Dariush Azimi-Garakani

Intercomparison of automatic fission track counting systems

Abstract The methods of counting fission tracks by two image analyzing computers and a spark counting system are compared with a standard microscopy technique. In this comparison, for automatic fission track counting, the two commercially available image analyzer instruments, the Quantimet 720 and the Leitz-Texture Analyzing System (TAS) and a specially designed spark counter, the UTASC system, have been used. The results showed that the relative counting efficiencies of the Quantimet 720, the Leitz-TAS and the UTASC system are 0.974±0.010, 0.988±0.013 and 0.955±0.010, respectively

Automatic fission track counting using the Quantimet 720

Abstract Several sets of Makrofol SSTR were irradiated on the natural uranium shell of the NISUS assembly at the University of London Reactor CONSORT. In each set pairs of films were placed one on the outer surface of the shell and the other on the inner surface. The ratio of the fission rates in the two positions were calculated by ANISN transport code and found to be 10.86. The etched films were counted by the Quantimet 720 and by eye using an optical microscope. The results showed that for the six pairs satisfactorily counted by eye the mean fission ratio was 10.31 with standard deviation of 1.4%. The mean fission ratio for the same pairs satisfactorily counted by the Quantimet was 10.53 with standard deviation of 2.3%. The relative efficiency of the Quantimet to eye was found to be 0.975±0.005 (random). This value is subject to a systematic error of ±2% attributable to the calibration of the fields of view.

A new automatic spark counting system

Abstract The design and construction of the University of Tehran Automatic Spark Counter (UTASC) are described in detail. The system is used to detect the etched fission fragment tracks in thin plastic SSTRs. The track-detection mechanism is based on scanning concentric circles of the specimen rather than the usual XY scanning methods. The circumference of the circle can be traversed to within ±2μm and the reproducibility of the rotation is to within 0.001°. The difference in radii of the concentric circles is preset in the range of 1 to 99,999 μm. The UTASC system is capable of obtaining reliable results for track densities up to 2 x 104 tracks cm-2 for normal-incidence irradiations. The counting efficiency of the system is about 97% compared with an optical microscope, for track density up to the just-mentioned figure.

Energy response and linearity of electrochemically etched PADC

Abstract The results of the response and linearity test of various electrochemically etched pollyallyl diglycol carbonate (PADC) track detectors at different neutron energies and angles are presented. The detectors were irradiated at the angles of 0°, 30°, and 60° with monoenergetic neutrons of 144 keV, 565 keV, 5.3 MeV and 14.8 MeV. The variations of the angle dependence response were found to be higher at 30° than at 60° for various types of PADC. Below 5.3 MeV, the response at the wedge angles is reduced up to 70%, but at 14.8 MeV, the reduction is less pronounced. All types of the PADC materials used in this study showed a very good linearity with dose.

A comparison of seasonal radon concentration and weekly screening measurements

Abstract Short-term radon measurements were used to make a comparison between weekly screening tests and seasonal concentration. The screening measurements were made in an indoor environment over a period of one quarter during early summer and the results are compared with the measured average radon level over that period. In these experiments, the envelope-type and plastic bag monitors were used for screening and long term radon concentration measurements, respectively. The results show that one cannot achieve predicting the seasonal mean radon concentration based on weekly measurements better than 50% under the conditions reported.

235U:238U fission-ratio measurements in a fast-neutron field

Abstract Fission-ratio of 235U to 238U has been measured in the fast neutron field generated by a 235U fission plate installed on the thermal column of the Tehran Research Reactor (TRR) with a Makrofol solid state nuclear track detector. The experiments were carried out with a set of a total of six enriched 235U and depleted 238U deposits with different masses and using Makrofol films of 0.025 mm and 0.060 mm thicknesses. The chemically etched tracks were counted by an optical microscope. No significant differences were observed with the thin and thick films. The results showed that the average 235U:238U fission-ratio is 3.83 ± 0.25.

Sensitivity analyses for the secondary intermediate-energy standard neutron field at the NISUS facility

Abstract Calculations are made to investigate sensitivities of the central NISUS spectrum and reaction-rate ratios to uncertainties in the macroscopic configuration. These uncertainties include density (of graphite, borone carbide and natural uranium), impurity (moisture and 10 B in graphite), abundance ( 10 B natural abundance) and tolerance (in Al cladding and B 4 C shell). The sensitivities to the variations in the fission cross section of 235 U and 238 U are also studied. In these calculations the ANISN one-dimensional transport code is used with a 37 group data set derived from the UKAEA Nuclear Data Library by the GALAXY processing code. The effects of uncertainties are studied in detail and a comparison is made between the NISUS and MOL-ΣΣ standard neutron fields.

Measurement of fission-rate distribution on a standard uranium shell

Abstract Makrofol KG solid-state track recorders (SSTRs) are used to measure the absolute fission-rate distribution in the NISUS natural-uranium shell in the three orthogonal planes. The results show that the fission-rate ratios of the outer surface to the inner surface of the shell at different positions are not constant, contrary to the prediction from the ANISN one-dimensional transport code. The minimum and maximum fission-rate ratios in the NISUS uranium shell are 7.64±0.24 and 11.58±0.27 in the horizontal midplane at θ = 30° and θ = 180°, respectively (θ = 0° is the out-of-pile direction). These ratios are compared with that of the ANISN calculation which gives the value of 10.86. The discrepancy is because of the non-uniformity of thermal neutron source distribution in the graphite cavity block.

Calculation of the radioactive releases from the Iran-1 and Iran-2 nuclear power plants

Abstract The concentration of radioactive material in air and on the ground surface, released from the normal operation of the Iran-1 and Iran-2 nuclear power plants, is calculated using the AIRDOS computer code. The plants are located in the Halileh site on the coast of the Persian Gulf. These two units are of the Kraftwerk Union standardized PWR type of the 1300 MW class. The time schedule for the first criticality of these two units is mid-1980 and 1981, respectively. The nearest population centre to the site is Bushehr, with a population of ∼62 000, to the north-west and at a distance of about 18 km from the site. The calculation shows that the concentration of radioactive material in air and the ground surface deposition are higher towards the north-west than to any other direction. The annual individual dose rates released from the site are 4.4, 2.3 and 29.8 mrem for the noble gases, aerosols (with half-life longer than 8 days) and radio iodines, respectively.