The use of a cooling jacket on a plug flow reactor is highly dependent upon the scale, degree of exotherm and temperature difference between coolant and reaction media.  In many applications the reactor is essentially a shell & tube heat exchanger in which a cooling media flows on the shell side and the reaction takes place in tubes packed with catalyst.  When there are large exotherms and the potential for runaway reactions this type of design is preferred.  The calculations required to determine whether the jacket is sufficient are fairly simple:  Do an energy balance to determine the heat removed and then determine what temperature cooling medium would be required to satisfy the heat removal with the available jacket area and an estimate of the heat transfer coefficient.  If you find that the required cooling medium temperature is not realistic or practical then you will have to revise the reactor design to contain more heat transfer surface than a jacket.