Visual and Profilometric Fuel Rod Inspection

Problem Definition
Current inspection of nuclear fuel cells requires the use of cumbersome hot cells. INL is investigating an alternative process for inspecting these fuel cells that can be located closer to reactor sites and does not require a dedicated building for operation. Our task is to specify segments of this process that will perform non-destructive profilometric and visual inspection of irradiated test specimens. The processes must be fast and easily serviceable while maintaining a high level of fidelity and flexibility.

Background
Inspection of nuclear fuel rods via current methods is quite cumbersome. Irradiated materials must be transported to an examination facility such as INL's HFEF. There, the fuel is inspected inside hot cells, large led lined rooms with argon atmospheres where technicians must use robot arms to interact with the material. It is difficult to implement new inspection solutions within this testing environment due to the long testing time. It is expensive to test and to improve testing methods. INL is devising a new environment for inspecting materials known as the Modular Examination Instrument for Transportable Nuclear Energy Research (MEITNER). This device is a modular stack of examination equipment that can simultaneously inspect materials via non-destructive, non-contact measurements.

Deliverables
Our mission in this project is to develop the modular test cells that perform the functions of profilometry and visual inspection. These cells must be capable of taking accurate measurements under the stress of radiation. The cells must be easy to service and operate remotely. We are to recommend high-end equipment for use at INL and demonstrate their effectiveness using comparable, rad-intolerant, equipment.

Profilometry
Within the HFEF at INL profilometric inspection is currently performed using a pair of LVDT sensors within their hot cell. These sensors are placed against the material and removed for every measurement at a resolution of 1,2,5, and 10 measurements per millimeter. This causes some examinations to last 8 hours for a single element. LVDT are contact tools for dimensional inspection though they do not present a significant risk of damaging test elements. Alternatively, laser methods may save time by eliminating the time required to reset the sensor for every measurement. Promising laser imaging techniques include laser interferometry and laser triangulation, laser micrometry, and line scan imaging.

Visual Inspection
Within HFEF standard digital cameras take pictures of test elements through 4 feet of oil filled glass. The discoloration of the glass causes images to lack true color. It is also difficult to image the entire specimen due to the hot cells fixed view point and cumbersome manipulation of specimens. Some inspection is done by using binoculars located at each window. Due to MEITNERS closed off system the current techniques for visual inspection are not possible, but the ability to significantly reduce the radiation impact on test equipment presents an opportunity. Standard digital cameras, who live for a very short time within the hot cell, will be able to withstand the duration of a parts testing cycle allowing true color photos of the element in 360 degrees. Rad shielded cameras may be used to extend the time between replacement and may allow them to be placed much closer to the test element. Snake cameras present an opportunity for testers to look around the far side of a specimen within the cell through a tortuous through hole, though the small length of articulating armature reduces versatility and may necessitate multiple insertion points.

Concept and Design
Each lead shielded ring of MEITNER will be capable of housing multiple inspection tools. Stepped wedge shaped plugs of standard sizes will be through cut from the walls of MEITNER. Testing methods may be devised using one of these wedges as their access point to the nuclear material within. In order to minimize radiation escaping from the vessel, a through cut hole that follows a tortuous path ( a path that does not have a line of site connection between each end) must be made through the lead wedge. This is critical to the safety of the facility and allows equipment to operate in a lower rad environment which reduces degradation. Due to the meandering of the through hole light must be bounced to meet testing equipment, or thinner equipment that can navigate corners must be used.

Document Archive
[[Media: ClientInterview1.pdf|First Client Interview]] [[Media: .pdf|All Meeting Minutes]]