a pressure vessel surrounding the outside wall of {HEAD ~ the reaction chamber}, thus forming {TAIL ~ a first annulus} 
a pressure vessel surrounding the outside wall of { HEAD ~ the reaction chamber } , thus forming { TAIL ~ a first annulus }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL