Neutron total cross section measurements near 24 keV were carried out with the Fe-filtered beam technique at the KUR 46-MeV electron linac laboratory. The cross sections of elemental Be, C and 0 were determined and found to be (5.903±0.011), (4.684±0.009) and (3.736±0.007)b respectively at a mean neutron energy of 23.5 keV. These data differ between 0.5 and 1.5% from the ENDF/B-III evaluated cross section at 23.5 keV.

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This paper discusses various alternative safety implications relevant to local faults in LMFBR, and evaluates the basic factors affecting the ability of the subassembly wrapper wall to contain the various effects of molten fuel release. The response of the wrapper tube is evaluated by the method proposed by Youngdahl. Firstly, an equation is derived for calculating the energy repartition between the portions consumed in wall deformation and sodium slug acceleration. Then, using this equation, analyses are performed covering various situations where molten fuel coolant interaction (FCI) significantly affects the surrounding matter. This analysis shows that the degree of coherence in fuel mixing process alters substantially the severity of the FCI. The peak pressure generated by the FCI depends on the volume of the mixing zone, which is closely related to the spatial randomness of fuel failure : For the case of a MONJU-type core design, if the height of the mixing zone is greater than 2 cm, the effects of the release of 200 g of molten fuel can be contained within the subassembly without damag-ing the unaffected wrapper tube. Melt-through of the wrapper tube is also analyzed, and it is found that the integrity of the adjacent wrapper tube is lost about 16 sec after deposition of the molten fuel, and that the melt-through process would differ substan-tially according to whether forced convection is present or absent in the subassembly gap.

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The spent fuels from the JPDR-I reactor were measured by means of a r-scanning facility installed in the fuel storage pool.
The spatial distributions of the fission products (¹³⁴Cs and ¹³⁷Cs) were measured and analyzed in reference to the effects of control rod pattern. The ratios holding between the products of neutron capture and of direct fission (¹³⁴/¹³⁷Cs and ¹⁵⁴Eu/¹³⁷Cs) were also examined for its relevance to non-destructive burnup determination. The activity ratios of the fission products can be expressed by a linear function of burnup, provided that corrections are made to account for differences in irradiation history and for spatial variations in the neutron spectrum.

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Concepts of " region of unity " and " region of influence " are introduced to interprete space-time flux behavior in general. The normalized fractional power change U is first defined by U(r, t)≡f/maxf, where f≡δψ(r, t)/ψ₀(r) is the fractional power change. Thefactor of unity is then defined by u(t) =minU(r, t). The fractional power change through-out the core is therefore estimated within the limits of [u, 1]. If the flux shape does not change, u is always equal to unity in a reactor core ; u can be a measure of coupling strength or " degree of unity " of the transient flux distribution inside a core. The region of unity is finally defined to be a region in which the normalized fractional power change U is larger than a predetermined number close to 1 (0.8 for example). Within the region of unity, approximations relevent to a point reactor are applicable, and the power change proceeds at the same pace throughout this region. Thus, one detector for each region of unity is sufficient for keeping track of the core power distribution.
The region of influence is similarly defined to be a region in which the normalized fractional power change U is larger than a predetermined number which is close to 0 (0.1 for example). Beyond the region of influence around a point, a change in power taking place at the point is no longer felt to any appreciable extent, and one detector per region of influence is necessary for discerning a disturbance in any part of the core.
Analysis on a model aimed at simplification leads to the conclusion that the factor of unity depends on two parameters-size of the core and that of the inserted dis-turbance. The former element has already been recognized as an essential factor in space dependent kinetics, but now the latter element is shown to be the more important parameter. In most cases, the radii of the regions of unity and of influence are of the same order as the radius of disturbance.

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An out-of-reactor experiment was conducted for the purpose of studying the external-pressure creep behavior of zircaloy-2 fuel cladding tubes. The hour-glass shape of UO₂ pellets acquired by thermal distortion was simulated by flanges machined out at both ends of stainless steel pellets 21 mm long. The mock-up specimens thus formed were pressurized externally in a furnace, and the changes brought upon the tube diameter were measured at intervals.
The external-pressure creep deformation was observed to proceed in three steps-diametral decrease, elliptical deformation and final collapse. In the case of hollow tubes tested devoid of the pellets, elliptical deformation was observed, which accelerated with time until abrupt final collapse. Elliptical deformation was not observed on the pellet-filled tubes.
Empirical equations were derived from the experimental results as functions of time, of hoop stress and of temperature, to express the external-pressure creep strain behavior of the stress-relieved tube, pellet-filled and thus internally supported at intervals of 20 mm.
No difference in the external-pressure creep deformation was observed between stress-relieved and recrystallized tubes under the condition of 350°C and 72.5 kg/cm².
The pellet-filled specimens showed larger deformation than the hollow tubes in the process of diameter reduction. A certain length of unsupported distance in the range of 020 mm appeared to maximize the external-pressure creep deformation at the pellet center, under conditions similar to that of the present experiment.

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A differential-difference equation model is introduced which can describe the dynam-ics of any type of extractor, whether, mixer settler, pulsed column or rapid contactor.
The differential or difference equation models used by several investigators prove to be particular cases of this model. From the results calculated by this model, it is shown that there exist an optimal stage and an optimal component for monitoring the performance in the control of extractors.
A computer control system for the solvent extraction step of the Purex process is devised with use made of a generalized version of the classical cascade control law, which the authors have named the Multivariable Cascade Control Law.
This law can easily be extended for application to the control of the Purex process as a whole.

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