Two types of films were tested and compared for the purposes of film autoradiography. Commercial black and white photographic film proved to have the highest sensitivity and the best resolution. The film was calibrated by specially prepared sources that contained alpha- and beta-emitting isotopes in the form of particles. Application examples for hot particle identification using the developed film autoradiographic technique are given.
Authors:P. Jaracz, E. Piasecki, S. Mirowski, and Z. Wilhelmi
The radionuclide fractionation process in fuel-like hot particles from the fallout after the Chernobyl accident is analyzed. Some processes which can be responsible for different kinds of fractionation of fission products in hot particles and nuclear fuel are suggested. These comprise: evaporation (Cs and Ru), thermal diffusion within fuel rods (visible mostly in Ce) and half-life effects, influencing the spatial dependence of relative content of isotopes of the same element (Ce and Ru). The analysis proves the local origin of hot particles, i.e. the absence of considerable mixing between fission products from different parts of the reactor in the process of hot particle formation.
A particulate form (hot particles) of the radioactive fallout in Poland after the accident at the Chernobyl Nuclear Plant has been studied. Parameters of the effective reactor campaign are obtained from the characteristics of -activity of the hot particles. The numerical INV program written to calculate time evolution of eight isotopes in the reactor is described. On the basis of these calculations the measured hot particles are classified into two groups: those originating from the first load and those from younger fuel rods. A procedure for dating younger hot particles is proposed. The results of the analyses constitute a basis for other investigations of hot particles.
Authors:N. Yanase, H. Isobe, T. Sato, Y. Sanada, T. Matsunaga, and H. Amano
Surface soil samples (0–1 cm) were collected to understand the role of hot particle (HP) in migration of radionuclide approximately 11 years after the Chernobyl accident. Three types of HPs were found by the analyses using alpha-track technique and scanning electron microscopy/energy dispersive X-ray spectrometer (SEM/EDX). The dissolution of HPs has been affected by the existing type of HPs. Six-stage sequential selective extraction procedure was carried out to define the chemical forms of uranium, 241Am and 137Cs. The chemical form of radionuclides in surface soil is significantly different between the west and the north traces of radioactive plumes approximately 11 years after the accident.
Authors:M. Bielewski, M. Eriksson, J. Himbert, M. Betti, F. Belloni, and G. Falkenberg
XANES has been recently used for the determination of oxidation states of actinides in environmental samples. To obtain reliable
results, however, a sufficiently long counting time at every probing energy and a large number of experimental points per
XANES spectrum are required, due to the complex mathematical model used to fit the measured spectrum. This makes micro-mapping
difficult, since the time required for data collection becomes unacceptably long. A simplified model for data collection and
evaluation is presented. Its effectiveness has been tested by measuring the distribution of Pu oxidation states in a “hot”
particle coming from a nuclear weapon test site.
The previously analyzed ruthenium particles from the Chernobyl fallout in Poland have been reexamined in a search for long-lived radioactive components. The established presence of125Sb and60Co reopens the question of particle formation mechanism. It is concluded that ruthenium particles have been formed at the time of accident and most likely outside the fuel rods. A summary of results supporting this conclusion is given.
Elemental composition and uranium isotope ratios for individual hot particles have been obtained by instrumental neutron activation analysis. It has been found that maximum235U enrichment factor in particles (K=3.6; 2.65%235U) does not differ much from the initial value of loaded fuel (K=2.8; 2%235U). From the abundances of fission radionuclides the fuel burn-up, depletion factors of Ru and Cs, and fuel content were calculated.
Authors:V. Kashparov, V. Yoshchenko, S. Levchuk, J. Tschiersch, and F. Wagenpfeil
The method of repeated mixing was applied to soil samples containing hot particles. The results were interpreted using a developed mathematical formulation, which describes the frequency distribution of results in the presence of one or more hot particles in a sample, the statistical characteristics such as mathematical expectancy and dispersion, and includes an approach to estimate the activity of a hot particle without its separation from the sample. It was shown that by application of the method to a limited number of repeated mixings/measurements, the estimated activity of hot particles can be referred as a value determining the uncertainty of the results at a given level of confidence. For instance: for 5 mixings/measurements in a 103 cm3 vessel, the difference between the actual activity of a sample and the averaged result with a probability of about 64% does not exceed the estimated value of the hot particle activity. The probability is increasing with increasing number of mixings (to about 84% for the same uncertainty range at 10 mixings). For a fixed number of mixings the probability is increasing with increasing uncertainty range. The probability is increasing with decreasing size of the measuring vessel, but in many situations small samples can not be a representative subject of study.
In order to determine physical location of contaminants in soil, solidified soil "thin" sections, which preserve the undisturbed structural characteristics of the original soil, containing weapons-grade plutonium from Rocky Flats Environmental Test (RFETS), were prepared. Two autoradiographic methods were used in radionuclide mapping, contact autoradiography using CR-39® plastic alpha-track detectors and neutron-induced autoradiography that produced fission fragment tracks in Lexan® plastic detectors. The combination of the two autoradiographic methods allowed to distinguish alpha-emitting particles of natural U, 239+240Pu and non-fissile alpha-emitters. ocations of 990 alpha "stars" caused by 239+240Pu and 241Am "hot particles" were recorded, particles were sized, their size-frequency and depth distributions were analyzed. Several large colloidal conglomerates of 239+240Pu and 241Am "hot particles" were found in soil profiles.
Authors:Terry Hamilton, Jussi Jernströem, Roger Martinelli, Steven Kehl, Mats Eriksson, Ross Williams, Marek Bielewski, Ariel Rivers, Thomas Brown, Scott Tumey, and Maria Betti
Runit Island on Enewetak Atoll was very heavily impacted by the U.S. nuclear testing campaign in the northern Marshall Islands
(1946–58). The primary source of contamination on Runit Island was the 1958 Quince safety test where a large quantity of device plutonium (Pu) was scattered over the area near the GZ. A second low-yield device was detonated
on the same site 10 days later, further disturbing the soil and leaving behind a very heterogeneous pattern of contamination
including milligram-size particles of plutonium. A limited cleanup of the Fig-Quince zone was carried out in 1979. During
this period, the effectiveness of the cleanup operations was primarily evaluated on the basis of bulk soil concentration data
with little consideration given to the heterogeneity and long-term material-, biological-, and environmental-specific impacts
of residual high activity (hot) particle contamination. The aim of the present study was twofold; (i) to characterize the
levels and distribution of residual contamination in the Fig-Quince zone, and (ii) to develop pertinent data on the frequency
distribution, elemental and isotopic composition, and physico-chemical properties of hot particles isolated from surface soils
from Fig-Quince with a view towards providing recommendations on the future management and possible cleanup of the site. Today,
Runit Island remains under an administrative quarantine.