Chemical Decontamination Process for NPPs Primary Circuits

The chemical decontamination process ASDOC_D-MOD

ASDOC_D-MOD uses well-known and freely accessible process chemicals in significantly reduced concentrations and with modified operating logistics. The chemical concentrates are injected into the reactor primary circuit via the site's dosing system and then circulated in the primary circuit.

Like in regular plant operation, the control of plant systems needed for the decontamination is performed by the operating personnel from the control room. Required parameters for e.g. dosing processes, throughputs or temperatures are given by Siempelkamp NIS. Dissolved ions and nuclides from the primary circuit’s oxide layers are removed by means of the site’s ion exchange water clean-up system. The ASDOC_D-MOD process may be interrupted and restarted at any time without any precipitations of chemical compounds.

The decontamination process which is subdivided in several processing steps can precisely be terminated at the interface between oxide layer and base material. An unintentional damage of the base metal and hence and increase of waste can thus be prevented safely.

ASDOC – Advanced System Decontamination by Oxidizing Chemistry

The process shows that a removal of the oxide layers can be performed and tracked in a controlled manner. This is due to the precisely dosed and limited amount of chemicals. After the individual process steps, the used chemicals are stoichiometrically converted. Therefore, no surplus chemicals remain in the decontamination cycle. The oxide layers dissolve during the individual process steps - This is achieved by nearly constant oxide layer removal rates. The process steps can be repeated several times until the desired decontamination result is achieved. The activity distribution on metal surfaces can thereby be lowered to the release limit. As the ASDOC_D-MOD process requires no external components which need to be assembled or disassembled, the accumulated operator dose rate during a decontamination campaign stands low at some mSv. Thanks to the precise process control, the ASDOC_D-MOD process reaches decontamination factors of > 75.