Patent Number: 043022863
Section: claims

1. An improved reactor vessel in-service inspection assembly having an inspection transducer positioning arm wherein the improvement comprises means for locating the positioning arm at a pre-established location within a hollow portion of the reactor vessel cavity wherein the locating means includes: means affixed to the positioning arm for generating and simultaneously, radially, directing acoustic signals around the circumference of the hollow portion of the vessel cavity and receiving the signals reflected off of the cavity walls and redirected to the location from which the signals were originally, radially directed, at a position within the hollow portion wherein the generating and receiving means comprises an acoustic transducer and reflector wherein the reflector is constructed to radially direct the acoustic signals generated by the transducer to the walls of the hollow portion of the reactor vessel cavity and redirect the acoustic energy reflected off the cavity walls back to the reflector to the transducer;  means for monitoring the received signals as a function of time; and  means for positioning the arm in response to the monitored difference in time of reception of the received signals, at the pre-established location within the hollow portion of the reactor vessel cavity.  means for generating and simultaneously, radially directing acoustic signals around the circumference of the cavity and receiving the signals reflected off of the cavity walls and redirected to the location from which the signals were originally, radially directed, at a position within the cavity wherein the generating and receiving means comprises an acoustic transducer and reflector wherein the reflector is constructed to radially direct the acoustic signals generated by the transducer to the walls of the cavity and redirect the acoustic energy reflected of the cavity walls back to the reflector to the transducer;  means for monitoring the received signals as a function of time; and  means for positioning the generating and receiving means in response to the monitored difference in time of reception of the received signals, at the pre-established location within the cavity. 2. The reactor vessel in-service inspection assembly of claim 1 wherein the generating and receiving means comprises an acoustic transducer having a cylindrical acoustic generating face. 3. The reactor vessel in-service inspection assembly of claim 2 wherein the axis of revolution of the cylindrical generating face is coincident with the axis of the positioning arm. 4. The reactor vessel in-service inspection assembly of claim 1 wherein the reflector is shaped as a cone. 5. The reactor vessel in-service inspection assembly of claim 1 wherein the reflector is shaped as a three-sided pyramid. 6. The reactor vessel in-service inspection assembly of claim 1 wherein the reflector is shaped as a four-sided pyramid. 7. The reactor vessel in-service inspection assembly of claim 1 wherein the reflector is positioned on the axis of the positioning arm. 8. The reactor vessel in-service inspection assembly of claim 6 wherein the means for locating the arm moves the arm in a forward and reverse direction along lines parallel to both the X and Y axes. 9. The reactor vessel in-service inspection assembly of claim 1 or 8 wherein the means for locating the arm positions the arm at the pre-established location automatically in response to the monitored difference in time of reception of the received signals. 10. The reactor vessel in-service inspection assembly of claim 1 wherein the pre-established location is substantially at the center of the hollow portion of the reactor vessel cavity. 11. The reactor vessel in-service inspection assembly of claim 10 wherein the means for locating the arm moves the arm in a direction to minimize the time difference between received signals. 12. Apparatus for identifying a pre-established location within a hollow cavity comprising: 13. The apparatus of claim 12 wherein the reflector is constructed as a pyramid. 14. The apparatus of claim 13 wherein the reflector is a three-sided pyramid. 15. The apparatus of claim 13 wherein the reflector is a four-sided pyramid. 16. The apparatus of claim 15 wherein the means for positioning the generating and receiving means moves the generating and receiving means in a forward and reverse direction along lines parallel to both the X and Y axes. 17. The apparatus of claim 12 or 16 wherein the means for positioning the generating and receiving means positions the generating and receiving means at the pre-established location automatically in response to the monitored difference in time of reception of the received signals. 18. The apparatus of claim 12 wherein the pre-established location is substantially at the center of the cavity. 19. The apparatus of claim 18 wherein the means for positioning the generating and receiving means moves the generating and receiving means in a direction to minimize the time difference between received signals.