Gamma dose rate profiles in fuelling machine vaults before and after PHT system decontamination in MAPS-1 for EMCCR campaign

Fuelling machine vault, an area on either side of the Reactor core, is the center stage for the En masse coolant channel replacement (EMCCR) campaign, a dose intensive mega exercise. During the EMCCR of Unit-2 (2002-2003), the collective dose consumption in FM vault was nearly 90 percent. In August 2003, Unit-1 was shut down for taking up EMCCR. Prior to the commencement of this campaign, the PHT system was decontaminated by Dilute Chemical Decontamination technique (DCD). To study the impact in FM vault, gamma dose rate mapping was carried out extensively before and after DCD. Critical observations of this study which had a bearing on the ALARA decisions during the EMCCR are highlighted in this paper. (author)