frequency corrosion fatigue crack growth in low-alloy steels

The mitigation effect of hydrogen water chemistry (HWC) on the low-frequency corrosion fatigue crack growth behaviour of low-alloy steels was investigated under those critical boiling water reactor (BWR) system conditions, where fast corrosion fatigue crack growth significantly above the ASME XI ‘wet’ reference fatigue crack growth curves was observed under normal water chemistry conditions (NWC). The experiments were performed under simulated BWR conditions at temperatures of 250, 274 or 288°C. Modern high-temperature water loops, on-line crack growth monitoring (DCPD) and fractographical analysis by scanning electron microscope were used to quantify the cracking response. HWC resulted in a significant drop of low-frequency corrosion fatigue crack growth rates by at least one order of magnitude with respect to NWC conditions and is therefore a promising and powerful mitigation method.

The Efficiency of Noble Metals in Reducing the Corrosion Potential in the Primary Coolant Circuits of Boiling Water Reactors Operating under Hydrogen Water Chemistry Operation

In order to promote the effectiveness of hydrogen water chemistry (HWC) and to achieve a more effective reduction in electrochemical corrosion potential (ECP) in the primary coolant circuits of boiling water reactors (BWRs), the technology of noble metal chemical addition (NMCA) was brought into practice about 10 years ago. NMCA aims at enhancing the oxidation of hydrogen on metal surfaces and lowering the concentrations of the oxidants (oxygen and hydrogen peroxide) via recombination with hydrogen on the catalyzed surfaces, and therefore reducing the corrosion potentials of the structural alloys in a BWR primary heat transport circuit. Previous research indicates that the effectiveness of NMCA in combination with a low HWC might be evaluated via model predictions of the hydrogen-to-oxidant molar ratio (MH/O) in the primary coolant circuit. If the MH/O at a certain location is calculated to be greater than 2, it is justified that the NMCA would be effective in reducing the ECP to much below the critical potential for Intergranular Stress Corrosion Cracking (IGSCC), EIGSCC, of --0.23 VSHE. However, this statement is true only when the recombination efficiency of hydrogen with oxygen and/or hydrogen peroxide at the location of interest is 100%. Otherwise, significant amounts of oxidants may still be present, even with a stoichiometric MH/O of greater than 2. With the aid of a computer model DEMACE, we explored the impact of incomplete recombination and found that the ECP might be reduced under given circumstances, but not to a great extent, and might remain well above EIGSCC. Accordingly, considerable caution should be exercised upon using the MH/O as a sole indicator for evaluating the effectiveness of NMCA with low HWC as a means of mitigating IGSCC in a BWR. An important finding of this study is that it is necessary to quantify the recombination efficiencies of hydrogen with oxygen and/or hydrogen peroxide on the noble metal treated stainless steel surfaces in order to qualify the use of MH/O as an indicator for NMCA effectiveness in the primary coolant circuit of a BWR.

Effect of Hydrogen Water Chemistry on Zircaloy-2 Fuel Cladding and Structure Material Performance

The effects of hydrogen addition to the feedwater on the corrosion and hydrogen uptake performance of Zircaloy-2 fuel cladding tubes, a water rod tube and spacer materials irradiated for four cycles in a BWR were evaluated. The uniform oxide behaviors of the cladding tubes, water rod and spacer materials were not affected by hydrogen water chemistry (HWC) condition. The hydrogen uptake and pickup fractions of the water rod and spacer materials were similar to those of water rods and spacer materials under normal water chemistry (NWC) conditions. As for the fuel rods, in spite of comparably heavy crud deposition, their hydrogen uptake and pickup fractions were clearly lower than the values under NWC conditions. Overall, the results indicated that HWC had no adverse effects on fuel performance.

