 INES 1 |
NON RETRACTION OF SOUTH FUELLING MACHINE GUIDE SLEEVE FROM CHANNELS S-12 |
Reactor was under shutdown for 3 months for ISI of coolant channels. On 7 October 94 channel S-12 was defuelled for ISI, and spent fuel bundls were received in the south machine. Channel shield plug was installed and guide sleeve was retracted. Then, in order to install seal plug in the channel from south end, Ram B was advanced. But it could not be advanced beyond 100 cm (approx.) from home. All the 12 spent fueld bundles were confirmed to be in the south fuelling machine. Investigation carried out indicated that the guide sleeve remained in advanced condition and was not getting retracted by normal manipulation of the fuelling machine. After final confirmation that guide sleeve was in advanced condition, channel shield plug was removed and all the bundles were pushed back into the
channel and shield plug was reinstalled. A special approved procedure was used for retrieval of south guide tube which involved draining of North Reactor Inlet Header (NRIH) and South Reactor Outlet Header (SROH) and allowing D2O flow from the north fuelling machine. With this procedure the guide sleeve was retrieved partially. Later the south fuelling machine was unclamped from the channel. Seal plug was installed in the manual mode.
The event occurred when the unit was in shutdown state for about 3 months and hence decay heat was very low. However, retrieval was outside the operational limits and conditions for a short period. The event is rated at level 1 on INES scale as per Section III 3.1.3 of User's manual.
Event date: Fri, 07-10-1994
