1. VHTR Methods R&D Plan: Overall Perspective
Richard R. Schultz, Program Manager
Very High Temperature Reactor Design Methods Development & Validation
Workshop: VHTR R&D Plan
Hosted by: Academic Center of Excellence for Thermal Fluids and Reactor Safety, Oregon State University
September 19-20, 2005

2. Outline Background Goals for VHTR
Needs: CFD and systems analysis software development & validation
The Role of CFD & systems analysis software
Approach for achieving goals
Summary of experimental R&D
Summary of PIRT

3. Energy Bill Was recently passed by Congress & signed by President
Calls for locating a prototype Very High Temperature Reactor (VHTR) at the INL.
Specifies that a consortium of appropriate industrial partners will be organized that will carry out cost-shared research, development, design, and construction activities, and operate research facilities on behalf of Project (see Energy Bill—Section 643—Subtitle C: Next Generation Nuclear Plant Project).

4. Why at the Idaho National Laboratory?
52 nuclear test reactors
First nuclear electricity to power a town
890 sq miles
Lead Lab for Nuclear R&D
Overview of the INEEL
HAVE DONE POOR JOB
ENGINEERS ASSUME TECHNOLOGY IS THE ANSWER!!
BURMA, LIBERIA, US – NON METRIC
Craters of the Moon National Monument is 25 miles away by road
Largest recent (10,000 years) basaltic lava field in the continental United States
INEEL Site is surrounded by wilderness

5. Energy Act… I’m not going to interpret anything in the Energy Act.
It is important to remember that although millions of dollars are mentioned in Energy Act—we won’t have dollars unless they are appropriated.
For your reference regarding “…enabling research, development, and demonstration activities on technologies and components for reactor and balance-of-plant design, engineering, safety analysis, and qualification” see Sec 643 pages 622 through 627.
R&D will be done for both pebble-bed and prismatic reference designs [Phase II, in which a design competition between concepts will be held, will not begin until NERAC determines that the objectives of Phase I have been achieved (see Sec 643 item (c)(3)(D), page 627)].
Appropriations—see pages 902 through 915.

6. The 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
Prismatic
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
Pebble-bed

7. Strengths & Weaknesses of Prismatic Design Relative to Pebble-Bed—INL Perception
Larger fabrication, operating, & licensing experience base in US.
Flow paths are well known and relatively controllable due to fixed core design; peak fuel temperature may be more predictable.
Placement of control rods in fuel region is easier.
Weaknesses:
Larger excess reactivity, higher control worth, and relatively high packing fractions required to get desired operating cycle length.
Must be shut down periodically for refueling and refueling is relatively complicated.
Fuel at hot spots remains at same location relatively long time.
Relatively strong reactivity increase upon significant water ingress.
_______________
Items in red font require methods R&D to demonstrate capability of tools.

8. Strengths & Weaknesses of Pebble-bed Design Relative to Prismatic Design—INL Perception
Very little excess reactivity is needed—thus (a) reactivity insertion accident essentially eliminated from consideration, (b) proliferation attempts easy to detect, and (c) significant reduction in reactivity insertion due to water ingress.
Very effective fuel utilization.
Few reactor shutdowns required (no refueling outages).
Fuel enrichment is lower, easier to fabricate fuel pebbles, thus probably lower fuel costs.
Peak fuel temperatures will probably be lower.
Pebbles pass through high power region relatively rapidly—so fuel duty is milder and shared among many more elements.
Weaknesses:
Likely to be more difficult to calculate flow and temperature variations.
More pebble withdraw tubes are needed for annular core than for a solid core; bridging and stuck pebbles are a possibility.
Larger pressure drops across core (for 10 m high core). However, cross-flow design may eliminate this issue.
Production of dust. AVR generated approximately 3 kg/year from control rod insertions, rubbing of fuel pebbles, and drag of fuel pebbles on vessel.
Potentially may be more difficult to license.
_______________
Items in red font require methods R&D to demonstrate capability of tools.