Effect of Hydrogen Water Chemistry on Zircaloy-2 Fuel Cladding and Structure Material Performance

The effects of hydrogen addition to the feedwater on the corrosion and hydrogen uptake performance of Zircaloy-2 fuel cladding tubes, a water rod tube and spacer materials irradiated for four cycles in a BWR were evaluated. The uniform oxide behaviors of the cladding tubes, water rod and spacer materials were not affected by hydrogen water chemistry (HWC) condition. The hydrogen uptake and pickup fractions of the water rod and spacer materials were similar to those of water rods and spacer materials under normal water chemistry (NWC) conditions. As for the fuel rods, in spite of comparably heavy crud deposition, their hydrogen uptake and pickup fractions were clearly lower than the values under NWC conditions. Overall, the results indicated that HWC had no adverse effects on fuel performance.

The Influence of ZrO2 Treatment on the Electrochemical Behavior of Oxygen and Hydrogen on Type 304 Stainless Steels in High Temperature Water

For enhancing the effectiveness of hydrogen water chemistry (HWC) in boiling water reactors (BWRs) in the aspects of lower hydrogen consumption and of a more effective reduction in electrochemical corrosion potential (ECP), the technique of inhibitive protective coating on structural materials was brought into consideration. The application of inhibitive treatment is aimed at deterring the reduction reactions of oxidizing species occurring on metal surfaces and the oxidation reaction of metals. In the current study, electrochemical polarization analyses at 288°C were conducted to characterize the electrochemical properties of ZrO2 treated and untreated 304 stainless steel specimens in pure water with dissolved oxygen or hydrogen. The polarization results showed that the treated specimens exhibited lower corrosion potentials, corrosion current densities, exchange current densities, and cathodic current densities than the untreated one in high temperature pure water with dissolved oxygen. For the environment with dissolved hydrogen only, reductions in anodic current density and exchange current density were observed, indicating that the ZrO2 treatment also deterred the oxidation reaction of hydrogen. However, in comparison with the data obtained, the ZrO2 treatment seemed to be relatively more effective in inhibiting the oxygen reduction reaction than inhibiting the hydrogen oxidation reaction. One additional beneficial outcome was that the anodic current density of the metal was also decreased, leading to a much lower overall corrosion current density of the ZrO2 treated specimen.

An Improved Model for Assessing the Effectiveness of Hydrogen Water Chemistry in Boiling Water Reactors

For nearly two decades, hydrogen water chemistry (HWC) has been used as a remedial measure to protect boiling water reactor (BWR) structural components against intergranular stress corrosion cracking (IGSCC). In this paper, computer modeling is used to evaluate the effectiveness of HWC for BWRs. The DEMACE computer code, equipped with an updated chemical reaction set, G values, and a Sherwood number, is adopted to predict the chemical species concentration and electrochemical corrosion potential (ECP) responses to HWC in the primary heat transport circuit of a typical BWR. In addition, plant-specific neutron and gamma dose rate profiles are reported. DEMACE is calibrated against the data of oxygen concentration variation as a function of feedwater hydrogen concentration in the recirculation system of the Chinshan Unit 2 BWR.The determinant result for assessing the effectiveness of HWC is the ECP. For a typical BWR/4–type reactor such as Chinshan Unit 2, it is found that protecting the core channel and the lower plenum outlet is quite difficult even though the feedwater hydrogen concentration is as high as 2 ppm, based on the predicted species concentration and ECP data. However, for regions other than those mentioned earlier, a moderate amount of hydrogen added to the feedwater (0.9 ppm) is enough to achieve the desired protection against IGSCC.

Evaluation of Effectiveness of Hydrogen Water Chemistry for Different Types of Boiling Water Reactors

Short period tests of hydrogen water chemistry (HWC) were carried out at Tsuruga-1 and Tokai-2 Nuclear Power Plants. The effects of HWC at Tsuruga-1, a non-jet pump plant, are larger than those at Tokai-2, a jet pump plant; this is caused by the much higher recombination rate of hydrogen and oxygen at the downcomer region under suitable gamma ray irradiation for the former. The effective oxygen concentrations ([O2]eff=[O2] + 1/2[H2O2]) in water measured at the reactor pressure vessel bottom are suppressed by HWC as effectively as those concentrations at the recirculating lines in both plants.The effects of HWC in both plants were analyzed and compared with literature data on HWC to evaluate the differences in the effectiveness of HWC as caused by reactor type. From the evaluation, it was concluded that the effectiveness of HWC is much more affected by the power density in the core and the average dose rate at the downcomer than by the reactor type itself. The authors propose an evaluation concept for HWC effectiveness. This is the recombination factor, which is defined as a function of dose rate factor at the downcomer.

