During a severe nuclear power plant accident, the integrity of the reactor pressure vessel must be assured. In response to a possible fuel meltdown, operators of the current generation of nuclear power plants are likely to inject water into the reactor pressure vessel to cool down the reactor vessel wall, preserving its integrity and avoiding leakage of radioactive material. This study considers the use of seawater to flood a reactor pressure vessel combined with the attachment of a honeycomb porous plate (HPP) on the vessel outer wall as a way to improve the safety margins for in-vessel retention of fuel. In long-duration experiments, saturated pool boiling of artificial seawater was performed with an upward-facing plain copper heated surface 30 mm in diameter. The resulting value for critical heat flux (CHF) was 1.6 MW/m 2 at atmospheric pressure, a value significantly higher than the CHF obtained when the working fluid was distilled water (1.0 MW/m 2). It was verified that sea-salt deposits could greatly improve surface wettability and capillarity, enhancing the CHF. The combination of artificial seawater and an HPP attached to the heated surface improved the boiling heat transfer coefficient and increased the CHF up to 110% (2.1 MW/m 2) as compared to distilled water on a bare surface. After the artificial seawater experiments, most of the wall micropores of the HPP were clogged because of sea-salt aggregation on the HPP top and bottom surfaces. Thus, the CHF enhancement observed in this case was attributed mainly to the separation of liquid and vapor phases provided by the HPP channel structure and improvement of surface wettability and capillarity by sea-salt deposition.
To enhance the reliability of in-vessel retention techniques during a nuclear power plant hazard, the viability of seawater as a coolant to flood the reactor pressure vessel was investigated. Pool boiling of distilled water, 3.5 wt. % artificial seawater, and 7.0 wt. % highly concentrated artificial seawater was performed on a 30-mm-diameter Cu bare surface (BS) with a honeycomb porous plate (HPP). The results revealed an increase in the critical heat flux (CHF) with both artificial seawater solutions, on the BS, when compared with distilled water. The improvement of surface wettability by sea salt deposits was assumed as the main reason for the improvement. A significant enhancement in the CHF was achieved with distilled water and 3.5 wt. % artificial seawater owing to the capillary properties of HPP and the separation of the liquid and vapor phases near the heated surface. When the HPP was employed with 7.0 wt. % highly concentrated artificial seawater, the performance did not improve. Although experiments with a honeycomb solid plate suggested that a high concentration of sea salt can clog the micropores in the HPP walls, resulting in loss of its capillary properties, highly concentrated artificial seawater still presented a better performance than distilled water in all cases investigated.
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