9. Portion of R&D Need Matrix…
Region of System
Operational Conditions
Depressurized Conduction Cooldown
Pressurized Conduction Cooldown
Inlet Plenum
IP1: Validation of CFD mixing calculation during transient.
Core
CO1: Nuclear data measurements to reduce calculational uncertainty.
CO2: Modification of cross-section generation code to treat low-energy resonances with upscattering.
CO3: Development of improved method for computing Dancoff factors.
CO4: Characterization of hot channel temperatures and fluid behavior at operational conditions.
CO5: Validation using integral experimental data.
CD1: Validation of systems analysis codes to demonstrate capability to predict thermal behavior.
CD2: Validation of models that calculate fission product release from fuel.
CD3: Validation and calculation of air ingress and potential water ingress behavior into reactor vessel and core region.
CP1: Validation of systems analysis codes to demonstrate capability to predict thermal and hydraulic behavior.
Outlet Plenum
PO1: Validation of CFD mixing using mixed index refraction (MIR) facility data & data available in literature. Perform calculation of fluid behavior with validated code.
PD1: Validation of CFD mixing during operational transients and effect on turbine operational characteristics. Perform calculation of fluid behavior.
PP1: Validation of CFD mixing during operational transients and effect on turbine operational characteristics. Perform calculation of fluid behavior.
RCCS
RO1: Validation of natural convection characteristics in cavity at operational conditions.
RO2: Characterization of natural convection characteristics in cavity at operational conditions.
RD1: Validation of heat transfer & convection cooling phenomena present in reactor cavity and via RCCS.
RP1: Validation of heat transfer & convection cooling phenomena present in reactor cavity and via RCCS.

10. VHTR Objectives
Demonstrate a full-scale prototype VHTR that is commercially licensed by the U.S. Nuclear Regulatory Commission
Demonstrate safe and economical nuclear production of hydrogen and electricity

11. Goal: Design Methods Development & Validation
Ensure the software tools are available to enable the VHTR to be designed and licensed to achieve Generation IV Program standards & objectives.

12. Effect of Goals on VHTR Software…
Because VHTR design goals are ambitious:
High efficiencies
High operating temperatures
Exceptional safety margins
And licensing the VHTR will be a challenge,
Software tools for VHTR must have demonstrated capability and low calculational uncertainty

13. VHTR Design Methods Development & Validation
For each plant, 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 a
ccident s c
enario
that require analysis are identified
PIRT:
Important
phenomena
are identified for each
scenario (P
henomena I
dentification & R
anking T
ables )
Validation:
Analysis tools are evaluated to determine
whether important
phenom
ena
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

14. The Calculation Process…
Consists of seven steps
It’s assumed to be equally likely that the VHTR 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
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.

15. Includes Software such as:

16. What exists: Thermal-Fluid Analysis…
Partially validated systems analysis codes that cannot predict localized hot spots.
Unvalidated computational fluid dynamics codes that will calculate the presence of hot spots—but the results cannot be trusted.
Identification of only some of the important phenomena.
Large incomplete validation data base.

17. Many of the Phenomena that Must Be Quantified & Analyzed Require CFD
Forced convection: turbulent behavior and mixing
Mixed convection & free convection
Analysis of flow behavior in plena and chambers
Isolation of local hot spots a special need
Coupled calculations required: that is, calculations that require coupled CFD codes and systems analysis codes (such as RELAP5) are quite important.

18. Thermal-Hydraulic Phenomena: CFD
Normal operation at full or partial loads
Coolant flow and temperature distributions through reactor core channels (“hot channel”)
Mixing of hot jets in the reactor core lower plenum (“hot streaking”)
Loss of Flow Accident (LOFA or “pressurized cooldown”)
Mixing of hot plumes in the reactor core upper plenum
Coolant flow and temperature distributions through reactor core channels (natural circulation)
Rejection of heat by natural convection and thermal radiation at the vessel outer surface
Loss of Coolant Accident (LOCA or “depressurized cooldown”)
Prediction of reactor core depressurized cooldown - conduction and thermal radiation

19. Role of CFD & Systems Analysis Codes
Relevance:
Key phenomena will greatly influence the material temperatures at operational conditions and accident conditions.
Some validation data are available and are being used to validate CFD & one-dimensional systems analysis codes.
Present focus is on maximum channel coolant exit temperature at operational conditions and turbulent mixing in lower plenum.
Importance: The software must be shown capable of calculating the maximum material temperatures to enable the VHTR to be licensed. The calculational uncertainty must be acceptably low to demonstrate the VHTR achieves its design claims and is licensable.

