Development of an Activity Transport Model and In Situ Measurements on Deposited Radionuclides in the Primary Coolant Pipelines of the Chinshan Nuclear Power Plant

Activated corrosion products deposited on the surfaces of fuel rods and pipelines contribute the majority of the radiation level in the primary system piping of a light water reactor and would have a significant impact on the safety of maintenance personnel or those involved in future decommissioning work. A computer model for site-specific applications, by the name of ACP_BWR, was developed to predict the distribution of activated corrosion products in the primary coolant circuit of a boiling water reactor (BWR). The prediction results were in reasonably good agreement with the data taken by periodic and in situ measurements at three locations after permanent shutdown of the BWR. Our analyses indicated that the ⁶⁰Co, ⁵⁴Mn, ⁵⁸Co, and ⁵⁹Fe activities in the core bypass, upper plenum, and lower downcomer regions were higher than those at other regions of the Chinshan Unit 1 reactor. Accordingly, the dose rates resulting from the activated corrosion products deposited at regions close to either side of the core shroud were comparatively high, surpassing those induced by neutron activation at these regions.