Analytical tests to study potential chemical effects on sump clogging
Résumé
During a
lost of coolant accident (LOCA) involving a breach in the primary circuit of a nuclear power
plant, debris are generated from insulation materials and concrete relatively quickly around the primary
break and can be partially transported to the containment spray system and safety injection circuit ( RIS
EAS filter in the sump located at the bottom of the reactor containment. These debris can contribute to
the “physical” and potentially “chemical” clogging of these fi lters. The “chemical” contribution
corresponds to the formation /aggregation of precipitates/gels inside the fibrous bed leading to a decrease
in the porosity of the filter bed . The formation of these precipitates results from the presence in solution
of ions following the dissolution of the debris . To be able to understand such complex coupled
phenomena , it is essential to better characterize the “chemical” clogging. The object ive of th is work is
to study th e origin, nature and influential parameters of the chemical effects and their extent, in order to
determine critical species concentration thresholds, below which the risk of chemical clogging is not
proven.
The first part co
nsists of the study under “static” conditions of the formation of the precipitates likely
to occur in a LOCA situation in the boric/soda buffer . To start, dissolution tests of the debris that can be
generated in case of LOCA were carried out. The objecti ve was to determine the dissolution kinetics of
the elements of interest (calcium ( Ca), silicon ( and aluminum ( Al)). It appears that the silicon
contribution in the recirculating water would come mainly from the fibers and the calcium input from
the concrete. The first tests focus ing on the reactivity between Si, Ca, Na and B showed the presence of
a precipitate/gel at concentrations of Si and Ca respectively higher than 300 and 50 mg/L. A temperature
effect was recorded since below 45/50 C no precipitate was observed . In the near future, XPS, DRX
and ToF SIMS surface analyses will be performed on the se precipitates/gels in an attempt to identify the
nature/structure of the precipitates. However, based on the literature review, it is likely that the
precipitates/gels obtained in the H 3 BO 3 /NaOH matrix are either calcium borates sodium borates
calcium carbonates or silicon oxide . These static tests will soon be completed by recirculation tests in
the COPIN (Clogging Of sumPs In the Nuclear in dustry) medium scale experimental loop , which will
b e operational in early 2021.