20. CFD: Commercial vs. Non-Commercial…
There are ongoing studies to evaluate non-commercial CFD codes.
Commercial CFD codes are user-friendly and have an extensive V&V matrix. They can be used to analyze a wide variety of problems.
Quite often, the opposite is true for non-commercial CFD codes since their development is often aimed at specific problems.
However, non-commercial CFD codes are frequently state-of-the art and unexcelled in selected areas.

21. Approach for Achieving CFD Validation Objectives…
The process begins by using what is available in commercial CFD codes and by using RANS.
As deficiencies are identified in commercial CFD codes, the R&D path is chosen based on magnitude of deficiency.
Use LES and DES as necessary
Define development, including need for non-commercial codes, as required.

22. Example*: To Quantify Capabilities of Selected Commercial CFD Codes…
__________
* Similar approach proposed for systems analysis software

23. CFD Tool Certification: for Use in Gen IV
Industrial quality standards recommended, e.g., ISO 9001:2000 standards or equivalent (for software quality, construction, and certification)—particularly for design calculations
CFD certification should be based on V&V matrix that contains dominant phenomena for key Gen IV system scenarios
CFD software V&V required for key phenomena identified in matrix. Acceptance based on degree of agreement with qualified data
Extent of commercial and non-commercial CFD capabilities & need for further development/R&D can be demonstrated by specifying a series of International Standard Problems—with results published in journals.

24. Proposal: To Quantify Capabilities of Selected Commercial CFD Codes & Systems Analysis Codes…
Form PMB-sponsored committees with charter to define CFD code V&V matrix and systems analysis code V&V matrix based on Gen IV needs (the Standard Problem Committee).
Sponsor forums, similar to those hosted by Coordinating Group for Computational Fluid Dynamics (1993-4) or the Stanford Olympics (1968), to define International Standard Problems for CFD.
Publish results in journals.
Use validation results as basis for achieving validation objectives.
In summary, base approach on that used by US Nuclear Regulatory Commission when certifying their software tools to be used for reviewing the AP600 design for LWRs.

25. Analysis Practices Should be Well-Defined
For CFD software:
Suggest following policy defined by Journal of Fluids Engineering (Vol 115, 1993)
Benchmark study requirements: suggest following lead of: C. J. Freitas, “Perspective: Selected Benchmarks from Commercial CFD Codes,” Journal of Fluid Mechanics, 117, 1995, pp. 208 to 218.
For systems analysis software—use directly practices and procedures implemented by USNRC.

26. Summary: CFD Code Certification
The CFD V&V matrix must be defined.
Proposed that:
a series of CFD International Standard Problems be specified,
commercial and non-commercial CFD organizations be solicited to participate in an ISP Forum
the analyses be performed using rigorous standards
the analyses be published in the literature.

27. The Punch Line This effort is critical to mission success.
Current software and methods are not ready to perform design and analysis to the standard that will be required by the VHTR–considerable validation, and probably development, are required.
The above conclusion also applies to present software capabilities to perform VHTR licensing calculations.
Practices and procedures acceptable to community must be defined and implemented.
This effort is critical to mission success.

28. For Validation Purposes: Some Data Sets Already Exist & Others Are Already Planned
Examples:
IAEA benchmark problems.
Integral facilities: HTTR, HTR-10
Various other experimental data recorded in GIF member experimental facilities
US DOE sponsored data: matched-index-of-refraction (INL) and NSTF (ANL)

29. Summary of INL Experimental R&D
Ongoing R&D
Plans

30. Thermal hydraulic benchmark experiments
Objectives: Provide benchmark data for assessment and improvement of codes proposed for NGNP designs and safety studies and
Obtain better understanding of related phenomena, behavior and needs
Two emphases: Spatial variations in local fission rate and material behavior will cause "hot channels" which may cause "hot streaking" in lower plenum – and possible structural problems
Started in August 2004
Plan view of lower plenum for
prismatic NGNP concept

31. Overview of INL experimental tasks
Scaling
Needs
Heated experiment
concepts
Isothermal lower plenum
flow experiment concepts
Design
Fabrication
Measurements
Documentation
Coolant channels
Lower plenum
Selection of first heated experiment
Pebble bed exits?
Design
Fabrication
Measurements
Documentation
Second heated experiment
Other important geometries

