Riitta Zilliacus

On the transport and speciation of ruthenium in high temperature oxidising conditions

Summary In this paper, the transport and speciation of ruthenium under conditions simulating an air ingress accident was studied. Ruthenium dioxide was exposed to an oxidising environment at high temperatures (>1200 °C) in a tubular flow furnace. At these conditions, volatile ruthenium species were formed. A major part of the released ruthenium was deposited in the tube as RuO2. Depending on the experimental conditions, 12–35 wt. % of the released ruthenium was trapped in the outlet filter as RuO2 particles. At completely dry conditions using stainless steel tubes, only 0.1–0.2 wt. % of the released ruthenium reached the trapping bottle as gaseous RuO4. However, when alumina was applied as tube material or the atmosphere contained some water vapour and silver seed particles, the fraction of gaseous ruthenium reaching the trapping bottle increased to 5 wt. % which is close to thermodynamic equilibrium. This indicates that RuO2 does not catalyse the decomposition of RuO4.

VAPORISATION RATES OF CsOH AND CsI IN CONDITIONS SIMULATING A SEVERE NUCLEAR ACCIDENT

Abstract The vaporisation rates of volatile fission product compounds are critical parameters for modelling aerosol formation following a severe nuclear accident. The vaporisation of CsOH and CsI was studied in a pure steam atmosphere at ambient pressure (85– 89 kPa ) by increasing the temperature of the flow furnace up to 1000°C. For this purpose, samples were doped with a small amount of radioactive tracer. The vaporisation rate was then determined from the decrease in sample activity with time, using a germanium gamma detector placed outside the furnace. Calculated vaporisation rates obtained by solving complete velocity, temperature and vapour concentration profiles surrounding the sample with FLUENT CFD-software, were in reasonable agreement with the data. A simple engineering calculation agrees almost perfectly with the FLUENT results, if a constant value, Sh≈8, for the Sherwood number is used.

Production and characterization of plutonium dioxide particles as a quality control material for safeguards purposes.

Plutonium (Pu) dioxide particles were produced from certified reference material (CRM) 136 solution (CRM 136-plutonium isotopic standard, New Brunswick Laboratory, Argonne, IL, U.S.A., 1987) using an atomizer system on December 3, 2009 after chemical separation of americium (Am) on October 27, 2009. The highest density of the size distribution of the particles obtained from 312 particles on a selected impactor stage was in the range of 0.7-0.8 μm. The flattening degree of 312 particles was also estimated. The isotopic composition of Pu and uranium (U) and the amount of Am were estimated by thermal ionization mass spectrometry (TIMS), inductively coupled plasma mass spectrometry (ICPMS), and α-spectrometry. Within uncertainties the isotopic composition of the produced particles is in agreement with the expected values, which were derived from the decay correction of the Pu isotopes in the CRM 136. The elemental ratio of Am to Pu in the produced particles was determined on the 317th and 674th day after Am separation, and the residual amount of Am in the solution was estimated. The analytical results of single particles by micro-Raman-scanning electron microscopy (SEM)-energy-dispersive X-ray spectrometry (EDX) indicate that the produced particles are Pu dioxide. Our initial attempts to measure the density of two single particles gave results with a spread value accompanied by a large uncertainty.

Organic iodine chemistry

A shared-cost action on Organic Iodine Chemistry has been completed as part of the CEC 4th Framework programme on Nuclear Fission Safety. Organisations from four EC countries are involved in an integrated programme of experiments and analysis to help clarify the phenomenology, and to increase confidence in the modelling of iodine behaviour in containment. The project is focused on identifying the main routes for organic iodine formation, and providing new experimental kinetic data which will be used to improve existing models and to stimulate code development.

AHMED experiments on hygroscopic and inert aerosol behaviour in LWR containment conditions: experimental results

Abstract Hygroscopic NaOH, CsI, CsOH and inert Ag aerosol behaviour at different temperatures and relative humidities (RH) has been studied in a well instrumented and controlled vessel of 1.81 m3 total free volume. Homogeneous thermal-hydraulic conditions for aerosol measurement in the vessel were achieved. The aerosol number and mass concentration were measured continuously during the experiments using a Condensation Nucleus Counter and a Tapered Element Oscillating Microbalance. The particle size distribution and chemical composition in the test conditions were measured by Berner low pressure impactors. In the case of NaOH the half life of the aerosol mass concentration was more than four times longer at low RH (22%) as compared to high RH (96%). The half lives of the CsOH and CsI aerosols were only twice as long at low RH as compared to high RH. Thus at high RH (96–97%) the half lives of CsOH and CsI were twice as long as the half life for the NaOH aerosol. The faster decay of the NaOH aerosol is due to the smaller density decrease of NaOH during water condensation. CsOH particles grew rapidly to their equilibrium size at all humidities. The measured equilibrium size for CsOH aerosol agree well with the calculated particle size at different RHs. Experimental results were also compared with calculations obtained by severe accident computer codes. These calculated results will be presented in a later paper.

