In the cooling system of a liquid metal fuel reactor, the container of liquid metal is considered to suffer a cavitation errosion due to its high speed flow. To obtain exact and detailed informations on a possibility of the occurence of cavitation and further on a factor upon the cavitation in liquid metals, a test apparatus, consisting of the magneto-striction vibrator and the ultrasonic oscillator (18 to 22kc), was assembled.
From the results of testing in various liquid metals, such as Pb, Bi and Hg, it was confirmed that the errosion, which is considered to be due to the cavitation effect, takes place. The macro-aspects of the cavitation damage differed widely by the kind of liquid metal, and the cavitation errosion effect became more marked with the rise of test temperature and with the increase of the content of elements in the tested materials which are resolvable into liquid metals.
It was concluded that the cavitation by liquid metals must be considered in the design of a liquid metal fuel reactor.

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We investigated the following subjects:
Various kinds of packing material permitting industrial use in the packed water rectification system for enriching heavy water
(1) Mechanical properties including:
(i) Deformation in long use
(ii) Relation between the column diameter and the requirement of packing
(iii) Void of packing
(2) Effects on rectification including:
(i) Variations in H. E. T. P. with column diameter and height
(ii) Increase in H. E. T. P. through long use of packing
(3) Effects on pressure loss by steam flow rate and column diameter.
(4) Hold-up
(5) Comparison of required periods to attain equilibrium on the basis of the factor of (H. E. T. P.)·H_T/L which represents the properties of packing
(6) Economic evaluation of packing
Our paper of the availability of various packings for industrial installation with major emphasis laid on the above-mentioned McMahon packing, indicates that 1/2'' McMahon packing is most preferable in effecting commercial production by the rectifying column for enriching low or medium-concentrated heavy water.

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Some people have been studied the corrosion phenomenon of steels by liquid sodium systems. A new type thermal convectional corrosion testing apparatus was set up in our laboratry.
In order to investigate several factors simultaneously, we have examined thermal calculation and structure of the apparatus and welding methodes of the test pieces in these NaK circulating loops. This experimental plan have done well. Therefore, we have succeeded in a long term corrosion testing of 18-8 stainless steel tubes by high temperature NaK.

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A study was made to determine the decontamination efficiency of a radiochemical waste evaporator system, consisted of evaporator, cyclone, mist-separator and condenser. The system was designed to handle the liquid radioactive waste, ranged in activity from 10^-4 to 10^-2 μc/ml, at the rate of 200 1/hr and to get a volume reduction ratio of 100200. The evaporator is single effect and vertical shell-and-tube type. The evaporator is operated for non-foaming liquid by fixing the liquid level above the upper tube sheet of the calandria as usual. For foaming liquid, however, the evaporator is. operated by lowering the liquid level below the middle of the calandria. In the latter case, the upper part of the tubes above the liquid surface serves as a foam breaker. The decontamination factors of the evaporator, the cyclone and the mist-separator and the over-all decontamination factor were measured for the boil-up rates varying from 50 to 300 l/hr. Lithium chloride and strontium nitrate solutions were used as test liquid. The decontamination characteristic of the evaporator is different for the two test liquids and depends on the liquid level. The over-all decontamination factor was measured to be 10⁶10⁸ and it was revealed that the required decontamination efficiency was achieved. Some discussions are given on the mechanism of the generation of liquid entrainment.

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⁵⁸Co was prepared by the reaction ⁵⁸Ni (n, p) ⁵⁸Co in carrier-free. Cobalt-free nickel was prepared by anion exchange and nickel was precipitated as carbonate. By the irradiation of 50 g of nickel carbonate in JRR-1 reactor for 60 hr, 230μc of ⁵⁸Co were prepared at maximum.
Being ⁵⁸Co formed with fast neutrons, the fast neutron flux was measured by this reaction. In No.1 experimental hole of JRR-1 the fast neutron flux was 2.1×10¹²n/cm²/sec.

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(1) Good linear relations were obtained between P and m, and the slopes were easily determined. This means that Eq. (3) is held satisfactorily under the conditions used in this experiment.
(2) K decreases slowly with temperature. This seems to be due to the temperature variation of λ₃, since the thermal conductivity of powdered Al₂O₃ (1.0g/cm³) increases slowly with temperature.
(3) For the enthalpy change of the oxidation of UO₂, the following values were obtained.
UO₂+1/6 O₂→1/3 U₃O₇
ΔH₁=-13.8±1.5 kcal/mol (230°C)
1/3 U₃O₇+1/6 O₂→1/3 U₃O₈
ΔH₂=-10.8±1.3 kcal/mol (380°C)
ΔH₁ (230°C)+ΔH₂ (380°C)=-24.6±2.8 kcal/mol agrees fairly well with the published value, ΔH(25°C)=-25.30 kcal/mol and ΔH (380°C)=-25.12 kcal/mol, for the reaction, UO₂+1/3 O₂→1/3 U₃O₈.
(4) A part of the deviation of the value of K comes from the non-uniformity of mixing, the deviations of ρ_s and λ₃ due to the tapping method, the errors in the values of ΔH of the standard reactions and the other experimental errors. However, these will be less than several percent.
(5) λ₃ during reaction is considered to be different from the static thermal conductivity, then K will be influenced by the type of reaction. This effect will occupy the greater part of the deviation of K, so it is desirable to calibrate K by the same type of reaction.
(6) Enthalpy change of the oxidation of UO₂ was also obtained preliminarily by the measurement of specific heat of UO₂ during heating in air. The values thus obtained, ΔH₁=-12.8 kcal/mol (230°C) and ΔH₂=-11.0 kcal/mol (380°C) agree fairly well with the D. T. A. results.
The authors wish to thank Dr. Keiichi Oshima for his helpful discussion. They are also indebted to Dr. Toshio Nakai and Dr. Kenjiro Kimura for their continuing encouragement during this study.

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The extraction behavior of about sixty inorganic ions was studied in the respective systems of tri-n-octyl phosphine oxide** -HCI and -HNO₃ for a contribution to the radiochemical separation techniques.
TOPO was dissolved in toluene and used as its 5% (w/v) solutions. The distribution ratios for each elements were determined in the same way as previous works. The acid dependence curves were obtained for the elements ranging from sodium to uranium, and arranged in the order of the periodic table. In general, the K_d values in HCI system are not only higher than those in HNO₃ but many curves show maximal K_d values in the acidity range from 2 to 10 M HCI while many curves show minimal values in HNO₃ system.
The K_d values or the shapes of curves were found to give strong resemblance to corresponding acid system among TBPO*-HCI and TBP**-HCI or -HNO₃ systems. However, different behavior to the TBP case was observed in the extraction of yttrium, lanthanum and lanthanide elements in HNO₃ system, i. e., they have high K_d values at 1 M acidity. Uranium also showed clearly different results to TBP extraction at 1 M HNO₃.
It is also found that the extractability with TOPO is higher than that with TBP.

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