Download - HTTF Analyses Using RELAP5-3D
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www.inl.govHTTF Analyses Using RELAP5-3DPaul D. Bayless
RELAP5 International Users SeminarSeptember 2010
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Outline
• HTTF description• Initial scoping analyses• Steady state and transient simulations• Code user observations
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High Temperature Test Facility (HTTF)• Integral experiment being built at Oregon State University• Electrically-heated, scaled model of a high temperature gas reactor
– Reference is the MHTGR (prismatic blocks)– Large ceramic block representing core and reflectors – ¼ length scale– Prototypic coolant inlet (259°C) and outlet (687°C) temperatures– Less than scaled power– Maximum pressure of ~700 kPa
• Primary focus is on depressurized conduction cooldown transient
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Initial Scoping Studies• Reference reactor simulations• Simulations using a scaled-down MHTGR model• Concerns with laminar flow and initial structure temperatures
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MHTGR RELAP5-3D Scoping Model Features• Three systems
– Primary coolant– Reactor cavity– Reactor cavity cooling system (RCCS)
• Coolant gaps between the core blocks modeled• Each ring modeled separately• 2-D (radial/axial) conduction in all vertical heat structures• Conduction between fuel blocks and to adjacent reflector blocks• Radiation across gaps between reflector rings• Radiation from core barrel to vessel to RCCS• Core barrel divided azimuthally
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MHTGR Reactor Vessel Core Region Cross SectionReactor vessel
Core barrel
Coolant channels
Central reflector
Fuel blocks
Side reflector
Control rod channels
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MHTGR RELAP5-3D Core Region Radial Nodalization
Reactor vessel
Core barrel
Coolant channels
Central reflector
Fuel blocks
Side reflector
Coolant gaps
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Fuel Block Unit Cell
Coolant hole
Fuel
MHTGR RELAP5-3D
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130,
175
132,134,136
158 140, 160,145, 162,150 164,
166 115
100
105
250 295255
110
200
120
170
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Reactor Vessel Nodalization
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Reactor Cavity and RCCS Nodalization
950900 940900
945
930955
960
925970
980 920
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Base Calculation Set• Steady state• Low pressure conduction cooldown (LPCC)
– 10-s forced depressurization to atmospheric pressure– Both reactor inlet and outlet open to He-filled volumes
• Conduction cooldown with intact coolant system– 60-s flow coastdown– Reactor inlet closed– Reactor outlet pressure reduced over 4-hr period– Three outlet pressures
• Normal operation (~6.3 MPa)• 3.0 MPa• 0.7 MPa
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Base Calculations – Peak Fuel Temperature
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Base Calculations – Peak Vessel Temperature
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Base Calculations – RCCS Heat Removal
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Base Calculations – Axial Conduction Effect
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MHTGR/HTTF Sensitivity Calculations• 25% power case
– Nominal coolant temperatures– Transient response uninteresting, no heatup
• 10% power case– Nominal coolant temperatures; laminar flow in bypass channels– Full power decay heat– Transient response similar to reference plant but with higher,
earlier temperature peaks• ¼ scale model
– Nominal coolant temperatures– Laminar flow in all flow channels– Core and reflector temperatures much higher than reference plant– Much higher transient fuel temperatures
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HTTF RELAP5-3D Model Description• Same components and approach as for MHTGR• No gaps between core and reflectors• All coolant holes are open at both ends without flow restrictions
– Loss coefficients adjusted to provide 11% core bypass flow• Control rod holes in reflectors modeled separately from solid regions• Radial heat transfer by conduction in core, central and side reflectors• Simplified model of the RCCS
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HTTF RELAP5-3D core region radial nodalization
Reactor vessel
Core barrel
Coolant channels
Central reflector
Core region
Permanent reflector
Coolant gaps
Heater rodCoolant hole
Side reflector
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HTTF Model Initial Unit Cells
Coolant channel
Heater rod
Ceramic
Reflector Core
Helium gap
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HTTF RELAP5-3D Model Unit Cells
Coolant channel
Ceramic
Reflector Core
Heater rod
Radiation
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Initial Steady State Calculations• Initial HTTF power was ~600 kW, but calculations showed that the
power needed to be >1250 kW to get turbulent flow in the core cooling channels
• Facility power subsequently upgraded to 2.2 MW• Sensitivity calculations looked at different reflector cooling hole
geometries to investigate effect on initial temperature and bypass flow rate
• Cooling hole geometry still being determined
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Transient Boundary Conditions• Decay power (compared to MHTGR)
– Power factor of 1/32– Time factor of 1/2
• Scram at transient initiation• Power held constant until decay power drops below 2.2 MW• 10-s depressurization in depressurized conduction cooldown (DCC)• 60-s flow coastdown in pressurized conduction cooldown (PCC)
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DCC Core Average Temperatures
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DCC Radial Temperature Profile (1)
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DCC Radial Temperature Profile (2)
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Peak Fuel Temperature Comparison
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Reactor Vessel Average Temperatures
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Heat Removal and Generation
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Transient Calculation Observations• Temperature response seemed reasonable and representative• Not a significant difference between DCC and PCC calculations
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Code User Observations• These studies exercised new or seldom-used models in the code
– 2-D conduction– Control variable-driven heat flux boundary condition on a heat
structure– Decoupled heat structures
• Code shortcomings– Inability to model both conduction and radiation from a heat
structure surface– No 2-D conduction in structures with an imposed boundary
condition