Chlorine release from hypalon cable insulation during severe nuclear reactor accidents

Pyrolytic dehydrochlorination of the electrical cable insulation Hypalon was studied as a function of time and temperature. The chlorine evolution was determined separately by means of on-line activity measurements and by neutron activation analysis in the temperature range 200°C to 300°C, with one test conducted at 500°C. The object of the research was to determine the chlorine release and the chlorine release fraction as a function of temperature. The data obtained were needed to formulate conclusions regarding the release mechanisms of chlorine. Estimates of the amount of hydrochloric acid released to the containment building in a severe reactor accident were also calculated. It can be concluded that the amount of chlorine release from the Hypalon cable is significant and will have an effect on iodine behavior in a severe accident.

Phase evolution and gas-phase particle size distributions during spray pyrolysis of (Bi,Pb)SrCaCuO and Ag(Bi,Pb)SrCaCuO powders

Phase evolution, gas-phase particle size distributions and lead loss were studied during formation of (Bi,Pb)SrCaCuO powders and their composites with silver by spray pyrolysis starting from nitrate solutions. The 10 wt% Ag/90 wt% Bi1.8Pb0.44Sr2Ca2.2Cu3Ox composite powders made at 700°C consisted of 20–60 nm grains of silver and mixed-oxide phases with a fine dispersion of Ag grains within the particles. At 700°C, the primary phases present in (Bi,Pb)SrCaCuO powders were (Bi,Pb)2Sr2CuOx (2201), Ca2PbO4 (plumbate), (Bi,Pb)2Sr2CaCu2Ox(2212), and (Bi,Pb)3Sr2Ca2Cu1Ox(3221). For T≥800°C, the powders were considerably depleted in lead, and the plumbate and 3221 phases were absent. For T = 900°C, a large number of ultrafine particles (<30 nm) were formed, probably from the PbO vapor released from the reactor walls. Using spray pyrolysis, it is easy to control stoichiometry and limit the phase segregation at the nanometer-scale so that homogeneous and phase-pure materials can be obtained rapidly during subsequent processing.

Gas Phase Oxidation of Elemental Iodine in Containment Conditions

The aim of the study was to verify the possible formation of iodine aerosol when gaseous iodine is exposed to radiation. The effect of oxygen, ozone and iodine concentration as well as that of radiation intensity on IOX aerosol formation was determined. Experimental evidence on kinetics of particle formation, growth and transport was gained. Experiments were carried out using EXSI facility at VTT. Gaseous iodine was produced from I2 -KI-water solution and carried into the facility with N2 -O2 mixture. Oxygen concentration was varied between 2–50 %-vol. Due to the production technique flow contained always some humidity. UVC lamps were used as source of ionizing radiation. Ozone concentration was also varied with an ozonator. The reactions took place in a flow furnace heated to 120°C. Reaction and aerosol kinetics were studied by varying the residence time between about 2–7 seconds. The formed particles were collected on filters, after which gaseous iodine was trapped in NaOH-water solution. The amount of iodine in filters and in trapping bottles was analysed with ICP-MS. Particle concentration and size distribution were measured online using aerosol instrumentation. Ozone concentration was measured online with FTIR. The morphology as well as the elemental composition of the particles were analysed with SEM-EDX. The conversion of gaseous iodine to aerosol particles was rapid and almost complete even with low ozone concentration. The fraction of gaseous iodine increased though with decreasing residence time. Diameter of the formed primary particles was approximately 10 nm. Particles grew by agglomeration and by surface reaction. Agglomerate size distribution was log-normal with NMD varying between 60–120 nm. Size of the agglomerates increased and number concentration decreased with increasing residence time. Agglomerate size also increased with iodine concentration. Presence of ozone promoted retention of iodine in the facility probably by surface reaction. Some iodine deposited on surfaces evaporated later and formed particles in the gas stream. According to SEM-EDX analysis, particles deposited on carbon foil contained iodine and oxygen. However, the exact speciation is not known. Particles deposited on copper grids had probably reacted to copper iodide.Copyright