Steam Generators for Nuclear Power Plants by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9780081009284
Publisher: Elsevier Ltd.
Published: 2017-05-25T00:00:00+00:00

Fig. 10.5 Schematic illustrating the model for NaCl concentration in a heated crevice under nucleate boiling heat transfer packed with carbon fiber.

Fig. 10.6 Schematic illustrating the model for NaCl concentration in a heated crevice under nucleate boiling heat transfer packed with carbon powder.

Studies of hideout and hideout return from solutions composed of mixtures of sodium hydroxide, sodium chloride and sodium carbonate were conducted by Brunet, Campan and Shoemaker using a single-tube model boiler incorporating a tube-support plate (TSP) crevice (Campan and Brune, 1987; Campan and Shoemaker, 1987) and a tube-sheet crevice (Campan and Shoemaker, 1987). The crevices were packed with either magnetite or carbon fiber to simulate a fouled crevice. Accumulation of sodium in the heated crevices was determined using a 24Na radio tracer. The accumulation of sodium in the TSP crevice increased with the product of the bulk concentration and the accumulation time until the thermodynamic limit was reached. The total accumulation depended only on the available superheat, and was independent of the bulk concentration of sodium. Hideout return was rapid when the crevice heat flux was reduced to zero, but return was negligible when the bulk solute concentration was reduced to zero while continuing to apply the crevice heat flux. For the tube-sheet crevice the concentration kinetics depended upon the bulk sodium concentration, with accumulation starting at the mouth of the crevice at the lower solute concentration (5 mg/kg) and accumulation starting at the bottom of the crevice at the higher bulk concentration (50 mg/kg).

Balakrishnan investigated hideout and hideout return of sodium in heated crevices formed at the land and broach regions of a trefoil TSP geometry using the radio tracer 24Na and a NaI gamma-ray detector (Balakrishnan, 1990). Fouled crevices were simulated by packing the TSP with stainless steel gauze, carbon cloth or magnetite to various packing densities. The studies were conducted in a high temperature, recirculating loop simulating conditions on the secondary side of a nuclear SG. Balakrishnan observed that hideout was constant when the heat flux was applied, reaching concentration factors of 103 to 104 within 10 h of applying heat to the crevice. The concentration factor rapidly decreased when the heat flux was reduced. Following removal of either the heat flux or the bulk solute by ion exchange with heat flux still applied, all of the accumulated solute rapidly diffused from the crevice. No consistent hideout was observed in clean crevices. Instead, solute accumulation was sporadic, building up a little before being suddenly released to the bulk water.

Hideout from solutions composed of mixtures of sodium chloride, sodium sulfate and calcium chloride in heated crevices packed with either carbon fiber or carbon powder was investigated by Balakrishnan using a refreshed autoclave system (Balakrishnan, 1991). The concentrations of the individual solute species were measured in the influent and effluent of the autoclave using ion-selective electrodes. The tube wall temperature was measured at several axial locations within the heated crevice. The results of the hideout tests with the crevice packed with carbon fiber cloth were similar to those observed by Mann and Castle.

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