A phenomenological model of the thermal hydraulics of convective boiling during the quenching of hot rod bundles

Technical Report · Tue Jan 01 04:00:00 EST 1991

DOI:https://doi.org/10.2172/5789820· OSTI ID:5789820

Nelson, R A; Unal, C

In this paper, a phenomenological model of the thermal hydraulics of convective boiling in the post-critical-heat-flux (post-CHF) regime is developed and discussed. The model was implemented in the TRAC-PF1/MOD2 computer code (an advanced best-estimate computer program written for the analysis of pressurized water reactor systems). The model was built around the determination of flow regimes downstream of the quench front. The regimes were determined from the flow-regime map suggested by Ishii and his coworkers. Heat transfer in the transition boiling region was formulated as a position-dependent model. The propagation of the CHF point was strongly dependent on the length of the transition boiling region. Wall-to-fluid film boiling heat transfer was considered to consist of two components: first, a wall-to-vapor convective heat-transfer portion and, second, a wall-to-liquid heat transfer representing near-wall effects. Each contribution was considered separately in each of the inverted annular flow (IAF) regimes. The interfacial heat transfer was also formulated as flow-regime dependent. The interfacial drag coefficient model upstream of the CHF point was considered to be similar to flow through a roughened pipe. A free-stream contribution was calculated using Ishii's bubbly flow model for either fully developed subcooled or saturated nucleate boiling. For the drag in the smooth IAF region, a simple smooth-tube correlation for the interfacial friction factor was used. The drag coefficient for the rough-wavy IAF was formulated in the same way as for the smooth IAF model except that the roughness parameter was assumed to be proportional to liquid droplet diameter entrained from the wavy interface. The drag coefficient in the highly dispersed flow regime considered the combined effects of the liquid droplets within the channel and a liquid film on wet unheated walls. 431 refs., 6 figs., 4 tabs.

• Research Organization: Los Alamos National Lab., NM (USA)
• Sponsoring Organization: DOE; USDOE, Washington, DC (USA)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 5789820
• Report Number(s): LA-UR-91-209; ON: DE91007319
• Country of Publication: United States
• Language: English

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ACCIDENTS
BOILING
BUBBLES
BURNOUT
COMPUTER CODES
COMPUTERIZED SIMULATION
COOLING
CRITICAL HEAT FLUX
DRAG
DROPLETS
DRYOUT
ENERGY TRANSFER
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FLUID MECHANICS
FRICTION FACTOR
FUEL ASSEMBLIES
FUEL ELEMENT CLUSTERS
HEAT FLUX
HEAT TRANSFER
HYDRAULICS
INTERFACES
LOSS OF COOLANT
MATHEMATICAL MODELS
MECHANICS
NUCLEATE BOILING
PARTICLES
PHASE TRANSFORMATIONS
PWR TYPE REACTORS
QUENCHING
REACTOR ACCIDENTS
REACTOR COMPONENTS
REACTOR CORES
REACTOR SAFETY
REACTORS
REYNOLDS NUMBER
SAFETY
SIMULATION
SUBCOOLING
T CODES
TRANSIENTS
TRANSITION BOILING
TWO-PHASE FLOW
VOID FRACTION
WATER COOLED REACTORS
WATER MODERATED REACTORS