32. Effect of turbulence model in CFD codes ("hot channel")
Run 618, turbulent, moderate q w
Twall (K)
v f
Turbulence
models
Shehata
CFD predictions of Richards, Spall and McEligot [2004]
Experiment of Shehata and McEligot [1998]
Selection of an adequate turbulence model is critical for CFD predictions

33. “Hot channel” experiment
Example of operating conditions for which code predictions are needed: non-dimensional heat flux
Tabulated benchmark data are available for these conditions
Vacuum vessel
Traversing table
Pressure
transducer
Multi-sensor
hot-wire probe
Thermocouples
Power
supply
Upflow or
downflow
Heat exchanger
Gas circulator
Flow meter
Potential concept to obtain benchmark
data for turbulence modeling –
low pressure to reduce buoyancy effects
For normal operation
Coolant channels have dominant forced convection with slight property variation
Parameters for buoyancy, streamwise acceleration and heat flux are low relative to thresholds for importance
Benchmark data are available to assess correlations in systems codes

34. Preliminary scaling studies -- lower plenum ("hot streaking")
One typical concept
Desired: T (or C), V, v as fns{x,y,z}, Nu for surfaces, f or L, Str
Parameters: Geometry, Rep, Rej, Vj/Vp, Ri or a buoyancy parameter and Tj/Tp for heated jets
Conditions: Normal, reduced power, transients
Dj/Dp  0.7 Dp
p/Dp  1.7

35. Lower plenum experiments
Parameter ranges in normal full power operation
Geometry: Posts under active core – pitch/D  1.7, height/D  7
Plenum Reynolds number, Replenum  24,000 (away from outlet)  3x106 (near outlet) "Mixed flow" Turbulent
Jet-to-crossflow velocity ratio, (Vj/Vp)  50 (away from outlet)  0.6 (near outlet)
"penetrating" "bent"
Qualitative flow visualization with dye injection [McCreery, 2004]
Model configuration
Example of flow away from outlet

36. Potential experiment concepts for lower plenum flows
Purpose: assessment of momentum equation solution, scalar mixing and turbulence models for typical plenum geometry in limiting case of negligible buoyancy and constant properties
Conceptual model designs (plan view)
Measurements
Flow visualization
Particle imaging velocimeter – flow patterns, mean velocities, mixing of passive scalars
Laser Doppler velocimeter – time-resolved mean velocity components and turbulence quantities in flows
Possible flow paths in NGNP lower plenum

37. How does refractive-index-matching help?
Optical techniques will be used with models in our large Matched-Index of Refraction (MIR) flow system
How does refractive-index-matching help?
Optical techniques avoid disturbing the flow to be measured
Typical approaches are LDV, PIV, PTV, flow visualization, PLIF, etc.
Laser Doppler Velocimetry
Particle Image Velocimetry
Snell’s Law
Unless the refractive indices are matched, the view may be distorted or impossible even with "transparent" materials and position measurements may be incorrect
Example of application of refractive-index-matching
Refractive index not matched
(Marking is on back of beaker)
Plexiglas model
Fluid
Laser beam
Laser
transmission
optics
Signal
collection
Internal
plexiglas
rods
Not matched
Matched
(Rod is resting on the bottom of the beaker)

38. Benefits of INL MIR flow system
Refractive index-matching and optical measuring techniques allow flow measurements when flow geometries are complicated
Most previous MIR experiments have been cm-scale; INL test section is about 0.6 m x 0.6 m x 2.5 m
Example of application of refractive-index-matching
(Marking is on back of beaker)
Not matched
Matched
(Rod is resting on the bottom of the beaker)
Apparatus to study fluid physics phenomena in idealized SNF canister for EM Science project
Advantages
Versatile - basic/applied research, internal / external / coupled flows
Non-intrusive, undistorted measurements of flow and transport
m-scale to building scale experience
Good spatial and temporal resolution
Benchmark measurements

