Experimental Study on Gamma Ray Shielding with Cracked Concrete Panels

In nuclear-related facilities, many reinforced concrete shielding panels are used against radioactive rays. Some shielding panels simultaneously serve as structural slabs or walls. Reinforced concrete shielding plates may crack due to the drying shrinkage of concrete, earthquakes, and other factors. The shielding performance of a cracked reinforced concrete panel against radioactive rays should be clarified. In the design process, engineering safety is based on knowledge of research. If the knowledge is short, conservative assumptions and large safety factors compensate the shortage of knowledge. On the other hand, it has to be recognized that the mental security of the people does not always correspond with the physical safety. In order to avoid misunderstanding and obtain the assurance of society, scientific data should be accumulated. Experimental results are the most fundamental. Therefore, in this study, gamma ray radiation tests on cracked concrete panels were carried out. In the tests, Co-60 and an ionization chamber were used as the source of gamma ray radiation and to measure the dose rate, respectively. A cracked concrete panel was placed between the radiation source and the ionization chamber, and the dose rate was measured. The purpose of this study is not only for the engineering safety but also for the mental security of the people. The previous tests were already reported [1]. The tests were carried out on six concrete panel specimens. Parameters of the tests were crack shape, panel thickness, and crack width. The crack shapes were natural crack and pre-made slit, the thicknesses were 50, 100, and 150 mm, and crack width was varied from 0 to 10 mm. In this paper, subsequent tests are reported. Two additional panel specimens 400 mm thick were prepared that have natural crack and pre-made slit, respectively. The useful data on the gamma ray shielding performance of cracked concrete plates were accumulated.