Baromembrane method for analysis of ultra-low concentrations of radionuclides in water samples

Abstract

This paper demonstrates the use of the baromembrane method for measuring ultra-low concentrations of radionuclides in water of freshwater reservoirs. The relevance is due to the need to determine radionuclides introduction into water cooling ponds used by enterprises of nuclear fuel cycle. Radionuclides of natural and technogenic origin, not associated with enterprise discharge, are always present in water cooling ponds, forming a natural or technogenic altered background. Its presence often makes it difficult to identify contribution of enterprise’s discharge to water activity, since routine monitoring methods are characterized by a very high detection limit for radionuclides. Traditional methods for determining background radionuclides concentrations require sampling of at least 500 L of water, followed by their evaporation to get a dry residue. This procedure takes at least 5 days. It is possible to reduce time and energy spent on vaporizing hundreds of liters of water by pre-concentrating radionuclides in a smaller sample volume with the baromembrane method. To demonstrate this method, a portable installation with osmotic membranes was used being characterized with initial productivity of 6.0 L·min−1. The osmotic membranes separate source water sample into two components: demineralized permeate and concentrate, containing radioactive substances. This method allows preliminary concentration of water samples from 500 to 20 L in 10–15 hours with minimal losses of radionuclides (time period depends on water mineralization level). The method is universal; it can be used for concentration of dissolved salts of any heavy metals and other organic compounds. It allows preparation of water countable samples in much shorter time that traditional method (evaporation).