Fast burn-up measurement in simulated nuclear fuel using ICP-MS

Abstract

A double focusing ICP-MS with pulsed laser deposition (PLD) of thin films as sampling tool has been used in simulated spent fuels for a quick measurement on burn-up of nuclear reactor fuels by measuring the atom ratio of U (representing total heavy elements of mass >225) to selected lanthanide fission monitors. A linear correlation is established between the measured intensity ratios of 238U/143Nd, 238U/(145Nd+146Nd) and 238U/139La against the actual atom ratios present in the samples. The samples in the form of solution are obtained by dissolving different concentrations of U, Nd and La in nitric acid medium, representing a wide burn-up range (0.19 to 19.98 at.%). In addition, PLD films were deposited using 1064 nm, 100 ps Nd:YAG laser pulses on solid targets of U and Nd mixed oxide, corresponding to different burn-ups. ICP-MS analysis of these films after dissolving in nitric acid showed values close to that of the solid target composition. Burn-up data obtained with films deposited at a high laser power density of 1.67×1011 W/cm2 agrees well with the values of the respective target compositions compared to the films deposited at 3.3×109 W/cm2. Present analytical method requires only a very small sample quantity, typically a few nanograms and generally does not require any chemical separation in comparison to the conventional mass spectrometry method, which is traditionally employed to determine the burn-up of a nuclear fuel.

Determination of intensity ratios of Nd, Cs, Zr and Sr against U and burn-up in simulated nuclear fuels by LA-ICPMS

“…Quantities of these elements present in the above pellets correspond to six different compositions, varying from 0.7 to 15.4 at% burn-up of FBR fuel. 24 The detailed procedure for sample preparation is given elsewhere. 31 Accurately weighed amounts of UO 2 and Nd 2 O 3 were taken as the 1 st set of samples [ESI Table 1†]; UO 2 , Nd 2 O 3 , ZrOCl 2 ·8H 2 O, CsCl and SrCO 3 were taken as the 2 nd set of samples [ESI Table 2†].…”

“…Our earlier studies on isotopic compositions of fast reactor fuel revealed that 238 Pu has very low abundance ($0.01%) in total Pu content. 24 Hence, 238 Pu will not affect the analysis of 238 U.…”

“…24,30,31 In such burn-up studies, the isotopic ratio of the heavy element (U) to burn-up monitor (Nd) is measured and fuel burn-up is determined based on the following equation. 24 X ðin at% fissionÞ ¼…”

“…Another technique established in our laboratory for spatial proling and isotope ratio measurement of irradiated fuel is pulsed laser deposition (PLD) followed by mass spectrometry, either with ICPMS or thermal ionization mass spectrometry (TIMS). 24,30,31 The advantages of sampling by PLD 30 are that (i) it can be done inside a hot cell or lead shielded mini-cell with a rotary vacuum pump ($10 À3 mbar); (ii) UV grade fused silica based laser optics can withstand a high radiation environment; 32,33 (iii) only a thin lm having minimum radioactivity (compared to an irradiated pellet) needs to be handled during mass analysis, thereby reducing the human radiation exposure to a considerable extent; (iv) PLD followed by mass analysis will give the spatial prole of the irradiated pellet more accurately (error $ 1%); 24 and (v) as the sample for mass analysis is in the form of a solution, the isotope dilution method can be adopted for accurate concentration measurements. However, PLD followed by ICPMS has limitations compared to the direct solid sampling technique (LA-ICPMS), namely it is time consuming and it is difficult to dissolve the large sized particulates co-deposited in the PLD lm of hard materials, for instance, metal alloy fuel containing Zr or B 4 C from the control rod.…”

“…This burn-up range covers the typical at% fission encountered in pressurised heavy water reactors (PHWRs), light water reactors (LWRs), and FBRs. 24 During irradiation, the ceramic fuel pellets present in a fuel pin experience a high thermal gradient across its radial direction; this will lead to redistribution of atoms – both fuel elements and fission products. Among the FPs, Cs is one of the most volatile, occurs in a larger abundance and is known to be transported radially towards the periphery of the oxide fuel pellet, typically through the vapor transport mode.…”