Yoshiki Wadachi

Leaching behavior of cesium-137 in cement-waste composites.

To assess the safety for disposal of a radioactive waste-cement composite, the leaching of I3’Cs from a waste composite into a surrounding fluid has been studied. Leaching tests were carried out in accordance with a method recommended by IAEA. The leachability was measured as functions of waste to cement ratio (Wa/C), concentration of the salt (Na,SO,), temperature of leachant and curing time of specimens. The fraction of 137Cs leached from a specimen of Portland cement is 0.3-0.4 at the leaching time of 100 days, whereas the corresponding value for a specimen of slag cement is 0.1-0.15. The leachability depends on the structure of cement composite which is influenced by such factors as Wa/C, salt concentration of the wastes, and curing time of the specimens. The leach coefficient of ‘37Cs increases with increasing porosity of the cement composite. At lower temperature, curing time of the specimens significantly affects the leachability, probably due to insufficient curing. A curing time of ca. 50 days before the leaching test is enough to eliminate the apparent effect of temperature.

Kinetics of Ion Exchange in the Chelating Resin Dowex A-1

The kinetics of ion exchanges of Ag+, Zn2+ and Cr3+ at extremely low concentrations on the chelating resin Dowex A-1 has been studied by means of finite volume method. The rate of exchanges for both Ag+ and Zn2+ is dependent on the ionic strength, particle size of the resin and reaction temperature. At higher ionic strength (0.1–0.05) the kinetics is controlled by particle diffusion, whereas at lower ionic one (0.01–0.001) film diffusion is predominant. The apparent activation energy obtained is 3.84 kcal/mol for Ag+ and 3.91 kcal/mol for Zn2+. The exchange rate of Cr3+ obeys a first-order rate equation independent of the ionic strength and particle size of the resin. The apparent activation energy is 15.5 kcal/mol. These results support the view that the ratedetermining step of this reaction is chelate formation reaction.

Skin Contamination by Radioisotopes, (V) Pig Skin Contamination by 239Pu

This paper deals with the contaminabilily and the permeability of Pu with varying soiling lime and acidity of the soiling solution applied to pig skin. It was found that the contaminability of Pu was affected by the formation of colloidal substances in soiling solution, as in the case of Pm, Sb, Po and U, described previously. It was also found that 0.05% of the Pu penetrated through the pig skin with pH 1 soiling solution after 60 min.

International Consensus for Radioactive Waste Disposal

The International Atomic Energy Agency (IAEA) shows leadership for the peaceful use of atomic energy. To encourage the safe disposal of radioactive waste, IAEA has published several documents as a “safety series”; especially noteworthy is that the principles of safety disposal recommended in the series have obtained international consensus. This paper explains the principles of safety disposal recommended in the safety series, namely, the objectives of disposal, the classification of waste, and the disposal option. It is expected that this paper will contribute to the reading public, helping it to well understand the purposes and methods of radioactive waste disposal.

Radiological safety assessment for a low-level radioactive solid waste storage facility: preliminary risk evaluation by reliability techniques.

Abstract-The applicability of reliability techniques was examined to determine the quantitative risks which would be caused by a low-level radioactive solid waste storage facility. Fault trees and event trees were defined based on many relevant assumptions to achieve the average occurrence rate of rare accidents which could lead to potential hazards to the general public. The amount of radioactivity which would be transported into the environment from a storage facility was calculated using assumptions and/or estimates of the magnitude of each accident, together with the estimates of probability of occurence, and was used as an index for measuring the potential risks. Some valuable results were obtained in this study under the limits considered. These are as follows: (1) Reliability techniques are effective and promising for achieving the quantitative risks due to storing radioactive wastes in a waste package storage facility for long time periods; (2) The main failures associated with an accident are summarized and listed; (3) The advantages and disadvantages of two types of waste package storage rooms and the amounts of radioactivity which would be released accidentally from them are also summarized and listed; and (4) The improvements desired for a storage facility are proposed from a radiological safety aspect.

SURFACE MATERIALS USED IN THE FACILITIES FOR NUCLEAR POWER AND RADIOISOTOPES.

原子力およびRI取扱施設に汚染防護用表面材料として用いられる塗料には, 汚染性が小さく, 除染性が大きく, そのうえ耐放射線性を示すものが望まれる。それゆえ各種の塗料試料を60Coでγ線照射をし, 塗膜への影響を調ベるとともに, γ線照射が汚染性および除染性に与える効果を調べた。その結果, γ線照射量が少ない場合 (～107R) , 汚染性が小で除染性が大なる塗料は, JIS規格の塩化ビニル樹脂塗料, 塩化ゴム塗料, およびニトロセルロース・アクリル樹脂塗料であり, 耐放射線性については, 2液硬化型のエポキシ樹脂塗料がよい結果を示した。そして塗料が汚染防護用表面材料としてその機能を果すことのできるγ線照射量は109Rまでであると認められた。

gamma

固体表面の放射性粉体汚染およびその除去実験に用いる放射性粉体として, 放射性同位体を吸着した活性炭を用いる可能性を調ベる目的をもって, これに必要な実験的条件を検討した。放射性粉体の除去実験によく用いられる水, およびドデシル硫酸ナトリウム (SDS) 水溶液で洗っても脱離しない条件を, 無担体の60Co, 144Ce, および147Pmについて調ベた。その結果, 粉体除染実験に水を除染剤として用いるときには60Co, 臨界ミセル濃度 (CMC) 以下のSDS溶液を用いるときは144Ce, および147Pmが適していることが知られた。CMC以上の濃度のSDS溶液を除染剤に用いる粉体汚染実験用には, どの同位体も完全によくはなかった。これらの実験から, 粉体汚染試料として活性体に吸着させて用いられる同位体は, その粉体の除染条件によってきめられるべきことが実験的に示された。固体表面の放射性粉体汚染およびその除去実験に用いる放射性粉体として, 放射性同位体を吸着した活性炭を用いる可能性を調ベる目的をもって, これに必要な実験的条件を検討した。放射性粉体の除去実験によく用いられる水, およびドデシル硫酸ナトリウム (SDS) 水溶液で洗っても脱離しない条件を, 無担体の60Co, 144Ce, および147Pmについて調ベた。その結果, 粉体除染実験に水を除染剤として用いるときには60Co, 臨界ミセル濃度 (CMC) 以下のSDS溶液を用いるときは144Ce, および147Pmが適していることが知られた。CMC以上の濃度のSDS溶液を除染剤に用いる粉体汚染実験用には, どの同位体も完全によくはなかった。これらの実験から, 粉体汚染試料として活性体に吸着させて用いられる同位体は, その粉体の除染条件によってきめられるべきことが実験的に示された。

RADIATION EFFECTS ON PAINTS.

In order to study the radioactive decontamination of various metal surfaces such as iron, stainless steel, copper, brass, lead, and aluminum, they were first contaminated with Co/sup 60/ and with fission products. Using a standard test washing machine, these contaminated sunfaces were rinsed with aqueous solutions of condensed phosphates. At the same time, the relationships between pH and complexforming abilities of the condensed phosphates were measured for CoCl/sub 2/ and fission products. The results obtained both for the decontamination and complex formation measurements indicated the suitable condition for decontamination of the metsl surfaces by the condensed phosphates. The suitable decontamination procedure is offered as follows: condensed phosphates; 0.1 to 0.01 mole/l, temperature; 30 deg C, acidity; pH 3 to 6. In this temperature, these condensed phosphates are not suffered from decomposition, moreover, general metal surfaces may be uncorrosive at this acidity. (auth)