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The deposition of corrosion products in the core causes CRUD (corrosion related unidentified deposit) induced power shift and CRUD induced localized corrosion, threatening the safety and economy of the reactor. Zinc addition is regarded as a widely used method to effectively alleviate corrosion product deposition in reactor core. Despite the wide spread use of zinc, the understanding of mass balance, thermodynamic equilibrium and kinetic substitution of zinc in the primary circuit is still not clear. This paper focuses on the balance and thermodynamic kinetic behaviors of zinc in the primary circuit from the perspectives of theoretical mechanism and numerical calculation analysis. A mass balance model of zinc in the primary circuit was established to evaluate the addition, removal, deposition, precipitation and substitution of zinc in the primary circuit. The thermodynamic equilibrium and substitution kinetics of zinc in coolant were also evaluated. Theoretical analysis shows that zinc in the coolant is involved in hydrolysis and chemical reactions with iron, nickel, silicon and other elements. Zinc mainly exists in the form of zinc hydroxide under the prototypical conditions of coolant water chemistry. When zinc replaces the iron and nickel elements in the oxide corrosion layer, it tends to replace the divalent ions at the tetrahedral positions in the normal spinel, and the ability of zinc to replace the divalent ions in the inverse spinel needs to be evaluated in combination with the hydrolysis and chemical equilibrium of zinc. Numerical analysis shows that the mass balance prediction results of the model are in good agreement with the observation value from Diablo Canyon 1 reactor plant. Gradually reducing zinc addition amount is an effective means to maintain the zinc concentration in the specific optimal range. Zinc addition can effectively alleviate corrosion release up to about 50% and the thickness of CRUD deposition after zinc addition is 42% of that before zinc addition. This study can provide theoretical support to develop the optimal zinc addition technique.

The unique crystalline structure and strong covalent bonding of TiB2 coating give it ultra-high hardness and chemical stability, but it also suffers from poor toughness and weak bonding with metal substrates. Herein, Ni-doped TiB2 coating was prepared by combining high-power pulse magnetron sputtering technology and radio frequency magnetron sputtering technology. Additionally, SEM, EPMA, XRD, XPS, nanoindentation instrument, scratch tester, high-temperature friction and wear testing machine were used to comparatively study the micromorphology, chemical composition, phase structure, mechanical properties, and tribological properties of TiB2-Ni coatings with different Ni contents. Results showed that the Ni-doped TiB2-Ni coating possessed a small amount of Ni element solidly dissolved in the TiB2 lattice, and the excess Ni element existed in the form of a metallic phase, forming a nanocomposite structure at the grain boundaries, which restricted the growth of TiB2 grains, and caused the refinement and nanometerization of the columnar grains of the coating. Besides, the Ni doping brought about a significant decrease in the hardness and elastic modulus of the TiB2 coatings. With the increase of the Ni content, the adhesion strength between the coating and the substrate and the toughness of coatings continuously increased, while the friction coefficient of the coating decreased first and then increased. Moreover, the wear morphology indicated the wear of the coating belonged to abrasive wear and adhesive wear. In conclusion, Ni doping improved the toughness of the TiB2-Ni coatings by generating Ni metal phase in the grain boundaries, which could absorb the fracture energy through deformation during crack expansion. The TiB2-Ni coating with a Ni content of 4.9% (atomic fraction) exhibited good hardness and toughness.