Powder Leaching Study for Grain Boundary Inventory of Two High Burnup Fuels

MRS Advances ◽  
2019 ◽  
Vol 4 (17-18) ◽  
pp. 981-986
Author(s):  
Alexandre Barreiro Fidalgo ◽  
Olivia Roth ◽  
Anders Puranen ◽  
Lena Z. Evins ◽  
Kastriot Spahiu ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Spent Fuel ◽  
Short Period ◽  
Fission Gas ◽  
Leaching Solution ◽  
Significant Release ◽  
Leaching Experiments ◽  
High Burnup ◽  
Fission Gas Release

ABSTRACTIn the context of safety assessment, the fraction of inventory that is expected to rapidly dissolve when water contacts the spent fuel is called the Instant Release Fraction (IRF). Conceptually, this fraction consists of radionuclides outside of the uranium dioxide matrix and therefore the fraction can be further divided into the radionuclides in the fuel/cladding gap and radionuclides in the grain boundaries. The relative importance of these two fractions is investigated here for two Swedish high burnup fuels through simultaneous grinding and leaching fuel fragments in simplified groundwater for a short period of time. The hypothesis is that this will expose grain boundaries to leaching solution and provide an estimate of the release of the grain boundary inventory upon contact with water. The studied fragments were used in previous leaching experiments and thus pre-washed to remove any pre-oxidized phases. The results showed a significant release of iodine, cesium and rubidium and to a lower extent molybdenum and technetium. The fraction of inventory in the aqueous phase of actinides and lanthanides was 1-2 orders of magnitude lower than for the elements associated to the IRF. Both fuels displayed a very similar behavior and no correlation as a function of burnup or fission gas release was found.

RN Fractional Release of High Burn-Up Fuel: Effect of HBS and Estimation of Accessible Grain Boundary

2008 ◽  
Vol 1107 ◽  
Author(s):  
F. Clarens ◽  
D. Serrano-Purroy ◽  
A. Martínez-Esparza ◽  
D. Wegen ◽  
E. Gonzalez-Robles ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Correction Factor ◽  
Core Sample ◽  
Gas Release ◽  
Spent Fuel ◽  
Fission Gas ◽  
Leaching Experiments ◽  
Fission Gas Release ◽  
Fractional Release ◽  
Number Of Particles

AbstractThe so-called Instant Release Fraction (IRF) is considered to govern the dose released from Spent Fuel repositories. Often, IRF calculations are based on estimations of fractions of inventory release based in fission gas release [1]. The IRF definition includes the inventory located within the Gap although a conservative approach also includes both the Grain Boundary (GB) and the pores of restructured HBS inventories.A correction factor to estimate the fraction of Grain Boundary accessible for leaching has been determined and applied to spent fuel static leaching experiments carried out in the ITU Hot Cell facilities [2]. Experimental work focuses especially on the different properties of both the external rim area (containing the High Burn-up Structure (HBS)) and the internal area, to which we will refer as Out and Core sample, respectively. Maximal release will correspond to an extrapolation to simulate that all grain boundaries or pores are open and in contact with solution.The correction factor has been determined from SEM studies taking into account the number of particles with HBS in Out sample, the porosity of HBS particles, and the amount of transgranular fractures during sample preparation.

Measurements of Grain-Boundary Inventories of 137Cs, 90Sr and 99Tc in Used Candu Fuel

1992 ◽  
Vol 294 ◽  
Author(s):  
S. Stroes-Gascoyne ◽  
J.C. Tait ◽  
R.J. Porth ◽  
J.L. Mcconnell ◽  
T.R. Barnsdale ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Source Term ◽  
Slow Release ◽  
Gas Release ◽  
System A ◽  
Fission Gas ◽  
Fission Gas Release ◽  
Upper Boundary

