DOI: 10.1556/JRNC.268.2006.1.10 Journal of Radioanalytical and Nuclear Chemistry, Vol. 268, No.1 (2006) 65–69
0236–5731/USD 20.00 Akadémiai Kiadó, Budapest
© 2006 Akadémiai Kiadó, Budapest Springer, Dordrecht
Analysis of high-level waste for tetraphenylborate using HPLC
T. L. White,* K. B. Martin, L. N. Oji, D. P. DiPrete, W. R. Wilmarth
Westinghouse Savannah River Site, Savannah River National Laboratory, Aiken, 773-A B-160, SC 29808, USA
(Received September 20, 2005)
One waste remediation process used at the Savannah River Site was the in-tank precipitation of the beta-emitting
137
Cs from high-level waste
(HLW) using sodium tetraphenylborate (NaTPB) followed by processing the resulting decontaminated filtrate into grout at the Saltstone Production
Facility (SPF). A simple method was developed for the monitoring of tetraphenylborate (TPB) in high-level waste (HLW) containing up to
0.38 Ci/gal of
137
Cs. Separation was achieved by extraction of the high sodium-bearing waste with acetonitrile followed by analysis using reversed-
phase high performance liquid chromatography (HPLC). The sample preparation method allowed for the handling of an organic extraction layer
that had 94% less acitivity than the HLW sample. The subsequent HPLC analysis of the extraction layer determined the TPB concentration in
HLW waste to 0.8 mg/l with a %rsd of 8.
Introduction
Radioactive byproducts from the production of
nuclear materials are stored at the Savannah River Site
(SRS) in underground high-level waste storage tanks
with a capacity of approximately one million gallons.
Efforts
1,2
are underway to process high-level waste
(HLW) into stable forms for disposal such as radioactive
waste immobilized in borosilicate glass to be sent to a
federal repository, and decontaminated radioactive waste
immobilized in grout and stored on site. One storage
tank of radioactive waste contains tetra-phenylborate
from a discontinued decontamination process. The
minimum allowable concentration of TPB, based on the
current tank volume at a specified height of 367 inches,
was calculated to be 0.8 mg/l to meet the 5% LFL
constraint and return to HLW system service.
Monitored tank samples are expected to contain
approximately 0.38 Ci/gal of
137
Cs and have a dose rate
of 2
.
10
8
dpm/ml. Prior to analysis, removal of some of
the
137
Cs from the samples in the shielded cells helps
reduce personnel exposure and allow for larger sample
volumes to be handled in radioactive laboratory hoods
where instruments used for radioactive samples are
housed in unshielded fume hoods. Samples prepared in
the shielded cells are handled remotely by manipulators
and the protocols should, therefore, have a minimum of
steps and idally be simple to implement. Further, any
cesium removal technique
3
cannot involve acidifying
the alkaline sample because of tetraphenylborate
stability concerns especially below a pH of 7.
4
The
sample preparation method chosen was solvent
extraction with
133
Cs isotopic dilution of the tank
samples. The acetonitrile extractant, has a high capacity
for tetraphenylborate salts and has a limited solubility in
highly ionic tank waste solutions. Acetonitrile extracts
* E-mail: thomas02.white@srs.gov
are then analyzed directly by high performance liquid
chromatography (HPLC) down to the 0.8 mg/l level.
The HPLC analysis was based on previous work
5
where
tetraphenylborate and other phenylborate compounds
were measured in radioactive alkaline waste down to the
10 mg/l level. Both simulated waste and real waste were
examined in this study. Our aim was to develop an
analytical method that would lower the activity of the
HLW sample before analysis followed by monitoring
the TPB concentration in the resulting lower activity
HLW sample down to a concentration of 0.8 mg/l.
Experimental
Chemicals and materials
Potassium tetraphenylborate (97%) was purchased
from Sigma-Aldrich Chemical Company. Acetonitrile
HPLC-grade was purchased from Fisher Scientific and
the HPLC mobile phase 33% (acetonitrile-27%,
methanol-40% and diammonium hydrogen phosphate
buffer) was purchased premixed from La-Mar-Ka, Inc.
All of the components used to make the simulated waste
were purchased from Fisher Scientific.
Instruments
An Agilent 1100 HPLC equipped with a photodiode
array UV/VS detector was used. The controlling
computer, solvent basin, degasser, and quaternary pump
are adjacent to a fume hood. A capillary connector runs
from the quaternary pump through the hood wall to the
autosampler. The autosampler, column compartment and
photodiode array detector are housed inside the fume
hood.