Flammable gas issues in double-contained receiver tanks. Revision 1 Page: 29 of 170
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sample (Shekarriz et al. 1997; Mahoney et al. 1997)(a). In addition to the measurement
difficulties, even a carefully protected sample may not be representative of the waste that is to be
transferred to the DCRT. The part of the tank waste that is sampled, if it is near the waste
surface, can be depleted in ammonia by mass transfer to the headspace.
The several types of ammonia measurement difficulties (as they pertain to DCRT
modeling) are discussed in the following subsections. The available ammonia measurements can
be found in the appendix.
2.1.2.1 Ammonia in Grab Samples
In general, only the drainable liquid from a grab sample is subjected to ammonia analysis.
Grab samples are exposed to the air while being centrifuged (if solids are present), while under-
going subdivision into subsamples, and while being analyzed. When there are no solids present
and the subsample is analyzed for ammonia before any other tests are made, the exposure time is
generally less than 10 minutes. Centrifugation (to settle solids) can add another 10 minutes and,
in some cases, more time (probably 10 minutes or less) can be spent on other analyses that
precede ammonia tests.
Handling and analysis procedures have varied over the period represented by the
ammonia measurements in the appendix to this report. In 1997, the procedure was revised so
that the subsample used for ammonia analysis was "preserved" with dilute acid (to convert
volatile ammonia to nonvolatile ammonium ion) and was taken from the sample before any other
analysis procedures. The most recent grab samples (AX-101, SX-103, and SX-104) were
subsampled, with some subsamples treated with acid and others left untreated so that the effect
of acid preservation could be tested. No significant effect was found.(b) The most recent samples
can therefore be considered to have undergone negligible volatilization.
Earlier grab samples (which provide most of the data in the appendix) probably spent 10
to 30 minutes exposed to the air, because the ammonia subsamples were not necessarily the first
ones taken, and were not acid-preserved. Under those circumstances, some volatilization loss
(a) The difficulty with determining ammonia from RG$ samples is that ammonia is highly soluble and
tends to remain in the liquid, and the RGS extraction process captures only the gas phase. Little ammonia
is in the extracted gas; most of it remains dissolved in the sample liquid. To determine the residual
dissolved ammonia, it is necessary to measure it directly or to find a physical relationship by which the
residual ammonia can be calculated from the extracted ammonia. Both alternatives have unsolved
technical problems. Direct measurement of the residual means scraping or draining the solids and liquid
out of the RGS vessel after gases have been extracted and sending part of the sample for ion-specific
electrode analysis. A significant amount of the ammonia is lost to hot-cell air in this process, so the
residual ammonia is underestimated (in the same way discussed in Section 2.1.2.3). The indirect
measurement of residual ammonia has been hindered by the difficulty of finding a relationship between
extracted and residual ammonia. The equilibrium relation that exists in the tank because the gas and
liquid spend a long time in intimate contact does not exist in the RGS process. Mass-transfer limitations
within the sample and at its surface prevent equilibrium being approached, so the actual relationship
between the extracted ammonia vapor and the dissolved residual ammonia is not well determined.
(b) Barton WB. May 20, 1997. Personal communication to LA Mahoney (PNNL), Richland,
Washington.
2.7
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Peurrung, L. M.; Mahoney, L. A.; Stewart, C. W.; Gauglitz, P. A.; Pederson, L. R.; Bryan, S. A. et al. Flammable gas issues in double-contained receiver tanks. Revision 1, report, June 1, 1998; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc702057/m1/29/: accessed April 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.