FINAL REPORT UFP RESTART AND SPARGER TESTING
Following a Design Basis Event (DBE), potential plugging of the PJM systems is highly probable after air compressors and/or electric power become unavailable for up to 100 hrs. Under such conditions, the rheologically bounding yield stress of the pretreated sludge simulant could reach 300-625 Pa. (Defined in WTP-RPP-100, Rev. 0, Sec. 6.1. [1] and WTP-RPP-98, Rev. 0, Secs. 5.1 and 5.2 [2].) The tests covered under this report are conservative since this range of bounding yield stress is based on the settled solids component in the tank. Also, note that CCN 065607 states that the design basis is 70 Pa for 'gelled material' over the entire tank. Three issues must be addressed by these tests: (1) Determine the required pressure and air flow to overcome the plugged sparger tube resistance following a DBE event. (2) Can the UFP PJMs be restarted with or without assistance from air spargers? (3) Show that solids can be mixed by air spargers following a DBE to allow generated hydrogen gas to rise and be vented to the vessel head space. This is to limit hydrogen concentrations below LFL level. In the first test, a full-scale sparger was simulated by a 2-inch dia. Schedule 160 pipe, installed in an 18-inch diameter plastic tank, 37-foot high (full scale height), 6-inch from the bottom. The bottom 5-ft. lower section was clear to facilitate visual observations. Two simulants were used: a 120 Pa Laponite solution and a 30 Pa/30 cP kaolin:bentonite clay mixture, which filled the tank to the 32-foot level. The first test with 120 Pa Laponite demonstrated breakthrough at an air pressure of 14.6 psig. The second test with the clay simulant resulted in breakthrough at 16.7 psig. Given the specific gravities of these simulants, the breakthrough pressures are very close to the hydrostatic pressures corresponding to the simulant elevations inside the sparger. The CRV test stand at the Engineering Development Laboratory, SRNL, was used to simulate the UFP at 1/4-scale, where the tank diameter was 40.5-inches. The simulant was a 30 Pa/30 cP kaolin:bentonite mixture loaded with 3.3 wt% dry laponite, which successfully achieved a 596 Pa yield stress (vane method) after 14 hrs. However, it apparently had a thicker consistency than the 30 Pa/30 cP rheology of real waste under flowing conditions. The vessel was filled to a H/D of 1.38 and the PJMs were initially filled to approximately full height (39-inch). During the initial drive phase, starting from the full PJM level, application of the same PJM air pressure during normal operation did push the gelled simulant the full travel distance. But on the refill or suction phase, the maximum simulant height in the PJM was only about a third (9.2-inch) of the original travel (27-inch). After 20 cycles of PJM operation only, air sparging, starting at 7 scfm, increasing to 10 scfm was introduced. This increased the PJM drive distance to a stable value of 64% of the full travel after 327 cycles. Visual observation suggests that the simulant was moving up and down as a solid plug and that the cavern may be very limited. Thus, air sparging did not reestablish full PJM operation, but this could be due to the higher consistency of the simulant as compared to the actual waste. A third test utilized 5 mm glass beads deposited at the bottom of the CRV vessel, which was filled with water. Enough glass beads were added to cover the tank bottom surface with a one-bead-thick layer. Based on empirical correlations, the glass beads simulate the behavior of solid particles in the waste. Two spargers were tested: a 2-inch dia. Sch. 160 pipe with straight end, and a 2-inch dia. Sch. 160 pipe with 4 (45 deg) notches around the perimeter, 3/4-inch deep. The objectives were to determine the required distance between the sparger end and the vessel bottom, air pressures, and air flows required to lift the glass beads off the vessel bottom. The test started with the spargers 6 inches from the bottom. For the flat faced sparger, no lifting was observed up to 50 scfm. Liftoff was observed only when the sparger end was 1-inch off the bottom. At 10 scfm, glass beads started to be lifted off. At 50 scfm, approximately 300 beads (or approximately 1.5% of all beads) were lifted off. A 30-inch diameter affected zone was observed where the bed was vibrating. For the notched sparger, no liftoff was observed until the sparger was 1-inch from the bottom with 40 scfm (approx. 10 beads or 0.05% of the total). At 50 scfm, 50% more beads were lifted off and a 12-inch diameter of bulk movement and 24-inch affected zone was established.
- Research Organization:
- Savannah River Site (SRS), Aiken, SC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC09-96SR18500
- OSTI ID:
- 935769
- Report Number(s):
- WSRC-TR-2004-00488; TRN: US200818%%537
- Country of Publication:
- United States
- Language:
- English
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