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Evaluation of Radionuclides in Concrete Shielding for Nuclear Power Plant Decommissioning

Yen-Fu Chen, Yen-Kung Lin, Rong-Jiun Sheu, Shiang-Huei Jiang

Nuclear Technology / Volume 168 / Number 2 / November 2009 / Pages 508-512

Shielding / Special Issue on the 11th International Conference on Radiation Shielding and the 15th Topical Meeting of the Radiation Protection and Shielding Division (Part 2) / Decontamination/Decommissioning

The paper aims to estimate the residual activity in the concrete shielding of a nuclear power plant (NPP) after 40 yr of design service life and to determine if the whole massive concrete shielding must be treated as radioactive waste for future decommissioning. The process was a combination of experiment and calculation. Nonradioactive concrete samples collected from the Lungmen NPP were measured to determine the initial concentrations of major, minor, and trace elements in the concrete shielding by neutron activation analysis, inductively coupled plasma-mass spectrometry, and elemental analysis. The neutron flux distribution and depth-dependent cross sections, which were generated by SAS1, in the 60-cm-thick reactor shielding wall and 200-cm-thick dry well wall of the Lungmen NPP were fed to the ORIGEN-S code to calculate the activity distribution in the concrete shielding after 40 yr of reactor full-power operation. Comparing the activity with the exemption levels, it was found that the dry well wall of the Lungmen NPP can be handled as construction waste for immediate decommissioning. However, most of the reactor shielding wall must be treated as radioactive waste even after a 25-yr cooling time.

 
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