The ornamental design for a reactor, as shown and described.
FIG. 1 is a perspective view of a reactor showing our new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a right side elevational view thereof; the left side elevational view is a mirror image of the right side elevational view;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The dot-dash broken lines and broken lines immediately adjacent to the full line showing of the claimed design represent the bounds of the claimed design while all other broken lines are directed to environment and are for illustrative purposes only; the broken lines form no part of the claimed design. In addition, the unshaded surfaces in the FIG. 6 view that directly adjoin the claimed solid line edge form no part of the claimed design.