National Nuclear Laboratory NNL

Warrington, United Kingdom

National Nuclear Laboratory NNL

Warrington, United Kingdom
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Tverberg T.,Institute for Energy Technology of Norway | Wiesenack W.,Institute for Energy Technology of Norway | Yagnik S.K.,EPRI | Rossiter G.,National Nuclear Laboratory NNL
LWR Fuel Performance Meeting/Top Fuel/WRFPM 2010 | Year: 2010

Two variants of MOX fuel were fabricated and pre-characterized with two quite distinct distributions of the Pu-rich phase, namely MOX-1 (homogeneous) and MOX-2 (heterogeneous). Fabrication routes, initial microstructures, and associated pre-characterizations of the two variants are discussed. These fuel variants were subsequently irradiated, as thin circular discs, in nearly isothermal conditions in two different instrumented fuel assemblies (IFAs) in the Halden test reactor. The two IFAs served complementary purposes. Experimental designs and details of these IFAs are described. In-pile release rate to birth rate (R/B) data for unstable isotopes are interpreted in terms of effective gas diffusivity or in terms of fuel surface-area-to-volume ratio (S/V). Comparative fuel densification, swelling and rod internal pressure data (vs. burnup) are evaluated, and it is shown that the heterogeneous MOX exhibits increased densification, increased swelling and increased fission gas release compared to the homogeneous MOX. Detailed PIE on these unique MOX variants is presently underway.

Oldham M.,Duke University | Clift C.,Montefiore Medical Center | Thomas A.,Duke University | Farfan E.,Savannah River National Laboratory | And 5 more authors.
Journal of Physics: Conference Series | Year: 2010

The RadBall dosimeter is a novel device for providing 3-D information on the magnitude and distribution of contaminant sources of unknown radiation in a given hot cell, glovebox, or contaminated room. The device is presently under evaluation by the National Nuclear Lab (NNL, UK) and the Savannah River National Laboratory (SRNL, US), for application as a diagnostic device for such unknown contaminants in the nuclear industry. A critical component of the technique is imaging the dose distribution recorded in the RadBall using optical-CT scanning. Here we present our initial investigations using the Duke Mid-sized Optical-CT Scanner (DMOS) to image dose distributions deposited in RadBalls exposed to a variety of radiation treatments. © 2010 IOP Publishing Ltd.

Yan P.,Beihang University | Yan P.,Catholic University of Leuven | Delannay L.,Catholic University of Leuven | Payne J.F.B.,National Nuclear Laboratory NNL | Tzelepi A.,National Nuclear Laboratory NNL
Carbon | Year: 2016

A micromechanistic model has been applied to understand the relation between the properties of individual graphite crystals and the properties of polycrystalline graphite. The proposed model accounts for irradiation-induced creep as well as microcracking in both intragranular (parallel to basal planes) and intergranular positions. The two types of cracks were found to have a combined effect on the predicted macroscopic dimensional change and coefficient of thermal expansion (CTE) in both stressed and unstressed graphite. Model predictions were assessed against experimental data. Although further improvement in the simulation of irradiation creep may be required, the model provides useful insights for the mechanisms underlying the effect of macroscopic load on the CTE changes of unirradiated and irradiated graphite. © 2015 Elsevier Ltd.

Butcher E.J.,National Nuclear Laboratory NNL | Borwick J.,National Nuclear Laboratory NNL | Collier N.,National Nuclear Laboratory NNL | Williams S.J.,NDA Radioactive Waste Management Directorate RWMD
Mineralogical Magazine | Year: 2012

Some of the illustrative concepts for the disposal of intermediate-level waste in a geological disposal facility in the UK employ a cementitious backfill around the waste packages. The concept for higher strength rocks would use a highly alkaline backfill composed of Portland cement (now known as CEM I), hydrated lime and limestone flour, referred to as Nirex reference vault backfill (NRVB). This paper reports a study of the extensive leaching of cured NRVB in a range of generic leachant compositions (deionized water, 0.1 M and 1 M NaCl solutions) under flow-through conditions using a flexible wall permeameter. The experiments were designed to run for up to two years and to pass at least 1000 volumes of leachant (defined as the cumulative leachate volume produced/NRVB solid specimen volume) through the NRVB samples. Results for the pH evolution profiles of the leachates and the microstructural analysis of the unleached and leached samples are presented. © 2012 The Mineralogical Society.

Delannay L.,Catholic University of Louvain | Yan P.,Catholic University of Louvain | Payne J.F.B.,National Nuclear Laboratory NNL | Tzelepi N.,National Nuclear Laboratory NNL
Computational Materials Science | Year: 2014

An original model is proposed that predicts the response of a polycrystalline graphite agglomerate to temperature change and irradiation. The model explicitly considers the graphite crystal anisotropy and the development of cracks along the interfaces between differently oriented grains. Using only graphite single crystal data, the model yields predictions of the macroscopic elastic stiffness, thermal expansion coefficient, irradiation-induced creep and irradiation-induced dimensional change (initial shrinkage followed by swelling at higher fast neutron fluence). The behaviour of the virgin polycrystal is properly predicted using a self-consistent mean-field model. However, predicting the pattern of inter-granular cracks requires a finite element model with cohesive zones. The latter simulations are performed on a periodic model polycrystal in 2D, leading to a qualitative agreement with experimental data. © 2014 Elsevier B.V. All rights reserved.

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