BEST-ESTIMATE METHODOLOGY

Transcription

1 BEST-ESTIMATE METHODOLOGY

2 CONTENT Recall of LB LOCA evaluation method EDF methodology presentation Principles DRM applied to LB LOCA CATHARE GB Key parameters PCT95 PCT DRM BE methodology feedback

3 LB LOCA EVALUATION METHOD CFR Appendix K Envelope operating conditions Penalised initial and boundary conditions Acceptable models PCT conservative estimation R & D Improvment in the understanding of the physical phenomena and in LOCA simulation Appendix K seems conservative Amendment of 10 CFR Regulatory guide Envelope operating conditions Initial and boundary conditions uncertainties statistically combined Use of best estimate code Uncertainties on code models Uncertainty on the result from IC, BC, models

4 LB LOCA EVALUATION METHOD In FRANCE Up to 1999, LOCA methodology in France conforming the 10 CFR and Appendix K EDF proposal of new methodology for LB LOCA based on: CATHARE code Surface response to estimate PCT 95 «Determinist Realistic Method»

5 EDF METHODOLOGY - PRINCIPLES Principle : six steps Statistical approach Scenario dominant physical phenomena identification 2. Code capability for the transient simulation 3. Key parameters 4. Uncertainties on key parameters 5. PCT95 Determinist approach 6. Determinist calculation (envelope value of PCT95)

6 DRM APPLIED TO LB LOCA EDF Methodology = Statistical approach + Determinist approach CATHARE GB code (CATHARE Code + improvement for LB LOCA transient) Keys parameters defined according to their importance on the dominant physical phenomena Use of response surface = Substitute of CATHARE code PCT 95 Penalised initial and boundary conditions Penalised code models PCT DRM

7 CATHARE GB CODE «A best estimate code must provide results that are qualitatively correct and quantitatively representative of the average of the experimental values (and not necessarily envelope values) where results are compared with representative test results» RG Elementary models of CATHARE Qualification covers the phenomena encountered in LB LOCA Global behaviour of CATHARE compared to experiment LOFT, UPTF, BETHSY Good simulation of the dominant physical phenomena Some model improvement for LB LOCA

8 Key parameters KEY PARAMETERS Only dominant parameters taken into account Global impact of the parameters of little importance? UNCERTAINTY RANGES Result from comparison between measurement / calculation What uncertainty when several code models are involved in a significant manner for a test simulation?

9 PCT95 evaluation Key parameters + uncertainties EDF Method PCT95 Categorisation of some key parameters into «macroparameters» Response surface & Monte Carlo «Macro-parameters» + uncertainties

10 Response surface construction PCT Response surface 1 key parameter : 2 CATHARE calculations Minimum value Maximum value 2 key parameters : 4 CATHARE calculations N key parameters : 2 N CATHARE calculations

11 RESPONSE SURFACE Response surface quality PCT Response surface «real» PCT Macro-parameter good and conservative approximation of CATHARE code

12 RESPONSE SURFACE CATHARE calculation for intermediate values of key parameters PCT Not conservative response surface Conservative Response surface? Macro-parameter

13 PCT DRM Penalised models «Penalised CATHARE GB» = conservative code + Envelope initial and boundary conditions Conservative result

14 PENALISED CATHARE GB CATHARE GB Penalised CATHARE GB essais essais Calculation Calculation

15 BE methodology feedback Uncertainty ranges determination Propagation methodology Global impact of all parameters not considered

16 UNCERTAINTY RANGES : Methodology One model involved Identification of separated effects test used for the qualification of this model Example: CANON vertical : depressurisation of a vertical pipe Measurements Pressure Void fraction Remain liquid mass Model : interfacial friction coefficient Qualification uncertainty [0.5;2] Uncertainty [0.5;10] to cover all the CANON experiments whatever the pressure initial value

17 UNCERTAINTY RANGES : Methodology Several models involved Infinite uncertainty range combination to envelop the experimental data Example : WINFRITH (reflood test) Model : heat exchange coefficient (film boiling and gas forced convection) CATHARE team : all the uncertainty on the film boiling Influence of another choice This uncertainty can t cover the experimental data considering the new grid of physical law Influence of the non dominant parameters on the uncertainty ranges

18 PROPAGATION METHODOLOGY Wilk s theorem Gives only an envelope value of PCT95 n uncertain parameters (uncertainty range and density probability function) m random and independant combination of these n parameters Number of calculations depends on confidence level PCT Envelope value of PCT95 then m>59 Envelope value of PCT95 PCT95 BE

19 PROPAGATION METHODOLOGY Surface response : how to define it? Linear on each parameter Require uncertainty ranges to be small since phenomena not linear Polynomial function Needs more calculations Problem of the definition of the reference points to build the surface response and have a good accuracy of PCT95

20 Which parameters to consider 30 parameters considered uncertain with 27 code models PCT 30 models 8 main parameters identification C PCT 30 models PCT 8 models 8 main parameters considered uncertain PTG 8 models Global impact of non dominant parameters PCT BE

21 CONCLUSION Improvement needed in Uncertainty ranges determination Propagation methodology Global impact of all parameters not considered

22 Key parameters + uncertainties PCT95 EVALUATION MONTE CARLO N random sample of Key parameters N CATHARE calculations N response surface calculations Distribution of PCT PCT95

23 Comparison between methodologies PCT Appendix K DRM PCT Margin T2 ( C) T3 ( C)

24 TRAITEMENT STATISTIQUE GLOBAL UNCERTAINTY EVALUATION Suggested list of parameters PARAMETERS :STATISTIC/DETERMINIST sufficiency justified (otherwise bias) code models :depend on the code used Key parameters may either Be fixed at their penalising values Be treated statistically TRAITEMENT DÉTERMINISTE Break size Single failure criterion LOOP assumption