Development of simultaneous helium generation technique during neutron irradiation

由于聚变堆环境中氦的产生率远大于裂变堆中的氦产生率，为了研究聚变材料中的辐照效应，必须在中子辐照的同时采取一些产氦措施。该项目的目的是开发一种同时产生氦的技术，该技术适用于常规技术难以应用的铁素体钢等材料。该技术的概念如下：可裂变材料，如铀，在裂变反应中以一定的概率产生高能α粒子。放置在这种材料块旁边的样品在裂变反应堆中受到照射时被注入氦。在典型的工程材料中，例如钢，这种氦的射程大约是几十微米。虽然这种方法的原理很简单，但只要样品的厚度小于几十微米，如果样品两边都夹着裂变材料，就可以获得均匀的氦注入。在目前的项目成功之前，它从未进行过测试。同样值得注意的是，该方法提供了一种在诸如铁素体钢之类的工程材料中同时产生氦的技术，其中不存在合适的同时产生氦的技术。将这项技术应用于高通量裂变反应堆中的铁素体钢，研究这些材料中的氦效应，结束长期以来关于铁素体钢氦脆的争论，是非常重要的。

Since the helium generation rate in fusion reactor environments is much greater than in fission reactors, in order to investigate irradiation effects in fusion materials some measure to generate helium must be undertaken simultaneously with neutron irradiation. The aim of this project is to develop a simultaneous helium generation technique which is applicable to materials such as ferritic steels where conventional techniques are difficult to apply.The concept of the technique is as follows : fissionable materials, e.g.uranium generate high-energy alpha particles at a certain probability in fission reactions. Specimens placed next to such material piece are injected with helium when they are irradiated in a fission reactor. The projected range of this helium is on the order of several tens micro-meters in typical engineering materials e.g.steels. Uniform helium injection may be obtained if the specimens are sandwiched with fissionable materials from both sides provided that the thickness of the specimens are less than several tens micro-meters.Although the principle of this method is rather simple. It has never been tested before until the present successful project. It is also very significant to note that this method provides a technique of simultaneous helium generation in engineering materials such as ferritic steels, where suitable simultaneous helium generation technique did not exist. It is very important that this technique be applied to ferritic steels using a high flux fission reactor to study the helium effects in these materials and bring to an end to the long controversy on the helium embrittlement of ferritic steels.