CRITICALITY ACCIDENT CODE
IDENTIFICATION SHEETS
POWDER
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GENERAL INFORMATIONS
( 1 )
Designation of
the code
Summary
(General purpose)
POWDER
Models the transient criticality of a wetted UO2 powder bed placed in an
open cylindrical vessel with vertical walls, so that the wetted powder is
able to expand (thermal dilatation of water, expansion effect of water
vapor pressure). The wetted powder vertical extent is divided with axial
meshes into a number of volumes that allows calculating the axial
movement of the wetted powder and the following reactivity effect. The
energy deposited in the volumes is calculated based on the power
profile (assuming fundamental neutronic mode), coupled with the
central power calculated with the point kinetic equation. In each mesh,
there is a representative UO2 spherical particle typical of the many at
that axial location. Heat transfer between the spherical particle and the
water is calculated by heat conduction equation accounting for nucleate
boiling.
Name(s)
Organization
Authors
Post mail address
e.mail address
First version released
D. J. MATHER , A. M. BICKLEY,
A. PRESCOTT.
P. FOUILLAUD, P. GIROUD,
P. GRIVOT.
UK/AEA (United Kingdom Atomic
Energy Authority).
CEA (Commissariat à l’Energie
Atomique).
CEA Centre de Valduc
DRMN/SRNC
21120 IS-SUR-TILLE Cedex
FRANCE.
pascal.grivot@cea.fr
patrick.fouillaud@cea.fr
philippe.giroud@cea.fr
POWDER (1990).
(date and reference number)
Current version released
POWDER V3.
(date and reference number)
Status of code
Current development
Language program / Modularity
Fortran 77.
Operating system
Windows.
(windows, linux, unix,…)
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Software requirements
(fortran compiler,…)
Portability
(PC / Workstation/Supercomputer))
Fortran 77 compiler.
PC.
Workstation.
Availability / web site
(executable, source files, data files, …)
Typical running time
(for one calculation)
10 s  10 min.
Comments
3
GENERAL INFORMATIONS
(2)
User Interface
Input data file for a POWDER run can be built by DATGEN code
or manually.
Time, power, energy released.
Reactivity inserted, reactivity feedback (doppler and neutronic
temperature effects, wetted powder expansion), total reactivity of
the system.
Calculated Standard
Outputs / and Units
Time step output : power,
energy, pressure,
temperature, …
Main characteristics : first
peak power, total energy
release, maximum pressure,
temperature, time of
boiling,…
Water temperature in contact with UO2 particle at top/mid/bottom
level of the wetted powder bed.
Average water temperature for neutronic temperature reactivity
effect.
Average particle temperature for doppler reactivity effect.
Depth of wetted powder bed ignoring expansion and total depth
of wetted powder bed accounting expansion.
Velocity of top wetted powder bed.
First peak power, first minimum, secondary peak powers and
minimums.
Time of vapor gas bubble formation (nucleate boiling).
Graphic editor
Quality Assurance
(data and code package)
Contact Person
(name of the contact for the
code)
Description of code modeling (report).
Code production (report).
Code comparison (report).
C. LAVARENNE
IRSN/DSU/SEC
BP 17
92262 FONTENAY-AUX-ROSES Cedex
France
caroline.lavarenne@irsn.fr
Comments
4
GENERAL DESCRIPTION
(3)
Physical Forms
Fissile Materials
Solution
(nitrate,fluorure,
sulfate,…)
Uranium
(isotopic content %)
Powder
(dry, wetted,…)
Metal
Fuel rods
…
(dry, wetted,…)
Wetted UO2 powder
(5% in 235U).
Plutonium
(isotopic content %)
Mixed Plutonium /
Uranium
(isotopic content %)
Cylindrical 1D with
free upper surface
allowing wetted
powder expansion.
Geometry description
Cylindrical, spherical,…
Space Dimension (1D, 2D,…),
Meshing / Region,
Finite Element Method, …
Axial meshing for
power profile.
In each axial mesh
there is a
representative
spherical particle of
UO2 surrounded by
water.
Radial meshing for
the representative
spherical particle of
UO2 surrounded by
water.
