J-type sliding closure mechanism used on the TRRP MPT, the door for the full-scale MPT will be moved against the closure face by using a two-direction cam design recommended by a commercial oven contractor. To close a door, this design moves the door vertically downward with a mechanical screw drive to its bottom position, and the door is then moved horizontally against the closure face. In addition, the seal material design has been altered to give the equivalent of two gaskets between the door and closure face. A prototype of this new arrangement has been developed and tested, but not under the expected operating conditions. Changes were also made in the structural support for the door closure and main chamber to make it easier to get a good seal. It is noted that all of this testing was done with doors for a 4-ft.-8-in.-diameter chamber and that the full-scale MPT will use a 6-ft.-6 in.-diameter main chamber.
Finding. The larger size of the full-scale MPT doors will pose additional challenges in maintaining seal face alignment and minimizing air in-leakage during operation.
Finding. The new closure mechanisms for the four doors on the full-scale MPT have not been tested at operating conditions.
Recommendation 3-1. The new closure mechanisms for the full-scale MPT should be tested and cycled at operating conditions at the fabrication facility prior to systemization.
The Graphalloy® bearings for the conveyor rollers in the main chamber experienced galling and other wear failures during TRRP testing.1 The bearing failures were attributed to oxidation/corrosion at the main chamber operating temperature. Three different bearing materials were evaluated: “improved” Graphalloy®, Stellite, and Deva (Deva-Mogul sintered metal). The Stellite and Deva bearings are more expensive than Graphalloy® bearings, and the Deva bearings are produced by a foreign manufacturer. The Stellite bearings exhibited surface galling and friction at temperature, causing the bearings to come loose from their mountings and interfere with the trays. All materials experienced wear. The BPBGT concluded that the “improved” Graphalloy® bearings were acceptable, although they exhibited some pitting. The BPBGT also developed a bearing-mounting design that allows for quick replacement of the bearings. The toncontainer MPT used at the Newport Chemical Destruction Facility, Indiana, has experienced similar bearing failures, and a repair and replacement approach was adopted.2 During full-scale MPT testing, the BPBGT intends to reconsider Stellite bearings that are interchangeable with the Graphalloy® bearings. The BPBGT believes that it has identified an acceptable path forward for resolving the problem of premature main chamber conveyor bearing failures. However, replacing the bearing mounts will require cooling the unit and reheating. Excessive temperature cycling could cause metal fatigue. The BPBGT has also developed maintenance protocols that shorten replacement times for bearings as much as possible.
Finding. The proposed conveyor bearing selection and replacement approach is appropriate, but actual demonstration of reliable performance has yet to be achieved. If bearing replacement is required more frequently than anticipated, it could reduce the MPT throughput rate.
Recommendation 3-2. The proposed approach for the replacement of conveyor bearings should be tested in conjunction with the testing of the full-scale MPT at operating temperature and design with tray loading at the fabrication facility.
The full-scale MPT will use two heating zones in the main chamber. Each will be capable of 450 kW of induction heating. The TRRP MPT used one 600-kW induction heater. It is unclear whether maintenance on one MPT would be possible while the other was in operation. If not, when one MPT required in-room maintenance, it could not be repaired until the second MPT was shut down. It would reduce the availability of the MPTs if both had to be shut down when either required in-room maintenance.
Finding. It is unclear that heat and magnetic fields generated by one MPT would allow maintenance on the second unit while the first was in operation.
Recommendation 3-3. The BPBGT should consider providing suitable spacing and electromagnetic and thermal shielding to allow maintenance on one unit while the other is operating.
TRRP testing and computational fluid dynamics (CFD) modeling showed that certain areas of some projectiles being heated in the main chamber were heating more slowly than most parts of the projectiles. This slower heating required longer heat-up times to achieve the 1000°F for 15 minutes for all projectiles. After its review of the chamber design, the BPBGT concluded that the slow heating resulted from “shadowing” of parts of the projectiles during the radiant heating process.