Spatial effect-the variations in space of transient neutron flux noted in pulsed neutron experiments, and which is ascribable to the occurrence in moderator of spatial harmonicss studied on the measured flight time spectra of neutrons reentering the atmosphere from parametrically varied depths of a graphite moderator. Measurements were made using moderator slabs of two different axial lengths, to examine the influence of differences in moderator size on the spatial effect. The master equation representing the scalar neutron flux as function of time and energy is solved by a semi-analytic method that takes account of spatial harmonics. Simulation of the solution thus obtained of the master equation proved to reproduce the measured flight time spectra with good accuracy. It was indicated that the spatial effect on the thermal neutron spectrum is stronger with a larger than with a smaller moderator slab. The neutron temperature in graphite moderator was calculated by formula fitted in Maxwellian distribution to the peaks of the thermal neutron spectra. It was indicated that in a graphite moderator of 120cm axial length, spatial harmonics caused a variation of more than 40K in neutron temperature between depths in moderator differing by 30cm.

抄録全体を表示

A pebble bed reactor generally has double heterogeneity consisting of two kinds of spherical fuel element. In the core, there exist many fuel balls piled up randomly in a high packing fraction. And each fuel ball contains a lot of small fuel particles which are also distributed randomly. In this study, to realize precise neutron transport calculation of such reactors with the continuous energy Monte Carlo method, a new sampling method has been developed. The new method has been implemented in the general purpose Monte Carlo code MCNP to develop a modified version MCNP-BALL. This method was validated by calculating inventory of spherical fuel elements arranged successively by sampling during transport calculation and also by performing criticality calculations in ordered packing models. From the results, it was confirmed that the inventory of spherical fuel elements could be reproduced using MCNP-BALL within a sufficient accuracy of 0.2%. And the comparison of criticality calculations in ordered packing models between MCNP-BALL and the reference method shows excellent agreement in neutron spectrum as well as multiplication factor.
MCNP-BALL enables us to analyze pebble bed type cores such as PROTEUS precisely with the continuous energy Monte Carlo method.

抄録全体を表示

A new method is proposed for estimating nuclide number densities of LWR equilibrium cycle by multi-recycling calculation. Conventionally, it is necessary to spend a large computation time for attaining the ultimate equilibrium state. Hence, the cycle in nearly constant fuel composition has been considered as an equilibrium state which can be achieved by a few of recycling calculations on a simulated cycle operation under a specific fuel core design. The present method uses steady state fuel nuclide number densities as the initial guess for multi-recycling burnup calculation obtained by a continuously fuel supplied core model. The number densities are modified to be the initial number densities for nuclides of a batch supplied fuel.
It was found that the calculated number densities could attain to more precise equilibrium state than that of a conventional multi-recycling calculation with a small number of recyclings. In particular, the present method could give the ultimate equilibrium number densities of the nuclides with the higher mass number than 245Cm and 244Pu which were not able to attain to the ultimate equilibrium state within a reasonable number of iterations using a conventional method.

抄録全体を表示

The influence of fast neutron irradiation was studied for CdTe radiation detectors in the range of fluence 1.0×108-1.8×1011n/cm2. The effect of γ-ray heavy irradiation toward the detector was also investigated for the comparison. Americium-241 and 137Cs γ-ray spectra measured before and after irradiation were compared to examine the change of the detector performance. A pulse height and a rise time of a radiation signal were simultaneously measured in order to evaluate the transport property of both electrons and holes. Peak shift toward lower energies was observed in the 241Am γ-ray spectrum after fast neutron irradiation. Electron μτ product showed large decrease with increasing the neutron fluence, while the one for holes remained unchanged. For the γ-ray irradiation, the spectrum shape of 137Cs changed due to the influence of carrier detrapping. Experimental results support that the electron-trapping center generated by fast neutrons degrades the detector performance of the CdTe detector.

抄録全体を表示

An intelligent reactor design system IRDS has been developed to support conceptual design of new type reactor cores in the fields of neutronics, thermal-hydraulics and fuel behavior. The features of IRDS are summarized as follows: 1) a variety of computer codes to cover various design tasks relevant to "static" and "burnup" problems are implemented, 2) all the information necessary to the codes implemented is unified in a data base, 3) several data and knowledge bases are referred to in order to proceed design process efficiently for non-expert users, 4) advanced man-machine interface to communicate with the system through an interactive and graphical user interface is equipped and 5) a function to search automatically a design window, which is defined as a feasible parameter range to satisfy design requirement and criteria is employed to support the optimization or satisfication process.
Applicability and productivity of the system are demonstrated by the design study of fuel pin for new type FBR cores.