ABSTRACTTwo methods were used to measure grain-boundary inventories of 137Cs, 90Sr and 99Tc in used CANDU fuel, to corroborate source term estimates based on a fission gas release code. Used fuels were partially oxidized at 200°C in air to overall compositions of UO2+x (0.15≤ × ≤0.25) to expose UO2 grain boundaries, followed by leaching in aqueous solution. Only a fraction (2 to 18%) of the calculated gap + grain-boundary inventories for 37Cs was released. This suggests that the calculations overestimate Cs release or that oxidation does not expose all grain boundaries, or that Cs release from grain boundaries is slow. Release of 90Sr (0.01 to 0.7%) agreed reasonably well with the source term estimates (0.001 to 0.3%). Release of 99Tc (0.3 to 1.5%) suggests that the source term estimate for the upper boundary of 99Tc release (25%) may be too high. A second technique involved leaching of crushed and size-fractionated used fuel in either a static or dynamic system. A direct one-to-one correlation between calculated and measured gap + grain-boundary inventories for 137Cs was found for low- and medium-power fuels.

Quantitative Assessment of the Instant Release Fraction (IRF) for Fission Gases and Volatile Elements as a Function of Burnup and Time under Geological Disposal Conditions

2003 ◽  
Vol 807 ◽  
Author(s):  
Cécile Ferry ◽  
Patrick Lovera ◽  
Christophe Poinssot ◽  
Lawrence Johnson
Keyword(s):  
Failure Time ◽  
Solid State Chemistry ◽  
Spent Fuel ◽  
Volatile Elements ◽  
Enhanced Diffusion ◽  
Labile Fraction ◽  
Fission Gas ◽  
Leaching Experiments ◽  
Fission Gas Release ◽  
Α Activity

ABSTRACTThe Instant Release Fraction at container failure time, IRF(t), is here considered as being the sum of (i) the initial labile fraction, corresponding to the sum of gap and grain boundary inventories of certain radionuclides on exit from the reactor, with a further possible contribution from segregation in the rim region and (ii) the time-dependent fraction of radionuclides accumulating at grain boundaries due to a self-irradiation enhanced diffusion through the grains. The initial labile fraction of radionuclides such as 14C, 36Cl, 79Se, 129I, and 135Cs has been estimated based on leaching experiments, post-irradiation fission gas release measurements and studies of solid-state chemistry of spent fuel, along with estimates of fission product segregation in the rim zone. The contribution of the a self-irradiation enhanced diffusion has also been estimated based on a diffusion coefficient decreasing with time proportionally with the volume α-activity of the spent fuel. Its contribution to the IRF is limited for UO2 fuels. The proposed bounding values of the IRF for fuel with a burnup of 55 GWd/tIHM for 14C, 36Cl, 79Se, 129I, and 135Cs are 11 % at t=0 and close to 15 % at a container failure time of 10,000 y.

Inventories of Iodine-129 and Cesium-137 in the Gaps and Grain Boundaries of LWR Spent Fuels

1999 ◽  
Vol 556 ◽  
Author(s):  
W. J. Gray
Keyword(s):  
Grain Boundary ◽  
Spent Nuclear Fuel ◽  
Yucca Mountain ◽  
Light Water Reactor ◽  
Gas Release ◽  
Spent Fuel ◽  
Fission Gas ◽  
Geologic Disposal ◽  
Cesium 137 ◽  
Fission Gas Release

AbstractPerformance assessment calculations that support geologic disposal of spent nuclear fuel in a potential repository at Yucca Mountain, Nevada, are based in part on the assumption that 2% of the total inventories of 135Cs, 129I, and 99Tc are located in the gap and grain-boundary regions where they could dissolve rapidly if the spent fuel were to be contacted by groundwater. Actual measured values reported here for a few light-water reactor (LWR) spent fuels show that the combined gap and grain-boundary inventories of 129I approximately equaled the fission-gas release fractions. For 137Cs, the combined gap and grain-boundary inventories were approximately one third of the fission-gas release fractions. These measured values can be used to replace the 2% estimate and thus reduce the uncertainties in the calculations.

