1. Pisa, Italy – September 5th, 2012
Relap 5 simulation of a natural circulation loop
Alessandro Del Nevo (ENEA UTIS-TCI)
3rd LEADER Int. Workshop
“Design and safety analysis of Alfred Design and safety analysis of Alfred”
Pisa, Italy – September 5th, 2012

2. Objectives of the lecture
To provide an introduction on TH/SYS codes (RELAP5)
To understand the role of computer codes and their capabilities/limitations
To see a sample RELAP5 input deck and its structure
To run a sample natural circulation case with RELAP5 and
To briefly discuss the results
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

3. TH SYS codes and their role Description of a RELAP5 input deck
Outline of the lecture
TH SYS codes and their role
Description of a RELAP5 input deck
Execution of RELAP5: simulation of a natural circulation loop
Summary of RELAP5 results
Conclusive remarks
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

4. The TH-SYS code
I & C
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

5. The TH-SYS codes
TH-SYS codes ≠ CFD codes. Same originating principles and fluid balance equations, but...
TH-SYS codes do not calculate “profiles” (e.g. velocity) in cross sections
TH-SYS codes need a “huge” number of constitutive empirical correlations
CFD codes can calculate the turbulence
CFD codes calculate fluid performances at the scale < 10-3m
TH-SYS codes are “RA approved” computational tools in nuclear reactor safety
Coupling between TH-SYS and CFD codes to solve complex multi-scale problems
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

6. Applications of TH-SYS in deterministic safety analysis
The TH-SYS codes domain of application
Independent verification of safety analysis
Applications of TH-SYS in deterministic safety analysis
Design and design modifications
Licensing
Support for EOPs and plant simulators
Support for PSA
Support for AM and emergency planning
Analysis of operational events
Regulatory audit analysis
Demonstration of capabilities of safety systems to maintain fundamental safety functions
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

7. The TH-SYS codes
To simulate the NPP behavior under a wide range of plant operating conditions and postulated accidents
To demonstrate the NPP safety  acceptance criteria
Intrinsic limitations, but it is the state of the art tool for safety analysis and licensing. No significant advancement expected in near future
Relevance of user effect, uncertainty and training
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

8. RELAP5 code and HLM reactor systems
BE TH-SYS (e.g. RELAP5) codes are the tools for DSA
All TH-SYS codes have closure laws, based on empirical correlations
RELAP5 is developed for LWR
Application of RELAP5 to HLM systems requires “identified” modifications
RELAP5 code modified by ENEA/UNIPI includes specific correlations for single-phase heat transfer to liquid metals (i.e. Seban-Shimazaki, Ushakov, Mikityuk).
Limited capabilities are expected in simulating specific HLM system phenomena: e.g. pool thermal-hydraulics behavior
V&V processes is “long lasting” activity needed for demonstrating TH-SYS reliability: this is a regulatory requirement
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

9. The TH-SYS code RELAP5 RELAP5: 1D TH system code
Developed at Idaho National Lab (USA)
2 phases, 6 equations code (mass, energy & momentum) + incondensable gases tracking
Extensively used by Safety Authorities, Industries & Research Institutions
Intensive validation campaigns since the 1970
Various versions available (US-NRC R5, R5-3D, R5-SCDAP)
Detailed TH Modeling of LWR (control volumes >~10 cm length)
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

10. RELAP5 input structure Input types are identified by unique numbers
Order of input lines can be arbitrary
Last occurrence of line replacing previous duplicates
Typical input file includes
Control options
Time step options
Plot request data
Trip logic and control system data
Hydrodynamic component data
Heat structure data
Reactor kinetics data
General table data
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

11. RELAP5 input card numbers
[ ] Control options
[ ] Time step options
[ ] Minor edits
[ ] Trips  [ ] extended format
[CCCXXNN] Hydrodynamic components
[1CCCGXNN] Heat structures
[201MMMnn] Heat structure thermal proprieties
[202TTTNN] General tables
[205CCCNN] Control variable
[ ] Point Kinetics
INPUT DECK
Let us model with RELAP5 a simple NC loop under design to test the SG bayonet tube of ALFRED reactor design
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

12. Modeling a NC loop by RELAP5 facility
The facility HERO is under design at CR Brasimone (Davide ROZZIA)
The activity is aimed at verifying the feasibility of the superheated steam, double wall, once-through bayonet type steam generator
Let us model the system using RELAP5 code (modified for Lead and LBE working fluids)
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

