Removal and Containment of High-Level Radioactive Polonium From Liquid Lead-Bismuth Coolant

Abstract

The channels of polonium nuclide formation in lead-bismuth target irradiated by high energy protons and secondary neutrons are considered. Under off blanket condition the activity of 200po -210Po, as well as the fission and spallation product activity are calculated for 15 MW target after 1 year operation. Polonium separation methods, including removal using alkaline extraction, vacuum sublimation, and so-called carrier method are analyzed. The engineering design for experimental apparatus to test polonium removal and containment using alkaline extraction using tellurium as a chemical analog of polonium is developed. The necessary degree of polonium removal to keep concentration below levels appropriate to meet the US and Russia safety standards is estimated. Comparative analysis of alkaline extraction and vacuum sublimation techniques from the viewpoint to achieve the necessary removal depth is carried out.

Alkaline extraction of polonium from liquid lead bismuth eutectic

“…Compared to the inert gases, a clearly lower extraction ratio of %20% was found for O 2 and air, which is in agreement with earlier works [13,15] on the extraction of polonium from Bi and tellurium from LBE. No significant difference in Po extraction ratios could be measured between both gases within the limits of error.…”

“…The use of this pyrochemical technique for decreasing the polonium activity, especially in LBE cooled reactors, was later proposed in [15] suggesting the use of an equimolar mixture of NaOH and KOH. With a melting temperature of 180°C this eutectic allows extraction at significantly lower temperatures than was reported in earlier scientific papers.…”

“…With a melting temperature of 180°C this eutectic allows extraction at significantly lower temperatures than was reported in earlier scientific papers. Experimental studies in [15] and later works [16,17] have, however, only used tellurium as a polonium surrogate in LBE. Having similar chemical behaviour, tellurium may serve as a chemical analogue for polonium without emitting hazardous radiation.…”

Removal of polonium from stainless steel surface contaminated by neutron irradiated lead-bismuth eutectic

“…To prevent the hazard, the measure for polonium contamination should be established. Some methods for removal of polonium from neutron irradiated LBE have been proposed and investigated (Yefimov et al, 1998;MacDonald and Buongiorno, 2001). For removal of polonium from material surface contaminated by neutron irradiated LBE, baking method has been investigated (Obara et al, 2003;Miura et al, 2004).…”

Polonium release from an ATW burner system with liquid lead-bismuth coolant

“…In a pool-type ATW burner, LBE coolant spill (as analyzed before [ 11) is much more unlikely than in a boiler-type reactor. However, Po can accumulate in the cover gas space and other parts of the gas system.…”