INES-event
INES 1

DROP TIME OF CONTROL RODS OUT OF CRITERION

After first refuelling outage of Unit 1, the rod drop test was performed in hot shutdown conditions on 14 February. The results showed an increase of rod drop time T5 (the drop time to the dash pot entry) of 0.3 seconds in average comparing with commisioning results and 7 control rods exceeding the criterion (2.15 seconds). The maximum drop time was 3.17 seconds for one control rod.
According to the opinion of Framatome 51 new nitrogen case-hardening control rods were loaded. Rod drop test was performed in hot shutdown on 28 March. The results showed that 16 control rods exceeded 2.15 seconds, 5 of the above 7 rods dropped very slowly.
The root cause investigation and the implementation of corrective
actions are in progress.


Location: GUANGDONG-1
Event date: Tue, 14-02-1995
Nuclear event report
Legenda & explanation