61
Section 17 Tritium–1
17.1 Micro Dist™ Method
CAUTION
Chemical hazard. Always follow appropriate laboratory safety
procedures when handling chemicals. Always wear personal
protective equipment appropriate for the chemicals you are
handling.
ATTENTION
Danger chimique. Suivez toujours les procédures de
laboratoire de sécurité lors de l'utilisation de produits
chimiques. Veuillez toujours porter l'équipement de protection
personnel approprié pour les produits chimiques que vous
manipulez.
As part of routine nuclear power station monitoring, process water
samples not directly from condensates, such as from release tanks,
and ion-exchange streams and resins, are distilled to collect the
volatile tritiated compounds, mainly tritiated water. The distillate is
then counted in a scintillation instrument and this activity is used to
determined the degree of contamination of the water sample. The
distillation discriminates against any non-volatile source of
contamination such as particles.
In the following procedure,
D and M refer to the marks on the ends
of the collector tube.
D means 'distillation' or 'discarded' end and M
means 'measuring' end. See Figure 2 on page 13.
1. Set the controller to 120
°C. Allow the heater block to warm up.
This will take about 40 minutes.
2. With the
M end up, put the required number of collector tubes
into the collector tube rack.
3. Put the required number of sample tubes into the sample tube
rack; up to 21 for one block. Place 6.0 mL of water sample (or
standard) into each sample tube with an automatic pipet. If the
sample appears to be primarily oil, do not distill, but count
directly with the scintillation counter.
4. Add 1 or 2 drops of 10 M NaOH to each sample tube.
5. Push the
D end of a Tritium–1 collector tube over the open end
of each sample tube to start the seal.
6. Place the assembly in the press, putting the sample tube
through the hole in the white base. Before pressing the user
should grip the collector tube firmly at the breakaway point to
keep the tube from shifting during the pressing procedure.
7. The pressing motion should be a smooth constant pressure
which is just enough to slide the sample tube inside the
collector tube. A jerky, forced motion may cause added strain to
the tube and could potentially crack it. Press down on the
handle until the stop ring on the sample tube hits the
D end of
the collector tube.
8. Put on the heat-resistant gloves. Push the sample tube and
D
end of each tube all the way into the preheated block so that
the collector tube stop ring touches the block. Placing 21 tubes
should take less than one minute.
9. Set the timer for 90 minutes.
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