The following is an artical for a company newsletter about the segmentation of the Plum Brook Reactor. It is dated 2/24/04, before segmentation of the reactor had been completed.

Although the dismantling of the nuclear reactor is a small part of the entire D&D of the Plum Brook Reactor Facility, it is on the main stage. While most of the Plum Brook Reactor Facility is being dismantled by hand or up close with power tools, the reactor disassembly must be done remotely. High levels of radiation and contamination do not allow a technician to get close to the work. Using unique tools operated 30 feet away by watching them on camera is the daily routine for the WTS technicians performing reactor segmentation.

NASA looked at decommissioning the reactor in the 1980's, but elected to wait for radiation levels to drop before attempting disassembly. High radiation levels require flooding the reactor with water to shield the technicians. Underwater disassembly and cutting of the reactor was anticipated to be difficult. The expected low-level radiation would allow for a dry disassembly using standard tools. The facility committed to removing all water and seal off the piping.

After sitting idle for 30 years protected by a nitrogen blanket to prevent corrosion it was decided to start decommissioning the reactor. A similar reactor disassembled just before the Plum Brook reactor allowed for dry hands-on disassembly. However, radiation levels in the Plum Brook reactor would be much greater than this other reactor. These higher levels would not allow technicians to do hands-on disassembly. Remote tools would need to be used.

Many commercial nuclear plants use under water torches, saws, and abrasive water jet cutters to remove components from those reactors. Because Plum Brook was a dry reactor now, the fumes and debris from these types of "normal" cutting tools would spread debris and radiation everywhere. A more controlled disassembly was the only option.

Since September 2003 technicians have been unbolting and cutting components inside the reactor vessel. After five months a majority of these components were out of the vessel. All of these components have been removed using long handle tools by technicians working 25 feet up and 6 feet to the side. A simple operation such as tuning a screw involves mounting a pneumatic wrench on a 30-foot pole, lowering it down through a protective shield, and then using a 6-foot horizontal pole to maneuver onto the bolt. Using cameras to watch the tool as it swings over the bolt takes a great deal of patience and practice. One component of the reactor has 138 bolts alone.

Early in the disassembly process the radiation levels at the protective shield reached over 1500 mR/hr (milli Rem per hour of radiation). Behind the shield, and standing 6 feet to the side, radiation levels to the technicians were reduced by 750 times. The usual daily limit for a technician is 100 mR per day. That means without this shield the technicians would only be allowed to work 4 minutes each day.

Before the dome covering the top of the reactor was removed some of the components were removed from side penetrations. Technicians practiced on "clean" mock-ups to quickly and safely place remote tooling in position. Using cameras and remotely controlled tools, items were pulled from the center of the reactor. The radiation exposure to the technicians was much lower than expected in part by the training they had done.

Packaging the Radiological Waste
After a component is removed from the reactor it is taken to a container to be shipped off site. Depending on the level of radioactivity and material, components may go in one of several different containers. The lowest level components (such as the bolts on the reactor dome) had no detectable radiation. Some facilities would "free release" these items and discard them in the trash. At Plum Brook all items from the reactor are being shipped off site in special containers.

Low level waste can go in small metal boxes or the large 20-foot long truck containers called "Sealands". Higher level items go in either Class A or Class B/C containers. The highest level waste is know as "Greater Than Class C" (GTCC) and require the highest integrity containers available. The higher the waste classification the higher the price tag for disposal at a burial site.

The WTS and PlantDecommissioning Design Team did detailed planning in the Segmentation and Packaging Plan to reduce the amount of high level waste containers required. In addition real time changes to the packaging plan have increased liner efficiency. At this point in segmentation two Class B/C liners have been filled with high level waste. The original estimates planned for this waste going into over three liners. By careful planing the packaging efficiency has doubled and the amount of liners to be buried is noticeably decreasing. This results in a very large dollar saving in the total burial costs.

Early in the project it was anticipated that the reactor would contain items that were "Greater Than Class C" (GTCC) and require the highest integrity containers available. To reduce the chances of having GTCC waste, segmentation of the reactor was planned out well in advance. If a reactor component is to be cut into 3 pieces and the middle piece had the bulk of the radiation, it can cause that middle piece to become GTCC. Looking at the drawings and running computer models will give an idea what components this may apply to. These and any other suspicious components are then checked real time for these "hot spots". If found, care must be taken not to cut into this area and avoid creating GTCC waste.

Disassembly of the Plum Brook reactor is proceeding efficiently and safely. Technician exposure is far below what was expected. Packaging of the waste in liners is more efficient than planned resulting in a noticeable reduction to expected burial costs. Unknown experiments and unexpected extra components have been handled real time and successfully. The dry disassembly of the Plum Brook reactor will be a success story in nuclear facility decommissioning.