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

Expert Group on Criticality Excursion Analysis 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 TRACYでは、調Ｔｒ棒の交換により、 新たに、添加反応度2.8２$までの超臨界実験を行なえるようになった。 今回は、過渡特性を測定した結果について報告する。 まず、測定の概要について September 22, 2005 Expert Group on Criticality Excursion Analysis

Expert Group on Criticality Excursion Analysis 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. September 22, 2005 Expert Group on Criticality Excursion Analysis

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%. September 22, 2005 Expert Group on Criticality Excursion Analysis

Expert Group on Criticality Excursion Analysis 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 September 22, 2005 Expert Group on Criticality Excursion Analysis

Expert Group on Criticality Excursion Analysis 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 1 2 3 4 5 6 Delayed neutron fraction 2.55x10-4 1.65x10-3 1.49x10-3 3.00x10-3 8.93x10-4 3.25x10-4 Precursor decay constant (s) 1.27x10-2 3.17x10-2 1.15x10-1 3.12x10-1 1.40 3.87 September 22, 2005 Expert Group on Criticality Excursion Analysis

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. September 22, 2005 Expert Group on Criticality Excursion Analysis

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 . September 22, 2005 Expert Group on Criticality Excursion Analysis

Expert Group on Criticality Excursion Analysis 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. Current (Benchmark 2) Benchmark 1 C0 : Micro void threshold value 15 G : Radiolytic dissociation rate 3x10-7 n : Energy-void transfer coefficient 1x10-9 1x10-7 CD (b0,b2)*: Resistance coefficent 4x10-8 8x10-8 * CD = b0 + b2 F2i,j September 22, 2005 Expert Group on Criticality Excursion Analysis

Sensitivity to Void Parameter; n n : Energy-void transfer coefficient = 1x10-7 to 1x10-11 The shape of bottoms is changed. September 22, 2005 Expert Group on Criticality Excursion Analysis

Sensitivity to Void Parameter; CD CD : Resistance coefficient = 2x10-8 to 8x10-8 The interval between peaks is changed. September 22, 2005 Expert Group on Criticality Excursion Analysis

Expert Group on Criticality Excursion Analysis 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 1 2 3 4 5 6 Delayed neutron fraction 2.54x10-4 1.65x10-3 1.49x10-3 2.99x10-3 8.87x10-4 3.23x10-4 Precursor decay constant (s) 1.27x10-2 3.17x10-2 1.15x10-1 3.12x10-1 1.40 3.87 September 22, 2005 Expert Group on Criticality Excursion Analysis

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. September 22, 2005 Expert Group on Criticality Excursion Analysis

Expert Group on Criticality Excursion Analysis 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 1 2 3 4 5 6 Delayed neutron fraction 2.52x10-4 1.64x10-3 1.48x10-3 2.98x10-3 8.81x10-4 3.21x10-4 Precursor decay constant (s) 1.27x10-2 3.17x10-2 1.15x10-1 3.12x10-1 1.40 3.87 September 22, 2005 Expert Group on Criticality Excursion Analysis

Example of Calculation: R159(0.50$, 0.15$/s) The 1st peak is well reproduced. The power is lower after the 1st peak. September 22, 2005 Expert Group on Criticality Excursion Analysis

Sensitivity to Excess Reactivity; 0.50$ Excess reactivity($) = 0.44 to 0.50 The profile with 0.46$ gives the best fit September 22, 2005 Expert Group on Criticality Excursion Analysis

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. September 22, 2005 Expert Group on Criticality Excursion Analysis