Residual Radioactive Isotope Effects on the Flushing Water during the Decommissioning Period of Heavy-Ion Treatment Facilities: Dependence of Concrete Models

Three different concrete models were chosen to calculate contamination of flushing water from concrete wastes of a heavy-ion accelerator facility after 50 years of operation (with $7.2\times {10}^{15}\mathrm{carbon}\mathrm{ions}/\mathrm{year}$) and one year of cool-down time. In addition to the main ingredients, isotopic trace elements such as Eu-151, Eu-153, Co-59, and Cs-133 were included in the chemical composition of the concrete for a more conservative estimation. Monte Carlo N-Particle eXtended (MCNPX) version 2.7.0 and CINDER’ version 90 activation simulation tools were used. After one year of decay time, the sum of the maximum ratio to the permitted limit, $\mathrm{\Sigma }(\text{specific}\text{activity}/\text{permitted}\text{limit})$, was 0.3, which means that the concrete wastes can be recycled with no radiological precautions. However, when water flushed out the activated part of the concrete and resolved the remnant radioactive isotopes into water, the waste water was severely contaminated. Many residual radioactive isotopes with long half-lives such as K-40, Co-60, Cs-134, Eu-152, and Eu-154 exceeded the unrestricted release limits. Thus, great care must be taken when the contaminated water from recyclable concrete wastes is discharged into the environment.