Development of an Inspection System for the Reactor Vessel/Containment Vessel of the PRISM and SAFR Liquid Metal Reactors

The integrity of the reactor vessel is of utmost importance in both the PRISM and SAFR concepts. The reactor vessel operates at elevated temperatures and contains molten liquid sodium. To ensure safe operation of the reactor, a periodic, visual inspection of the walls of the containment vessel is required by ASME specifications. This inspection would be conducted during a time when the reactor is shut down for refueling or maintenance. Nuclear Systems Associates, Inc. (NSA) was issued a PRDA contract by the Department of Energy to design, develop, and test a Closed Circuit Television (CCTV) camera system. The purpose of the system is to inspect the welds and wall surface of the Reactor Vessel/Container Vessel for both the PRISM and SAFR type reactors. The system was designed to function at the reactor's normal shutdown temperature, and provide a clear indication of flaws in the wall's weld seams and any cracks that might develop. The project was performed in three phases. The first phase concentrated the efforts on producing a compact camera system with the required resolution, self -contained lighting, and remote control focus and viewing angle. The proposed camera was then tested in a vessel mock-up and found to perform to required specifications at room (cold) temperatures. Simulated flaws, cracks, and a sodium leak were observed with required clarity on both a commercial and blackened stainless steel surfaces. The camera was tested with a single clear glass dome, a single coated glass dome, and a dual-glass dome covering the camera lens and mirror. The second phase of the project was conducted in two parts. The first part involved testing the vessel mock-up at elevated temperatures to verify that the required temperatures can be obtained. The mock-up was constructed with imbedded heaters and both control and indicating thermocouples. Stable operating temperatures over 400°F were achieved. During the second part of this phase, the camera was inserted into the heated mock-up to verify proper operation at elevated temperatures. Several methods were employed to maintain a temperature within the camera assembly below the camera's maximum rating. In the final configuration, the in-annulus time of the camera substantially exceeded requirements. Picture resolution and clarity were not compromised. In the final phase, the camera was subjected to increasing temperatures within the mock-up until image degradation was observed. This occurred at a camera temperature significantly above the rated value. The camera was then returned to the manufacturer for a complete factory evaluation of any permanent damage. Their report indicated that no discernible damage had occurred. Suggestions are offered for further refinement of the techniques described in this report. One improvement is the use of digital image processing to readily detect cracks and flaws, and to objectively compare the current surface condition to that. of a previous inspection