Auto-trip of R21, following trip of Main Boiler Feed Pump, subsequent breach of Gas Circulator 22 Inlet Temp. limit

Reactor 21 automatically tripped from full load on rate of change of Boiler Gas Outlet Temperature (BGOT) following a trip of the Main Boiler Feed Pump. The Emergency Boiler Feedpump was unavailable at the time of the trip due to maintenance. The Start-Up Boiler Feedpump was put into service manually when it did not automatically start, but it had to be shut down soon afterwards due to a priming oil pump problem which caused a small fire. The station fire team extinguished the fire using hand held extinguishers, but the Fire Brigade were called as a precaution.With no high pressure feed pumps available the boilers were part depressurised using the Boiler Emergency Depressurisation (BED) Valves and the reactor cooled with feed provided from the Shut-Down Boiler Feedpump. Approximately one hour after the auto-trip of Reactor 21, the average Gas Circulator Inlet Temperature for Boiler 22 (calculated by the Data Processing System) exceeded the Operating Rule Limit of 300 degrees Celsius by 2.3 degrees Celsius for approximately 30-40 seconds. This was a consequence of starting the Gas Circulator Low Speed Pony Motors whilst the boilers were being fed by the low capacity Shut-Down Boiler Feed Pump.

Event date: Fri, 11-07-2003
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