ngnp program ngnp methods: summary of approach and plans richard r. schultz
TRANSCRIPT
NG
NP
Pro
gra
m
Pioneering Science andTechnology
Pioneering Science andTechnology
Pioneering Science andTechnology
NGNP Methods:Summary of Approach and
Plans
Richard R. Schultz
NGNP Program
November 19, 2008
Overview
• NGNP Methods: Objectives• Discussion of Evaluation Models & NGNP
Methods Approach• Overview of NGNP Reference Reactors• How we are defining needs in NGNP Methods• Discussion of Phenomena Requiring Analysis• Standard Problem • Other potential standard problems• Potential issues
NGNP Program
November 19, 2008
Objectives of NGNP Methods
• Ensure that tools are available to analyze the behavior of the NGNP for DOE programs (and NRC).
• Analysis tools must have demonstrated capability and low calculational uncertainty
• Analysis software adequacy will be demonstrated using guidelines expressed in Reg Guide 1.203.
• Hence software used for NGNP analyses are being assembled to create NGNP Evaluation Models
NGNP Program
November 19, 2008
NGNP Evaluation Models (EMs)
• The calculational framework for evaluating the behavior of the NGNP during postulated transients or design basis accidents. This includes the:– Development of practices and procedures for treating the input and
output for software in EMs.– Specification of the calculational envelope for the software to be used
for various portions of scenarios of importance.– Specification for how the software shall be used by the plant analysts so
several analysts analyzing the same problem using the same software calculate the same answer.
– The validation procedures and requirements—including the requirements for designing and performing validation experiments.
• NGNP methods is focused on best estimate models aimed at calculating plant behavior at most challenging conditions, e.g., identify localized hot spots and unacceptable thermal gradients when plant is operating at maximum outlet temperatures and efficiency.
NGNP Program
November 19, 2008
NGNP Methods Development & Validation • The R&D Process is
based on…– Identifying the most
demanding scenarios for candidate plant design
– Isolating key phenomena in scenarios
– Determining whether analysis tools can be used to confidently analyze plant behavior scenarios (Validation)
– Performing R&D to upgrade analysis tools where needed
Scenario Identification: Operational and accident scenarios that require analysis are identified
PIRT: Important phenomena are identified for each scenario (Phenomena Identification & Ranking Tables)
Validation: Analysis tools are evaluated to determine whether important phenomena can be calculated
Development: If important phenomena
cannot be calculated by analysis tools, then further development is undertaken
Analysis: The operational and accident scenarios that require study are analyzed
No Yes Yes
NGNP Program
November 19, 2008
The Calculation Process…
• Requires the analysis tools to have reasonable† agreement with data for key phenomena.
† Reasonable agreement: calculated value sometimes lies within data uncertainty band and shows same trends as data.
• Consists of seven steps • It’s assumed to be equally likely that the plant will be either
pebble-bed or block-type reactor
a. Material Cross Section Compilation and Evaluation
b. Preparation of Homogenized Cross Sections
c. Whole-Core Analysis (Diffusion or Transport), Detailed Heating Calculation, and Safety Parameter Determination
d. Thermal-Hydraulic and Thermal-Mechanical Evaluation of System Behavior
f. Fuel Behavior: Fission Gas Release Evaluation
g. Fission Gas Transport
e. Models for Balance of Plant Electrical Generation System and Hydrogen Production Plant
a. Material Cross Section Compilation and Evaluation
b. Preparation of Homogenized Cross Sections
c. Whole-Core Analysis (Diffusion or Transport), Detailed Heating Calculation, and Safety Parameter Determination
d. Thermal-Hydraulic and Thermal-Mechanical Evaluation of System Behavior
f. Fuel Behavior: Fission Gas Release Evaluation
g. Fission Gas Transport
e. Models for Balance of Plant Electrical Generation System and Hydrogen Production Plant
NGNP Program
November 19, 2008
Includes Software such as:
Thermal-Fluids Experim ental Validation
Benchm arks(Prismatic)
NewComputational Fluid Dynam ics
Models
Thermal-Fluids Experim ental Validation
Benchm arks(Pebble Bed)
RELAP5 / FLUENT
CombinedReactorKineticsModule
NESTLEReactorKinetics
PEBBED (t)ReactorKinetics
PrismaticAssembly Spectrum
Code:DRAGO N
MCNP / MOCUP
(M onte Carlo)ORIGEN
NJOYBasic Cross Section
Processing
ENDF/BDatabase
New Cross Section Measurem entsPu, Pu, Pu240 241 242
DIF-3D /REBUS
PEBBED
Physics V&VBenchm arks
Physics V&VBenchm arks
Direct data flow
Validation
Data consistency requirement
0 4-G A 5 00 8 9-0 5
Coupled Fluid Dynam ics and Reactor Physics
Reactor Physics
Existing capability
Improvements needed
New capability developm ent required
DiscreteOrdinatesTransport:DECART
DiscreteOrdinatesTransport:
ATTILA
PARFUME
Fission Product
Transport Fuel & M aterialsBehavior and Fission Product Transport
a.
