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