Hopefully, the only reason you need to do this is as part of trying to port
some old MacLisp code to Common Lisp. These functions predated the
inclusion of strings as a first-class data type in Lisp; symbols were used
as strings, and they ere EXPLODEd to allow the individual characters to be
manipulated in a list.
Probably the best approximations of these are:
 (defun explode (object)
 (loop for char across (prin1-to-string object)
 collect (intern (string char))))
 (defun implode (list)
 (read-from-string (coerce (mapcar #'character list) 'string)))
An alternate definition of EXPLODE which uses MAP instead of LOOP is:
 (defun explode (object)
 (map 'list #'(lambda (char) 
 (intern (string char)))
 (prin1-to-string object)))
The creation of N conses of garbage to process a string of N
characters is a hideously inefficient way of doing the job. Rewrite
EXPLODE code with PRIN1-TO-STRING, or better STRING if the arguments
are symbols without funny characters. For IMPLODE, try to make its
caller use strings and try to make the result usable as a string to
avoid having to call INTERN or READ-FROM-STRING.