noun
melt-through
Technical term in nuclear engineering: the melting of nuclear fuel through the reactor containment vessel.
メルトスルーが発生すると、放射性物質が環境中に放出される危険性が高まる。
If a melt-through occurs, the risk of radioactive materials being released into the environment increases.
メルトダウン (meltdown) refers to the melting of the reactor core itself, while メルトスルー specifically means the melted fuel breaches the containment vessel.
Borrowed from English 'melt-through', a compound of 'melt' and 'through'.