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                             GENERAL INFORMATIONS
                                      ( 1 )

Designation of      POWDER
the code
                    Models the transient criticality of a wetted UO2 powder bed placed in an
Summary             open cylindrical vessel with vertical walls, so that the wetted powder is
(General purpose)   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

                    Name(s)                            D. J. MATHER , A. M. BICKLEY,
                                                       A. PRESCOTT.
                                                       P. FOUILLAUD, P. GIROUD,
                                                       P. GRIVOT.

                                                       UK/AEA (United Kingdom Atomic
                    Organization                       Energy Authority).
Authors                                                CEA (Commissariat à l’Energie
                                                       CEA Centre de Valduc
                    Post mail address                  DRMN/SRNC
                                                       21120 IS-SUR-TILLE Cedex
                    e.mail address           

Status of code      First version released             POWDER (1990).
                    (date and reference number)

                    Current version released           POWDER V3.
                    (date and reference number)

                    Current development

                    Language program / Modularity      Fortran 77.

                    Operating system                   Windows.
                    (windows, linux, unix,…)

           Software requirements                       Fortran 77 compiler.
           (fortran compiler,…)

           Portability                                 Workstation.
           (PC / Workstation/Supercomputer))

           Availability / web site
           (executable, source files, data files, …)

           Typical running time                        10 s    10 min.
           (for one calculation)


                                GENERAL INFORMATIONS

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            Water temperature in contact with UO2 particle at top/mid/bottom
                               level of the wetted powder bed.
Time step output : power,      Average water temperature for neutronic temperature reactivity
energy, pressure,              effect.
temperature, …                 Average particle temperature for doppler reactivity effect.
Main characteristics : first
peak power, total energy
release, maximum pressure,     Depth of wetted powder bed ignoring expansion and total depth
temperature, time of           of wetted powder bed accounting expansion.
boiling,…                      Velocity of top wetted powder bed.

                               First peak power, first minimum, secondary peak powers and

                               Time of vapor gas bubble formation (nucleate boiling).

Graphic editor

                               Description of code modeling (report).
Quality Assurance              Code production (report).
(data and code package)
                               Code comparison (report).

                               C. LAVARENNE
Contact Person                 BP 17
(name of the contact for the   92262 FONTENAY-AUX-ROSES Cedex
code)                          France


                                  GENERAL DESCRIPTION

                                                                  Physical Forms

Fissile Materials
                                Solution                  Powder              Metal          Fuel rods   …
                              (nitrate,fluorure,       (dry, wetted,…)     (dry, wetted,…)

Uranium                                            Wetted UO2 powder
(isotopic content %)                               (5% in 235U).

(isotopic content %)

Mixed Plutonium /
(isotopic content %)

                                                   Cylindrical 1D with
                                                   free upper surface
                                                   allowing wetted
                                                   powder expansion.

                                                   Axial meshing for
                                                   power profile.
                                                   In each axial mesh
Geometry description                               there is a
Cylindrical, spherical,…                           representative
Space Dimension (1D, 2D,…),
Meshing / Region,
                                                   spherical particle of
Finite Element Method, …                           UO2 surrounded by

                                                   Radial meshing for
                                                   the representative
                                                   spherical particle of
                                                   UO2 surrounded by


                       DESCRIPTION OF MODELS USED

                           Point kinetic equation,               Point kinetic equation.
Neutronic Power / Kinetics transport or diffusion theory

                             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
Reactivity and Reactivity    coefficients : Doppler, dilatation,..)
                                                                    wetted powder expansion is
feedback                     …
                                                                    calculated with one group
                                                                    perturbation formula.
                                                                    Doppler and neutronic
                                                                    temperature coefficients are
                                                                    input data for user.

                             Thermal (heat conduction,           Axial meshing for power profile.
                             convection, boiling…) / Meshing     Heat conduction equation is
                             and region
                                                                 solved for a representative
                                                                 spherical particle surrounded by
                                                                 a water layer in each axial
                                                                 There is a radial meshing in the
                                                                 particle and in the water layer to
                                                                 solve the heat conduction
                                                                 equation, the nucleate boiling is
Thermal – hydraulics                                             taken into account.

                             Multi-phase flow
                                                                 The displacements of axial
                             Fluid motion / Meshing and          mesh positions are calculated
                             region                              considering thermal dilatation of
                                                                 water and equation of motion
                                                                 with water vapor pressure and
                                                                 hydrostatic pressure.
                                                                 The water vapor pressure is
                             Pressure modeling                   calculated from tabulated
                                                                 internal data.

(for solutions)                       Radiolytic formation and
                                      migration models

                                      Neutronics – kinetics            k∞ , doppler and neutronic
                                      (cross sections libraries, k∞,      temperature coefficients are
                                      neutron lifetime, delayed neutrons)
                                                                       input data for user.
                                                                       Neutron lifetime and delayed
                                                                       neutron constants are internal
Data libraries :
                                                                       data for UO2 powder (5% in
External or/and Internal                                               235
(constants, calculated / tabulated,
experimental, bibliography, …)
                                                                      Heat capacity and conductivity
                                      Thermal and hydrodynamics are calculated from tabulated
                                      (heat capacity, conductivity,…) internal data or formula.

                                      Radiolysis (yield, threshold
                                      formation, velocity,…)

                             VALIDATION BASE OF THE CODE

                                      The power is calculated with point kinetic equation and a
                                      power profile assuming fundamental neutronic mode. The
Summary of the main
                                      reactivity feedback takes into account the wetted powder
assumptions in the code
                                      expansion (thermal dilatation of water, expansion effect of
                                      water vapor pressure), doppler and neutronic temperature

                              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

                                      Validation of the modeling
                                      with standard codes
                                      (neutronics, thermal,…)

Codes comparison                      Accidents code               Comparison with “SKINATH-WP”
                                                                   a similar code of “The University
                                                                   of Tennessee , USA”

Domain of validation and              Experimental study of the moderator penetration and the
level of confidence                   densification of the wetted oxide powder.

                                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
References                  “Accident de criticité en milieu poudre – Guide d'utilisation et
(reports, communications,
                            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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