39. Initial INL MIR experiment on lower plenum flow for assessment of CFD tools
Some desired features
Represent generic features of flows near LP outlet (crossflow) and away from outlet (no crossflow)
Well-defined geometry; ratios as in NGNP point design
Turbulent flow in jet entry ducts
Crossflow in "mixed flow" or "turbulent" regime [Zukauskas, 1972]
Jet velocity ratio: ½ < (Vjet/Vplenum) < "large"
Limited domain to ease initial CFD modeling
Measurements concentrating in important regions
U, V, W, u, v , w , uv, etc. as function of x, y, z
Flow visualization
Mixing of passive scalars
Inlet flow quantities for boundary conditions

40. Fabrication sketch of model
Jet inlet ducts
Milestones/deliverables
Fabrication sketches
(for code developers)
Initial measurements
Proposed for later years*
Measurements and comparisons
Documented databases
Technical papers and reports
*Depending on funding from FY US Gen IV program
Sep 2005 H
Support posts
Flow
Dimensions:
Dpost = 31.8 mm (1.25 in.), p/Dp = 1.7
Djet/Dp = 0.7, Hplenum/Dp = 6.85

41. Example of comparable PIV data from INL MIR flow system (idealized SCWR coolant channels in US/Korea I-NERI project [2005])
Flow
Streamwise velocity field

42. Supporting PIV measurements by Prof. B.L. Smith at Utah State U.
Purpose = determine the minimum flow rate (Reynolds number) to achieve "mixed flow" in the crossflow of the INL lower plenum model Experimental configuration
Geometry
Measurements

43. PIV measurements Re  400 Deduced contours of stream "Raw" photograph
function, steady laminar flow
Results include instantaneous and mean velocity fields, mean stream
functions, Reynolds stresses and 2-D "turbulence kinetic energy"

44. Preliminary classification
Re > 2 x 105 [Zukauskas, 1972]
Steady laminar flow
Unsteady laminar flow
Mixed partially-turbulent flow
Mixed turbulent flow
Turbulent flow
Visualizations and tabulations on web site (

45. Potential experiment concept for heated flows in lower plenum
Objective: assessment of codes predicting thermal mixing under influence of buoyancy for typical plenum geometry
Fluid: heated air or water with salt solution for density variation
Measure temperature field with miniature multi- sensor probes of Vukoslavcevic and Wallace [U. Maryland, NERI project] and possibly velocity and turbulence fields
Possible
model

46. INL thermal-hydraulic experiments - plans
FY-05
Complete fabrication sketches for MIR LP experiment
Complete fabrication and installation for first MIR LP experiment = jet inflow without imposed crossflow (i.e., away from LP outlet)
Continue evaluation of experiment concepts for heated flows
Submit deliverable (fabrication sketches)
Initiate measurements with MIR LP experiments (milestone)
FY-06
Complete measurements for MIR LP experiment without crossflow; document
Design and cost system to provide crossflow in MIR LP model
Fabricate and install system to provide crossflow in MIR LP experiment
Initiate measurements with imposed crossflows
Complete fabrication sketches for second MIR LP experiment
Continue design and selection of experiments for
Turbulence and stability data for vertical cooling channels
Heated flows in lower plenums
Initiate design of MIR experiments on exit flows in pebble beds (if funding permits)

47. Other recommended INL experiments for code validation
Core heat transfer experiments
Turbulence and stability data from vertical cooling channels
Bypass flow studies
Exit flows in pebble beds
Upper and lower plenum fluid behavior experiments
Fluid dynamics of lower plenums
Heated flows in lower plenums
Interactions between hot plumes in an upper plenum and parallel flow instabilities
Air ingress experiments: heat transfer and pressure drop of mixtures of air and helium
Larger scale vessel experiments: to examine the behavior in the core, in the plenums and the interactions between them

48. VHTR - Scalability of the ANL Natural Convection Shutdown Heat Removal Test Facility (NSTF)
Identified major scaling parameters & phenomena and constructed a semi-analytical scaling model for air cooled RCCS
Evaluated available RCCS designs, reviewed archival NSTF data, and identified needs for additional sets
Constructed CFD models of available RCCS designs and NSTF and performed accident condition analyses which showed strong 3-D effects and heat transfer differences with existing 1-D correlations

49. R&D Plans are Based on a Preliminary Phenomena Identification & Ranking (PIRT)
Based on prioritization of scenarios and phenomena :
Identified by experienced gas-cooled system designers
Engineering judgment
Aimed at requirements for performing reasonable calculations of plant behavior for:
Operational conditions (rated power): neutronics and working fluid behavior
Pressurized conduction cooldown transient scenario (PCCS)
Depressurized conduction cooldown transient scenario (DCCS) including possible air/water ingress
Focus is on maintaining integrity of fuel, core, and reactor vessel.

