STRESS CORROSION CRACKING SUSCEPTIBILITY OF HIGH LEVEL WASTE TANKS DURING SLUDGE MASS REDUCTION
Aluminum is a principal element in alkaline nuclear sludge waste stored in high level waste (HLW) tanks at the Savannah River Site. The mass of sludge in a HLW tank can be reduced through the caustic leaching of aluminum, i.e. converting aluminum oxides (gibbsite) and oxide-hydroxides (boehmite) into soluble hydroxides through reaction with a hot caustic solution. The temperature limits outlined by the chemistry control program for HLW tanks to prevent caustic stress corrosion cracking (CSCC) in concentrated hydroxide solutions will potentially be exceeded during the sludge mass reduction (SMR) campaign. Corrosion testing was performed to determine the potential for CSCC under expected conditions. The experimental test program, developed based upon previous test results and expected conditions during the current SMR campaign, consisted of electrochemical and mechanical testing to determine the susceptibility of ASTM A516 carbon steel to CSCC in the relevant environment. Anodic polarization test results indicated that anodic inhibition at the temperatures and concentrations of interest for SMR is not a viable, consistent technical basis for preventing CSCC. However, the mechanical testing concluded that CSCC will not occur under conditions expected during SMR for a minimum of 35 days. In addition, the stress relief for the Type III/IIIA tanks adds a level of conservatism to the estimates. The envelope for corrosion control is recommended during the SMR campaign is shown in Table 1. The underlying assumption is that solution time-in-tank is limited to the SMR campaign. The envelope recommends nitrate/aluminate intervals for discrete intervals of hydroxide concentrations, although it is recognized that a continuous interval may be developed. The limits also sets temperature limits.
- Research Organization:
- SRS
- Sponsoring Organization:
- DOE
- DOE Contract Number:
- AC09-96SR18500
- OSTI ID:
- 920661
- Report Number(s):
- WSRC-STI-2007-00414
- Country of Publication:
- United States
- Language:
- English
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