(The) measurement and analysis of radiation streaming phenomenon in the beam tube of research reactor

Abstract

One of the most important utilization areas of research reactors is the neutron beam research by means of beam tubes such as the material structure analysis, material irradiation test and inspection of complex structural materials, which is usually not possible with X-ray or gamma- ray. For the implementation of effective research on these fields, it is essential to design the beam tubes in a way that thermal neutron flux can be made available as high as possible at the beam tube exit. Therefore, the radiation streaming phenomenon in the beam tube should be thoroughly scrutinized so as to be reflected in the beam tube design. Fluid enters and leaves the reactor core to cool the nuclear fuel at an elevated temperature and pressure during the normal operation of reactor. To make such operation possible and effective, provision is made in and out the reactor for the installation of many components and auxiliary systems, and some of them are instrumentation and control systems which are usually encased in mechanical conduits. In addition, there are also many ducts and cavities in the structure of power reactor, which are provided to accommodate large-sized coolant pipes and cables leading to the reactor core through shield and external structure. In particular, penetrations are embedded in primary shield, and, above all, spacious cavity exists in the upper plenum of the pressure vessel of reactor. The neutrons produced in reactor core normally stream out through the ducts and cavities causing nuclear heating and activation of the reactor components and surrounding materials. The resulting radiation also induces radiation exposure to reactor operators and maintenance crew. In fusion reactors, a number of ducts and penetrations are installed in the blanket and shield assembly so that the neutrons from the deuterium-tritium reaction in a plasma region may easily leak out through the cavities. Hence it is very important to shield these ducts, cavities and penetration...