When this occurs there is {HEAD ~ a rapid rise} in temperature and pressure within the reactor causing emergency vent valves to open in order to reduce the pressure within {TAIL ~ the reactor} and vent the reactor contents 
When this occurs there is { HEAD ~ a rapid rise } in temperature and pressure within the reactor causing emergency vent valves to open in order to reduce the pressure within { TAIL ~ the reactor } and vent the reactor contents
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH