The accumulation of
corrosive and radioactive wastes in the primary system, including nuclear fuel
assembly, significantly increases workers’ exposure to radiation. Zinc
injection from 5 to 40 ppb into the Reactor Coolant System (RCS) of Pressurized
Water Reactors (PWRs) has been known as an effective method to decrease the
radiation fields and Primary Water Stress Corrosion Cracking (PWSCC). Zinc
injection affects both corrosion product concentrations and characteristics of
the deposited crud on oxide layers, because zinc is incorporated into the oxide
films by displacing nickel, cobalt, and iron in primary systems. Radiation
fields and corrosion might be mitigated as radioactive products, such as Co,
which are removed by zinc injection. However, the zinc injection effects on
fuel assembly in Nuclear Power Plants (NPPs) have not been much reported yet,
even though some lab tests were carried out in USA and France. In this paper,
we studied effects of zinc injection on the fuel assemblies in the Ulchin 1
NPP. The chemical and radiation analysis of radioactive corrosion products was
performed to evaluate zinc injection effects on the fuel assembly in the Ulchin
1 NPP. Gamma spectroscopy was used to analyze crud samples for radioisotope
contents. The Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES)
was used to analyze crud samples for elemental contents. The concentration of
was decreased after zinc injection to 1/22 times that before the zinc
injection. 1% - 2% wt% of zinc was incorporated
through the substitution of Ni in the crud oxide layer. The Ni/Fe ratio was decreased
to 0.69 from 1.12 after the injection, due to the Ni substitution by zinc. It
was found that NiO and NiFe2O4 were converted to ZnO and
ZnFe2O4, respectively. In conclusion, zinc injecttion was
found to be an essential method to reduce the amount of radioactive Co-58 in the fuel assemblies of primary systems in
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