App Rx401 - Deactivation of spent fuel cooling ponds water of the first stage of B401 nuclear power plant - Case Study
As a result of the long storage of spent fuel assemblies and decommissioning works of 2 out of 4 nuclear reactors at B401 nuclear power station, radioactivity of water in 2 cooling ponds (Cp#1 and CP#2) reached the value of 3.0 x 10-3 Ci/l, mostly due to cesium radionuclides. The high level of radioactivity and the considerable quantity of water (2,000 m3 each pond) created potential danger to personnel and surrounding environment.
Due to its high sorption capacity and selectivity to cesium radionuclides, a closed-loop deactivation system based on RAXORB inorganic ion-exchanger was put into operation. More specifically, radioactive water from each pond was pumped through a mechanical filter and a RAXORB sorption filter before returning back to the pond. To minimize investment costs, the two ponds were deactivated sequentially for 13 days each (Cp#1 from day 0 to 13 and Cp#2 from day 13 to day 26)
The mechanical filter was loaded with 1,300 Kg of RAXORB1/3 consisting in radiation proof granular titanium dioxide. The sorption filter was filled with 1,000 Kg of RAXORB3/A (ion-exchange sorbent).
The water flow of 30 m3/hour, equivalent to 30 times of the RAXORB3/A sorption filter volume, was downwards.
Monitoring the deactivation process it was also noticed that:
- During the 26 days of operation the deactivation system removed 6,920 Ci while 62.9 Ci remained in the cooling ponds. The final radioactivity of the water in the ponds was lowered to a much safer 1.7 ÷ 1.8 x 10-5 Ci/l.
- The exposure radiation measured at 20 cm from the sorption filter loaded with RAXORB3/A reported a value 930 R/h.
- The water transparency at the exit of the deactivation system was constantly 2 ÷ 5% above the input value indicating that there successfully occurred a mechanical clearing of water from colloidal and suspended particles.
- Purification factor of salts of hardness was about 10. At the end of deactivation process the salt content of hardness was reduced in Cp#1 of 16 times, and in Cp#2 of 40 times.
- In symbiosis with the change of salt content of hardness there occurred a clearing from radionuclide 90Sr that is a chemical analog of salts of hardness.