Estimation and control of beryllium-7 behavior in liquid lithium loop of IFMIF

In the IFMIF liquid lithium target system, beryllium-7 (7Be) produced by deuteron–lithium (D–Li) reaction is the dominant radioactive nuclide at maintenance of the lithium loop components, since the dose equivalent rate of the 7Be is several orders of magnitude larger than that due to other nuclides. Behavior of 7Be, such as solubility and deposition in the liquid lithium was estimated considering temperature gradient in the loop. The result showed that all most all 7Be, 5.02 × 1015 Bq, would be deposited on most downstream part of the heat exchanger with the lowest temperature among the main flow. Subsequent estimation for dose equivalent rate due to this localized radioactive source showed that, without radiation shielding, the rate would be 8.5 × 107 μSv/h, about seven orders of magnitude higher than a guideline of 10 μSv/h for yearly working time of 2000 h. Required thickness of radiation shield made of lead was found to be 8 cm.