The irradiated fuel-burnup experiment of Tehran Research Reactor using nondestructive gamma-ray spectroscopy.

In this work, a nondestructive gamma scanning technique has been applied to determine the irradiated fuel burnup of Tehran Research Reactor (TRR). Thereby, a system was designed and installed at the rim of the TRR pool, which includes a High-Purity Germanium (HPGe) detector and associated electronics-devices, a proper shield, a collimator, and an elevator to radioactive fuel handling for any longitudinal and transverse fuel movement. In the system, it also was possible to measure fuel burnup for fuels with short cooling times at the minimum distance between the fuel and the detector. Five Standard Fuel Elements (SFEs) have been studied with U3O8Al fuel in burnup range of 14%-60% FIMA and cooling time range of 60 days-550 days. Then, by analyzing the gamma-ray emitted from 137Cs isotope as a fuel burnup indicator, an axial profile of fuel burnup was measured in the active fuel length of 61.5 cm and an active width of 6 cm. Finally, verification of results from reactor physics calculations was conducted based on fuel burnup measurements using a nondestructive gamma scanning technique that represents a well enough agreement between calculations and measurements.

An efficient method for detecting damaged FAs; burnup and PPF estimations by gamma spectroscopy.

The purpose of this study is to provide a quick and efficient experimental method to identify and find damaged fuel assemblies (FAs) among all assemblies of the core. This method is based on gamma spectroscopy by measuring the activity ratio of the desired fission fragments that leaked into the coolant. Using the 134Cs/137Cs activity ratio, and considering the history factor for each FA, we determine the fuel burnup. Furthermore, from the 133I × 135I /133Xe activity ratio, the power peaking factor can be determined. This spectroscopy is carried out for the Tehran Research Reactor to find its failed FA positions. Then, the spectrum at different cooling times has been studied. Specifically, from the 134Cs/137Cs (0.1212 ±â€¯0.003) activity ratio and the fuel history factor (2.1023), the fuel burnup of damaged fuel is anticipated to be 33.9%, and the result of the computational codes is found to be 33.1%; these two results are consistent with each other. The results of both experiment and code analysis show the relatively reasonable estimation of this method in finding the location of damaged FAs.

Investigation on the reflector/moderator geometry and its effect on the neutron beam design in BNCT.

In order to provide an appropriate neutron beam for Boron Neutron Capture Therapy (BNCT), a special Beam Shaping Assembly (BSA) must be designed based on the neutron source specifications. A typical BSA includes moderator, reflector, collimator, thermal neutron filter, and gamma filter. In common BSA, the reflector is considered as a layer which covers the sides of the moderator materials. In this paper, new reflector/moderator geometries including multi-layer and hexagonal lattice have been suggested and the effect of them has been investigated by MCNP4C Monte Carlo code. It was found that the proposed configurations have a significant effect to improve the thermal to epithermal neutron flux ratio which is an important neutron beam parameter.

Feasibility study of using laser-generated neutron beam for BNCT.

The feasibility of using a laser-accelerated proton beam to produce a neutron source, via (p,n) reaction, for Boron Neutron Capture Therapy (BNCT) applications has been studied by MCNPX Monte Carlo code. After optimization of the target material and its thickness, a Beam Shaping Assembly (BSA) has been designed and optimized to provide appropriate neutron beam according to the recommended criteria by International Atomic Energy Agency. It was found that the considered laser-accelerated proton beam can provide epithermal neutron flux of ∼2×10(6) n/cm(2) shot. To achieve an appropriate epithermal neutron flux for BNCT treatment, the laser must operate at repetition rates of 1 kHz, which is rather ambitious at this moment. But it can be used in some BNCT researches field such as biological research.

Optimization of the beam shaping assembly in the D-D neutron generators-based BNCT using the response matrix method.

Optimization of the Beam Shaping Assembly (BSA) has been performed using the MCNP4C Monte Carlo code to shape the 2.45 MeV neutrons that are produced in the D-D neutron generator. Optimal design of the BSA has been chosen by considering in-air figures of merit (FOM) which consists of 70 cm Fluental as a moderator, 30 cm Pb as a reflector, 2mm (6)Li as a thermal neutron filter and 2mm Pb as a gamma filter. The neutron beam can be evaluated by in-phantom parameters, from which therapeutic gain can be derived. Direct evaluation of both set of FOMs (in-air and in-phantom) is very time consuming. In this paper a Response Matrix (RM) method has been suggested to reduce the computing time. This method is based on considering the neutron spectrum at the beam exit and calculating contribution of various dose components in phantom to calculate the Response Matrix. Results show good agreement between direct calculation and the RM method.

