Is the accidental detonation of an explosive device, resulting in the death of another person due to flying shrapnel, considered a case of unintentional killing that necessitates blood money (Diyya) and expiation (Kaffarah) upon the one who detonated it?

What happened to your brother is considered accidental killing, because it occurred without intent to commit the act or target the person. So there is no sin upon him, but expiation is obligatory for him, and the blood money is obligatory upon his 'Aqilah (male relatives on the father's side).