Interaction of melt components with zirconium dioxide ceramic

Conclusions The interaction rate of zirconium dioxide ceramic at ∼2300 K depends on the composition of the gas environment (partial pressure of oxygen), the ratio of the oxide and metal phases of the melt (especially iron oxides and zirconium), and the porosity. The temperature distribution affects the region where the zirconium dioxide interacts with the oxides. The region of the ceramic penetrated by the oxides of nickel, titanium, and chromium is larger under isothermal conditions than for a temperature gradient of 100 deg/mm. These research results can be used to estimate the mass of the ceramic trap for a major accident in air. In this case erosion of the ceramic is determined by the iron oxide. The experimental data also show that the mass of a ceramic trap should be at least five times larger than the mass of iron oxide. This relationship is independent of time, but it can be changed due to the superposition of effects from the interaction of all the melt materials with the ceramic. Ceramic samples 20 mm diameter and 10 mm thick did not break down in a temperature gradient of 100 deg/mm at a heating rate of 200 deg/min with natural cooling. Because the erosion of the two types of zirconium dioxide ceramic by metal oxide melts was the same, it may be possible to use cheaper ceramics with calcium oxide stabilizers. Materials Research Center, Technology Novosiberian Department, United Institute of High Temperatures of the Academy of Sciences (NITs TIV NO IVTAN). Translated from Atomnaya énergiya, Vol. 81, No. 6, pp. 468–471, December, 1996.     

Interaction of a model melt of a reactor core with zirconium dioxide ceramic with different porosity

The results of an experimental investigation of the interaction of zirconium dioxide ceramic with different porosity with a model composition of a core melt are presented. The experiments were performed with melt composition (in mass%) UO₂ 46.6, ZrO₂17.6, and Fe₂O₃ under isothermal conditions at 1800°C in an argon atmosphere. Data were obtained on the rate of erosion of the dense ceramic, the character of the permeation of the pores and the pore morphology, and the distribution of the melt elements along the height of the porous layer, 11 figures, 1 table, 3 references. Deceased. Russian Science Center “Kurchatov Institute.” Translated from Atomnaya énergiya, Vol. 88, No. 4, pp. 266–277, April, 2000.     

Behavior of plasma-sprayed zirconium dioxide ceramic under the thermochemical effect of components of the reactor core melt

Conclusion The investigations have shown that, even though the zirconium dioxide layer sprayed on the metal interacts considerably with molten oxides of other metals (Fe, Ti, Ni), forming a porous loose structure, the saturation zone even with air cooling (not to mention water cooling) of the cold surface does not reach the metal, i.e., a considerable part of the zirconium dioxide remains integral and capable of transmitting large heat fluxes with no substantial damage. That attests to a promising outlook for the construction of a protection refractory layer of both an external and in-reactor core catcher by plasma-spraying ceramic onto a metal substrate. NITs TIV OIVT RAN. Translated from Atomnaya énergiya, Vol. 85, No. 2, pp. 115–119, August, 1998.     

Shock-wave deformation and fracture of zirconium dioxide ceramic and concrete

It is noted that interest has increased in refractory materials such as zirconium dioxide ceramic and concrete for use as linings of traps for the melt of a reactor core. The shock-wave profiles are investigated under dynamic conditions, the dynamic strength is determined, and comparative experiments are performed to investigate the spallation resistance of these materials. It is noted that damping properties of ceramic are manifested: this is the reason why ceramic is more resistant to spallation than concrete. 5 figures, 3 tables, and 14 references. Translated from Atomnaya énergiya, Vol. 88, No. 2, pp. 113–119, February, 2000.     

Fluid-solid interaction of reactor core components, a preliminary analysis

A simple analytical model is used to examine the mechanical interaction of LMFBR core components with the surrounding coolant. Approximating a subassembly duct by a single degree of freedom oscillator and the coolant by a thin layer of viscous fluid, the problem was reduced to a nonlinear differential equation governing the motion of the oscillator. Approximate analytical and numerical solutions are presented which enable parametric studies useful in LMFBR core design.     

