Abstract
The design of concrete for radiation shielding structures is principally based on the selection of materials of adequate elemental composition and mix proportioning to achieve the long-term durability in nuclear environment. Concrete elements may become radioactive through exposure to neutron radiation from the nuclear reactor. A selection of constituent materials of greatly reduced content of long-lived residual radioisotopes would reduce the volume of low-level waste during plant decommissioning. The objective of this investigation is an assessment of trace elements with a large activation cross section in concrete constituents and simultaneous evaluation of susceptibility of concrete to detrimental alkali-silica reaction. Two isotopes 60Co and 152Eu were chosen as the dominant long-lived residual radioisotopes and evaluated using neutron activation analysis. The influence of selected mineral aggregates on the expansion due to alkali-silica reaction was tested. The content of 60Co and 152Eu activated by neutron radiation in fine and coarse aggregates, as well as in four types of Portland cement, is presented and discussed in respect to the chemical composition and rock origin. Conflicting results were obtained for quartzite coarse aggregate and siliceous river sand that, despite a low content, 60Co and 152Eu exhibited a high susceptibility to alkali-silica reaction in Portland cement concrete. The obtained results facilitate a multicriteria selection of constituents for radiation-shielding concrete.
Highlights
Biological shielding structures in nuclear power plants are exposed to ionizing radiation during their service life
The coarse aggregates, which were characterized by expansion of mortar bars of less than 0.1%, were further analyzed according tetnetnwtiams e0s.5l9es±s.0T.0h3epcpomnt,eannt dofin cEeumaelnsot Csi4g,ntihfiiscawnatlsy0d.2if5feprpedm;.inThceem60CenotscoCn1t–eCnt3,inthPeocrot-nlatnedntcwemasen0t.5s9(C±10–.0C33)ppwmas, acnodmipnarcaebmleentot Cth4e, tchoisntwenats o0f.2t5hipspimso.tTophee 6i0nCqoucaorntzteitnet cinoaPrsoertaglagnredgcaetem(eQn1ts), (9C.012–Cpp3)mwfaosr 6c0oCmo.parable to the content of this isotope in quartzite coarse aggregate (Q1), 9.02 ppm for 60Co
The concentration of 60Co and 152Eu activated by neutron radiation in natural fine aggregate was lower than in natural coarse aggregate
Summary
Biological shielding structures in nuclear power plants are exposed to ionizing radiation during their service life. After such exposure, certain parts of shielding structures may become a source of decay radiation, producing the low-level radioactive waste that has to be properly disposed of during the decommissioning of nuclear power plants. Assessment of the activation level of concrete components is required for the proper selection of methods of waste disposal. If the activation criteria were taken into account during construction at the stage of concrete mix design, the amount of radioactive waste could probably be significantly reduced. The selection of concrete constituent materials of highly reduced content of long-lived residual radioisotopes will not diminish the essential load-bearing and shielding function of concrete, nor impair its durability. Almost in all cases more than one radionuclide is involved, so the mixture of radionuclides below CL is expressed as ∑in=1 ci cli
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