1,721,038 research outputs found
Further analysis on Identification of Thermalhydraulic Phenomena for PWR Transient Analysis and Simulation
No full textIn the domain of reactor transient simulation, the identification of thermalhydraulic phenomena (THP) plays a major role. The system codes should model all influent THP and should be validated against integral effect tests (IET) and separate effect tests (SET) which cover all influent THP. The uncertainty quantification should cover every model related to an influent THP. A list of 116 THPs synthesizes more than 30 years of OECD and IAEA activities conducted by many world high-level safety analysis experts. It covers all water-cooled reactors and DBA analyses. A new tentative method to identify THP was proposed based on two sources of information, the observed parameter evolutions in transients (depressurization, voiding, refill, heating,..) and the set of balance equations with source and sink terms for convection, diffusion, interfacial transfers, wall transfers. The analysis is made at system, component, and basic process levels.
This paper compares the two approaches for the particular case of GEN-2 PWRs. No major contradiction is found. Both methods identified phenomena at system, component, and process level. The 116 list intends to cover system code validation needs and better identified phenomena that require ‘special models’. The use of equations identified many more local process THPs, which may help identifying validation needs and ranking phenomena in a scaling analysis. The comparison confirms a potential synergy and complementarity between the two approaches and suggests further efforts to combine them and complement them in a new international collaborative context.
This analysis reports on-going discussions between members of the FONESYS network of system code developers
Identification of thermal hydraulic phenomena for PWR transient analysis and simulation
No full textNEEDS AND CONTEXT
2/6
New situations:
New reactors: SMR, GEN Iii, Passive systems, GEN IV,...
Newsafetyregulationsrequirenew investigations (e.g. LBLOCA-IBLOCA)
New simulations tools(Sys-TH, CFD-porous, CFD-open)
New needs:
Revisiting transient analysis with PIRT, scaling, V&V, UQ
Include information from recent experiments
Possible use of multiscale simulation
Identification and rankingTHP ispart of the new need
Proposal for a scaling activity
No full textSeveral scaling methods and scaling criteria are available for PWR IET design: Power-to-Volume Scaling , 3-level Ishii scaling, H2TS, FSA, DSS,...
All scaling methods identify scaling distortions and try to minimize them
Various scaling criteria were applied in various existing IET, demonstrating a high “User effect in scaling”:
- There is a need to give Guidelines for scaling when designing a facility and/or an integral test for a specific transient
- There is a need to identify a qualitative and quantitative framework (precision targets) for judging the quality of a scaling approach pursued in licensing or safety analysis. This is connected with the acceptance criteria for scaling distortions and with the quantification of uncertainty due to scaling (e.g. conclusion of the CSNI Scaling SoAR)
Mantilla experiments: void fraction and flow regimes evaluation
No full textFollowing a suggestion of D. Bestion, [1], the Scientific Secretariat performed the direct application of the horizontal stratification criteria implemented into some SYS-TH codes to the TPTF 8-inch and Mantilla 2-inch airwater experimental data, [2], (no code calculations).
Measurements performed at the Mantilla 2-inch and 6-inch flow loops do not allow a straightforward application of the horizontal stratification criteria implemented into SYS-TH codes. These criteria require the knowledge of the gas and liquid velocities and of the void fraction, but the void fraction was not measured.
1.1. Objectives and Scope of the Activity
The objective of the present activity is to estimate the void fraction at the metering station and to quantify its uncertainty for the Mantilla 2-inch and 6-inch experiments in separated flow regimes or transition flow regimes, using the available experimental data.
This task fits in the scope of a running FONEYS activity on the assessment of the capability of SYS-TH codes in predicting flow regime transitions in horizontal pipes
TPCF Benchmark Report - Summary and Conclusions
No full textSection 2 - Tests for code-to-code comparison
Comments from J.L. Vacher and D. Bestion considered
Some improvements and further check performed by M. Lanfredini
KAERI calculations, UNIPI calculations, containment simulator pressure behavior, ....