Modelling of heat and mass transfer processes during core melt discharge from a reactor pressure vessel

The objective of this paper is to study the heat and mass trasnfer processes related to core melt discharge from a reactor vessel in a light water reactor severe accident. The phenomenology modelled includes the convection in, and heat transfer from, the melt pool in contact with the vessel lower head wall, the fluid dynamics and heat transfer of the melt flow in the growing discharge hole and multi-dimensional heat conduction in the ablating lower head wall. A research programme is underway at the Royal Institute of Technology (Kungliga Tekniska Högskolan, KTH) to (1) identify the dominant heat and mass transfer processes determining the characteristics of the lower head ablation process: (2) develop and validate efficient analytical/computational models for these processes; (3) apply models to assess the character of the melt discharge process in a reactor-scale situation; (4) determine the sensitivity of the melt discharge to structural differences and variations in the in-vessel melt progression scenarios. The paper also presents a comparison with recent results of vessel hole ablation experiments conducted at KTH with a melt simulant.     

Electrorefining of metallic fuel with burn-up of ~7 at% in a LiCl-KCl melt

Electrorefining of irradiated metallic fuels (burn-up ~ 7 at%) in a LiCl-KCl melt at 773 K was successfully demonstrated: Actinides in the fuels were anodically dissolved in the melt. Both a selective U metal deposition on a solid cathode and a grouped recovery of actinides, U, Pu, Np, Am, and Cm, in a liquid Cd cathode were confirmed. The behavior of fission products, such as lanthanides, alkali metals, alkaline earth metals, and noble metals, were also investigated. It was found that the behaviors of actinides and fission products in the electrorefining of the fuels with ~ 7 at% burn-up were similar to those in electrorefining of fuels with ~ 2.5 at% burn-up.     

Thermal stability of the lining in a zirconium dioxide trap in a major accident

Test results are presented on the thermal stabilities of specimens and full-scale components (bricks) made of a new ceramic based on zirconium dioxide. The thermal resistance has been improved by using a certain ratio of coarse-grained and fine-grained fractions. The resistance has been determined by the use of single or repeated heating and cooling cycles. The data give a forecast of the resistance when these components are used in the coating of a trap subject to the action of molten core material in major nuclear power station accidents. Research Center, Tomsk Division, Combined High Temperatures Research Institute, Russian Academy of Sciences. Translated from Atomnaya énergiya, Vol. 87, No. 2, pp. 140–144, August, 1999.     

Interaction of self-interstitials with oxygen atoms in electron-irradiated zirconium

High purity zirconium and dilute zirconium-oxygen alloys (200–600 at ppm) were irradiated at temperatures between 10 and 191 K with 3 MeV electrons. From resistivity recovery and damage rate measurements, the interaction of migrating zirconium interstitials with oxygen was determined. The analysis of the data shows that oxygen atoms do not trap self-interstitials in zirconium.     

Design of a supercritical water-cooled reactor with a three-pass core arrangement

The Supercritical Water-cooled Reactor (SCWR) is one of the six concepts of the Generation IV International Forum. In Europe, investigations have been integrated into a joint research project, called High Performance Light Water Reactor (HPLWR). Due to the higher heat up within the core and a higher outlet temperature, a significant increase in turbine power and thermal efficiency of the plant can be expected.Besides the higher pressure and higher steam temperature, the design concept of this type of reactor differs significantly from a conventional LWR by a different core concept. In order to achieve the high outlet temperature of over 500 °C, a core with a three-step heat up and intermediate mixing is proposed to keep local cladding temperatures within today's material limits. A design for the reactor pressure vessel (RPV) and the internals has been worked out to incorporate a core arrangement with three passes. All components have been dimensioned following the safety standards of the nuclear safety standards commission in Germany. Additionally, a fuel assembly cluster with head and foot piece has been developed to facilitate the complex flow path for the multi-pass concept. The design of the internals and of the RPV is verified using mechanical or, in the case of large thermal deformations, combined mechanical and thermal stress analyses. Furthermore, the reactor design ensures that the total coolant flow path remains closed against leakage of colder moderator water even in case of large thermal expansions of the components. The design of the RPV and internals is now available for detailed analyses of the core and the reactor.