Investigation of cooling coil corrosion in radioactive-waste storage tanks
The high frequency of cooling coil leaks observed in high-heat waste storage tanks soon after sludge removal operations is attributed to pitting. Experimental evidence showed that the most likely series of events leading to coil leakage was (1) excessive dilution of basic nitrite in the waste, (2) initiation of attack in crevices due to oxygen depletion cells, and (3) acceleration of the attack by sulfate dissolved from the sludge. When sludge was slurried with water, the interstitial liquid was diluted. Nitrite, the anodic inhibitor that prevented attack on coils and tanks in normal operation when its concentration was 0.5 to 3.0M, could accelerate attack if it was diluted to 10/sup -4/ to 10/sup -3/M. Attack was presumably initiated at oxygen depletion cells. The presence of sulfate, which was leached from the sludge, produced a conductive solution that could produce high current densities at the corroding steel surface. The proposed series of events leading to coil leakage agrees with the observations previously made on one leaking coil that was removed from Tank 2F after sludge removal in 1967. Examination revealed pitting that had originated on the outside of the coils. This pitting was attributed to oxygen depletion cells in coil crevices. This type of attack is not likely to affect the tank walls because of the absence of crevices in the walls. Leaks produced by pitting attack have not been observed in tank walls. To prevent recurrence of the pitting attack on cooling coils during future sludge removal operations, the sludge should be slurried (1) with waste diluted by no more than one hundredfold with water, or (2) with a 500-ppM nitrate-H/sub 2/O solution at pH 12.
- Research Organization:
- Du Pont de Nemours (E.I.) and Co., Aiken, SC (USA). Savannah River Lab.
- DOE Contract Number:
- E(07-2)-1
- OSTI ID:
- 7331464
- Report Number(s):
- DP-1425
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
CHEMICAL REACTIONS
COOLING
CORROSION
CORROSIVE EFFECTS
HEAT EXCHANGERS
LEAKS
MANAGEMENT
NITRITES
NITROGEN COMPOUNDS
OXYGEN COMPOUNDS
PITTING CORROSION
RADIOACTIVE MATERIALS
RADIOACTIVE WASTE STORAGE
RADIOACTIVE WASTES
REMOVAL
SLUDGES
STORAGE
SULFATES
SULFUR COMPOUNDS
TUBES
WASTE MANAGEMENT
WASTE STORAGE
WASTES