Nanocrystalline diamond protects Zr cladding surface against oxygen and hydrogen uptake: Nuclear fuel durability enhancement

Abstract

In this work, we demonstrate and describe an effective method of protecting zirconium fuel cladding against oxygen and hydrogen uptake at both accident and working temperatures in water-cooled nuclear reactor environments. Zr alloy samples were coated with nanocrystalline diamond (NCD) layers of different thicknesses, grown in a microwave plasma chemical vapor deposition apparatus. In addition to showing that such an NCD layer prevents the Zr alloy from directly interacting with water, we show that carbon released from the NCD film enters the underlying Zr material and changes its properties, such that uptake of oxygen and hydrogen is significantly decreased. After 100–170 days of exposure to hot water at 360 °C, the oxidation of the NCD-coated Zr plates was typically decreased by 40%. Protective NCD layers may prolong the lifetime of nuclear cladding and consequently enhance nuclear fuel burnup. NCD may also serve as a passive element for nuclear safety. NCD-coated ZIRLO claddings have been selected as a candidate for Accident Tolerant Fuel in commercially operated reactors in 2020.

Diamond Coating Reduces Nuclear Fuel Rod Corrosion at Accidental Temperatures: The Role of Surface Electrochemistry and Semiconductivity

“…The obtained results demonstrated that after performance of the hot steam treatment at 900-1000 • C, the uncoated ZIRLO rods exhibited a higher hydrogen concentration (1166 ppm) compared to the ZIRLO rod protected by the diamond coating (164 ppm). The ratio of the hydrogen content in the hot steam-processed-uncoated ZIRLO and ZIRLO rods with diamond coating corresponds well to our previous results-after hot steam (for 1100 • C and 1200 • C) the uptake of hydrogen into uncoated ZIRLO was an order of magnitude higher than in the case of the diamond layer protected ZIRLO rods [19].…”

“…These changes, which strongly depend on the temperature and diamond content in the coating, support and also reduce corrosion of ZIRLO fuel rods. According to our previous accidental temperature tests of polycrystalline diamond coated nuclear rods [19] in 1000 • C hot steam/water (60 min) and in 1100 • C (60 min) and 1200 • C (20 min) hot steam/water, the corrosion of diamond layer coated nuclear tubes was always lower than the corrosion of uncoated rods subjected to the same treatment [19]. In [19,21,24], we presented that the diamond-coated Zr nuclear fuel rods were protected against accidental temperature hot steam/water corrosion due to the fact that the carbon diffused from the diamond coating into ZrO2, changing its physical property of semi conductivity.…”

“…In our recent works, we showed that a water-permeable polycrystalline diamond film (PCD) [ 18 , 19 , 20 , 21 , 22 , 23 , 24 ], which contained more than 95% of diamond and fully covered Zr alloy fuel rods, effectively reduced Zr-alloy nuclear fuel rod hot steam/water corrosion.…”

Kinetic Model of Incipient Hydride Formation in Zr Clad under Dynamic Oxide Growth Conditions

“…However, the high thermal stability of these hydride phases also makes them a matter of concern for reactor safety due to the potential for hydrogen storage and release during loss-of-coolant conditions and core meltdown. Palliative measures such as increasing the enthalpy of formation of δ-ZrH by microstructure tailoring [108], or by hindering H diffusion in Zr oxide by selective alloying in the clad [109,110], have been proposed for future candidate materials in novel nuclear fuel designs.…”

Measuring the Thickness of Metal Films: A Selection Guide to the Most Suitable Technique

“…The theoretical resolution of an optical microscope, not taking into account optical aberrations, using white light, is about 0.2 microns. However, more realistically, the measurement of films with a thickness of less than one micron is difficult and features consistent uncertainty [50][51][52][53].…”