プルトニウム含有ガラス固化体からのプルトニウムの溶解挙動に関する研究

Study on dissolution behavior of plutonium from Pu-doped glass

黒羽 光彦; 澁谷 朝紀; 山田 一夫; 油井 三和; 岡崎 充宏*; 乾 真一*

Kuroha, Mitsuhiko; not registered; Yamada, Kazuo; Yui, Mikazu; not registered; not registered

ガラス固化体からのプルトニウム(Pu)の溶解挙動の把握及び、Puの熱力学データの整備を目的としてPu含有ガラス固化体からのPuの浸出試験、Puの溶解度試験を実施した。浸出試験に先立ち239PuO2の溶解度試験を実施した。溶解度試験は、Puを過飽和として初期濃度を6.2310-5mol/lに調整して行った。試験はいずれも大気下で実施した。溶解度試験では、全pH領域にわたってpHが増加するとPuの溶解度は減少した。これらの傾向は、これまで報告されている239PuO2(c)の溶解度とよく一致していた。また、既存のPuの熱力学データを用い、地球化学計算コードPHREEQEを用いて熱力学的解析を行った。本試験で得られた溶解度は高pH領域において計算値より高い値となった。浸出試験は、Puをドープしたガラス固化体を用い、MCC-3法に準拠してPu濃度のpH依存性を測定すると共に、熱力学的解析により、ガラス固化体表面でのPuの溶解度制限固相の推定を行った。浸出試験では、溶液中のPu濃度はpHに依存し、pH6ではpHの増加に従ってPu濃度が10-6から10-9mol/lへ低下した。また、得られたPu濃度は、これまでに報告されている239Pu(OH)4(am)の溶解度と傾向が一致しており、pH6ではPu含有ガラス固化体からのPuの溶解度を支配している固相は239Pu(OH)4(am)であることが示唆された。

In order to study the migration behavior of plutonium from high-level vitrified waste in a deep repository condition, plutonium doped simulated high-level vitrified waste was prepared in a laboratory. Pu-doped glass was prepared with 1wt.% of PuO. The simulated high-level vitrified waste was crushed to less than 75m and put into platinum crucible (17 mm 80 mm) with PuO powder sieved to less than 75m. The crucible was set into an electric furnace and the temperature was raised up to 1300 C and kept for 2 hours. The melt was cooled down after annealing at 650 C for 2 hours. The specimen was cut and homogeneity of Pu in Pu-doped glass was observed by -autoradiography. As a result of observation, plutonium was distributed homogeneously in the middle of the glass, but was distributed heterogeneously in the bottom of glass. And then the whole of the glass was crushed and melted again in the same way. Leaching experiments of Pu-doped glass and solubility experiments of Pu were carried out under aerobic conditions at room temperature. Leaching experiments of Pu-doped glass were carried out by using batch method with NaNO solution. The particle size of glass powder was under 75m and pH were adjusted by HNO and NaOH in the pH range 4-10. The experimental period was 151-340 days. Solubility experiments of Pu were also carried out from over saturation in 0.1M NaNO solution and pH were adjusted by HNO and NaOH in the pH range 4-12. The experimental period was 42-233 days. These leachate were filtered through a 10,000 molecular weight cut off (MWCO) ultrafilter to separate solution and solid. These experiments were carried out in the teflon vessel. The Pu concentration in leachate was analyzed by -spectrometry. The Pu concentration from the Pu-doped glass was around 10 mol/l in the pH range 4-6, and decreased to 10 mol/l with increasing pH. The leaching ...