13. RELAP5 input description
[ ] Control options
[ ] Time step options
INPUT DECK
* Problem Type and Option
new transnt *
* Unit System
* si si
* Noncondensible Gas
nitrogen
* Hydrodynamic System Control
* RefVol Elev Fluid SysName
h2o tube
pb channel
* TIME STEP
* tend dtmin dtmax NumMeth mEFrq MEFrq RstFrq e e e e
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

14. RELAP5 input description
[ ] Trips  [ ] extended format
INPUT DECK
* TRIPS
* end program
expanded *
time 0 lt null e6 n * always true
time 0 gt null e6 n * always false
tempf lt tempf e n -1.0
p gt null e n -1.0
** High pressure signal in the water tank
and 2 n -1.0
or 1 n -1.0
* power
and 1 n 0.0
* END OF PROGRAM
time 0 gt null n *
199 or 1000 variable trips Each card defines a logical statement or trip condition concerned with the quantities being advanced in time. A trip is false or not set if the trip condition is not met, and true if it is met. On restart, new trips
199 or 1000 logical trips Each card defines a logical relationship with the trips defined on these cards or on the variable trips.
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

15. RELAP5 Hydrodynamic components
[CCCXXNN] Hydrodynamic components
The fluid system consists of a set volumes and junctions interconnected. Different (separate) systems are possible
Basic requirements are: all flow areas and volumes; vertical orientations; hydraulic diameters; flow loss geometries and initial conditions
Possible component options:
Single volume, single junction and multiple junction
Time dependent volume and time dependent junction
Pipe, annulus and Branch
Special components: Separator (branch with special models); Valve (different types); Pump; Accumulator; Jetmixer; Turbine; Eccmix
INPUT DECK
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

16. RELAP5 Hydrodynamic volumes
[CCCXXNN] Hydrodynamic components
Hydrodynamic volumes
The entire space filled with the working fluid is divided in volumes
The numerical approximation for conservation of mass and energy is done over the hydrodynamic volumes
INPUT DECK
Primarily 1D approximation (multi-dimensional flow is provided): connections possible to all 6 faces of the volume
Basic 1D flow is along the X coordinate
Typical volumes quantities: flow areas; flow lengths; elevation changes; volumes pressures temperatures; void fractions; energies, mass transfer rates; average volume velocities; wall heat fluxes
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

17. RELAP5 Hydrodynamic junctions
[CCCXXNN] Hydrodynamic components
Hydrodynamic junctions
Staggered node extended from the center of one hydraulic volume to the center of a connected hydrodynamic volume
Numerical approximation for conservation of momentum equation is done over hydrodynamic junctions
A junction connects two faces of two different volumes (multiple junctions can connect up to 99 couple of faces)
Junctions interconnect the volumes to form a flow system
The center of the “from” space and the center of the “to” face are assumed to occupy the same point space
INPUT DECK
Junctions
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

18. Modeling the hydraulic system
[CCCXXNN] Hydrodynamic components
INPUT DECK
Bayonet tube (water)
Lead NC loop
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

19. RELAP5 sample input: “PIPE” component
INPUT DECK
Lead NC loop
* CCCXXNN
LBEtube pipe e
e e e e e e e e e e e e
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

20. RELAP5 sample input: “BRANCH” component
Lead NC loop
INPUT DECK
* CCCXXNN
LBE5 branch e e
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

21. RELAP5 sample input: “SNGLJUN” component
Bayonet tube (water)
INPUT DECK
* CCCXXNN
junc sngljun e
Single Junction is a connection between pipes CV100 and CV110
Single Junction is a connection between SG tube ascending and descending sides
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

22. RELAP5 Heat structures [1CCCGXNN] Heat structures
Representation of solid portion of the TH system: outside characteristics
Suitable to model: pipe walls, vessel walls, SG tube walls, reactor internal structures, fuel rods, electrical heaters,
Calculation of the heat transferred across solid boundaries of hydrodynamic volumes
Structural behavior of solid materials up to core damage
Conduction inside the structure
Convection: heat transfer from a surface to fluid and viceversa
Special models:
Gap conductance model
Surface-to-surface radiation model
Metal-water reaction model
Cladding deformation model
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