Gap and Grain-Boundary Inventories of Cs, Tc, and Sr in Spent LWR Fuel

1991 ◽  
Vol 257 ◽  
Author(s):  
W. J. Gray ◽  
D. M. Strachan ◽  
C. N. Wilson
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Surface Area ◽  
Dissolution Behavior ◽  
Strongly Correlated ◽  
Spent Fuel ◽  
Geologic Repository ◽  
Metallic Particles ◽  
Waste Container ◽  
Fission Gas Release

ABSTRACTSoluble radionuclides concentrated within the gap and grain-boundary regions of spent fuel could dissolve relatively rapidly were the waste container to fail and the fuel to be contacted by water in a geologic repository. To provide an estimate of the quantities of radionuclides that may be rapidly released, fractional inventories of Cs, Tc, and Sr concentrated within the fuel/cladding gap region have been measured for U.S. LWR spent fuels with fission gas release (FGR) values ranging from 0.25% to 18%. Separate measurements of the grain-boundary inventories of Cs, Tc, and Sr have been made for the same fuels. The Cs gap inventories were generally found to be about one fourth of the FGR values. The Cs grain-boundary inventories were generally less than 1% of the total Cs inventories and were not strongly correlated with FGR. Both the gap and grain-boundary inventories of Tc and Sr were near the detection limits of the methods used, less than 0.2% of the total inventories of these elements. However, some of the Tc may reside at the grain boundaries in the form of relatively insoluble metallic particles and not be detected by these experiments. Data obtained by comparing the dissolution behavior of fuel fragments with that of fuel grains were used to estimate the dissolution rate of Cs from the grain boundaries of one of the fuels. Surface-area normalized dissolution rates determined for fuel fragments in these same tests exceeded those determined for grains. A likely explanation is that the estimated fragment surface area did not take into account the “effective” grain-boundary surfaces.

Grain Subdivision Fission Gas Swelling Model for UO2

MRS Advances ◽  
2016 ◽  
Vol 1 (35) ◽  
pp. 2465-2470
Author(s):  
Thomas Winter ◽  
Richard Hoffman ◽  
Chaitanya S. Deo
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Gas Diffusion ◽  
Fine Grain ◽  
Fuel Pellets ◽  
Model And Simulation ◽  
Nucleation Sites ◽  
Fission Gas ◽  
High Burnup ◽  
Swelling Model

ABSTRACTUnder high burnup UO2 fuel pellets can experience high burnup structure (HBS) at the rim also known as rim effect. The HBS is exceptionally porous with fine grain sizes. HBS increases the swelling further than it would have achieved at a larger grain size. A theoretical swelling model is used in conjunction with a grain subdivision simulation to calculate the swelling of UO2. In UO2 the nucleation sites are at vacancies and the bubbles are concentrated at grain boundaries. Vacancies are created due to irradiation and gas diffusion is dependent on vacancy migration. In addition to intragranular bubbles, there are intergranular bubbles at the grain boundaries. Over time as intragranular bubbles and gas atoms accumulate on the grain boundaries, the intergranular bubbles grow and cover the grain faces. Eventually they grow into voids and interconnect along the grain boundaries, which can lead to fission gas release when the interconnection reaches the surface. This is known as the saturation point. While the swelling model used does not originally incorporate a changing grain size, the simulation allows for more accurate swelling calculations by introducing a fractional HBS based on the temperature and burnup of the pellet. The fractional HBS is introduced with a varying grain size. Our simulations determine the level of swelling and saturation as a function of burnup by combining an independent model and simulation to obtain a more comprehensive model.

Identification of Radial Position of Fission Gas Release in High-Burnup Fuel Pellets under RIA Conditions

2010 ◽  
Vol 47 (2) ◽  
pp. 202-210 ◽  
Author(s):  
Hideo SASAJIMA ◽  
Tomoyuki SUGIYAMA ◽  
Toshinori CHUTO ◽  
Fumihisa NAGASE ◽  
Takehiko NAKAMURA ◽  
...  
Keyword(s):  
Radial Position ◽  
Gas Release ◽  
Fuel Pellets ◽  
Fission Gas ◽  
High Burnup ◽  
Fission Gas Release
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