a.
b.b. b.
c. c.
f.
c. c.
g.
d. d, f.
d.
GRSACVerification
Benchm arks
MELCORVerification
Benchm arks
Pebble BedAssembly Spectrum
Code:COMBINE
b.
a.
b, c.
d. d. d.
c.
RadiationEffects
NGNP Program
November 19, 2008
The Very High Temperature Gas Reactor is Reference Design
• Utilize inherent characteristics– Helium coolant - inert, single phase– Refractory coated fuel - high temp
capability, low fission product release
– Graphite moderator - high temp stability, long response times
• Simple modular design:–Small unit rating per module–Low power density–Silo installation
• Passively safe design:–Annular core –Large negative temperature
coefficient–Passive decay heat removal –No powered reactor safety
systems
Reactor
Core Barrel Conditioning
SystemMaintenance Isolation/Shutdown Valve
Generator
Power Turbine
Recuperator
High Pressure Compressor
Low Pressure Compressor
Gearbox
Inter-Cooler
Core Conditioning System
Pre-Cooler
ReactorReactor
Core Barrel Conditioning
System
Core Barrel Conditioning
SystemMaintenance Isolation/Shutdown ValveMaintenance Isolation/Shutdown Valve
GeneratorGenerator
Power TurbinePower Turbine
RecuperatorRecuperator
High Pressure Compressor
High Pressure Compressor
Low Pressure Compressor
Low Pressure Compressor
GearboxGearbox
Inter-CoolerInter-Cooler
Core Conditioning System
Core Conditioning System
Pre-Cooler
Prismatic
Pebble-bed
NGNP Program
November 19, 2008
NGNP Methods: Focused on Work Generally Applicable to Both Prismatic & Pebble-Bed Design
• Since design has not been chosen yet (It is planned to choose design in fiscal year 2009 though.)
• Work scope applicable to either design is still large and includes:– Performing PIRTs to identify most challenging
scenarios and highly ranked phenomena for prismatic and pebble-bed designs.
– Selecting overall software repertoire compatible with known design characteristics, most challenging scenarios, and calculational requirements for highly ranked phenomena.
NGNP Program
November 19, 2008
From General Perspective…
• Most challenging scenarios are the same for both prismatic and pebble-bed type reactors.
• Highly-ranked phenomena for the most challenging scenarios are similar.
• Differences rest with (for example):– Core geometry: moveable vs stationary; core cross-
flow vs no core cross-flow; definition of bypass flow; nonuniform core flow area vs uniform core flow area
– Quantity of dust generation– Geometry of RCCS.– IHX designs
NGNP Program
November 19, 2008
Many of the Phenomena that Must Be Quantified & Analyzed Require Advanced Tools
• System behavior, i.e., comprehensive model of reactor plus balance-of-plant, will be calculated using RELAP5-3D
• RELAP5-3D will be used to provide boundary conditions to CFD calculations for transient scenarios where localized hot spots must be identified and studied.
