Effect of nitrogen compounds on transport of ruthenium through the RCS

Abstract

Ruthenium is a fission product that can be released from the fuel in case of a severe nuclear accident. In this work the impact of the atmosphere composition, including air radiolysis products, on the transport of ruthenium through a primary circuit was examined. Experiments were performed at temperatures 1300, 1500 and 1700 K in a slightly humid air. In the experiments significant effect of nitrogen oxides (N2O, NO2) and nitric acid on the ruthenium chemistry in the model primary circuit was observed. The obtained results indicate a strong effect of air radiolysis products on the quantity partitioning of transported ruthenium to gaseous and aerosol compounds.

Ruthenium behavior in the reactor cooling system in case of a PWR severe accident: study of oxidative conditions with stainless steel tube

“…With N2O feed, the results obtained with the two studies (IRSN test 10 and test #8 [12], Fig. 10) showed the same tendency, with no influence on the Ru transport at the outlet.…”

“…As for IRSN test 7 with steam, the main difference comes from the nature of the species transported, mainly in aerosols form at the opposite of IRSN result, it is consistent with that VTT facility seems to promote nucleation processes (higher source of Ru and lower outlet temperature). I. Kajan et al [12] observed a decrease of the formation and transport of particles significantly when NO2 gas (75 ppm) was fed. At the same time, the transport of gaseous ruthenium increases by about two orders of magnitude (8.8% of Ru released, test #3) compared to pure air experiment (0.2%, test #2) and total Ru amount transported at the outlet remains similar.…”

“…and the revaporization process (3 % i.i.). So, concerning the N2O feed (test 10), no noticeable effect was observed on the total Ru amount transported at the tube outlet similarly to [12] even if the partition gas/aerosol is a bit different. The gaseous Ru amount was lower, but the Ru deposited into the dipping tube was higher.…”

“…No significant influence was observed on the Ru amount transported at the outlet. Based on previous literature works [12,13], it was assumed that the low concentration of NO2 did not have a significant effect on the Ru vaporization from the crucible. So, for tests performed with the higher flow rate, the NOx feed was done at the entry of the TGT with the flow rate over the crucible of 4.15 NL/min completed by 0.5 NL/min of NO2 feed (50 ppm).…”

Identification of a chemical fingerprint linking the undeclared 2017 release of 106 Ru to advanced nuclear fuel reprocessing

“…To amplify the oxidative power of the mixture, oxidants such as ceric ammonium nitrate can be added to encourage the evolution of the volatile and highly reactive RuO 4 , which can then be driven off with carrier gas and subsequently trapped or passivated. At this early dissolution stage, and later during the vitrification of raffinates, the condensation and decomposition of RuO 4 to relatively inert oxides inside the containment vessels can lead to problems of accumulated dose and accelerated corrosion (14,15,19,20). To address this, considerable investigative effort has been made to remove ruthenium at the fuel dissolution phase (17,21,22).…”