Release behaviors of elements from an Ag-In-Cd control rod alloy at temperatures up to 1673 K

1673K以下におけるAg-In-Cd制御棒合金の元素放出挙動

永瀬 文久 ; 大友 隆; 上塚 寛*

Nagase, Fumihisa; Otomo, Takashi; Uetsuka, Hiroshi*

Ag-In-Cd制御棒合金をアルゴンあるいは酸素中、1073-1673Kで60-3600s間加熱し、元素放出挙動を調べた。1123Kと1173Kの間の温度で合金の明らかな液化が起こるが、それ以下の温度では元素放出は少なかった。アルゴン中では、1173Kで3600s後に、1573Kでは60s後にほぼ全てのCdが放出されたが、AgとInの放出割合はそれぞれ3%以下及び8%以下であった。酸素中では、1573K以下でのCd放出は非常に少ないが、1673Kでは短時間に30-50%が放出された。調べた範囲では酸素中のAgとInの放出は少なかった。実験結果との比較から、従来の経験モデルはシビアアクシデント時に制御棒が破損した直後に相当する比較的低い温度範囲でCdの放出を過小評価している可能性がある。

An Ag-In-Cd control rod alloy was heated in argon or oxygen at 1073-1673 K for 60-3600 s and the release behavior of the elements was examined. Complete liquefaction of the alloy occurred between 1123 and 1173 K, and elemental release was quite limited below the liquefaction temperature. In argon, almost all of the Cd content was released within 3600 s at 1173 K and within 60 s at 1573 K, while the released fractions of Ag and In were 3% and 8%, respectively. In oxygen, the release of Cd, which was quite small at temperatures up to 1573 K, drastically increased to 30-50% at 1673 K for short periods. Releases of Ag and In were also small in oxygen under the examined conditions. Comparison with the experimental data suggests that conventional empirical release models may underestimate the Cd release at lower temperatures just after control rod failure in severe accidents.