Abstract
Ruthenium is a semi-volatile element existing as a
fission product in nuclear reactor fuel that can be
released in case of a severe nuclear accident. This
release is promoted by air ingress, high humidity, high
temperature and oxidative conditions in the reactor
containment when the consistency of primary circuit is
lost. In the severe accident conditions, ruthenium will
be released from the fuel in form of volatile oxides RuO3
and RuO4. According to thermodynamic equilibrium
calculations, 91% of ruthenium will be released in form
of RuO3 and 9% in form of RuO4 in dry air at 1500 K. When
the temperature in primary circuit drops under 1000 K,
RuO3 readily decomposes to solid RuO2. Therefore,
ruthenium will be transported to the containment mainly
in form of RuO2 aerosols and gaseous RuO4.
In this work, the impact of gaseous atmosphere
composition on the transport of ruthenium through a model
primary circuit was examined. The first experiments were
conducted in an air atmosphere at 1500 K. In these
experiments impact of humidity on the release and
transport of ruthenium species was examined. In the
following experiments, additional silver nanoparticles
were used to simulate aerosols transporting in the
primary circuit. Furthermore, the impact of NO2 gas, as a
product of air radiolysis, was also examined.
The amount of ruthenium transported both as gas (RuO4)
and aerosol was quantified with use of neutron activation
analysis method. The number size distribution and total
number and mass concentrations of the formed aerosol
particles were monitored online during experiments.
Chemical composition of ruthenium species was evaluated
by XPS and Raman spectroscopy techniques.
Chemical speciation of the transported aerosols was
concluded to be RuO2 in all performed experiments.
Transported gaseous ruthenium was trapped in sodium
hydroxide solution. The solution was then analysed with
use of UV-VIS spectroscopy. Obtained absorbance spectra
showed peaks typical for ruthenium in oxidation state
+VII. This is a strong indication that the transported
gaseous ruthenium was in form of RuO4, which got reduced
in the hydroxide solution.
Tests of humidity impact on the ruthenium transport at
1500 K showed lower amount of RuO4 transported through
the circuit when compared with dry conditions.
Introduction of silver particles into the model primary
circuit led to a decreased transport of gaseous RuO4 but
to an increased amount of aerosols (RuO2). The transport
of gaseous ruthenium through the circuit increased
significantly, when NO2 gas was mixed with the airflow.
Addition of both silver particles and NO2 to the airflow
promoted also the transport of ruthenium. It was
concluded that the composition of gaseous atmosphere in
the primary circuit has a significant effect on the
amount and chemical form of ruthenium transported to the
containment during a severe accident.
Original language | English |
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Publication status | Published - 2015 |
Event | 7th Conference on Severe Accident Research, ERMSAR 2015 - Marseille, France Duration: 24 Mar 2015 → 26 Mar 2015 Conference number: 7 http://www.sar-net.eu/sites/default/files/flyer_ermsar2015.pdf (ERMSAR 2015) |
Conference
Conference | 7th Conference on Severe Accident Research, ERMSAR 2015 |
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Abbreviated title | ERMSAR 2015 |
Country/Territory | France |
City | Marseille |
Period | 24/03/15 → 26/03/15 |
Internet address |
Keywords
- ruthenium
- air radiolysis
- severe accident
- source term
- primary circuit
- nuclear power plant