Section 3.1 - Super CANON experiment
Issue in Apros nodalization identified and addressed. The same issue may affect COSINE model
Calculations not repeated (Edwards pipe experiment is sufficient to support the main conclusions)
Comments from D. Bestion considered
Section 3.2 - Edwards pipe experiment
No major comments
Section 3.3 - Comments on SUPERCANON and Edwards pipe tests (transient tests)
Section added to the report
Codes can capture the qualitative behavior rather well but are never very precise quantitatively
Code which use fine 1D modelling of critical flow cannot expect to improve significantly such predictions
Codes which use a 0-D choked flow modeling may just conclude about the relative merits of the various choked flow option
SB-LOCA Counterpart Test - LOBI, SPES, BETHSY, LSTF, PSB - Preliminary ATLAS calculation
No full textCounterpart test on SB-LOCA was conducted in early ‘90 on four ITF + one in early 2000’s
- LOBI – power-to-volume, Kv = 1/712 [KWU-PWR, 4 loops]
- SPES – power-to-volume, Kv = 1/427 [Westinghouse-PWR, 3 loops]
- BETHSY – power-to-volume, Kv = 1/100 [French-PWR, 3 loops]
- LSTF – power-to-volume, Kv = 1/48 [Westinghouse-PWR, 4 loops]
- PSB – power-to-volume, Kv = 1/300 [VVER-1000] - Performed in 2000’s
Break area/ ITF volume ≃ 6.52e-5 (6%-4% break at reference reactors scale)
Main features of the tests (some distortions exit):
- SB-LOCA in CL – Loop with PRZ
- Low initial power (∼ 10%) – LOBI and SPES tests repeated at high power (100%)
- Same core outlet temperature
- SG interconnected and isolated
- MCP trip occurs
- HPIS not available
- Accumulator injection at 42 bar – Intact loops
- LPIS simulated in LOBI and SPES (and PSB) – Intact loops
Detailed evaluation of the experimental database performed
Extensive post-test analyses conducted with RELAP5 and CATHARE2 code
Proposed activity on 3D modeling of passive systems and other mixing problems using coarse nodalization
No full textSystem transient include 3D phenomena
Transient simulation for safety require low CPU to allow many runs for UQ
Coupling between reactor circuits, containment and passive systems may be necessary
Many types of 3D simulation tools exist (CFD in open medium, porous body CFD, 3D modules of system codes? Multi-1D+crossflows) with many options for physical models (e.g. turbulence model)
How to select the right 3D tool depending on the objective?
FONESYS Meeting, June 2020,
Mixing problems are encountered in reactor thermalhydraulics which may require 3D modelling of some components: MSLB, Boron dilution, H2 mixing, PTS, passive systems,...
Turbulence controls the efficiency of the mixing
Buoyancy effects and density stratification may play a role
Predicting turbulence mixing requires CFD with very fine nodalization in all shear layers, high order numerical schemes and needs very high CPU cost
3D models of system codes use coarse nodalization and first order numerical schemes: low CPU cost
When buoyancy effects are dominant or sufficiently high, the mixing may be low and a coarse nodalization may predict the behavior rather wel
Tracking and minimizing compensation of errors in reactor experimental and numerical simulation
No full textORIGIN OF COMPENSATING ERRORS
2/9
Reactornumericalsimulationdoesnotuseexactequationsbutimperfectmodels
Anyfitting(tuning)ofmodelsondatacreatesacompensationoferror
Reactorexperimentalsimulationusereducedscaleexperiments(withpossibledistortions)
Howtheerrorcompensationmaybescaledependent?
Possiblenon-compensatingerrorsatreactorscal
Summary Outcomes of two SWINTH Workshops on Measurement Techniques for Nuclear Reactor Thermal Hydraulic Experiments
No full textThe SWINTH workshop series was initiated in 2016 by the SILENCE Network with the purposes of gathering information on the state-of-the-art in the area of instrumentation and measurement techniques for nuclear thermal-hydraulics experiments and promoting technical exchanges among specialists, including experts in code validation.
Two SWINTH workshop were held in Livorno, Italy (June 2016 and October 2019), hosted by the University of Pisa, two decades after the international OECD/NEA specialist meeting on the same subject held in Santa Barbara, CA, U.S.A., in 1997. The second SWINTH workshop, co-organized by SILENCE and by the OECD/NEA/CSNI /WGAMA, was extended to TH experiments relevant to Severe Accident.
SWINTH workshops attracted over sixty participants from Europe, Asia and North America and provided a wide picture of the ongoing research in the international community and of the major challenges being faced by experimentalists. Recent progress in the development of new instrumentation techniques and improvements of consolidated state-of-the-art technology were presented. The difficult challenge of quantification of measurement uncertainty, which received an increasing interest, along with other recommendations and lessons learned, constitute the key outcomes of the SWINTH workshops. They are summarized in the present paper
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