Fluid composition in the tube sheet crevices of a nuclear steam generator
A useful understanding has been gained of the conditions needed for a crevice liquid to exist and what determines how alkaline this liquid will be. We believe that corrosive agents other than hydroxides, silica and organic salts must play a role in crevice corrosion. The presence of organic anions and silica in the condensate argues against a strongly alkaline crevice environment. In many cases, there may be insufficient caustic in the crevice fluid to account for the corrosion observed, and another explanation must be sought. Among the organic compounds, only acetate, formate, and lactate are quantitatively important, and acetate is innocuous. Formate decomposes to produce carbonate, which is corrosive. If formate is an important ion in the condensate or carbonates are found in the crevice, remedial measures should focus on eliminating formate and bicarbonate from the condensate. Hydrazine and other AVT compounds should be screened for ability to reduce carbonate to formate and selected accordingly. The possible corrosiveness of decomposition products of lactate also deserves some attention. In principle, acetic acid or silica might be added to the condensate in order to decrease the alkalinity of the crevice liquid, but this benefit must be balanced against possible harmful effects elsewhere in the system. Adding boric acid to the condensate will cause a sodium borate liquid to form in the crevices, likewise reducing alkalinity but with less likelihood of harmful side effects. The activity of NaOH in a sodium acetate liquid will be controlled by the sodium silicate buffer system in many cases. Therefore, adding silica will always enable the alkalinity of a sodium acetate liquid to be reduced to that of the sodium disilicate - quartz buffer. In the absence of acetate, adding silica will cause the crevice fluid to dry up completely. 8 refs., 5 figs., 5 tabs.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6497573
- Report Number(s):
- LBL-20252; CONF-851129-1; ON: DE86002889
- Resource Relation:
- Conference: 46. international water conference, Pittsburgh, PA, USA, 4 Nov 1985
- Country of Publication:
- United States
- Language:
- English
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CREVICE CORROSION
ACETATES
FORMATES
LACTATES
MOLTEN SALTS
OXALATES
PH VALUE
PHASE DIAGRAMS
POTASSIUM SILICATES
SODIUM SILICATES
ALKALI METAL COMPOUNDS
BOILERS
CARBOXYLIC ACID SALTS
CHEMICAL REACTIONS
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POTASSIUM COMPOUNDS
REACTORS
SALTS
SILICATES
SILICON COMPOUNDS
SODIUM COMPOUNDS
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WATER MODERATED REACTORS
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