Computational Fluid Dynamic Analysis of Core Bypass Flow Phenomena in a Prismatic VHTR

Journal Article · Wed Sep 01 00:00:00 EDT 2010 · Annals of Nuclear Energy

DOI:https://doi.org/10.1016/j.anucene.2010.04.021· OSTI ID:989273

Sato, Hiroyuki; Johnson, Richard W; Schultz, Richard R

The core bypass flow in a prismatic very high temperature gas-cooled reactor (VHTR) is one of the important design considerations which impacts considerably on the integrity of reactor core internals including operating fuels. The interstitial gaps are an inherent presence in the reactor core because of tolerances in manufacturing the blocks and the inexact nature of their installation. Furthermore, the geometry of the graphite blocks changes over the lifetime of the reactor because of thermal expansion and irradiation damage. The occurrence of hot spots in the core and lower plenum and hot streaking in the lower plenum (regions of very hot gas flow) will be affected by the bypass flow. In the present study, three-dimensional computational fluid dynamic (CFD) calculations of a typical prismatic VHTR are conducted to understand better the bypass flow phenomenon and establish the evaluation method in the reactor core using commercial CFD code FLUENT. Parametric calculations changing several factors in a on-twelfth sector of a fuel column are performed. The simulations show the impact of each factor on bypass flow and the flow and temperature distributions in the prismatic core. The factors inlcude inter-column gap-width, turbulence model, axial heat generation profile and geometry change from irradiation-induced shrinkage in the graphite block region. It is shown that bypass flow provides a significant cooling effect on the prismatic block and that the maximum fuel and coolant channel outlet temperatures increase with an increase in gap-width, especially when a peak radial factor is applied to the total heat generation rate. Also, the presence of bypass flow causes a large lateral temperature gradient in the block that may have repurcussions on the structural integrity of the block and on the neutronics. These results indicate that bypass flow has a significant effect on hot spots in the core and on the temperature of jets flowing from the core into the lower plenum.

• Research Organization: Idaho National Lab. (INL), Idaho Falls, ID (United States)
• Sponsoring Organization: DOE - NE
• DOE Contract Number: DE-AC07-05ID14517
• OSTI ID: 989273
• Report Number(s): INL/JOU-09-16775; TRN: US1007059
• Journal Information: Annals of Nuclear Energy, Vol. 37, Issue 9; ISSN 0306-4549
• Country of Publication: United States
• Language: English

Related Subjects

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
COMPUTERIZED SIMULATION
COOLANTS
FLUID MECHANICS
GAS COOLED REACTORS
GAS FLOW
GEOMETRY
GRAPHITE
HOT SPOTS
INTERSTITIALS
IRRADIATION
LIFETIME
MANUFACTURING
REACTOR CORES
SHRINKAGE
TEMPERATURE DISTRIBUTION
TEMPERATURE GRADIENTS
THERMAL EXPANSION
TURBULENCE
CFD
core bypass flow
prismatic
VHTR