CRITICALITY ACCIDENT CODE
( 1 )
Designation of CRITEX
Models the transient criticality of a fissile solution contained in an open
Summary cylindrical vessel with vertical walls, so that the solution is able to
(General purpose) expand vertically (thermal dilatation, production of radiolytic gas
bubble). The solution vertical extent is divided with axial meshes into a
number of volumes that allows to calculate the axial movement of the
solution 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.
Name(s) D. J. MATHER , A. M. BICKLEY,
P. FOUILLAUD, P. GIROUD,
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 firstname.lastname@example.org
First version released CRITEX V4.3 (1993).
(date and reference number)
Current version released CRITEX V6.1 (2001).
(date and reference number)
Status of code
Language program / Modularity Fortran 90.
Operating system Windows.
(windows, linux, unix,…)
Software requirements Fortran 90 compiler.
(PC / Workstation/Supercomputer))
Availability / web site
(executable, source files, data files, …)
Typical running time 10 s 10 min.
(for one calculation)
User Interface Input data file for a CRITEX run can be built by INITAL code or
Time, central specific power, inverse period, total power, total
Calculated Standard energy released.
Outputs / and Units Reactivity inserted, reactivity feedback (doppler, solution
expansion), total reactivity of the solution.
Time step output : power,
energy, pressure, Solution temperature at top/mid/bottom level of the vessel.
Main characteristics : first
First peak power, first minimum, secondary peak powers and
peak power, total energy
release, maximum pressure, minimums.
temperature, time of
boiling,… Time of radiolytic gas bubble formation (nucleation).
Gas inverse time constant (diffusion).
Description of code modeling (report).
Code production (report).
Quality Assurance Selection of Experimental Benchmarks (reports).
(data and code package)
Code qualification synthesis (report).
Contact Person BP 17
(name of the contact for the
92262 FONTENAY-AUX-ROSES Cedex
Solution Powder Metal Fuel rods …
(nitrate,fluorure, sulfate,…) (dry, wetted,…) (dry, wetted,…)
Nitrate (93%, 5%,
(isotopic content %) Fluoride (1% 8%).
Plutonium 95/5/0, 80/20/0,
(isotopic content %)
Mixed Plutonium / Pu
( 10 ou 30% ).
Uranium U Pu
(isotopic content %) Fluoride.
Cylindrical 1D with
free upper surface
Geometry description allowing solution
Cylindrical, spherical,… expansion.
Space Dimension (1D, 2D,…),
Meshing / Region,
Finite Element Method, … Axial meshing.
DESCRIPTION OF MODELS USED
Point kinetic equation, Point kinetic equation.
Neutronic Power / Kinetics transport or diffusion theory
Transport or diffusion Reactivity inserted by step,
theory, mathematical ramp or buckling formula.
formulas, Reactivity feedback of the
Reactivity and Reactivity input or calculated data solution expansion is calculated
feedback (reactivity insertion, temperature with one group perturbation
coefficients : Doppler, dilatation,..)
Doppler coefficients are
tabulated internal data.
Thermal (heat conduction, Axial meshing, heat conduction,
convection, boiling…) / Meshing natural convection.
Multi-phase flow Radiolytic gas bubble formation
Thermal – hydraulics
Fluid motion / Meshing and
Radiolytic gas bubble migration
Radiolytic formation and is modeled by means of a
Radiolysis migration models conservation equation with
bubble migration velocity and a
Neutronics – kinetics k , neutron lifetime, delayed
(cross sections libraries, k , neutron constants and doppler
neutron lifetime, delayed
neutrons) coefficients are tabulated internal
Data libraries : data , they have been calculated
External or/and Internal with WIMS or APOLLO
(constants, calculated / tabulated, deterministic neutronic codes.
experimental, bibliography, …)
… Internal data determined from
Thermal and hydrodynamics laboratory measurements.
(heat capacity, conductivity,…)
Internal data determined from
Radiolysis (yield, threshold CRAC and SILENE experiments.
VALIDATION BASE OF THE CODE
The power is calculated with point kinetic equation and a
power profile assuming fundamental neutronic mode. The
reactivity feedback takes into account solution expansion
Summary of the main
(thermal dilatation , void effect of bubbles) and doppler effect.
assumptions in the code
Solution temperature is calculated using a thermal balance
equation with heat capacity and natural convection.
Bubble migration is calculated using a conservation equation
with bubble migration velocity and a source term.
Aqueous solution of fissile media.
Limitations to the use of the
No treatment of the boiling phase.
CRAC, SILENE: Uranyl nitrate (93%, 22 g/l 218 g/l,
=30 cm, 80 cm, 36 cm).
Experimental benchmarks SHEBA: uranium fluoride (5%, 979 g/l, =49 cm).
(reactor : fissile media, geometry,
reactivity insertion, duration,…) Reactivity pulse or ramp from 0.035 to 3 $.
Tokai-Mura (JCO , 1999).
Validation of the modeling
with standard codes
Domain of validation and Comparison with experimental benchmarks from SILENE ,
level of confidence CRAC and SHEBA experiments show correct agreement for
first peak power and total energy released (within 20 to 40%).
D. J. MATHER, A. M. BICKLEY, A. PRESCOTT
“CRITEX – a code to calculate the fission release arising from
transient criticality in fissile solutions”
D. J. MATHER , A. M. BICKLEY, A. PRESCOTT
F. BARBRY, P. FOUILLAUD, J.P. ROZAIN
“Validation of the CRITEX code”
Proceedings of the ICNC'91
References P. GRIVOT, P. FOUILLAUD
“Description du code CRITEX”
CEA/IPSN/DPEA/SRSC n°96.02 (1996)
“Mise en production du code CRITEX version 6”
CEA/IPSN/DPEA/SRSC n°01.09 (2001)
P. GIROUD, P. GRIVOT
“Accident de criticité en solution – Synthèse de la qualification
du code CRITEX“
CEA/IPSN/DPEA/SRSC n°00.05 (2000)