高放射性废物是核燃料再处理中制造的废物，主要以两种形式存在：核燃料再处理中产生的废液以及液态高放射性核废料在玻璃化过程中生成的废物。

液态高放射性废物在等待玻璃化的过程中一般保存在罐中埋藏于地下。曼哈顿计划中和冷战中武器计划产生的高放射性废物目前仍处于这种状态，因为通常这些武器计划不负责废物的处理和处置。经过一段时间冷却之后的乏燃料和玻璃态核废料都是可以接受的长期保存形态。

高放射性废物含有核反应堆产生的核裂变产物和超铀元素。这些产物的放射性很强烈，占核电站所产生的全部放射性的95%还多。也就是说，核电站产生的核废料中，大部分都是低放射性废物和中等放射性废物，比如反应堆的钢制结构部件、受到沾染的保护性衣物和设备等等。

High-level waste (HLW) is a type of nuclear waste created by the reprocessing of spent nuclear fuel. It exists in two main forms:

Liquid high-level waste is typically held temporarily in underground tanks pending vitrification. Most of the high-level waste created by the Manhattan project and the weapons programs of the cold war exists in this form because funding for further processing was typically not part of the original weapons programs. Both spent nuclear fuel and vitrified waste are considered as suitable forms for long term disposal, after a period of temporary storage in the case of spent nuclear fuel.