Analysis of Groundwater Flows under the Fukushima Daiichi Nuclear Power Plant Reactors Using Contaminated Water from 42 Subdrain Pits

We analyzed groundwater collected from 42 subdrain pits (wells) located around the reactor buildings of plant units #1 to #4 of the Tokyo Electric Power Company Fukushima Daiichi Nuclear Power Plant (F1-NPP) to understand the groundwater dynamics and water flows around F1-NPP. Since water samples collected from this small area exhibit very similar water quality, there are difficulties in understanding the flow dynamics of the groundwater using conventional chemical analyses. In this study, we clarified the groundwater flows using an altitude-modified principal component analysis (PCA) with a total of 798 data items (19 factors x 42 pits) in the chemical analyses. The PCA results showed that six specific pits deviated from the common values and that the others contained contributions from both the natural elements and radioactive nuclides. The groundwater flows under units #1-#4 into two flow lines originating from two main water sources were classified, and these lines merged around the bayside of unit #2 due to the lower groundwater head. This method proved suitable for elucidating the groundwater dynamics and water flows in this small area by the proposed altitude-modified PCA.