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Title: QUANTIFICATION OF ACTINIDE ALPHA-RADIATION DAMAGE IN MINERALS AND CERAMICS

Abstract

There are large amounts of heavy alpha-emitters in nuclear waste and nuclear materials inventories stored in various sites around the world. These include plutonium and minor actinides such as americium and curium. In preparation for geological disposal there is a consensus that actinides that have been separated from spent nuclear fuel should be immobilised within mineral-based ceramics rather than glass. Over the long-term, the alpha-decay taking place in these ceramics will severely disrupt their crystalline structure and reduce their durability. A fundamental property in predicting cumulative radiation damage is the number of atoms permanently displaced per alpha–decay. Currently, this number is estimated as 1000-2000 atoms/alpha decay event. Here, we report nuclear magnetic resonance, spin-counting experiments that measure close to 5000 atoms/alpha decay event in radiation damaged natural zircons. New radiological NMR measurements on highly radioactive, 239Pu zircon show damage similar to that created by 238U and 232Th in mineral zircons at the same dose, indicating no significant effect of dose rate. Based on these measurements, the initially crystalline structure of a 10 wt% 239Pu zircon would be amorphous after only 1400 years in a geological repository. These measurements establish a basis for assessing the long-term structural durability of actinide-containing ceramicsmore » based on an atomistic understanding of the fundamental damage event.« less

Authors:
; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
898087
Report Number(s):
PNNL-SA-51828
19194; 19852; KP1301020; TRN: US0701570
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nature, 445:190-193
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; 12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; ACTINIDES; ALPHA DECAY; AMERICIUM; ATOMS; CERAMICS; CURIUM; DECAY; DOSE RATES; GLASS; NUCLEAR FUELS; NUCLEAR MAGNETIC RESONANCE; PLUTONIUM; RADIATIONS; RADIOACTIVE WASTES; ZIRCON; SPENT FUELS; Zircon; NMR; Radiation Damage; Amorphization; Environmental Molecular Sciences Laboratory

