Treatment of Water in Nuclear Fuel Storage Basins
to Control Radioactivity Release
EDWIN C. BERTSCHE, Senior Engineer
Reactor Technology Section
E. I. duPont de Nemours and Company
Savannah River Plant
Aiken, South Carolina
INTRODUCTION
The Savannah River Plant of the Atomic Energy Commission (operated by E. I.
du Pont de Nemours & Co.) has nuclear reactors that use heavy water (D2O) as
moderator and coolant. Irradiated fuel components discharged from the reactor carry
removable radioactivity both dissolved in residual heavy water clinging to the
components and adsorbed in the oxide film covering component surfaces. These
components are stored underwater in the storage basin for cooling and radiation
shielding. After short-lived isotope and fission product radioactivity decay sufficiently, the fuel is shipped to the separation areas.
Good water clarity is required to control storage, disassembly, and loading
operations conducted under 30 ft of water. However, untreated water becomes
turbid because of the growth of algae and bacteria, corrosion of mild steel
equipment, and spalling of oxide film from component surfaces. Algae and bacteria
growths have been eliminated by excluding food materials from the basins (especially
phosphate-containing detergents) and by using soft soap for floor cleaning and cask
decontamination.
Water in the fuel storage basin contains both radioactivity and turbidity.
Radioactivity in the heavy water clinging to the components disperses in the basin
water within minutes; however, most of the radioactivity in the oxide surface film
diffuses in about a week. The storage basin is always isolated from the disassembly
basin until the fuel has aged sufficiently and all significant radioactivity has been
removed from the water. In the past, radioactivity was removed from the storage
basin water by recirculation through a portable diatomaceous earth filter followed by
a portable mixed bed deionizer. The deionizers and filters operated without unusual
problems. These portable units were cleaned and regenerated in separate facilities and
radioactive wastes were stored in monitored underground waste storage tanks as
shown in Figure 1.
PROGRAM FOR MINIMIZING RADIOACTIVITY RELEASES
A three-part program was developed to decrease the amount of radioactivity
released to plant effluent streams: 1) Minimizing tritium entering the storage basin;
2) Improving the soluble radioactivity removal process; and 3) Maintaining water
clarity and minimizing release of particulate radioactivity.
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