Abstract
During the operation of a nuclear power plant (NPP), a
significant amount of ruthenium is built up in the fuel
as a product of the nuclear fission. The importance of
ruthenium from the radiological point of view is mainly
due to the isotopes 103Ru and 106Ru with half-lives of
39.35 days and 373.5 days, respectively. When ruthenium
is released from the fuel to the environment in a severe
NPP accident, these ruthenium isotopes cause a radiotoxic
risk to the population both in a short and long term by
building-up to the human body and external exposure to
the radiation, thus possibly leading to a development of
cancer.
The transport of ruthenium through a reactor coolant
system (RCS), after being released from the fuel, has
been investigated in several experimental programmes
recently. The VTT Ru transport programme has shown that
the release of Ru from RuO2 powder was dependent on the
oxygen partial pressure in air-steam atmospheres at 827,
1027, 1227 and 1427 °C. The highest fraction of gaseous
RuO4 at the outlet of the model primary circuit was
observed at 1027 °C oxidation temperature. At higher
temperatures, ruthenium transported mainly as RuO2
aerosol. In the experiments of RUSET programme it was
observed that the presence of other FPs, e.g. BaO and
CeO2, as mixed with the metallic Ru precursor when the
sample was oxidized at 1100 °C, decreased the fraction of
gaseous RuO4 in the outlet air over the stainless steel
surface compared to the pure Ru oxidation. It was also
shown that the transport of RuO4 was dependent on the
surface material in the coolant circuit. In both VTT and
RUSET programmes it was noticed, that the partial
pressure of RuO4 reaching the outlet of model primary
circuit was in the range of 10-7 to 10-6 bar, which is
significantly higher than what is expected based on
thermodynamic equilibrium calculations.
As the previous studies have mainly been conducted in
pure air-steam atmospheres, the current study was
dedicated to air ingress conditions with representative
airborne fission product/control rod (Ag) and air
radiolysis (NOx) species which were mixed with vaporized
Ru oxides. The aim was to study the impact of these
additives on the transport of ruthenium as gas and
particles through the primary circuit of nuclear power
plant in a severe accident. As a main outcome, the
transport of gaseous ruthenium through the facility
increased significantly when the oxidizing NO2 gas was
fed into the atmosphere. The feed of pure silver
particles into the gas flow showed a significant decrease
in gaseous RuO4 reaching the outlet of the facility.
Simultaneously, a noticeable increase of ruthenium in
form of RuO2 trapped on the filter was observed. When
both silver aerosol and NO2 in form of AgNO3 compound
were fed into the atmosphere, the transport of ruthenium
in gaseous and aerosol forms was promoted. Based on
experiments it was concluded that the composition of
atmosphere in the primary circuit will have a notable
effect on the speciation of ruthenium transported into
the containment building during a severe accident.
Original language | English |
---|---|
Title of host publication | Proceedings of NENE 2016 |
Number of pages | 13 |
Publication status | Published - 2016 |
MoE publication type | A4 Article in a conference publication |
Event | 25th International Conference Nuclear Energy for New Europe, NENE 2016 - Portoroz, Slovenia Duration: 5 Sept 2016 → 8 Sept 2016 |
Conference
Conference | 25th International Conference Nuclear Energy for New Europe, NENE 2016 |
---|---|
Abbreviated title | NENE 2016 |
Country/Territory | Slovenia |
City | Portoroz |
Period | 5/09/16 → 8/09/16 |
Keywords
- severe accident
- source term
- ruthenium
- RCS
- air radiolysis