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• In SNB condition, corrosion nodules were detected on zirconium cladding surface. • No discernible differences of zirconium oxide caused by Zn injection were found. • No Zn enrichment in the zirconium oxide was detected. • Thermodynamic analyses verify Zn cannot be incorporated into the ZrO 2 oxide film. The effects of Zn injection on the oxide film characteristics of zirconium alloy fuel cladding were investigated following corrosion tests in borated and lithiated high-temperature pressurized water, with and without subcooled nucleate boiling (SNB). In the absence of SNB, the thickness, elemental distribution and crystallographic detail of the oxide film, weight gain of the cladding specimen were examined. No obvious differences caused by Zn injection were found. In SNB condition, corrosion nodules were found on cladding surface and the crud tended to deposit on these corrosion nodules. However, Zn injection did not obviously affect the density and characteristic of the corrosion nodules. The mechanism of crud deposition on corrosion nodules was discussed. Regardless of SNB implementation, no discernible Zn enrichments in the zirconium oxide, second-phase particles and oxide-metal interface region were found. Thermodynamic analyses further affirmed that Zn cannot be incorporated into the zirconium alloy oxide spontaneously. [ABSTRACT FROM AUTHOR]

BackgroundUnder the condition of sub-cooled nucleate boiling (SNB), corrosion products in primary coolant of nuclear reactor will deposit on the outer surface of fuel cladding, which is commonly called fuel crud. Previous literature shown, zinc injection in primary coolant is an important method to inhibit the fuel crud deposition on the fuel cladding surface.PurposeThis study aims to investigate the influence of zinc concentration on the behavior of fuel crud deposition, and eventually provide guidance for zinc injection in primary coolant of nuclear power plant.MethodsThe fuel crud deposition tests of domestic zirconium alloy fuel cladding in different zinc concentrations were carried out by using a self-made fuel crud deposition device. Tubular crud deposition test specimen with built-in heating unit was designed and prepared for simulation study. After the tests, stereo microscope (SM) and scanning electron microscope (SEM) were employed to observe the macro and micro morphology of fuel crud whilst the composition of of fuel crud was observed and analyzed by the energy dispersive spectroscopy (EDS) with SEM, and X-ray photoelectron spectroscopy (XPS) was used to analyze the contents of Zn and B elements in the crud phase and inside the crud.ResultsObservation results show that the chimney-like crud formed on the fuel cladding surface becomes less obvious with increasing the zinc concentration in the coolant and the crud surface becomes flatter. Simutabeously, the crud thickness, the ratio of Ni/Fe and the boron precipitation mass within the crud are decreasing with increase of the zinc concentration. When the zinc concentration increases to 100 μg‧L-1, new Zn-containing phases precipitate within the crud.ConclusionsWithin the zinc concentration of 0~100 μg‧L-1, zinc injection in primary coolant of reactor can significantly inhibit the crud deposition on the fuel cladding surface.

Cladding failure in a fuel rod during operation in a BWR is analyzed using a FALCON code-based model. Comparative calculation with a neighbouring, intact rod is presented, as well. A considerable ‘hot spot’ effect in cladding temperature is predicted with the SLICE-DO model due to a thermal barrier caused by the localized crud deposition. Particularly significant overheating is expected to occur on the affected side of the cladding of the failed rod, in agreement with signs of significant localized crud deposition as revealed by Post Irradiation Examination. Different possibilities (criteria) are checked, and Pellet-Cladding Mechanical Interaction (PCMI) is shown to be one of the plausible potential threats. It is shown that PCMI could lead to discernible concentrated inelastic deformation in the overheated part of the cladding. None of the specific mechanisms considered can be experimentally or analytically identified as an only cause of the rod failure. However, according to the current calculation, a possibility of cladding failure by PCMI cannot be excluded if the crud thickness exceeded 300 μm.

BackgroundFor a pressurized water reactor (PWR), under the synthesis effects of primary water chemistry, reactor operation mode, system facilities replacement, fuel design and management, the corrosion products in primary coolant will deposit on the outer surface of fuel cladding, which is commonly called fuel crud. Fuel crud formed on the cladding surface may result in crud induced localized corrosion (CILC), crud induced power shift (CIPS) and raise the primary source term. The deposition behavior of fuel crud is affected by both the corrosion products concentration and the core boiling rate.PurposeThis study aims to investigate the influences of core power variation on the corrosion products concentration and the core boiling rate, and eventually evaluate the fuel crud deposition states under different core powers.MethodsThe core crud mass and the maximum crud thickness on fuel cladding surface were estimated by the CAMPSIS, an independent crud behavior analysis software developed by China Nuclear Power Technology Research Institute Co., Ltd (CNPRI). Influence of core power variation and the combined effect of core boiling rate and corrosion product concentration were analyzed.ResultsComputational results that, within the range of 75%⁓100% full power (FP), the lower the core power is, the smaller the core crud mass will be, but the maximum crud thickness will increase. When the core power decreases to 50% FP, the maximum boiling rate is close to zero, and both of the core crud mass and the maximum crud thickness are minimum.ConclusionsThe core power reduction of a nuclear reactor may lead to the increase of local fuel crud thickness, and adversely affect the heat transfer between the fuel cladding and the coolant. It is suggested that the influence of core power reduction on fuel crud deposition should be considered if a nuclear reactor tends to operate at a lower core power.

• Novel method of trace substance transport in a BWR fuel assembly. • Mechanistic model for the influence of disturbance waves developed. • Investigation of underlying reasons of a novel type of zinc-rich CRUD observed at a Swiss nuclear power plant. • Highest trace substance concentration found near locations observed at the power plant. A transport model was developed and numerically solved for trace substances dissolved in the coolant flowing through a complete BWR fuel element. The integration of the trace substance transport equations is carried out on the same computational grid used by a two-phase three-field subchannel code, the output of which provides the necessary coolant mass flow data, including field exchange terms. The results consist of complete, field specific trace substance distributions within the domain of the simulation and with the same spatial resolution as used by the subchannel code. Downstream the onset of annular flow, it was observed that the trace substance concentrations in liquid films on heated rods are significantly higher than the concentrations in droplets and in films on unheated surfaces. A mechanistic model for disturbance waves was further introduced to assess the additional trace substance concentration increase in the time period of base film evaporation between two successive disturbance waves. The highest trace substance concentrations were found next to part-length rods in the corner of the considered fuel assembly just upstream of the two uppermost spacer grids, which approximately corresponds to the location of trace substance deposition observed during fuel inspections at a Swiss nuclear power plant. [ABSTRACT FROM AUTHOR]

The effects of Zn injection on corrosion behavior and crud deposition of FeCrAl fuel cladding in high-temperature pressurized water were investigated under subcooled nuclear boiling condition. The crud deposition and the growth of double-layered oxide films under the crud occurred simultaneously. Zn injection decreased the oxide films thickness and reduced the quantity/size of the outer oxide particles. These effects changed the surface roughness and wettability of the oxide films, resulting in a reduction of deposited crud at the initial stage. Both Zn and released matrix elements could be incorporated into the crud and Zn reduced the size of crud particles. • Crud deposition and corrosion behavior are studied under subcooled nuclear boiling. • Crud deposition and external oxide film growth of FeCrAl alloy occur simultaneously. • Fe, Cr, Al and Mo released from matrix could be incorporated into the crud layer. • Zn-incorporated spinel oxide phases increase corrosion resistance of FeCrAl. • Zn modified surface characters of oxide films on FeCrAl, reducing crud deposition. [ABSTRACT FROM AUTHOR]