An analysis of tank and pump pit flammable gas data in support of saltwater pumping safety basis simplification
Hanford Site high-level waste tanks are interim stabilized by pumping supernatant and interstitial waste liquids to double-shell tanks (DSTs) through a saltwell pump (SWP). The motor to this SWP is located atop the tank, inside a pump pit. A pumping line extends down from the pump motor into the well area, located in the salt/sludge solids in the tank below. Pumping of these wastes is complicated by the fact that some of the wastes generate and retain potentially hazardous amounts of hydrogen, nitrous oxide, and ammonia. Monitoring of flammable gas concentrations during saltwell pumping activities has shown that one effect of pumping is acceleration in the release of accumulated hydrogen. A second effect is that of a temporarily increased hydrogen concentration in both the dome space and pump pit. There is a safety concern that the hydrogen concentration during saltwell pumping activities might approach the lower flammability limit (LFL) in either the tank dome space or the pump pit. The current Final Safety Analysis Report (FSAR) (CHG 2000) for saltwell pumping requires continuous flammable gas monitoring in both the pump pit and the tank vapor space during saltwell pumping. The FSAR also requires that portable exhauster fans be available by most of the passively ventilated tanks to be saltwell pumped in the event that additional air flow is required to dilute the headspace concentration of flammable gases to acceptable levels. The first objective of this analysis is to review the need for an auxiliary exhauster. Since the purpose of the exhauster is to diffuse unacceptably high flammable gas concentrations, discovery of an alternate method of accomplishing the same task may provide cost savings. The method reviewed is that of temporarily stopping the saltwell pumps. This analysis also examines the typical hydrogen concentration peaks and the rates of increase in hydrogen levels already witnessed in tanks during saltwell pumping activities. The historical data show that these rates and maximum concentrations are so low as to make it unlikely that the LFL concentration would ever be approached. The second objective of this analysis is to review the data provided by two separate flammable gas measurement systems on each tank being saltwell pumped to see if there is an unnecessary redundancy. Eliminating redundant measurement systems would provide cost savings if the quality of data and resultant margin of safety during saltwell pumping activity are not compromised.
- Research Organization:
- LMHC (US)
- Sponsoring Organization:
- USDOE Office of Environmental Management (EM) (US)
- DOE Contract Number:
- AC27-99RL14047
- OSTI ID:
- 804242
- Report Number(s):
- RPP-6334, Rev.0; TRN: US200303%%101
- Resource Relation:
- Other Information: PBD: 26 Jul 2000
- Country of Publication:
- United States
- Language:
- English
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