Experiments on the leak path factor of ruthenium volatilized from high-level liquid waste tanks in a reprocessing plant in case of the boiling and drying accident

Abstract

In case of the boiling and drying accident of a high-level liquid waste (HLLW) tank, a large amount of ruthenium (Ru) will be volatilized. In order to suppress the release of radioactive materials to the environment, the vapor may be led to the neighboring cells in which it will contact with the cell walls to be partially condensed. To understand the behavior of Ru in this situation, we have prepared an experimental apparatus. It consists of a small tank in which 60 mL simulated HLLW is heated to dryness, a 9.6 L stainless steel box which mimics the neighboring cell accepting the vapor from the small tank, and a condenser where the vapor coming out from the box is cooled to collect the condensate. The results show that more than 99% of the volatilized Ru is removed from the vapor in the box if its temperature is below about 120 • C.

Experimental study of ruthenium volatilization from boiling nitric solution

“…3 The Ru amount released obtained in these tests (2 ± 0.2)% i.i. is consistent with values obtained in Ishio works [14] (4% between 160°C and 400°C), Kodama et al [10] (4.9% up to 400°C), Sawada et al [15] (1.2% with a simpler solution and with a simulated HLLW solution: 1.3% at 140°C and 1.7% at 180°C, with HNO3 2 M) and Nerisson et al [16] (2.3% at 130°C with [HNO3] = 3.5 M and [Ru] = 0.02 M in 700 mL of initial simplified solution) but smaller than the value of 12% reported by Philippe et al [4]. The value of 12% includes fractions of insoluble RuÜ2 (1.7%) deposited on the glass tank wall and soluble Ru recovered from the rinse solution of the glass tube between the glass tank and the condenser (< 3.3%), both measured after the run.…”

“…The value of 12% includes fractions of insoluble RuÜ2 (1.7%) deposited on the glass tank wall and soluble Ru recovered from the rinse solution of the glass tube between the glass tank and the condenser (< 3.3%), both measured after the run. Even if subtracting these values, the remaining value (7%) seems still higher than the value obtained in our study but the smaller temperature and the higher heating rate in our tests could explain the difference observed, as mentioned by Kodama et al [10]. Mass transfer phenomena may also impact this gaseous fraction and they depend on the reactor characteristics and gas flow patterns.…”

“…In the boiling accident, the vapour discharged from the HLLW tanks is assumed to be led to the neighbouring cells, where it is mixed with the ambient air and comes to contact with cold walls, where a significant amount of the vapour would be condensed. Kodama et al [10] studied the fate of the volatilized Ru in the neighbouring cells, along the transfer pathways with a Steel Use Stainless box (9.6 L) and a cooled condenser (15°C). The simulated HLLW solution (60 mL) containing many elements as fission products and ruthenium nitrosyl nitrate in HNO3 (2 M) was heated up to dryness, with a superficial vapour velocity of 0.013 m s-1 corresponding to a decay heat of 5 W L-1.…”

Behaviour of ruthenium in nitric media (HLLW) in reprocessing plants: a review and some perspectives

“…The objective of studies by Kodama et al [72] and Shibata et al [61], carried out on a synthetic prototypic solution (2M acidity, ruthenium concentration 0.09 mol.L-1) is to determine the LPF (Leak Path Factor4) in accident conditions on a FP tank. It aims in particular to determine the temperature where the discharge cell should be maintained in order to fully trap ruthenium.…”

“…In a boiling accident, the vapour discharged from the HLLW tanks is assumed to go to the neighbouring cells, where it is mixed with the ambient air and comes to contact with cold walls, where a significant amount of the vapour could be condensed. Kodama et al [72] studied the fate of volatilized Ru in the neighbouring cells, along the transfer pathways with a Steel Use Stainless box (9.6 L) and a cooled condenser (15°C). The simulated HLLW solution (60 mL) containing many elements as fission products and ruthenium nitrosyl nitrate in HNÜ3 (2 M) was heated to dryness, with a superficial vapour velocity of 0.013 m/s corresponding to a decay heat of 5 W/L.…”