NobleChem™ is a technology developed by General Electric to reduce stress corrosion cracking (SCC) in reactor internals and recirculation pipes of boiling water reactors (BWRs) while preventing the negative side effects of classic hydrogen water chemistry. Noble metals (Pt, Rh) acting as electrocatalysts for the recombination of O₂ and H₂O₂ with H₂ to H₂O and thus reducing the corrosion potential more efficiently are injected into the feedwater during reactor shutdown (classic method) or on-line during power operation. They are claimed to deposit as very fine metallic particles on all water-wetted surfaces, including the most critical regions inside existing cracks, and to stay electrocatalytic over long periods of time. The effectiveness of this technology in plants still remains to be demonstrated. Based on highly credible laboratory experiments down to the sub-µg · kg^–1 Pt concentration range, SCC mitigation may be expected, provided that a stoichiometric excess of H₂ and a sufficient surface coverage with very fine Pt particles exist simultaneously at the critical locations [1]. Very little is known about the deposition and (re-)distribution behaviour of the Pt in the reactor.

For the validation of this technique the research project NORA (noble metal deposition behaviour in BWRs) has been started at the Paul Scherrer Institute (PSI) with two main objectives: (i) to gain phenomenological insights and a better basic understanding of the Pt distribution and deposition behaviour in BWRs; (ii) to develop and qualify a non-destructive technique to characterise the size and distribution of the Pt particles and the local concentration of Pt on reactor components. This paper presents the objectives of the project, the planned work and a brief description of the status of the project.

In the current study numerical analyses of the flow field and mass transport in various fittings were performed using computational fluid dynamics (CFD) methods. Their main aim was defined as the evaluation of the concentration profiles and local mass transport flux characteristics and the investigation of the transport factors affecting the flow-accelerated corrosion (FAC) wear mechanism. The cases studied here include the flow in nozzles and two T type bifurcations. In all cases, a good match between the predictions for the turbulent mass transfer distribution and observations was found. These findings suggest that the mass transfer flux at the wall and transfer coefficient, and thus the FAC rate and location, are in fact primordially determined by the local turbulent concentration and velocity fluctuations near the wall, as given by the turbulent mass transport term and not by the mean axial flow or other hydrodynamic variables to which they are generally linked. Interestingly, the results show that this turbulent mass transfer mechanism explains why FAC can take place even in locations where the local axial flow is relatively low. The approach implemented here seems to satisfactorily predict the mass transfer coefficients and locations prone to single-phase FAC and seems to be straightforwardly applicable to other fittings and geometries.

Corrosion of carbon steel on the steam side of condensers has long been observed by power plant operators, but the mechanism has not been well understood. Characteristics of the corrosion are areas of bare metal resulting from intergranular attack intermixed with black or red iron oxide, condensing high-purity steam with high local velocities, the lowest temperature in the steam cycle, and relative constancy over time in the macroscopic corrosion pattern. Effective mitigation would reduce iron transport into the steam cycle from the condenser, and might also reduce the likelihood of through-wall leaks in the cooling tubes of air-cooled condensers.

Flow-accelerated corrosion (FAC) of carbon steel (CS) piping has been one of the main issues in light-water nuclear reactors (LWRs). Wall thinning of CS piping due to FAC increases the potential risk of pipe rupture as well as the costs for inspection and replacement of damaged pipes. In particular, corrosion products generated by FAC of CS piping can lead to steam generator (SG) tube corrosion and degradation of thermal performance when they enter and accumulate on secondary side of pressurized water reactors (PWRs). To maintain SG integrity by suppressing the corrosion of CS, high pH all-volatile treatment (AVT) chemistry (High-AVT) (feedwater pH 9.8±0.2) was adopted in Tsuruga-2 (1 160 MW PWR, in commercial operation since 1987) in July 2005 to replace the conventional Low-AVT chemistry (feedwater pH 9.3). After adopting High-AVT, the accumulation rate of iron in the SG decreased to one-quarter of that observed under conventional Low-AVT. As a result, the previously declining SG thermal efficiency was improved. However, it has become clear that High-AVT chemistry is ineffective against FAC in the regions where the flow turbulence is much greater.

By contrast, wall thinning of CS feedwater pipes due to FAC has been successfully controlled by oxygen treatment (OT) for long time in boiling water reactors (BWRs). This is due to the fact that the magnetite film formed on CS surfaces under AVT chemistry has a higher solubility and porosity in comparison with hematite film, which is formed under OT. In this paper, the behavior of FAC under various pH and dissolved oxygen concentrations is discussed based on actual wall thinning rates of BWR and PWR plants and on experimental results in a FAC test-loop. It has been established that FAC is suppressed even under extremely low dissolved oxygen concentrations such as 2 µg · kg^–1 under AVT conditions in PWRs. Based on this result, we propose oxygenated water chemistry for PWR secondary systems, as it can mitigate FAC of CS piping without any adverse effects on the SG integrity. Furthermore, the applicability and effectiveness of this concept developed for FAC suppression in PWR secondary systems is discussed based on results of an in-plant test at Tsuruga-2.

Flow-assisted (or -accelerated) corrosion (FAC) is one of the most common failure mechanisms in heat recovery steam generators (HRSGs). FAC risk is affected by boiler water chemistry and design factors. This paper focuses on the effects of design factors, including velocity, impingement, temperature profile, materials of construction, and steam quality. Case studies of several HRSGs with serious FAC damage are provided, including photographs and the design background. These examples emphasize the need for HRSG FAC risk design review, analysis, and monitoring.

In 2009, Consolidated Edison's East River heat recovery steam generator units 10 and 20 both experienced economizer tube failures which forced each unit offline. Extensive inspections indicated that the primary failure mechanism was flow-accelerated corrosion (FAC). The inspections revealed evidence of active FAC in all 7 of the economizer modules, with the most advanced stages of degradation being noted in center modules. Analysis determined that various factors were influencing and enabling this corrosion mechanism. Computational fluid dynamics and full-scale air flow testing showed very turbulent feedwater flow prevalent in areas of the modules corresponding with the pattern of FAC damage observed through inspection. It also identified preferential flow paths, with higher flow velocities, in certain tubes directly under the inlet nozzles. A FAC risk analysis identified more general susceptibility to FAC in the areas experiencing damage due to feedwater pH, operating temperatures, local shear fluid forces, and the chemical composition of the original materials of construction. These, in combination, were the primary root causes of the failures. Corrective actions were identified, analyzed, and implemented, resulting in equipment replacements and repairs.