Multi-nozzle spray cooling of a reactor pressure vessel steel plate for the application of ex-vessel cooling

• Published in: Nuclear engineering and design 2021-04, Vol.375, p.111101, Article 111101
• Main Authors: Bandaru, Satya V. Ravikumar, Villanueva, Walter, Thakre, Sachin, Bechta, Sevostian
• Format: Article
• Language: English
• Subjects: Accidents; Arrays; Cones; Convection; Convection cooling; Cooling; Downward-facing surface; Flow rates; Flow velocity; Free convection; Heat; Heat flux; Heat transfer; High surface heat flux; In-vessel retention; Inclination angle; Light water reactors; Metal foils; Multi-nozzle array; Ohmic dissipation; Pressure vessels; Reactor pressure vessel steel; Reactors; Resistance heating; Spray cooling; Spray nozzles; Sprays; Steel; Steel plates; Structural steels; Surface area; Surface temperature; Upward-facing spray system; Water flow; Water sprays
• ISSN: 0029-5493; 1872-759X; 1872-759X
• DOI: 10.1016/j.nucengdes.2021.111101

•Use of an upward-facing spray on high power-large area reactor steel is studied.•Inclination effect on spray cooling is found insignificant compared to flow rate.•Expected heat transfer mechanism of horizontal upward spray cooling is described.•A surface heat flux margin of ~ 2.97 MW/m2 is obtained for the IVMR application. Spray cooling is a versatile technology for various cooling applications involving high surface heat fluxes. Experimental facility was built to study heat transfer performance of an upward multi-nozzle array of water sprays impacting a surface of heated plate made of reactor vessel grade steel. The effect of inclination angles of the steel surface on the cooling performance was investigated to assess heat transfer in complex semispherical/semielliptical geometry of large reactor lower head and to address possible application of spray cooling in severe accident management (SAM) of light water reactors (LWRs) based on In-vessel melt retention with external reactor vessel cooling (IVR-ERVC). Joule heating of SA302B steel foil of 0.15 mm thickness and surface area of 96 cm2 enabled prototypic heat fluxes to be evacuated during reactor accident. A 2 × 3 array of full jet narrow-coned pressure-swirl spray nozzles was used to reproduce multi-nozzle cooling. The tests were conducted as a series of consequent steady states realized at stepwise increasing power and surface heat fluxes up to the maximum values of 29 kW and 2.97 MW/m2 limited in the specific facility design. Seven surface inclinations, between 0° and 90° were tested and no significant variations in spray cooling performance with the inclination of the heated surface was found. The results indicated a promising prospect of using a multi-nozzle array system for cooling of large surface area of reactor lower head. Much higher heat fluxes can be safely extracted by spray cooling in comparison with the critical heat fluxes that appeared at RPV water pool cooling at natural convection. The maximum value of heat flux at direct spray impact zones and its drop-off slightly from the center to the periphery of the spray cone was detected in the tests. The water flow rate and liquid subcooling significantly influenced maximum steel surface temperature but had no noticeable effects on surface temperature uniformity. The spray-to-spray interaction had no observable effects on local surface temperatures, however, the colliding zones where four spray cones have visible effects on local surface te