CBRN event in Pakistan on Wed 19th October 2011

Plant was in shutdown state since October 05, 2011 because of maintenance activities. As per normal procedure during shutdown state, Standby Cooling System (SH) was in service to remove decay heat from the reactor core while Primary Heat Transport (PHT) system was in depressurized state. On October 19, 2011, inspection of channel S-11 grayloc seal was carried out to find out any foreign material in the orifice. During normalization of the system, Boiler Room (B/R) floor beetle alarm received in control room. Later, 'Tritium in Air High' alarm also annunciated. Immediately, survey of boiler room was performed. Area operator reported that heavy water was leaking from south end inlet feeder of fuel channel S-11 near the location where inspection was carried out. Standby cooling pumps were switched off and B/R purging was terminated. Standby emergency was declared at 0121 hrs which was later upgraded to plant emergency because the leak was not isolatable. 
Afterwards, leakage was controlled using temporary means and reduced to drop wise state. Special canopy arrangement was made to collect leaked heavy water via flexible hose. The situation was brought under control and plant emergency was terminated at 0524 hrs. Approximately 1200 kg heavy water was collected. As per preliminary corrective action, channel S-11 has been defueled and temporarily plugged. Further corrective actions are to be taken after detailed investigation and analysis.