[en] In the X-ray CT, the reconstructed image of a moving object is contaminated by the artifacts. In the present paper, a mechanism of the artifacts is considered in case of a point object revolving around the center of the scan area. A projection of the point object from a view angle φ is given by the line: xcosφ + ysinφ = lcos(θ-φ), where l is the distance of the object from the scan center and θ the revolution angle of the object from its initial position. The envelope of the lines for all θ and φ constitutes the reconstructed image, and it is a part of the epicycloid or hypocycloid according to the direction of the revolution. This appears as the motion artifact of the point object. This is also confirmed by computer simulation. (author)

[en] Many algebraic reconstruction techniques (ART) image reconstruction algorithms, for instance, simultaneous iterative reconstruction technique (SIRT), the relaxation method and multiplicative ART (MART), have been proposed and their convergent properties have been studied. SIRT and the underrelaxed relaxation method converge to the least-squares solution, but the convergent speeds are very slow. The Kaczmarz method converges very quickly, but the reconstructed images contain a lot of noise. The comparative studies between these algorithms have been done by Gilbert and others, but are not adequate. In this paper, we (1) propose a new method which is a modified Kaczmarz method and prove its convergence property, (2) study performance of 7 algorithms including the one proposed here by computer simulation for 3 kinds of typical phantoms. The method proposed here does not give the least-square solution, but the root mean square errors of its reconstructed images decrease very quickly after few interations. The result shows that the method proposed here gives a better reconstructed image. (author)

[en] In the X-ray CT, when a given object moves in the scan area during scan-time, its cross sectional image is degraded and contaminated by the artifacts. In the present paper, the mechanism of the CT image degradation and motion artifacts (stroboscopic images) are considered in the case of a 'rigid' object rotating around the center of the scan area. The reconstruction image of a revolving point source is regarded as a point spread function for the CT reconstruction system. The degraded reconstruction image of a rotating rigid object can be expressed as a linear sum of the point spread functions. For a rigid object, or a line source, the reconstruction image is also expressed by the point spread function. When a line source rotates around its one end, its CT image contains motion artifacts called stroboscopic images. The stroboscopic image consists of motion blurs for the point sources of the line object. The motion blurs and the stroboscopic images of rotating rigid phantoms are also confirmed by computer simulations. (author)

[en] The Kaczmarz method is known as one of the Algebraic Reconstruction Techniques (ART) image reconstruction methods. This is the method solving linear equations by projection method. The convergent property of the projection points was proven by Tanabe. The geometrical properties of these convergent points, however, is still not clear. This paper discusses the geometrical properties of the periodic solution constructed by the convergent points on all the hyper planes for a given projection order when the number of equations (M) is larger than the number of variables (N). The sum of the square of the distance between every two consecutive convergent points for a given projection order is equal to that for the reverse projection order. The property of the periodic solution for M = N + 1 is investigated as a special case. (author)

[en] Compton scattering imaging can demonstrate the electron density of a given object which could be important for medical diagnosis. However, clinical application of the technique has not yet been developed, because a clear image can not be obtained for several reasons. The image is seriously contaminated by multiple scattering which is inevitable with Compton scattering. The electron density in a small region of the object is not obtained correctly unless multiple scattering is handled carefully. In the present paper, methods to eliminate multiple scattering in Compton scattering imaging system are discussed. A general purpose Monte Carlo code called EGS4 was used to simulate the processes of an incident photon interacting with a substance inside an object. Simulations were performed using a water sphere phantom with a radius of 10 cm irradiated by a beam of monochromatic X-rays at 100 keV. Scattered photons emitted from the phantom were observed and the ratio of the amount of single Compton scattering from a focal point to that of multiple scattering was calculated. To improve the image quality, elimination of multiple scattering in Compton scattering is indispensable. To this end, θ and Φ-collimators and an energy window were proposed and their effects were estimated quantitatively by simulations. It was shown that by introducing of the proposed methods in the imaging system, the ratio of the Compton scattering signal to the multiple scattering noise, S/N, could be improved from 0.022 to 40. Quantitative results derived from the simulations may be useful for the design of a practical Compton scattering imaging system. (author)

[en] Uncertainty quantification of calculated nuclear material inventories in a spent fuel caused by uncertainty in nuclear data were performed for analysis on factors causing Shipper/Receiver Difference (SRD) of nuclear materials. Uncertainty quantification procedures have been developed by adding Shell sequences that can manipulate ORIGEN output files (f71 files) to Sampler and Polaris sequences in the SCALE Code system (Version 6.2.3). This procedure allows us to perform uncertainty quantification using the latest lattice physics code, Polaris, which adapts Method of Characteristics (MoC) as a neutron transport calculation. Cross section and covariance data generated based on the ENDF/B-VII.1 library were used. As a result of analysis in a fuel assembly geometry, uncertainty of the calculated ²³⁵U, ²³⁹Pu and ²⁴¹Pu inventories were found to be 2.3, 2.1 and 2.1%, respectively. Sensitivity analysis were also performed in a fuel rod geometry under various conditions, such as high enriched ²³⁵U, high boron concentration in moderator, high temperature fuel and moderator, etc. These results are expected to be used to explain one of the causes generating SRD by depletion calculations. (author)