抄録全体を表示

Two-phase flow dynamics of a marine propulsion reactor-of the steam generator in particular-subjected to heaving acceleration were studied on a small-scale rig simulating the primary and secondary circuits of those of N. S. Mutsu. To impart the heaving acceleration, the rig was mounted on a suspended platform oscillated in vertical direction by hydraulic device. Heaving acceleration applied to this rig proved the responding variations of circulating flow, of evaporator steam void fraction and of downcomer water level to be proportional in amplitude to that of the acceleration. The circulating flow was found to pulsate with phase lag behind the heaving acceleration indicative of a second order lag function. Constriction of flow channel downstream of the evaporator-producing resistance against flow amounting to 1.15 times that of the entire loop-proved to amplify significantly the responding pulsations of circulating flow. The pulsations were conversely appreciably diminished by the insertion of a second channel constriction upstream of evaporator-producing 2.7 times loop resistance. When devoid of heaving acceleration, with insertion of flow constriction downstream of evaporator, circulating flow was indicated to be controlled by density wave oscillation, whereas upon application of heaving acceleration, the flow came to be controlled by the external acceleration.

抄録全体を表示

The authors have developed a measurement system which is composed of an ultrasonic velocity profile monitor and a video data processing unit in order to clarify its multi-dimensional flow characteristics in bubbly flows and to offer a data base to validate numerical codes for multi-dimensional two-phase flow. In this paper, the measurement system was applied for bubbly countercurrent flows in a vertical rectangular channel. At first, both bubble and water velocity profiles and void fraction profiles in the channel were investigated statistically. Next, turbulence intensity in a continuous liquid phase was defined as a standard deviation of velocity fluctuation, and the two-phase multiplier profile of turbulence intensity in the channel was clarified as a ratio of the standard deviation of flow fluctuation in a bubbly countercurrent flow to that in a water single phase flow. Finally, the distribution parameter and drift velocity used in the drift flux mode for bubbly countercurrent flows were calculated from the obtained velocity profiles of both phases and void fraction profile, and were compared with the correlation proposed for bubbly countercurrent flows.

抄録全体を表示

The erosion of pyrolytic graphite and titanium doped graphite RG-Ti above 1, 780K was investigated by 5keV Ar beam irradiation with the flux from 4×1019 to 1×1021m-2•s-1. The total erosion yields were significantly reduced with the flux. This reduction would be attributed to the reduction of RES (radiation enhanced sublimation) yield, which was observed in the case of isotropic graphite with the flux dependence of RES yield of φ-0.26 (φ: flux) obtained in our previous work. The yield of pyrolytic graphite was roughly 30% higher than that of isotropic graphite below the flux of 1020m-2•-1 whereas each yield approached to very close value at the highest flux of 1×1021m-2•s-1. This result indicated that the effect of graphite structure on the RES yield, which was apparent in the low flux region, would disappear in the high flux region probably due to the disordering of crystal structure. In the case of irradiation to RG-Ti at 1, 780K, the surface undulations evolved with a mean height of about 3μm at 1.2×1020m-2•s-1, while at higher flux of 8.0×1020m-2•s-1 they were unrecognizable. These phenomena can be explained by the reduction of RES of graphite parts excluding TiC grains.

抄録全体を表示

This paper describes a new model to quantify the chemical interaction of tellurium vapours with silver aerosols in the primary system of pressurized water reactors under severe accident conditions. The silver-tellurium interaction alters the tellurium transport mechanisms through the primary system and could modify the source term. The model considers that the diffusion of tellurium in gaseous phase is the rate-controlling step at temperatures higher than the melting point of the silver-telluride formed (1, 232K) and that the diffusion of silver ions through the product layer controls the reaction at temperatures lower than 1, 232K. The main point of this article is the calculation of the reaction rate at temperatures below 1, 232K. The reaction rate equations have been drawn based upon Wagner's theory of oxidation. The model has been incorporated into the RAFT 1.1 transport code and it has been assessed by simulating the MARVIKEN Aerosol Transport Test 4. The results show that the tellurium-silver interaction is the mechanism which controls the transport in the first five volumes of the facility. The partial pressure of tellurium is reduced and therefore tellurium condensation and chemisorption on walls are also reduced. The inclusion of the new model improves the agreement of the calculation results with the experimental data.

抄録全体を表示

Magnetite is one of the important corrosion products of pressurised heavy water reactors (PHWRs) where carbon steel is the dominant surface in the primary heat transport system. Designing of formulations capable of dissolving magnetite is important for effective decontamination of such surfaces. The rate of dissolution of synthetically prepared magnetite was studied in low concentrations of PDCA containing acidic formulations. The effect of addition of ascorbic acid, citric acid, Fe2+-PDCA complex on the rate was also studied. The effects of pH and the temperature on the dissolution rate were determined. The PDCA as a complexant has some positive factors like low protonation constant and enhanced stability to radiation.