Comments
5
DESCRIPTION OF MODELS USED
Point kinetic equation,
Neutronic Power / Kinetics transport or diffusion theory
….
Reactivity and Reactivity
feedback
Point kinetic equation.
Transport or diffusion theory, Reactivity inserted by step,
mathematical formulas,
ramp, reactivity data input file,
input or calculated data
wetted bed collapse.
(reactivity insertion, temperature
Reactivity feedback of the
coefficients : Doppler, dilatation,..)
wetted powder expansion is
…
calculated with one group
perturbation formula.
Doppler and neutronic
temperature coefficients are
input data for user.
Thermal (heat conduction,
convection, boiling…) / Meshing
and region
Thermal – hydraulics
Hydrodynamics
Axial meshing for power profile.
Heat conduction equation is
solved for a representative
spherical particle surrounded by
a water layer in each axial
mesh.
There is a radial meshing in the
particle and in the water layer to
solve the heat conduction
equation, the nucleate boiling is
taken into account.
Multi-phase flow
Fluid motion / Meshing and
region
Pressure modeling
The displacements of axial
mesh positions are calculated
considering thermal dilatation of
water and equation of motion
with water vapor pressure and
hydrostatic pressure.
The water vapor pressure is
calculated from tabulated
internal data.
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Radiolysis
(for solutions)
Radiolytic formation and
migration models
Neutronics – kinetics
(cross sections libraries, k ,
neutron lifetime, delayed neutrons)
Data libraries :
External or/and Internal
(constants, calculated / tabulated,
experimental, bibliography, …)
k , doppler and neutronic
temperature coefficients are
input data for user.
Neutron lifetime and delayed
neutron constants are internal
data for UO2 powder (5% in
235U).
Heat capacity and conductivity
Thermal and hydrodynamics are calculated from tabulated
(heat capacity, conductivity,…)
internal data or formula.
Radiolysis (yield, threshold
formation, velocity,…)
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VALIDATION BASE OF THE CODE
Summary of the main
assumptions in the code
The power is calculated with point kinetic equation and a
power profile assuming fundamental neutronic mode. The
reactivity feedback takes into account the wetted powder
expansion (thermal dilatation of water, expansion effect of
water vapor pressure), doppler and neutronic temperature
effects.
Wetted oxide powder (5% in 235U) but can be easily modified
for any enrichment.
Limitations to the use of the The penetration of water in the dry powder is simulated by
code
increasing the total depth of wetted powder with constant
growth and constant H/U ratio.
Experimental benchmarks
(reactor : fissile media, geometry,
reactivity insertion, duration,…)
Past Accidents
(simulations)
Validation of the modeling
with standard codes
(neutronics, thermal,…)
Comparison with “SKINATH-WP”
a similar code of “The University
of Tennessee , USA”
Codes comparison
Accidents code
Domain of validation and
level of confidence
Experimental study of the moderator penetration and the
densification of the wetted oxide powder.
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References
(reports, communications,
publications,…)
 D. J. MATHER , A. M. BICKLEY
“POWDER, a computer code to model the transient criticality
behaviour of a bed of wetted uranium dioxide powder”
AEA/SRD R 549 (may 1991)
 D. J. MATHER , A. M. BICKLEY, A. PRESCOTT
F. BARBRY, P. FOUILLAUD, J.P. ROZAIN
“Criticality excursions in wetted UO2 powder”
Proceedings of the ICNC'91
 P. GRIVOT, P. GIROUD
“Accident de criticité en milieu poudre – Guide d'utilisation et
mise en production du code POWDER V3”
CEA/IPSN/DPEA/SRSC n°00.12 (2000)
 P. GRIVOT
“Description des modèles physiques du code POWDER”
CEA/IPSN/DPEA/SRSC n°00.13 (2000)
 P. GRIVOT
“Comparaison entre les codes POWDER et SKINATH-WP
sur un scénario d'accident de criticité avec de la poudre
d'oxyde d'Uranium enrichi à 5%“
CEA/IPSN/DPEA/SRSC n°01.05 (2001)
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