Criticality Accident Analysis

Criticality Accidents

To date 22 criticality accidents have been reported in process facilities. A further 38 accidents have been reported in experimental facilities and research reactors.

Detailed descriptions of these can be found in:

• LA-13638 A Review of Criticality Accidents. T.P. McLaughlin, S.P. Monahan, N.L. Pruvost, V.V. Frolov, B.G. Ryazanov, V.I. Sviridov. Los Alamos National Laboratory. May 2000.

Criticality Excursion Analysis Codes

Understanding the consequences of criticality is important in the development of long term repository safety cases and criticality emergency planning. Various computer codes are available to simulate criticality excursion analyses.

The FETCH code (Imperial College) allows modelling of the transient behaviour of fissile solutions, with sloshing and pressure feedback.

The OECD Expert Group on Criticality Excursion Analyses maintains a list of resources including the codes

• CHATEAU (CEA) - Models the transient criticality of UO₂ fuel rods array in an open cylindrical shipping cask, so that the water is able to expand (thermal dilatation of water, void effect of vapor bubbles).

• CRITEX (UKAEA/CEA) - Models the transient criticality of a fissile solution contained in an open cylindrical vessel with vertical walls, so that the solution is able to expand vertically (thermal dilatation, production of radiolytic gas bubble).

• POWDER (UKAEA/CEA) - 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).

• AGNES (JAERI) - Models the transient criticality of a fissile solution contained in a cylindrical vessel with vertical walls

• INCTAC (JNES) - INCTAC is applicable to the analysis of criticality accident of aqueous homogeneous fuel solution system.