Investigation on the effect of 238U replacement with 232Th in small modular reactor (SMR) fuel matrix

Effect of 238U replacement with 232Th in small modular reactor fuel matrix was studied. Four different 235U enrichment levels (10, 13.8, 16.5 and 19.8 wt%) were used in a pairwise manner for UO2 and (ThO2 + 235U) fuels. The calculation was performed using Monte Carlo N-particle code integrated with CINDER90 for burn-up calculations in a homogeneous fuel assembly. The results show that enrichment level <17 wt% for thorium fuel produced virtually no plutonium isotopes but became visible only at 19.8 wt% enrichment. The number of neutrons produced per fission () for ThO2 + 235U was less than that of UO2 because its averaged contribution from 235U and 233U was smaller compared to the similar contribution from 239Pu, 241Pu and 235U. Large amount of 239Pu and actinides were produced from UO2 fuel due to the impact of 238U. The reactivity of thorium at the beginning of cycle (BOC) was smaller compared to uranium but higher at end of cycle (EOC) resulting to higher excess reactivity in all thorium fuel. Production of little plutonium isotopes by thorium fuel suggests that it would make a good proliferation resistance fuel and could be used in any W-SMR to incinerate stockpiled plutonium

A comparative study on the impact of Gd2O3 burnable neutron absorber in UO2 and (U, Th)O2 fuels

The performance of gadolinium burnable absorber (GdBA) for reactivity control in UO2 and (U, Th)O2 fuels and its impact on spent fuel characteristics was performed. Five fuel assemblies: one without GdBA fuel rod and four each containing 16, 24, 34 and 44 GdBA fuel rods in both fuels were investigated. Reactivity swing in all the FAs with GdBA rods in UO2 fuel was higher than their counterparts with similar GdBA fuel rods in (U, Th)O2 fuel. The excess reactivity in all FAs with (U, Th)O2 fuel was higher than UO2 fuel. At the end of single discharge burn-up (~ 49.64 GWd/tHM), the excess reactivity of (U, Th)O2 fuel remained positive (16,000 pcm) while UO2 fuel shows a negative value (−6,000 pcm), which suggest a longer discharge burn-up in (U, Th)O2 fuel. The concentration of plutonium isotopes and minor actinides were significantly higher in UO2 fuel than in (U, Th)O2 fuel except for 236Np. However, the concentration of non-actinides (gadolinium and iodine isotopes) except for 135Xe were respectively smaller in (U, Th)O2 fuel than in UO2 fuel but may be two times higher in (U, Th)O2 fuel due to its potential longer discharge burn-u

Feasibility study of a minibeam collimator design for a 60Co gamma irradiator

Recently much attention has been paid to microbeam and minibeam irradiations, present interest focusing on their use in study of the behaviour of single cells, groups of cells, also their application in spatially fractionated radiotherapy. Synchrotrons are the most common source for microbeam radiotherapy (MRT), albeit limited in access and typically offering photon energies very much lower than familiar in the practice of conventional radiotherapy. In this study of feasibility, the design has been investigated of a collimator coupled to a conventional 60Co gamma-irradiator sample chamber to produce a minibeam. MCNPX code Monte Carlo simulations were used to model a Gammacell 220 60Co irradiator with lead and tungsten collimators. The dose profile was evaluated in the absence and presence of the collimator, seeking to optimize collimator design. The results pertain to specific shapes of lead and tungsten collimators producing narrow (millimeter dimension) beams, sufficient in thickness but yet still fitting within the sample chamber, with a peak-to-valley dose ratio (PVDR) greater than 15. The beam size can be tailored with modification in the size of the perforated part, the collimator optimized to minimize the dose-rate at points away from the collimator centre. However the dose-rate at the centre is reduced to between 2 to 20% of that in the absence of collimator. The findings of this study encourage the development of minibeam collimator for gamma irradiators, useful for preclinical minibeam radiotherapy research in centres with little or no access to other appropriate sources

Measurement of photoelectron generation in a gold coated glass slide

In thin low-Z media irradiated by photon energies of several tens of keV, the presence of a high-Z additive can result in manifest locally modified secondary electron dose. Present study analyses the photoelectron dose enhancement resulting from nanometre thickness gold (atomic number Z = 78) coated on commercial borosilicate (B2O3) glass microscope cover-slips. Two thicknesses of B2O3 cover-slip have been utilized, 0.13 ± 0.02 mm and 1.00 ± 0.01 mm, with single-sided Au coatings of 20, 40, 60, 80 and 100 nm. An additional uncoated glass slide has been kept as a comparator. The samples have been exposed to X-rays generated at kVp potentials, delivering a fixed dose of 2 Gy. Dose enhancement resulting from the 1.00 mm glass has been observed to be ~1.32 × that of the 0.13 mm thickness glass. The elemental composition of the samples has been obtained via Electron Dispersive X-ray (EDX), elemental content differences between the two thicknesses of glass leading to a difference in effective atomic number of less than 0.3%. The influence on photon yield of the gold coating and variations in elemental content has been modelled using Monte Carlo simulation, allowing comparison with the measured values of enhanced TL yield

The impact of gadolinium on the reactor production of 153Sm

Radioisotopes represent major sources of ionizing radiation, not least for use in medical applications, brachytherapy and nuclear medicine included. In this, the nuclear reactor is the main source of β- - γ emitting isotopes, an example product being 153Sm used in the treatment of pain arising from bone metastases. Present analysis relates to the potential of gadolinium neutron capture reaction, its impact on reactor production of radioisotopes and the proliferation resistant potential of thorium fuel cycle. A comparative analysis has been made of the impact of gadolinium on the production of 153Sm by UO2 and (Th, U) O2 fuels in a Westinghouse small modular reactor. Five fuel assemblies were investigated: one containing no gadolinium, the other four containing 16, 24, 34 or 44 gadolinium fuel rods. The code Monte Carlo N-Particle eXtended (MCNPX) integrated with the CINDER90 burn-up code was used for calculations. In the production of 153Sm the same trend is followed for the fuels containing gadolinium, increasing significantly with the number of gadolinium fuel rods. Zero production results from fuel assemblies without gadolinium. The concentration of 153Sm increases significantly with burn-up, indicating that gadolinium has a positive impact on the production of 153Sm