Citation Formats

Farnan, Ian E., Cho, Herman M., and Weber, William J. QUANTIFICATION OF ACTINIDE ALPHA-RADIATION DAMAGE IN MINERALS AND CERAMICS. United States: N. p., 2007. Web. doi:10.1038/nature05425.
Farnan, Ian E., Cho, Herman M., & Weber, William J. QUANTIFICATION OF ACTINIDE ALPHA-RADIATION DAMAGE IN MINERALS AND CERAMICS. United States. doi:10.1038/nature05425.
Farnan, Ian E., Cho, Herman M., and Weber, William J. Thu . "QUANTIFICATION OF ACTINIDE ALPHA-RADIATION DAMAGE IN MINERALS AND CERAMICS". United States. doi:10.1038/nature05425.
@article{osti_898087,
title = {QUANTIFICATION OF ACTINIDE ALPHA-RADIATION DAMAGE IN MINERALS AND CERAMICS},
author = {Farnan, Ian E. and Cho, Herman M. and Weber, William J.},
abstractNote = {There are large amounts of heavy alpha-emitters in nuclear waste and nuclear materials inventories stored in various sites around the world. These include plutonium and minor actinides such as americium and curium. In preparation for geological disposal there is a consensus that actinides that have been separated from spent nuclear fuel should be immobilised within mineral-based ceramics rather than glass. Over the long-term, the alpha-decay taking place in these ceramics will severely disrupt their crystalline structure and reduce their durability. A fundamental property in predicting cumulative radiation damage is the number of atoms permanently displaced per alpha–decay. Currently, this number is estimated as 1000-2000 atoms/alpha decay event. Here, we report nuclear magnetic resonance, spin-counting experiments that measure close to 5000 atoms/alpha decay event in radiation damaged natural zircons. New radiological NMR measurements on highly radioactive, 239Pu zircon show damage similar to that created by 238U and 232Th in mineral zircons at the same dose, indicating no significant effect of dose rate. Based on these measurements, the initially crystalline structure of a 10 wt% 239Pu zircon would be amorphous after only 1400 years in a geological repository. These measurements establish a basis for assessing the long-term structural durability of actinide-containing ceramics based on an atomistic understanding of the fundamental damage event.},
doi = {10.1038/nature05425},
journal = {Nature, 445:190-193},
number = ,
volume = ,
place = {United States},
year = {Thu Jan 11 00:00:00 EST 2007},
month = {Thu Jan 11 00:00:00 EST 2007}
}
  • This paper discusses how high-resolution solid-state nuclear magnetic resonance (NMR) can be used to characterise and quantify radiation damage in natural minerals and ceramic nuclear waste forms that contain actinides. The scientific goal is to identify the nature of the amorphous component of the radiation damaged material through similar approaches to those where NMR has been used to study glasses and amorphous materials1. NMR also allows the amount of amorphous material to be quantified as an atomic number fraction of the total. This is in contrast to traditional methods that express the damaged amorphous component as volume fractions of themore » total. Very old mineral samples of ZrSiO4 (zircon) containing 238U and 232Th with varying alpha radiation doses can be used to provide samples with differing levels of radiation damage2,3. Radiation damage due to the emission of an alpha particle by an actinide nucleus is believed to occur through two distinct processes4. The alpha particle itself (4.5 – 5.5 MeV), will mainly cause ionisations during its flight through a material, it is also thought to cause a few hundred atomic displacements (Frenkel defects) as it is stopped by collision with atomic nuclei. The recoil of the heavy actinide nucleus (70 -100 keV) is believed to cause the majority of the localised structural damage (amorphisation) as it creates a cascade of collisions with surrounding ions. The extent and nature of this ‘displacement cascade’ is the subject of extensive modelling by both ballistic5,6 and increasingly molecular dynamics7-15 methods. There is a profound need for experimental data to distinguish between these models.« less
  • Impact recovery experiments on confined ceramic rods and multi-layer ceramic targets are performed for failure identification and damage quantification. In-material stress measurements with manganin gauges and velocity histories are recorded with interferometric techniques. Observations on recovered samples are made through Optical Microscopy. Microscopy results show that microcracking is the dominant failure mode in ceramic rods and multi-layer ceramic targets. Macrocrack surface per unit area is estimated on various sections along several orientations. Correlation between dynamic loading and crack density is established. Moreover, multiple penetrator defeat is observed in ceramic targets recovered from penetration experiments.
  • A preferential dissolution by a factor of 1.1 to about 10 of the radiogenic nuclides /sup 234/U, /sup 230/Th, and /sup 228/Th relative to their corresponding structurally incorporated isotopes /sup 238/U and /sup 232/Th has been observed upon leaching of natural monazite samples in a bicarbonate-carbonate solution. This isotopic fractionation may be attributed to radiation damage caused by alpha recoil atoms. The observations have implications for the storage of crystalline nuclear waste forms in deep geological formations. The damage may endanger the integrity of any crystalline phase that contains alpha-emitting nuclides in groundwater environments. It is inferred that in monazite-likemore » phases the overall alpha-recoil damage may increase nearly in proportion to the alpha-particle dose over the long time range ( about 10/sup 5/yr) required for the isolation of actinide wastes.« less
  • Purpose: Radiation induced lung damage (RILD) is an important dose-limiting toxicity for patients treated with radiation therapy. Scoring systems for RILD are subjective and limit our ability to find robust predictors of toxicity. We investigate the dose and time-related response for texture-based lung CT image features that serve as potential quantitative measures of RILD. Methods: Pre- and post-RT diagnostic imaging studies were collected for retrospective analysis of 21 patients treated with photon or proton radiotherapy for NSCLC. Total lung and selected isodose contours (0–5, 5–15, 15–25Gy, etc.) were deformably registered from the treatment planning scan to the pre-RT and availablemore » follow-up CT studies for each patient. A CT image analysis framework was utilized to extract 3698 unique texture-based features (including co-occurrence and run length matrices) for each region of interest defined by the isodose contours and the total lung volume. Linear mixed models were fit to determine the relationship between feature change (relative to pre-RT), planned dose and time post-RT. Results: Seventy-three follow-up CT scans from 21 patients (median: 3 scans/patient) were analyzed to describe CT image feature change. At the p=0.05 level, dose affected feature change in 2706 (73.1%) of the available features. Similarly, time affected feature change in 408 (11.0%) of the available features. Both dose and time were significant predictors of feature change in a total of 231 (6.2%) of the extracted image features. Conclusion: Characterizing the dose and time-related response of a large number of texture-based CT image features is the first step toward identifying objective measures of lung toxicity necessary for assessment and prediction of RILD. There is evidence that numerous features are sensitive to both the radiation dose and time after RT. Beyond characterizing feature response, further investigation is warranted to determine the utility of these features as surrogates of clinically significant lung injury.« less