Patent Number: 042742056
Section: summary

BACKGROUND There are numerous components in industrial and utility installations which require on-site, pre-service inspection and/or periodic in-service inspection to verify continued serviceability. Such inspection frequently includes dimensional measurements. A notable example is the on-site inspection of components of a nuclear reactor, especially replaceable components such as control rods, fuel elements and fuel channels. For example, a typical fuel assembly having a removable and reusable flow channel is shown in U.S. Pat. No. 3,689,358. Such an elongated square tubular fuel channel may be in the order of 13 cm in transverse cross section dimensions and in the order of 4 m in length. It is necessary to assure that the four major surfaces of such channels are sufficiently flat so as not to interfere with the insertion of control rods between fuel assemblies during operation in the nuclear reactor core. Dimensional tolerances over the length of such a channel may be in the order of 0.127 mm. To perform the necessary flatness measurement of such a component, an elongated accurate and stable measuring fixture is required. Since flow channels, and other reactor components, which have been subjected to reactor service are radioactive, it is necessary that the measuring device be remotely operable under water to protect the equipment operators from radiation. It is desirable that the measuring device be sufficiently portable for repositioning within a water pool, for movement from one pool to another, and for removal to dry storage when not in use. Thus an object of the invention is a portable device or fixture for accurate dimensional measurement of radioactive components. SUMMARY The dimension measuring fixture of the invention comprises a vertically oriented, elongated, accurately formed straight edge member which serves as a plane of reference and as a track for an instrument bearing carriage. The straight edge member is rectangular in transverse cross section and, as a feature of the invention, it is formed with a series of relatively large holes along its longitudinal axis for enhanced heat distribution to minimize thermal deformation and to provide a high stiffness-to-weight ratio. The straight edge is supported by an elongated support beam such as an I beam, the straight edge being attached thereto by pivot pins at one end and a sliding spherical bearing at the other end whereby transmission of deforming loads is minimized. The flow channel, or component to be measured, is supported adjacent the straight edge by a bearing mounted support at the bottom end and an adjustable clamp arrangement at the top end. As the carriage is moved along the straight edge, measurement devices engage the channel, the measurement direction being such that thermal patterns are symmetrical to reduce thermally-induced-bow measurement errors and in the direction of maximum straight edge stiffness.