为什么铀裂变为钚后,就不再适合作为核燃料了?

2025-03-16 20:44:48
推荐回答(2个)
回答(1):

你在哪儿看的这东西?准确的说,这种说法有点毛病……而且92号元素无论怎么裂变也不可能裂变出94号元素!简单的说1斤水煮花生,不管你怎么分,也不可能分出1.5斤出来! 

要解释这个问题,首先得说明核燃料的分类:“易裂变核(素)燃料”和“可裂变核(素)燃料”。 

易裂变核素有:铀(U)-233/235、钚(Pu)-239/241等; 

可裂变核素有:钍(Th)-232、铀(U)-238、钚(Pu)-240/242等。 

你自己也可以总结一个表象规律,易裂变,通常用做商用热中子堆的燃料都是易裂变核燃料,它们核子数都是奇数。而可裂变核燃料的都是偶数。 

这不是巧合,从核的稳定性来说,原子核中中子和质子都有成对的趋势,如果单出一个中子或者是质子,核普遍都不稳定。这个解释起来有些复杂,如果你想深究的话可以找本《原子核物理》来看看,里边涉及到对能、对称能等。 

U-238+n→U-239→β衰变→Np-239→β衰变→Pu-239(燃料增殖,这是热中子堆中可裂变核素转变为易裂变核素的一个途径;其中n是中子。) 

Th-232+n→Th-233→β衰变→Pa-233→β衰变→U-233。 

适不适合做核燃料主要看堆型,比如热中子堆中U-238不裂变,但是在快堆中它也就和U-235一样也很快就裂变了。 

这是由于对能的关系,U-238的核子数是成对的,比U-235稳定,平均高出0.5~0.7个MeV的能量,而U-239的裂变势垒也比U-236高近0.4MeV,所以,热中子能够使U-235裂变而不能使U-238裂变。但是对于1.4MeV的快中子而言,U-238所筑起的那个势垒并不算太高,它能够通过那个势垒,所以能裂变。 

【PS:】你说的那个可能是经过多次中子俘获后形成的Pu-240/242/244等可裂变核燃料,所以不适合用在热堆中。

回答(2):

谁说不能?只是钚的反应方能不是太多,用来发电还不如用来造核弹,钚原子弹当量小,各国都急缺。钚在自然中的含量极低,一般用核反应堆生产,甚至有专门用来生产部的反应堆。

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