Evaluation of Effectiveness of Hydrogen Water Chemistry for Different Types of Boiling Water Reactors.

Short period tests of hydrogen water chemistry (HWC) were carried out at Tsuruga-1 and Tokai-2 Nuclear Power Plants. The effects of HWC at Tsuruga-1, a non-jet pump plant, are larger than those at Tokai-2, a jet pump plant; this is caused by the much higher recombination rate of hydrogen and oxygen at the downcomer region under suitable gamma ray irradiation for the former. The effective oxygen concentrations ([O2]eff=[O2] + 1/2[H2O2]) in water measured at the reactor pressure vessel bottom are suppressed by HWC as effectively as those concentrations at the recirculating lines in both plants. The effects of HWC in both plants were analyzed and compared with literature data on HWC to evaluate the differences in the effectiveness of HWC as caused by reactor type. From the evaluation, it was concluded that the effectiveness of HWC is much more affected by the power density in the core and the average dose rate at the downcomer than by the reactor type itself. The authors propose an evaluation concept for HWC effectiveness. This is the recombination factor, which is defined as a function of dose rate factor at the downcomer.

Susceptibility of Sensitized Type 304 Stainless Steel to Intergranular Stress Corrosion Cracking in Simulated Boiling-Water Reactor Environments

Abstract Slow strain rate tests (SSRT) were conducted to evaluate the mitigating effect of hydrogen water chemistry (HWC) on intergranular stress corrosion cracking (IGSCC) of sensitized type 304 (UNS S30400) stainless steel (SS) used for in-reactor components of boiling-water reactors (BWR). The in-reactor environment was simulated by controlling water chemistry parameters such as dissolved oxygen (DO), dissolved hydrogen (DH), hydrogen peroxide (H2O2), and corrosion potential (Ecorr). Effects of the products of water radiolysis on SCC behavior were examined in the presence of a γ-radiation field. IGSCC susceptibility of sensitized type 304 SS decreased with decreasing concentrations of DO and H2O2, which suggested IGSCC of sensitized type 304 SS could be mitigated even in the in-reactor environment under HWC conditions. IGSCC susceptibility clearly was dependent upon Ecorr, as controlled by the concentrations of stable radiolytic products (e.g., O2, H2O2, and H2), regardless of short-lived radicals gene...

Chemical Behavior of Radioiodine in Boiling Water Reactor Systems II: Effects of Hydrogen Water Chemistry

The investigation of the chemistry and steam transport behavior of radioiodine in boiling water reactors has been extended to four more reactors during fullscale hydrogen water chemistry (HWC) tests. Under the reducing coolant chemistry environment, most of the radioiodine was found in the iodide (I-) form. The iodine steam carryover was found to increase in varying degree under HWC conditions in two reactors and was practically unchanged in the other two reactors. The variations in radioiodine chemical forms and steam carryover are discussed in terms of radiolytic reactions, and the effect of copper ions in the reactor water is qualitatively evaluated. The effect of HWC on radioiodine transport is not significant.

Pourbaix Diagrams for Mixed Metal Oxides — Chemistry of Copper in BWR Water

Abstract Thermodynamic information for copper compounds and aqueous species, including estimated values at elevated temperatures, is analyzed. Potential-pH diagrams (Pourbaix diagrams) for the CuH2O, FeH2O, and FeCuH2O systems are presented, and the solubilities of copper and iron oxides (including mixed copper-iron oxide) are evaluated. These results are used to interpret the observed precipitation of oxides on boiling water reactor (BWR) fuel and to estimate the effect of hydrogen water chemistry on their behavior.