Treatment of low level liquid waste by an in-situ freezing-melting process

This paper is to present the results of an initial study of applying a new purification process for the treatment of low level liquid waste (LLLW) pro duced by nuclear power plants, the so-called in-situ freezing-melting proce ss. In order to purify the liquid waste, the wastewater is first frozen to form clean ice. The clean ice is then melted to yield purified water that i s allowable to be discharged. The in-situ freezing-melting process utilizes the ice formation of falling film on a vertical wall of ice-former as a wa stewater treatment procedure. A falling film of an aqueous lithium bromide solution (LiBraq) is formed on the inner wall surface as a coolant. The thr ee tested experimental statuses on the outer wall surface include pre-exist ing nucleus of crystallization, no pre-existing nucleus of crystallization, and the affixed fiber grids. The effects of the three experimental statuse s on the amount of ice formation, the degree of purification, and the overa ll heat-transfer coefficient were investigated. The present study found tha t the maximum values of both the amount of ice formation and the degree of purification could be found by varying rhp Reynolds number of wastewater. A lower inlet temperature of wastewater or aqueous lithium bromide solution can increase the amount of ice formation, but causes a decrease in the degr ee of purification. In addition, the pre existing nucleus of crystallizatio n has positive effects on both the amount of ice formation and the degree o f purification. However, when the wastewater is able to wet the outer surfa ce of the wall thoroughly, affixing fiber grids to the surface will, contra rily, cause unfavorable effects on the degree of purification.