Since the vitrification lines at La Hague began operation in 1989, ORANO (formerly AREVA) has faced difficulties in controlling the calciner. Actions taken to significantly reduce these problems have considerably eased them, but without completely eliminating them. Most of the recommended actions are based on expert opinions, which themselves are based on inactive test results that don't cover all situations encountered by ORANO. To definitively resolve these control difficulties, it was decided to launch a more theoretical modeling study, while simultaneously investigating new calciner control instrumentation.