[ RadSafe ] Methods for Sr-90 detection

[Olsson Mattias :MSO]

There is a need to measure Sr-90 at NPP:s, mostly due to environmental
follow-up and repository inventories. Sometimes it is also interesting
for calculations regarding consequenses from damaged fuel. The only
trouble is the method that is used to determine Sr-90.

In Sweden the most common method is the simplest
extraction-equilibrium-extraction-LSC one that (on top of having to wait
for several weeks for a radioactive equilibrium and then measure with
LSC for a week or so) has trouble with Ba-/La-140 interference. The
interference can be reduced by another solvent extraction before it all.
Anyway...

There are some quicker methods to analyze Sr-90. I wonder about the
quality! This list has an amazing range of people, so why not ask... The
methods that I have come in contact with (but not tried myself) are:

- The use of Eichrome element specific columns followed by LSC
- The use of an IC to separate the SR from contaminants (collect the SR
fraction) followed by LSC

A reference for the second method is pasted at the end of this mail. Any
experiences, good or bad? This would be quite helpful since the demands
from regulatory bodies (at least in Sweden) are always increasing.

All the best,

Mattias Olsson, Forsmark NPP

****
Individual Quantification of 89Sr and 90Sr in Nuclear Reactor Effluent. 

Papers 

Health Physics. 73(4):601-610, October 1997.
Senaratne, Uditha P. M.; Jester, William A.; Bleistein, Charles D. 
Abstract: 
An analytical method utilizing ion chromatography, a non-radioactive
strontium carrier, and liquid scintillation spectroscopy to individually
quantify 89Sr and 90Sr in nuclear reactor effluent is presented. It is
observed that this method is less time consuming than traditional
procedures for quantifying radio-strontium, deals comprehensively with
separation and subsequent isotopic quantification of strontium, and
avoids difficulties reported in previous research. The equipment,
solutions and operating conditions for the chromatographic separation of
strontium in aqueous solution are identified, and the strontium fraction
is shown to elute between 7 and 7.5 min after injection. The beta
spectra of 90Sr, 89Sr and 90Y are obtained using liquid scintillation
spectroscopy, and the effects of quenching are shown to be negligible.
The positions of the liquid scintillation windows within the combined
beta spectra facilitating isotopic analysis of 89Sr and 90Sr are
identified, followed by the system of equations to quantify 89Sr and
90Sr within a sample. The performance of the method is evaluated using
five solutions representing effluent containing radio-strontium at known
concentrations. It is observed that when the 89Sr and 90Sr
concentrations each are approximately 37 Bq mL-1 or more, the method
over-estimates the 89Sr activity by 15-20% and under-estimates the 90Sr
activity by 10-30%, while yielding the total radio-strontium activity to
within 1-4% of expected. The lower limit of detection of the system for
either 89Sr or 90Sr is shown to be approximately 0.8 Bq mL-1 of
effluent.