50. PIRT: Components
PIRT based on following components:

51. Example: Depressurized Conduction Cooldown Scenario has 3 Phases
Blow down (depressurization),
Molecular diffusion: following blowdown, there is not sufficient helium left in reactor vessel to have natural circulation—however, air from confinement moves into reactor vessel via diffusion. Heat removal dominated by radiation and conduction heat transfer.
Natural convection: Sufficient air has moved into reactor vessel via diffusion that natural circulation is initiated and convective cooling becomes an important ingredient.

52. Blowdown—Sample of Phase Description…
Event initiated by rupture of largest system pipes
System depressurizes
Helium working fluid discharged into volume that surrounds reactor
“Rapid” heat-up of core occurs by the loss of forced convection
Graphite dust from reactor core is transported to volume (the reactor confinement building) that contains reactor
The confinement relief valves lift and gas is discharged to environment. Filters minimize distribution of dust to environment. Relief valves close when pressure has been reduced sufficiently.

53. Phenomena are ranked… High if important.
Medium if phenomena may have supporting role in system behavior or may be important and thus should be carefully evaluated.
Low if can be neglected.

54. A Sample PIRT Table (for core)…
Phenomena
HPCC
LPCC LC 1 2 3
flow distribution H M
heat transfer (forced convection)
heat transfer (mixed and free convection)
pressure drop (forced convection)
pressure drop (mixed and free convection)
thermal mixing and stratification
jet discharge
thermal striping
bulk CO reaction
molecular diffusion
Fluid properties (gas mixture)
Graphite oxidation (PBR)

55. CFD Validations Required Based on PIRT…
Region of System
Operational Conditions
Depressurized Conduction Cooldown
Pressurized Conduction Cooldown
Inlet Plenum
IP1: Validation of CFD mixing calculation during transient & action of plumes on pressure heat boundary..
Core
CO4: Characterization of hot channel temp and fluid behavior at operational conditions.
CD3: Validation and calculation of air ingress and potential water ingress behavior into reactor vessel and core region.
CP1: Validation of systems analysis codes to demonstrate capability to predict thermal and hydraulic behavior.
Outlet Plenum
PO1: Validation of CFD mixing using mixed index refraction (MIR) facility data & data available in literature. Perform calculation of fluid behavior with validated code.
PD1: Validation of CFD mixing during operational transients and effect on turbine operational characteristics. Perform calculation of fluid behavior.
PP1: Validation of CFD mixing during operational transients and effect on turbine operational characteristics. Perform calculation of fluid behavior.
Reactor Cavity Cooling System
RO1: Validation of natural convection characteristics in cavity at operational conditions.
RO2: Characterization of natural convection characteristics in cavity at operational conditions.
RD1: Validation of heat transfer & convection cooling phenomena present in reactor cavity and via RCCS.
RP1: Validation of heat transfer & convection cooling phenomena present in reactor cavity and via RCCS.

56. Preliminary PIRT Being Used to Define CFD Related NGNP R&D…
Most applications are at low Mach numbers—thus CFD techniques used for incompressible flows will be most used.
A few applications for compressible, high-velocity CFD software are foreseen:
Perhaps blowdown
Pressure pulse propagation during turbomachinery transients, e.g. compressor surges.

57. Conclusions—Methods R&D
Passage of Energy Bill has authorized the project for siting the VHTR at INL, execution requires appropriations.
Candidate VHTRs are both prismatic & pebble-bed designs.
The VHTR will:
Make possible the efficient and cost effective production of either or both electricity and hydrogen
Excel in safety and reliability
Discharge waste that is suitable for long term disposal
Provide a bridge to a low-emissions economy based on water as our primary transportation fuel
The current Generation IV/VHTR methods R&D is centered on ensuring the software tools are available to enable the VHTR to be designed and licensed to achieve Generation IV Program standards & objectives.