[en] As a factor causing Shipper/Receiver Differences of nuclear material mass between nuclear power plants and reprocessing plants, effects of adjacent fuel assemblies in depletion calculations are focused in this report. In an equilibrium core, a fuel assembly is surrounded by fuel assemblies with different nuclear property every cycle. The amount of nuclear material, however, is evaluated by depletion calculations in single assembly geometry. In the present study, depletion calculations are carried out in 3 by 3 assembly geometry considering typical fuel loading patterns in a 3 loop PWR equilibrium core with the MVP-BURN code. Here, the detailed geometries of core structures are neglected for simplicity. These calculations are done for each node with axial burnup distribution evaluated by three-dimensional single assembly geometry. Depletion calculations in single assembly geometry are also performed in the same calculation condition for comparison. The results showed that the effects considering the adjacent fuel assemblies are -2.1 ∼ -3.9% for ²³⁵U, +0.046 ∼ +0.077% for ²³⁸U, +0.016 ∼ +0.031% for U-Total, -0.52 ∼ -2.4% for ²³⁹Pu, -0.40 ∼ -2.1% for ²⁴¹Pu and -1.2 ∼ -2.3% for Pu-Total in the end of cycle 4. These results show detailed modeling of adjacent fuel assemblies and boundaries are required for accounting fuel material mass. (author)

[en] Numerical simulation on measurement of burnup indicator in assembly-wise geometry was carried out for burnup credit application. Variation of measured value of burnup indicator was evaluated for asymmetric burnup distribution inside a fuel assembly caused by loading patterns. Depletion calculation in multi assembly geometry, considering loading pattern in a typical PWR equilibrium core, was carried out by the MVP-BURN code, and pin-wise distribution of burnup and nuclide composition in the fuel assembly were evaluated to obtain pin-by-pin distribution of photon source. All types of fuel assembly in the equilibrium core were evaluated. Photon transport calculation was also performed by the PHITS code to design measurement system of burnup indicators, ¹³⁷Cs activity, ¹³⁴Cs/¹³⁷Cs activity ratio, ¹⁵⁴Eu/¹³⁷Cs activity ratio, and ¹⁰⁶Ru/¹⁴⁴Ce activity ratio in assembly-wise geometry and detector response function was calculated for each fuel pin in fuel assembly. As a result, each burnup indicator varied within 6% relative standard deviation for fuel assembly discharged in 4th-cycle even by measurement from single direction of assembly and it is possible to estimate burnup of a target assembly within 6% accuracy by any burnup indicator. By measurement from 4 symmetric directions, variety of measured burnup indicator was decreased for fuel discharged in any cycle, and burnup could be estimated in 6% accuracy for fuel assembly in any cycle by any burnup indicator. (author)

[en] We have investigated the effect of level density in the generalized evaporation model (GEM) implemented in PHITS on exaggerated odd-even staggering (OES) seen in calculations of isotopic production in proton- and deuteron-induced spallation reactions on ⁹³Zr and ¹⁰⁷Pd. It was found that the level density with a back-shifted Fermi gas model with energy dependence results in weaker OES than the Gilbert and Cameron level density used in the original GEM, and the agreement with the experimental data was improved. This work was funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan). (author)

[en] Average burnup of damaged fuels loaded in Fukushima Dai-ichi reactors is estimated by using the ¹³⁴Cs/¹³⁷Cs ratio method for actually measured radioactivities of ¹³⁴Cs and /¹³⁷Cs in contaminated soils within the range of 100 km from the Fukushima Dai-ichi nuclear power plants. The numerical analysis of radioactivity ratio of ¹³⁴Cs/¹³⁷Cs is carried out by two deterministic codes (SRAC2006/PIJ, SCALE6.0/TRITON) and a Monte Carlo code (MVP-BURN). Moreover, the void fraction effect for ¹³⁴Cs/¹³⁷Cs ratio is also investigated with two recent evaluated nuclear data libraries (JENDL-4.0, ENDF-B/VII.0). As a result, the measured ¹³⁴Cs/¹³⁷Cs ratio from the contaminated soil is 0.996±0.07 as of March 11th, 2011. By using the ¹³⁴Cs/¹³⁷Cs ratio method, the estimated burnup of Fukushima Dai-ichi units 1, 2, and 3 is approximately 17.2±1.5 [GWd/t] in the present research. (author)