NGNP Program
November 19, 2008
RELAP5 Model Summary: Reactor Vessel Model
• Coolant active and stagnant volumes• Structures in the core region
– inner and outer reflectors– upper and lower reflectors– core barrel– upper plenum shield– reactor vessel wall and upper head
• Structures below the core are being ignored
NGNP Program
November 19, 2008
VHTR Vessel Hydraulic Nodalization—Bypass Not Shown
120
130 140
152
110
170100 105
160
154 156
NGNP Program
November 19, 2008
Other Candidate Coupled Calculations
• Reactor cavity cooling system
• Coupled through heat transfer boundary
NGNP Program
November 19, 2008
RELAP5 Model Summary: Ex-vessel Model
• Containment air volume• Reactor cavity cooling system (RCCS)
– Inlet plenum/downcomer piping– Lower distribution plenum– Riser/outlet plenum– Riser, downcomer, and outer metal walls
• Containment concrete wall and surrounding soil (behind RCCS downcomer)
• Other structures/walls neglected
NGNP Program
November 19, 2008
VHTR Reactor Cavity Nodalization
905 975 955
965
900 900
970 960
950980
NGNP Program
November 19, 2008
RELAP5 Model Summary:Heat Transfer Modeling with RCCS Model
Core
Inner reflector
conductionconduction
Outer reflector
Reactor vessel
RCCS riser wall RCCS downcomer wall
Containment wall
radiation
radiation
radiation
convection, radiation
convection
convection
convection
He coolant
Axial conduction incore and reflectors
convection
NGNP Program
November 19, 2008
Thermal-Hydraulic Phenomena: RELAP5-3D
• Normal operation at full or partial loads– Coolant flow and temperature distributions through reactor core
channels (“hot channel”)– System behavior at operational conditions– Calculation of heat balance between reactor vessel and
confinement volume, confinement walls, and cooling water flow behavior in walls.
• Loss of Flow Accident (LOFA or “pressurized cooldown”)– Modeling of all 1-D systems– Boundary conditions for CFD calculation of fluid behavior in
plena– Calculation of two-phase conditions in water cooling passages
in RCCS.– Prediction of system behavior during transient.
• Loss of Coolant Accident (LOCA or “depressurized cooldown”)– Prediction of reactor core depressurized cooldown - conduction
and thermal radiation– Rejection of heat by natural convection and thermal radiation at
the vessel outer surface
NGNP Program
November 19, 2008
Flow in Lower Plenum
Objective: The flow in the lower plenum of the VHTR will involve multiple jets entering from the core into a crossflow moving toward the exit duct and having to negotiate the presence of rows of support pillars. The modeling strategies (e.g. turbulence model, grid characteristics, time stepping, etc.) for simulating this complex turbulent flow must be validated.
Courtesy of Fluent
NGNP Program
November 19, 2008
Coupling of RELAP5-3D© & CFD Software
– RELAP5-3D and Fluent presently coupled: however parallel calculational capability using multiple CPUs must be improved.
– Embarking on coupling with STAR-CD and STAR-CCM+ this fiscal year.– STAR CFD codes have immense potential due to their focus on the calculation of
massive problems.– Mesh cell requirements for the plena are on the order of tens of millions of cells.
NGNP Program
November 19, 2008
Fluent model
Zone 2 of Fluent model
Zone 3 of Fluent model
SNGLJUN Component 115: upcrin
Blowup of Fluent model linked to RELAP5-3D© model
NGNP Program
November 19, 2008
RELAP5-3D© coupled to enable detailed analysis of lower plenum flow patterns
Core
UpperPlenum
LowerPlenum
BalanceOf
Plant
CFD model
RELAP5-3Dmodel
RELAP5-3Dmodel
CFD model
RELAP5-3D coupled to Fluent, GAMMA, and STAR
NGNP Program
November 19, 2008
INL Will Develop Standard Problems for Systems Analysis Codes (RELAP5)
• Based on the need to calculate highly ranked phenomena identified in PIRT.
• Potential standard problems include:– Mixed convection heat transfer in core– Two-phase flow behavior in reactor cavity cooling
system (RCCS) water cooling channels: natural circulation with flow stagnation and both forward and backward flow.
– Coupled problems: RELAP5-3D and CFD• Will follow same process presently being undertaken
with CFD for the lower plenum turbulent mixing problem.
NGNP Program
November 19, 2008
Capabilities of CFD & Systems Analysis Codes Validated Using Standard Problems…
Standard Problem Committee defined by GIF Methods Project Management Board: specifies required problems
Problem Oversight Committee: industry experts assign problems to participants and evaluate results of participants
Problem participants
Publish results
NGNP Program
November 19, 2008
Experimental R&D Needs—to Validate RELAP5-3D are Under Development…
• Major efforts are shown in planning schedule.
NGNP Program
November 19, 2008
Conclusions
Application of RELAP5-3D to analyze flow in gas-cooled reactor systems must be qualified and applied using appropriate practices and procedures to ensure code verification, minimize numerical error, quantify uncertainty and validate calculations. The NGNP Methods Program is formulating plans to ensure the project objectives are achieved.