In the present work, we examined the possibility of in vivo measurement of ¹⁰B concentrations in dermal tumor for boron neutron capture therapy. Until now, the microanalysis system of ppm-order ¹⁰B concentrations in tissue has been already established for small samples including tissue from the measurement of the ratio of prompt γ-rays emitted from ¹⁰B (n, αγ)⁷Li reactions and from H(n, γ)D reactions, by using the thermal neutron beam at the KUR Neutron Guide Tube. In the application to a human body, unlike a small sample of homogeneous medium of ¹⁰B and H, the ¹⁰B/H Gamma-ray Counting Ratio depends mainly on (1) the neutron flux distributions in a body, (2) the shape and size of tumor and (3) the neutron beam position on tumor. Then, we carried out phantom experiments in order to study the relation among those factors. On the other hand, we developed a calculation method for estimating ¹⁰B/H Gamma-ray Counting Ratio and for investigating general tendency among those factors. In calculations, DOT 3.5 and MORSE-MT were used for the calculation of neutron flux distributions and a hand-made program named BORAD was developed to calculate the ¹⁰B/H Gamma-ray Counting Ratio by using the former neutron flux distributions. As a results of these experiments and calculations, it proved to be possible to know ¹⁰B concentrations in dermal tumor, of which volume was known in advance, within 20% permissible accuracy for boron neutron capture therapy.

View full abstract

Corresponding with each non-equilibrium state given by the pressure p, the specific enthalpy of the two-phase mixture h and the void faction α, an equilibrium state defined by p and h is assumed to exist. The relaxation equation for α which relates the non-equili-brium state to the corresponding equilibrium state is derived from the mass and energy equations for the gas phase. The conservation equations for the mixture are spatially differenced in such a way that direct node-node coupling can not take place. Then, the space differencing scheme brings about the three step reduction of the conservation equations, for each of which the physical interpretation is possible. The hydraulic boundary conditions as well as the pump and valve behaviors are incorporated in the model in a natural manner. The model has been implemented in the THYDE-P code to analyze the various dynamic behaviors of the coolant systems.

View full abstract

The microstructural change in pure nickel was continuously observed with a high voltage electron microscope during electron-irradiation with applying external load at 723 K. Frank loops with diameter larger than 10 nm were observed to unfault during the irradiation under external stress. The unfaulting of the radiation-produced Frank loops, which nucleated without external load, was induced by the loading of resolved shear stress of 3.7 MPa or larger along <122> unfaulting direction. The growth rate of the unfaulted loops was fairly larger than that of Frank loops. Unfaulted loops were observed to glide during irradiation under the external stress when they grew to exceed a certain critical size by climb.

View full abstract

With the aim to establish a method for reprocessing molten salt nuclear fuels, the liquid-solid distribution of ²³³Pa between molten LiF-NaF-KF eutectic and either BeO, MgO or CaO was studied at 600°C under various conditions. The deposition of ²³³Pa was the highest on CaO, next on MgO, the lowest on BeO. Slow dissolution of the oxides made the kinetics of deposition quite complicated and equilibria could not be attained even after 40 h of reaction. The rate of deposition of ²³³Pa was explained in terms of the dissolution behavior of the oxides.

View full abstract

Release of ¹³¹I associated with burning of contaminated Na, decay of airborne concentration of the released ¹³¹I and the size distribution of aerosols referred to radioiodine are investigated in experimental runs conducted on laboratory scale. These investigations are carried out in conjunction with similar investigations for the Na matrix. An experimental chamber (5.4 m³) is used for burning a small pool of Na (50 g) containing spiked ¹³¹I (40500 μCi). Values of the specific activity ratio, viz, the ratio of the concentration of ¹³¹I in the aerosol Na to that in pool Na lay in the range of 0.9×10^-25.7×10^-2 at pool temperatures of about 300°C. The concentration decay half-time and the aerosol size distribution charac-teristics referred to ¹³¹I remain similar to those applicable to the Na content of the aerosols. Surface concentrations of ¹³¹I in the residues examined differ from the bulk concentrations (calculated) in the pool and are lower by a factor of 20. The concentrations of ¹³¹I in the aerosols released are further lower than the surface concentrations in the residues by a factor of 2.

View full abstract

The lithium isotope separation in the liquid-liquid extraction system H₂O/CHCl₃ is investigated using benzo-15-crown-5 as complexing agent. The maximum single stage separation factor α_max for ⁶Li/⁷Li obtained in the present study was 1.044±0.003. For the chemical exchange reactions without valence change, this value is the second largest behind one obtained using cryptand (2_B, 2, 1) polymer. The lithium salt was extracted into the organic phase with highly concentrated crown ether forming Li⁺[crown]₂ complexes. The chemical and isotopic equilibria were attained rapidly. The separation factors were 1.026, 1.032 and 1.035 at 25°C for I^-, SCN^- and trifluoroacetate (TFA) as counter anions, respectively. In regard to the separation factor, the distribution coefficient and the stability to the change of temperature, lithium iodide would be most suitable for the industrial application. The isotope effects in Li⁺-crown complex are hindered by the hydration of the complex ion, but the obstraction can be avoided by using the organic solvent with highly concentrated crown ether.

View full abstract

A sensitivity study on the fuel cost of an extended burnup BWR core has been carried out on the basis of a realistic model of discharge burnup extension. Full power operating length in months in a refueling cycle and the number of refueling batches are chosen as independent variables in the model to describe extended burnup cores of various types. The reference core for the sensitivity study adopts 9-month full power operation and 4-batch refueling scheme. The difference in the plant cost between the extended burnup core and the reference core, which is referred to as plant capacity factor (PCF) credit, is estimated and combined with the fuel cost to calculate the fuel cost with PCF credit.
The results show that the fuel cost with PCF credit decreases for the extended burnup core with stretched operating length as the burnup extends in cases of constant non-operat-ing length in a cycle, and that it may increase for the extended burnup core with decreased batch number in cases of constant plant capacity factor. It is also suggested that the cost minimum combination of the independent variables can be found to a given discharge burnup for the extended burnup core with decreased batch number in an intermediate case between these two extreme cases. Extended burnup cores with fixed batch number tend to have a lower natural uranium requirement, but larger separative work requirement.
The economic break-even condition for the extended burnup core with decreased batch number is discussed based on the fraction of fixed part in the non-operating length, which is insensitive to the cycle length stretch-out.

View full abstract

Scaling considerations have been made for liquid line small break simulation tests of a BWR affected by the stored heat released from loop structures. Necessary scaling parameters were given from lumped energy and mass balances equations. It was possible to compensate for excess stored heat released in the reduced-scale facility by increasing the coolant discharge flow area A_D. Although this compensation accelerated the blowdown process, actual pressure and coolant mass changes of the reactor system could be obtained by altering the time scale of the test results by the ratio of A_D/V (V: vessel volume) between the test loop and the reactor system. A semi-experimental evaluation of the stored heat release rate in the Two Bundle Loop (TBL) during blowdown after the operation of Auto-matic Depressurization System (ADS) was also presented on the basis of comparison of experimental diathermic and analytical adiabatic blowdown pressure changes. The obtained results were used in the determination of simulated ADS nozzle diameter for small break tests at the TBL.

View full abstract