Development and Systematic Application of Surface Inspection Methods Used for In-Service Inspection of Reactor Pressure Vessel

Abstract

Both from the mechanics of fracture and from actual instances of defects observed in reactor pressure vessels, it is indicated that greater importance should be attached to surface than to internal defects in the in-service inspection of these components.

In the JPDR, the reactor pressure vessel has undergone ISI three times since 1968, with emphasis placed on surface inspection, and using both remote bore scope and remote Smeck methods. The two methods gave the same results on all three occasions, so that both methods can be considered effective.

With the remote Smeck method, the lower limit of detectable defect size was found to be less than ±lmm, and the reproducibility of defect position, measured on a mock-up nozzle was better than ±3 mm. For the bore scope a newly devised “shadowing technique” is described, which appreciably enhances its ability to detect and to accurately observe surface defects.

The results of ISI in JPDR indicate that significant improvements in detection ability and accuracy could be expected by systematic application of ISI methods.

KEYWORDS:

• BWR type reactor
• pressure vessels
• bore scope
• electric resistance method
• bore scope shadowing technique
• cracks
• surface inspection
• volumetric inspection
• accuracy
• in-service inspection