ISO 8298 pdf download – Nuclear fuel technology一Determination of milligram amounts of plutonium in nitric acid solutions – Potentiometric titration with potassium dichromate after oxidation by Ce(IV) and reduction by Fe(II).
4.4 Up to 0,07 mmol of Iluorosilicate and 0.7 n,mol of fluonde do not interfere if 2.5 mmol to 3 mmol of aluminium(lll) are added. 3 mmol of sulfuric acid can be tolerated in the plutonium aliquot without any interference. Up to 0,4 mg of chromium(Vl). 0,3 mg of chromium(lll), 0.3 mg of manganese(U) and 0,2 mg of gallium(llI) do not interfere
4.5 0.5 mmol of nitrite causes no statistically significant bias when present at the moment of oxidation of the plutonkim. Indeed, most of the nitntes should be decomposed by the an’iidosulfonic acid which is contained in the nitric acid mixture used for the dution of the plutonium aliquot.
4.6 However, adding more than about 0.5 mmol of amidosulfonic acid with the nitric acid mixture causes a positive bias due to Incomplete reduction of the permanganate by the oxalic acid.
4.7 About 40 ig of iodate leads to a significant bias of about -i’ 0.2%.
4.8 Vanacum(IV) and vanadium(V) interfere almost quantitatively.
4.9 The neptunium present is titrated together with the plutonium. invoMng the exchange of approximately
I mole of electrons per mole. For neptuniumplutonlum ratios up to 0.01. an emplrlcal formula can be established
and used to correct for this interference, provided the neptunium content Is known or measured to an accuracy of
± 10%. The following is an example of sudi an empirical correction equation:
T— F/Il ÷ k(NplPu)J where
F is the iound plutonium content, expressed in arbitrary units (e.g. mg, mass percent);
T is the laken or true plutonium content, expressed m the same units as F
A is the mass fraction of neptunium, determined by titration with plutonium;
Np/Pu is the mass ratio of neptunium to plutonium in the sample.
The coefficient A is close to 0.57 and has to be measured experimentally. it is sufficiently reproducible provided that the reagents used In clause 7 are added carefully in accordance with the procedure, complying in particular with the potentials and timing specified.
4.10 The effect of americium remains to be studied.
5 Reagents
Use only reagents of recognized analytical grade and distilled or deionized waler.
5.1 0,5 moLl solutIon of ammonlum hexanltratocerate, (NH4)2(Ce(NO3), in nitric acid.
Dissolve 27,59 of amrnonium hexanitratocerate in a 1 mel/i nitric acid solution and dilute to 100 ml using the same solution.
5.2 NItric acid mIxture: I molt nitric acid. 0,013 moth amidosulfonic acid, 0,002 5 molt ironf ill) nitrate and
0,05 moth alumm.um nitrate.
Add 70 ml of concentrated nitric acid (p = 1,40 kg/l) to 500 ml of water. Dissolve in this solution successively 1.26 g of amidosultonic aced. 1,01 g of iron) nitrate nonahydrate and 18.759 of aluminium nitrate nonahydrate and dilute with water to II of solution.
5.3 0.25 % (mit) osmium tetroxide solution.
Verify the litre of the plutonium reference solution against the potassium chchromate reference solution in aocordance with ISO 10980. titrating at least five aliquots with the potassium dichrornate reference solution using the procedure specified above or a more accurate one. Repeat this verification on at least one other day- The solution is acceptIe if the calculated titre and the mean of the measured titres agree wittn 0,1 %. If not, repeat the Preparation of the reference solutions.
6 Apparatus
Normal laboratory equlpmenl for a laboratory analysing piutonlum, plus the following:
6.1 High-impedance millivoltmeter, 100 MO input resistance, with a digital read-out cepable of discriminating to 1 mV.
6.2 Burettes, capacity 1 ml and 10 ml, capable of delivering increments down to 4 al, with non-return valves controlling the addition of the reagent into the titration cell through polyethylene tubes, and filled with a Labyrinth- type anti-diffusion tip. The bureltes used for the addition of won(ll) sulfate solution and potassium dlchrornate titrant solution shall be calibrated gravinietrically.
6.3 MagnetIc stIrrer, with speed control and plastic-coated stirrer bar.
6.4 Temperature sensor, with cgital read-out, to measure the temperature of the solutions of iron(ll) sulfate (5.8) and potassium dictiromate (5.9).
ISO 8298 pdf download – Nuclear fuel technology一Determination of milligram amounts of plutonium in nitric acid solutions – Potentiometric titration with potassium dichromate after oxidation by Ce(IV) and reduction by Fe(II)
