So the core of this reactor, since it's not under pressure and it doesn't have this chemical reactivity, means that there's no inclination for the fission products to leave this reactor.
新しい原子炉の炉心には 圧力は加わっていないので 化学的な反応は起こらず 中の核分裂の生成物が 炉の外に出ることもないのです