Effective delayed neutron fraction and prompt neutron lifetime of Tehran research reactor mixed-core.

In this work, kinetic parameters of Tehran research reactor (TRR) mixed cores have been calculated. The mixed core configurations are made by replacement of the low enriched uranium control fuel elements with highly enriched uranium control fuel elements in the reference core. The MTR_PC package, a nuclear reactor analysis tool, is used to perform the analysis. Simulations were carried out to compute effective delayed neutron fraction and prompt neutron lifetime. Calculation of kinetic parameters is necessary for reactivity and power excursion transient analysis. The results of this research show that effective delayed neutron fraction decreases and prompt neutron lifetime increases with the fuels burn-up. Also, by increasing the number of highly enriched uranium control fuel elements in the reference core, the prompt neutron lifetime increases, but effective delayed neutron fraction does not show any considerable change.

Verification of MCNP simulation of neutron flux parameters at TRIGA MK II reactor of Malaysia.

A 3-D model for 1 MW TRIGA Mark II research reactor was simulated. Neutron flux parameters were calculated using MCNP-4C code and were compared with experimental results obtained by k(0)-INAA and absolute method. The average values of φ(th),φ(epi), and φ(fast) by MCNP code were (2.19±0.03)×10(12) cm(-2)s(-1), (1.26±0.02)×10(11) cm(-2)s(-1) and (3.33±0.02)×10(10) cm(-2)s(-1), respectively. These average values were consistent with the experimental results obtained by k(0)-INAA. The findings show a good agreement between MCNP code results and experimental results.

Inhibitory effects of dietary caraway essential oils on 1,2-dimethylhydrazine-induced colon carcinogenesis is mediated by liver xenobiotic metabolizing enzymes.

The effects of dietary essential oils prepared from caraway seeds on colon carcinogenesis induced by 1,2-dimethylhydrazine (DMH) in rats has been studied. The number of aberrant crypt foci (ACF) and aberrant crypt (AC) induced by DMH were found to be significantly inhibited in colon of rats treated with essential oils in diet (0.01 and 0.1%). To find out the mechanism(s) by which the essential oils reduced colon premalignancies, plasma, liver, and colon tissues were collected and analyzed for parameters related to oxidative stress and xenobiotic metabolizing enzymes. Lack of influence of caraway extracts on hepatic lipid peroxidation products, superoxide dismutase (SOD), catalase (CAT) and ferric reducing ability of plasma (FRAP) may suggest that the oils do not interfere with these factors. However, it was clearly shown that DMH-related changes in hepatic and colonic cytochrome P4501A1 (CYP1A1) and glutathione S-transferae (GST) activities were recovered in liver but not in colon tissue in animals treated with caraway oil preparations. In conclusion, histopathological and biochemical data clearly showed that inhibition of colon premalignant lesions induced by DMH is mediated by interference of caraway oil components in the activities of the main hepatic xenobiotic metabolizing enzymes.

Hepatoprotective effects of gamma-irradiated caraway essential oils in experimental sepsis.

Irradiation is an important method of processing herbal drugs, while our understanding of the effects of gamma-irradiation on pharmacological properties of seed products such as caraway essential oils is however still very limited. In this study, caraway seeds were irradiated at dose levels of 0, 10 and 25kGy. After extracting the essential oils, the effects of fresh and gamma-irradiated caraway oils (100mg/kg b.w) on preventing septic-related oxidative liver injury induced by cecal ligation and puncture (CLP) model were investigated by measuring oxidative stress parameters in the liver. CLP operation caused a marked increase in myeloperoxidase (MPO) activity which was readily reversed in rats treated with fresh and irradiated caraway oils. Likewise, thiobarbituric acid reactive substances (TBARS) level in the liver was compensated in rats treated with the fresh and irradiated caraway oils. Moreover, liver GSH which was initially depleted due to CLP was recovered by essential oil treatments. The protective role of oils was further confirmed by showing that liver function tests (ALT/AST) as well as histopathological changes following CLP operation were recovered in rats treated with oils from either fresh or irradiated caraway seeds. These data may suggest that gamma-irradiation to caraway seeds at 10 and 25kGy has no influence on the antioxidative properties of caraway essential oils.

A new method for separation of 131I, produced by irradiation of natural uranium.

Separation of 131I from natural uranium fission product mixtures has been accomplished by sorbing the 131I on special platinum-charcoal sorbent and desorbing by buffer solution (NaHCO3+Na2S2O3). High radiochemical and chemical purity is obtained by this method. Important parameters such as temperature, distillation rate, sorbing and desorbing rates and 131I separation yields have been investigated.