Both the Model 5A (Monel 400) and 5A (Monel 400) Modified five-inch cylinders have been used at the Portsmouth GDP to withdraw, store, and ship highly enriched uranium hexafluoride. As a result of a generic cracking problem with Monel 400 valve-boss material, a cylinder modification was implemented in the mid 1970s. This modification resulted in the violation of the ASME ''Code'' stamp status of the Model 5A Modified cylinder. Hydrostatic testing-to- rupture data indicated that the Model 5A Modified cylinders had ruptured strengths equivalent to that of the original Model 5A cylinders. An independent consultant reviewed the available information and confirmed that the Model 5A Modified cylinders ''will with proper maintenance continue to perform satisfactorily for many additional years of service.'' Based on the test data and consultant's review, DOE approved continued use of the 5A Modified cylinder and also requested procurement of replacement 5B cylinders be expedited. Currently, the 5A modified cylinders are in the production, storage, shipment cycle, and a sufficient number of 5B cylinders has been ordered to accommodate the projected product shipping requirements for the Navy flow. 3 tabs.