23. RELAP5 Heat structures [1CCCGXNN] Heat structures
Represented by one-dimensional heat conduction in various geometries (slab, cylindrical, spherical)
Surface multipliers to convert one-dimensional calculation to actual heat structure surface
Spatial dimension of the calculation is along any one of the coordinates in rectangular geometry and is along the radial coordinate in cylindrical or spherical geometry
SPHERE
SLAB
CYLINDER
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

24. RELAP5 Heat structures [1CCCGXNN] Heat structures
Heat structures are modeled in mesh intervals
Different mesh spacing possible
Different compositions: materials characterized by thermal conductivity [k] and volumetric heat capacity [Cp]) possible
Mesh points must be placed such that they lie on the two external boundaries and at any interface between different compositions. Additional mesh points may be placed at desired intervals between the interfaces or boundaries
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

25. RELAP5 Heat structures [1CCCGXNN] Heat structures
Different boundary conditions are possible:
Insulated (no heat transfer at the surface)
Correlation package covering the various modes of heat transfer from a surface to fluid, and the reverse heat transfer from fluid to the surface
Table of surface temperature versus time
Heat transfer rate as a function of time or surface temperature
Heat transfer coefficient as a function of time or surface temperature
Convection boundary types
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

26. RELAP5 Heat structures [1CCCGXNN] Heat structures
The heat transfer modes:
Convection to noncondensable-water mixture.
Single-phase liquid convection at supercritical pressure.
Single-phase liquid convection, subcooled wall, low void fractions.
Subcooled nucleate boiling.
Saturated nucleate boiling.
Subcooled transition boiling.
Saturated transition boiling.
Subcooled film boiling.
Saturated film boiling.
Single-phase vapor convection or supercritical pressure with the void fraction > 0.
Condensation when the void is < 1.
Condensation when the void = 1
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

27. Bayonet tube inner wall
Modeling the heat structures
[1CCCGXNN] Heat structures
INPUT DECK
Bayonet tube inner wall
NC loop/Bayonet tube HEX
Lead NC loop inner wall
Lead NC loop outer wall
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

28. NC loop/Bayonet tube HEX
RELAP5 sample input: heat strucutre
[1CCCGXNN] Heat structures
INPUT DECK
NC loop/Bayonet tube HEX
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

29. RELAP5 sample input: heat strucutre
NC loop/Bayonet tube HEX
INPUT DECK *
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

30. RELAP5 input card numbers
[201MMMnn] Heat structure thermal proprieties
[202TTTNN] General tables
INPUT DECK *
* AISI 316 conductivity (W/m/K) *
* * AISI 316 heat capacity (J/m3/K)
* e+06
e+06
e+06
e+06
e+06
e+06
power e
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

31. RELAP5 input card numbers
[205CCCNN] Control variable
Provides the capability to evaluate simultaneous algebraic and ordinary differential equations
May be used to simulate control systems in a hydrodynamic system
Provides algebraic relationship, differentiation and integration for plotting of derived quantities, e.g. delta-p, total quantity of a discharged mass through a valve, total energy exchanged in a SG, etc.
INPUT DECK
* Power exchanged 1110 lato interno
Wlbeenv sum e
htrnr
htrnr
htrnr
htrnr
htrnr
htrnr
htrnr
htrnr
htrnr
htrnr
Mh2oves sum p p
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

32. RELAP5 MANUALS Main RELAP5 manuals
Volume I (Code structure, system models, and solution methods)
Volume II (User guide)
Volume II Appendix (Input requirements)
Volume IV (Models and correlations)
Volume V (User guidelines)
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

33. RELAP5 input card numbers
Execute RELAP5 code
RELAP5 code executable
Input deck
Fluids proprieties (water and Pb for HERO calculation)
Command line: relap533.exe i input.inp o output.out -r restart.rst
RUN RELAP5 CODE
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

34. Sample application and analysis of results
HERO facility is designed to investigate the performances of the bayonet tube of ALFRED SG (scaled 1:1) in conditions representative of the reactor operations
RELAP5 is applied to support the design of HERO facility
HERO facility shall be designed to have a mass flow rate larger than 6.4kg/s, relying on natural circulation. The lead flow area is expected to dominate the mass flow rate.
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

35. Sample application and analysis of results
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012

36. SUMMARY
RELAP5 code has been outlined, pointing out its roles in nuclear reactor safety analysis
TH-SYS codes are developed for LWR
Sample RELAP5 input deck and its structure has been presented
Sample application of RELAP5 for supporting the design of HERO facility is presented
3rd LEADER Int. Workshop – Pisa, Italy - September 5th, 2012