抄録全体を表示

Numerical simulation of neptunium concentration profiles is carried out in order to understand the extraction behavior of neptunium in the co-decontanimation stage which decontaminates through two extraction banks before the uranium and plutonium partitioning steps. Simulation results show that leaking of neptunium to the waste stream at the second extraction bank is caused by reduction from Np(VI) to Np(V) unextracted by TBP in the presence of nitrous acid of 10-3mol/l. It is found that the prevention of the reduction reaction from Np(VI) to Np(V) is effective for the recovery of neptunium with uranium and plutonium into the product stream. Two methods for the recovery of neptunium are suggested; i) to decrease residence time in the acid adjustment vessel located between first and second extraction banks, ii) to diminish nitrous acid in the aqueous phase by hydrazine. Simulation results show that the recovery of neptunium with uranium and plutonium is improved from 40 to 60% and from 40 to 70% by the first and the second methods, respectively.

抄録全体を表示

The LiNO3 effect on aluminum corrosion prevention after land disposal of cement-solidified dry active wastes was examined quantitatively, in the event that the LiH (AlO2)2•5H2O (Li-Al) preservation film was not formed on aluminum surfaces during the solidification process. It is especially probable for these bare surfaces to be left when the wastes include components of complex shapes. LiNO3 dissolves from the waste forms into underground water to form the Li-Al preservation film. So, we thought that the LiNO3 addition would prevent the corrosion. We measured the volume of hydrogen gas generation in mortar-soaked water during the Li-Al preservation film formation, as functions of LiNO3 addition amount, the weight ratio of water to mortar when the mortar-soaked water was produced, and the aluminum surface area, to quantify the effect.
We found that aluminum corrosion was inversely proportional to the LiNO3 addition. For the corrosion to be less than 10-5m in 103h, the initially added amount of LiNO3 must be 1.5wt% of the sum of cement and sand. Regardless of the weight ratio of water to mortar when the mortar-soaked water was produced, hydrogen gas generation with LiNO3 was 10% as much as that without it, in 5×103h. Because of the Li-Al preservation film formation reaction, hydrogen gas generation was proportional to the cubic root of the aluminum surface area.

抄録全体を表示

Influence of humic acid (HA) on the sorption of 60Co, 85Sr and 241Am onto Ando soil was examined with respect to HA of various molecular sizes. Distribution coefficient (Kd) in the sorption of 60Co on this type of soil was only slightly affected by the presence of HA. The Kd of 85Sr as the HA concentration increased. The Kd of 241Am decreased as the HA concentration increased and the Kd of HA showed a similar trend. In the solution, 241Am selectively formed stable compounds with an HA ranging from 30, 000 to 100, 000 in molecular weight (MW), whereas 60Co and 85Sr preferentially but weakly interacted with HA fractions smaller than 100, 000MW. These results suggest that the Kd in the case of 60Co and 85Sr is mainly controlled by sorption of both cationic species and humic compounds, while the Kd of 241Am is controlled by the sorption of HA.

抄録全体を表示

It is advantageous for an emergency response system to have a forecast function to provide a time margin for countermeasures in case of a nuclear accident. We propose to apply an atmospheric dynamic model PHYSIC (Prognostic HYdroStatic model Including turbulence Closure model) as a meteorological forecast model in the emergency system. The model uses GPV data which are the output of the numerical weather forecast model of Japan Meteorological Agency as the initial and boundary conditions. The roles of PHYSIC are the interface between GPV data and the emergency response system and the forecast of local atmospheric phenomena within the model domain.
This paper presents a scheme to use PHYSIC to forecast local wind and its performance. Horizontal grid umber of PHYSIC is fixed to 50×50, whereas the mesh and domain sizes are determined in consideration of topography causing local winds at an objective area. The model performance was examined for the introduction of GPV data through initial and boundary conditions and the predictability of local wind field and atmospheric stability. The model performance was on an acceptable level as the forecast model. It was also recognized that improvement of cloud calculation was necessary in simulating atmospheric stability.

抄録全体を表示

An integrated software tool for scoping analysis of in-core fuel management, INSIGHT, has been developed to automate the scoping analysis and to improve the fuel cycle cost using advanced optimization techniques. INSIGHT is an interactive software tool executed on UNIX based workstations that is equipped with an X-window system. INSIGHT incorporates the GALLOP loading pattern (LP) optimization module that utilizes hybrid genetic algorithms, the PATMAKER interactive LP design module, the MCA multicycle analysis module, an integrated database, and other utilities. Two benchmark problems were analyzed to confirm the key capabilities of INSIGHT: LP optimization and multicycle analysis. The first was the single cycle LP optimization problem that included various constraints. The second one was the multicycle LP optimization problem that includes the assembly burnup limitation at rod cluster control (RCC) positions. The results for these problems showed the feasibility of INSIGHT for the practical scoping analysis, whose work almost consists of LP generation and multicycle analysis.

抄録全体を表示

A simple calculation method for estimating gamma-ray skyshine dose rates has been developed on the basis of the line beam response function (LBRF). The new data of LBRFs were generated by the single scattering with point kernel technique (single-scattering method). These resulting LBRFs were compared with the EGS4 and MCNP Monte Carlo calculations. The values of the new LBRFs for the large emitted angle become smaller than the LBRFs obtained with the Monte Carlo calculations with an increase of the distance from the source. This discrepancy increases with an increase of the photon energy.

抄録全体を表示