On-Line Measurements of the Volatilization of Ruthenium in a Vitrification Process
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ON-LINE MEASUREMENTS OF THE VOLATILIZATION OF RUTHENIUM IN A VITRIFICATION PROCESS R. ODOJ, M. SCHWITZ Institute for Chemical Technology,
Kernforschungsanlage
Julich,
FRG
ABSTRACT The studies were performed using Ru-103 as a tracer. The volatilization of Ru from ruthenium containing liquids, like HAW-solutions, is about 15 %. A chemical denitration of these solutions with HCHO or HCOOH reduces the volatilization to about 2 %. Additional catalytic reduction with Fe-powder lowers the volatilization to about 4 0/oo. The carry over of Ru seems to depend on the aerosol production rate and not the vapor pressure. Only RuO 2 could be detected in the off-gas. INTRODUCTION During nuclear waste treatment, ruthenium is of concern for off-gas treatment, safe re-use of the distilled nitric acid and influence on the crystallization of the glass. Considering the off-gas, ruthenium is not only a radiotoxical problem with its isotopes Ru-103 and Ru-106, but also a technological problem []]. Present nuclear fuel plant processing pratize call for the dissolution of fuel elements in nitric acid. Therefore the Ru-compounds in the liquid phase will have the general formula [2] RuNO(NO 3 )x(OH)3_x(H20)2.yH20. In the presence of strong oxidants, there will be an autoxidation from Ru (III) to Ru (VIII) i.e. RuO4 . RuO4 is thermodynamicaly unstable. The melting point 0 is approximately 25 C and under standard pressure the boiling temperature is approximately JOOC. In contrast to RuO 4 , RuO2 is a very stable compound. Therefore during nuclear fuel waste treatment an attempt is made to reduce RuO4 to RuO 2 . The reduction can be made by catalytic, electrolytic or chemical reduction [3]. The subject of these investigations is the effectivity of the denitration process by use of chemical reducing agents and their relation to the volatility of ruthenium. The following steps of the solidification process were accomplished with radioactive tracers. 1. chemical denitration 2. concentration and drying 3. glazing of the dry product Inactive tests. These tests were necessary to establish the amount of volatile ruthenium and to prove the experimental system, which was made from quartz. A schematic diagram is shown in Fig. 1.
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three-necked vessel with heating jacket 2
Stockthermometer
3
dropping funnel with nressure compensation
4
intensive condenser with spiral tube sealed to body
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condensate collecting tank
6
scintillation counter
7
Ratemeter
8
differential radiation measurement
9
PD-requlator
10
cooling trap
11
lead screen shielding
A
~tt
_ 10
Fig. 1.
Altt
l 10_
Schematic diagram of the experimental system.
In three-necked vessel the rutheniumnitrate-solution (15,6 g Ru(N0 3 ) 3 /1 in 0 5 M HNO3 ) was heated to approximately 90 C. HCHO was added through a dropping funnel in an equimolar amount. To get a constant flow rate, the dropping funnel was pressure compensated. The denitration condensate was collected in a calibrated condensate collecting bottle. could be perceived by the alteration of the diCo
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