|
|
|
|
 |
Reactor
Decommissioning
History Overview The main Plum Brook reactor was a 9-foot (2.7-meter) diameter x 31-foot (9.4-meter) tall PWR test reactor. Operated by NASA (NRC license TR-3) it had a generating capacity of 60 MW and was not capable of producing electricity. It was operated from 1963 to 1973 with full power operations totaling 98,000 MW-days. It was decommissioned while the facility was in a "cold and dark" state. Reactor disassembly began in 2003 and was completed early 2005. A second reactor (NRC license R-93) was also decommissioned at this facility during this time. It is not discussed in this document. Reactor Decommissioning
Specifics Internals Removal To minimize a potential Tritium release no thermal cutting of the reactor internals was done inside the reactor. Remote shears, saws, and wrenches were extensively used. Two of the thirty-four Beryllium components were believed cracked (from 1972 log books) and potentially would release large quantities of Tritium if jarred, dropped, or heated. Special tools were designed and these two items successfully removed and packaged. Also, a Secondary Cutting Station was occasionally used to size reduce large components using thermal cutting. Internals were cut and removed in a sequence opposite that of most reactor decommissionings (see our Yankee Rowe listing for an explanation). The higher activated components were cut before the lower activated components. This was to reduce the source term as quickly as possible. This approach was desired because of lack of water shielding and the high quantity of components to be removed from the vessel. Strict engineering controls resulted in very little, if any, high level particles found mixed with the low level components. All work on the internals was done by Wachs Technical Services (WTS). Reactor Vessel Removal Segmentation
and Packaging Plan (S&P Plan) Key
People Contractors
Comments Related Publications and Documents
References Click here to return to the Reactor Decommissioning History main page.
|
|
|||||||||||
 |
||||||||||||||
All
work was performed dry because of the condition of the reactor tank and
the lack of water processing on the site. All the work on the internals
was done remotely until dose levels allowed the final pieces to be removed
hands on. Dose levels prohibited using standard long handle tools from
a platform. Instead, operators were positioned 20-feet (6-meters) above
the work and 6-feet (2-meters) from the edge. Although a shield was used
it's ALARA benefit was to keep the operators outside of the gamma "plume"
that was exiting the vessel opening. 
The
pressure vessel was carbon steel with a stainless clad and a maximum thickness
of 2-inches (50mm). Because the reactor was imbedded in the concrete bio-shield
an intact removal was considered cost prohibitive. Mechanical segmentation
was performed dry by Wachs Technical Services. Because of low dose rates
all cutting was done hands on. Most of the cutting was done using "Wall
Mills" (a type of milling machines used successfully on commercial
nuclear reactors and their internals for decades).