1994
Decommissioning Services - FORT ST. VRAIN
Underwater Construction Corporation (UCC), provided nuclear diving services in support of the Fort St. Vrain (FSV) decommissioning. The Westinghouse Team, which was responsible for the decommissioning, was a joint effort by Westinghouse Electric Corporation, the MK-Ferguson Group, and the Scientific Ecology Group. UCC was a subcontractor to MK-Ferguson.
The nuclear diving operations continued for eighteen months during 1994 and 1995. During this time, UCC supplied 22 divers to the decommissioning project. More than 1650 dives were made in the Pre-Stressed Concrete Reactor Vessel (PCRV)) to successfully complete 37 major underwater tasks, as well as, numerous minor underwater tasks. Upon completion of decommissioning diving services, more that 3400 in-water man-hours were logged and documented by UCC personnel.
The use of divers in the PCRV corresponded with FSV's ALARA concerns. The average radiation dose field the divers were working in was less than 16mRem/hr. With the onset of PCRV shield water chemistry problems, remote tooling would have been difficult and the divers close proximity to the work proved to be beneficial.
Water depths in the PCRV ranged between 15 and 60 feet throughout the project. FSV is located 4800 feet above sea level. This altitude increased the in-water working depths experienced by the divers to between 30 and 80 feet. The PCRV water temperature ranged from 85 to 98 degrees F. The average water visibility in the divers work area was less than 24 inches for most of the diving operations. Contact radiation levels on reactor components ranged from 40 mRem/hr to 70 Rem/hr.
The diving tasks were divided into two work evolutions. The first, which included most of the assigned tasks, was all the work associated with the 300 ton Core Support Floor (CSF) removal. The second evolution was the removal of all medium to high dose material between the CSF and the plenum floor, including the four helium circulators and the twelve steam generator primary modules. More than 680 tons of radwaste was removed from the PCRV by the divers.
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