Development of simultaneous helium generation technique during neutron irradiation

由于聚变反应堆环境中氦的生成速率远远大于裂变反应堆环境，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生氦的措施。该项目的目的是开发一种同时产生氦气的技术，该技术适用于传统技术难以应用的材料，如铁素体钢。该技术的概念如下：可裂变物质，如铀，在裂变反应中以一定的概率产生高能α粒子。在裂变反应堆中辐照时，放置在这种材料片旁边的样品被注入氦。在典型的工程材料（如钢）中，这种氦的投射范围约为几十微米。在试样厚度小于几十微米的情况下，如果试样两侧夹有可裂变材料，则可获得均匀的氦气注入。虽然这种方法的原理相当简单。在目前成功的项目之前，它从未被测试过。同样值得注意的是，该方法为铁素体钢等工程材料提供了一种同时产生氦气的技术，而在这些材料中没有合适的同时产生氦气的技术。将这一技术应用于高通量裂变堆铁素体钢中，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，具有十分重要的意义。

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.