Method for removing contaminant material from a contaminated article comprising contacting the contaminated article with a reactive cleaning fluid comprising water and an oxidant material at a temperature at or above the critical temperature of the reactive cleaning fluid and a pressure at or above the critical pressure of the reactive cleaning fluid, oxidizing at least a portion of the contaminant material to yield a cleaned article and a product mixture comprising unreacted reactive cleaning fluid and removed contaminant material, and separating the product mixture from the cleaned article.