Structural phase transitions in the LaMnOs

The rotational diffusion coefficients for rodlike micelles of C14DAC and C14DAB are smaller than those of dodecyldimethylammonium chloride and poly(7-benzyl L-glutamate)s, depending on the long contour length.Schmidt and Stockmayer23 presented approximately an equationfor semiflexible polymer chains. If ( 23) is transcribed to semiflexible rodlike micelles, the contribution by the anisotropy of the translational diffusion, which is omitted in (8), can be described by -(/>" -D±)/3 = -(1 /4)Z>0[ 1 -0.5(¿C/2«)V4] (24)Numerical values can be calculated by using the contour length and persistence length of rodlike micelles and the translational diffusion coefficient listed in Table I. The -(Z)¡| -Z)±)/3 values are definitely small in comparison with the Da and (Lc* 2/ 12)0r values, as seen in Table I. This proves that the assumption of the negligible contribution by the anisotropy of the translational diffusion in ( 7) is reasonable.At high micelle concentrations above 2 X 10"2 g cm"3 4which belong to the semidilute or concentrated regime, mutual diffusion coefficients for 2.6 M NaCl solutions of C14DAC and 4.3 M NaBr solutions of C14DAB reached a constant value at high µ2. Constant values are listed in Table II, where the Z>(0) and Afl(°°) values are also included. The AZ)(=°) values are negative, and their (23) Schmidt, M.; Stockmayer, W. H. Macromolecules 1984, 17, 509. absolute values increase with an increase in micelle concentration, independent of the temperature.The AZ> d(°°) values in the semidilute and concentrated regimes change from ( 13) to (20), with increasing micelle concentration.At the high limit of micelle concentration, where the rotational diffusion and the perpendicular translational diffusion are restricted ADM/D(0) = D'¿?°)D\{c^v")/DW)D\{c-c"Q) -1 » -1 (25) from ( 1) and ( 19). The AD(=°)/Z)(0) values were calculated and included in Table II. They approach -1 as micelle concentrations are increased.It is stated that, in solutions of rodlike molecules at higher concentrations, the field correlation functions at nonzero scattering angles decay in a double-exponential fashion.24 It is due to the coupling of the restricted rotational diffusion to the translational diffusion, in which the perpendicular translational diffusion is precluded. Such non-single-exponential curves of the field correlation function at finite scattering angles were observed for aqueous sodium halide solutions of surfactants at the semidilute and concentrated regimes examined here. This observation must confirm that rodlike micelles in such surfactant solutions behave similar to the rodlike molecules at high concentrations.Acknowledgment. I am grateful to Drs. S. Fujime and T. Maeda for their valuable suggestions to apply their theory.

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The results of calculations of the neutron-physical characteristics of three variants of the fuel load in a VVÉR-1000 core are presented: a load consisting completely of enriched natural uranium (standard fuel) or reprocessed uranium-plutonium fuel from the first and second recycles. The calculations were performed for a stationary load of the core with a four-year fuel run. The difference between the neutronphysical characteristics of a core with a full load of uranium and reprocessed uranium-plutonium fuel is discussed. An analysis of the neutron-physical characteristics did not show any fundamental limitations for a possible 100% load of reprocessed uranium-plutonium fuel in a VVÉR-1000 core.Recirculating reprocessed uranium and plutonium in thermal reactors could increase the utilization efficiency of nuclear fuel and expand the resource base of nuclear power [1]. At the present time, experience has been gained in using reprocessed uranium and plutonium separately in thermal reactors. In our country, the uranium separated from spent VVÉR-440 fuel is mixed with the uranium extracted from spent BN-600 fuel and then usud for fabricating RBMK-1000 fuel [2]. The same scheme is used to fabricate fuel for experimental-commercial operation of fuel elements with reprocessed uranium in VVÉR-440 and -1000 reactors [3]. Plutonium separated from spent PWR fuel is used abroad, mainly in France, as a component of mixed fuel (a mixture of reprocessed plutonium and depleted or natural uranium) which is loaded into 30% of the PWR core [4,5].It has been proposed that fuel made from uranium and plutonium which are separated from the spent fuel of thermal reactors be used in these reactors as fuel after other actinides and fission products are removed and enriched natural uranium is added, taking account of the compensation of the even isotopes of uranium and plutonium [6,7]. It was supposed that because the content of plutonium in the reprocessed uranium-plutonium fuel is relatively low such fuel can make up 100% of the load of a VVÉR-1000 core.To check this assumption, the neutron-physical characteristics of three variants of a stationary load of a four-year run of fuel in a VVÉR-1000 reactor were analyzed. In the first variant, the load consisted entirely of fuel enriched with natural ura-UDC 621.039.516

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