1. Calculation Result for SILENE Benchmark II using AGNES code
Expert Group on Criticality Excursion Analysis September 22, 2005
Calculation Result for SILENE Benchmark II using AGNES code
Yuichi YAMANE, Kiyoshi OKUBO, Yoshinori MIYOSHI
Japan Atomic Energy Research Institute

2. Expert Group on Criticality Excursion Analysis
SILENE Benchmark II
Ramp reactivity insertion by withdrawal of the reactivity rod.
Excess reactivity; 2.0$.
Initial reactivity; subcritical
U conc.; gU/Lit.
Effective delayed neutron fraction; 7.94x10-3.
Neutron generation time; 3.28x10-5.
- External neutron source was used.
September 22, 2005
Expert Group on Criticality Excursion Analysis

3. Expert Group on Criticality Excursion Analysis
Parameters : LE1-641
Kinetic parameters
SRAC + TWODANT with JENDL-3.2
Neutron generation time: 3.28x10-5
beff : 7.94x10-3
Reactivity Temperature Coefficient : -4.1 cent/K, -3.5 cent/K2
Reactivity Void Coefficient : -6.8x101 cent/%, -1.6 cent/%2
Void parameters(the same as those for BenchMark1)
CD=15mol/m3, G=6×10-7mol/J, n=1×10-7 1 2 3 4 5 6
Delayed neutron fraction
2.62x10-4
1.72x10-3
1.56x10-3
3.06x10-3
9.00x10-4
3.28x10-4
Precursor decay constant (s)
1.24x10-2
3.05x10-2
1.11x10-1
3.01x10-1
1.14
3.01
September 22, 2005
Expert Group on Criticality Excursion Analysis

4. Heat Transfer Model of AGNES
Heat transfer from solution to structural material is considered.
Heat transfer to the air is assumed to be ignorably small.
Fuel solution
Container wall
h1 : Heat transfer coef. between solution and container,
A1: Heat transfer area between solution and container.
air
Values for LE1-641
h1 = 400 (w/m2/°C)
A1 = (m2)
x = 1 (m)
Vi: Volume of mesh i (m3),
r : Density (kg/m3),
Cp: Specific heat (J/kg/°C),
Ti: Temperature of mesh i(°C)
gi : Power distribution ratio for mesh i (W/m3),
P : Power (W),
(hA)i : Heat transfer coefficient x Transfer area (W/ °C).
x (m)
Based on surface
area of container
Structural material
September 22, 2005
Expert Group on Criticality Excursion Analysis

5. Example of Calculation: LE1-641 1/2
The 1st peak power is higher than LE1-641.
The power after some oscillations is lower.
September 22, 2005
Expert Group on Criticality Excursion Analysis

6. Example of Calculation: LE1-641 2/2
The power profile for h1=400 shows a peak at 1500s.
Each power approaches almost the same value.
September 22, 2005
Expert Group on Criticality Excursion Analysis

7. 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

8. Sensitivity to Void Parameter; G
G : Radiolytic dissociation rate = 3x10-7 to 9x10-7
The depth of the bottom in 1000s is changed.
September 22, 2005
Expert Group on Criticality Excursion Analysis

9. Sensitivity to Void Parameter; n
n : Energy-void transfer coefficient = 1x10-6 to 1x10-8
The shape of bottoms is changed.
September 22, 2005
Expert Group on Criticality Excursion Analysis

10. Preliminary Result and Summary
The 1st peak power and total released energy were reproduced within 9 to 22%.
Simple heat transfer model reproduced well power profile during very long duration time.
September 22, 2005
Expert Group on Criticality Excursion Analysis