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Comprehensive Analysis of TRACY Benchmark II using AGNES Code

Explore the calculation results and methodology for the TRACY Benchmark II experiment conducted with AGNES code, including core specifications, reactivity insertion methods, kinetic parameters, sensitivity analyses, and void reactivity feedback model.

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Comprehensive Analysis of TRACY Benchmark II using AGNES Code

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  1. Expert Group on Criticality Excursion AnalysisSeptember 22, 2005 2005-09-22 Calculation Result for TRACY Benchmark II using AGNES code Yuichi YAMANE, Yoshinori MIYOSHI Japan Atomic Energy Research Institute

  2. TRACY Core • Core specifications • Fuel : 10wt% enriched uranyl nitrate • aqueous solution • Shape : Annular (50cm/7.6cm) Transient rod at the center hole • Limitations • Maximum Power ：5000MW • Total energy : 32 MJ/experiment ( = 1018 fissions) • Maximum excess reactivity: 3.0 $ • Reactivity insertion method • Rod withdrawal • Pulse withdrawal (Step insertion) • Ramp withdrawal • Fuel feed • Ramp feed Expert Group on Criticality Excursion Analysis

  3. TRACY Benchmark II • Ramp reactivity insertion by feeding fuel solution. • Excess reactivity; 0.5$ - 2.66$. • Initial reactivity; subcritical • U conc.; 379 – 422 gU/Lit. • Effective delayed neutron fraction; 7.5x10-3. • Neutron generation time; 4.6x10-5. - No external neutron source was used. Expert Group on Criticality Excursion Analysis

  4. Solution Level Difference Method • The inserted reactivity is evaluated as follows; C: 7.671x108 (cent/mm2), l: 102 (mm) Hc1: critical height without Tr-rod Hf: height at the end of reactivity insertion The estimated error of r is about 5%. Expert Group on Criticality Excursion Analysis

  5. AGNES code • One-point kinetics code • One-dimensional thermal conductivity model (solution-container-coolant) • The heat effects of the structural material and the air convection outside the core tank • Radiolytic dissociation gas void model Expert Group on Criticality Excursion Analysis

  6. Kinetic Parameters: R61 • SRAC + TWODANT with JENDL-3.2 • Neutron generation time : 4.51x10-5 • beff : 7.63x10-3 • Reactivity Temperature Coefficient : -3.9 cent/K, -1.8 cent/K2 • Reactivity Void Coefficient : -5.0x101 cent/%, -2.2x10-1 cent/%2 Expert Group on Criticality Excursion Analysis

  7. Example of Calculation: R61(2.64$, 0.05$/s) • The 1st peak and 2nd peak are well reproduced. • The 3rd peak is delayed and lower. Expert Group on Criticality Excursion Analysis

  8. Void Reactivity Feedback Model of AGNES • Void ratio is proportional to power density and excess gas concentration. • Gas concentration is proportional to power density. • C0, G, n, CD are main parameters and n and CD have been tuned. • Fi,j: Void ratio (%), • Ci,j: Concentration of radiolytic dissociation gas (mol/m3), • P : Power density (W/m3), • : energy – void transfer coefficient,(m6/J mol) C0 : Saturation concentration of gas (mol/m3), G : Radiolytic dissociation rate (mol/J), • : Decay constant of radiolytic gas (s), gi,j : Power distribution ratio H(x) : =1 for x>0, =0 for x<0. • vi,j: upward velocity of void (m/s2), • ri,j: Void radius in mesh i,j (m), • g : gravity acceleration (m/s2), • : energy – void transfer coefficient, CD : Resistance coefficient, CD = b0 + b2 F2i,j . Expert Group on Criticality Excursion Analysis

  9. Void Parameters: R61 • Energy-void transfer coefficient and resistance coefficient have been tuned so that the 2nd power peak has been reproduce well for R61. • AGNES’s void model ignores that Fi,j and Ci,j are lowered by pumped solution and convection due to pumping. * CD = b0 + b2 F2i,j Expert Group on Criticality Excursion Analysis

  10. Sensitivity to Void Parameter; n n : Energy-void transfer coefficient = 1x10-7 to 1x10-11 The shape of bottoms is changed. Expert Group on Criticality Excursion Analysis

  11. Sensitivity to Void Parameter; CD CD: Resistance coefficient = 2x10-8 to 8x10-8 The interval between peaks is changed. Expert Group on Criticality Excursion Analysis

  12. Kinetic Parameters: R76 • SRAC + TWODANT with JENDL-3.2 • Neutron generation time : 4.74x10-5 • beff : 7.59x10-3 • Reactivity Temperature Coefficient : -4.0 cent/K, -1.5 cent/K2 • Reactivity Void Coefficient : -4.7x101 cent/%, -1.9x10-1 cent/%2 Expert Group on Criticality Excursion Analysis

  13. Example of Calculation: R76(2.66$, 0.18$/s) • The 1st peak is well reproduced. • The 2nd peak and 3rd peak are delayed and lower. Expert Group on Criticality Excursion Analysis

  14. Kinetic Parameters: R159 • SRAC + TWODANT with JENDL-3.2 • Neutron generation time : 4.86x10-5 • beff : 7.55x10-3 • Reactivity Temperature Coefficient : -4.0 cent/K, -1.7 cent/K2 • Reactivity Void Coefficient : -4.3x101 cent/%, -1.5x10-1 cent/%2 Expert Group on Criticality Excursion Analysis

  15. Example of Calculation: R159(0.50$, 0.15$/s) • The 1st peak is well reproduced. • The power is lower after the 1st peak. Expert Group on Criticality Excursion Analysis

  16. Sensitivity to Excess Reactivity; 0.50$ Excess reactivity($) = 0.44 to 0.50 The profile with 0.46$ gives the best fit Expert Group on Criticality Excursion Analysis

  17. Preliminary Result and Summary • The 1st peak power and total released energy were reproduced within 2 to 15%. • Some values of the inserted reactivity and inverse period should be re-evaluated. Expert Group on Criticality Excursion Analysis

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