Cladding embrittlement during postulated loss-of-coolant accidents.

Billone, M.C.; Yan, Yong; Burtseva, Tatyana; Daum, Robert S.

doi:10.2172/946677

Cited by 135 publications

(115 citation statements)

References 16 publications

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“…On the basis of previous observations of the hydrides in high-burnup ZIRLO™ with 300-600 wppm hydrogen [4,9,10], the primary difference in hydride distribution is in the thickness of the outer-surface hydride rim. Hydrides below the rim, particularly within the inner two thirds of the cladding wall, were sparsely distributed circumferential hydrides, and the C H values within this region appeared to be low.…”

Section: As-irradiated High-burnup Zirlomentioning

confidence: 99%

Used Fuel Disposition Campaign - Baseline Studies for Ring Compression Testing of High-Burnup Fuel Cladding

Billone

Burtseva

Liu

et al. 2012

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SUMMARYStructural analyses of high-burnup fuel require cladding mechanical properties and failure limits to assess fuel behavior during long-term dry cask storage and transportation. Pre-storage drying-transfer operations and early stage storage subject cladding to higher temperatures and much higher pressure-induced tensile hoop stresses relative to in-reactor operation and pool storage. Under these conditions, radial hydrides may precipitate during slow cooling and provide an additional embrittlement mechanism as the cladding temperature decreases below the ductile-to-brittle transition temperature (DBTT). On the basis of previous test results, susceptibility to radial-hydride precipitation depends on cladding material, microstructure, and pre-drying distribution of hydrides across the cladding wall, as well as peak hoop stresses and temperatures during drying operations and storage. Susceptibility to embrittlement depends on the extent of radial-hydride precipitation and the thickness of the outer-surface hydride rim.Consistent with the Argonne Test Plan (December 31, 2011), baseline studies were conducted with asirradiated cladding to determine hydrogen distribution and hydride morphology across the cladding wall; strain-rate sensitivity; and temperature sensitivity of high-burnup M5 ® , ZIRLO™, and Zircaloy-4 (Zry-4) cladding subjected to ring compression test (RCT) loading. The results also serve as the baseline for highburnup cladding exposed to drying-storage conditions that do not lead to radial-hydride precipitation.Baseline mechanical properties and failure limits for irradiated M5 ® and ZIRLO™ are particularly important because they are not publicly available. Cladding samples used for baseline studies were from sibling high-burnup rods irradiated to high-burnup in the same assembly as cladding samples used to study radial-hydride-induced embrittlement. RCT displacement rates were 0.05-50 mm/s (1000-fold increase in elastic strain rate). High-burnup M5 ® with <100-wppm hydrogen exhibited high strength (based on maximum load) and high ductility (>10%, based on offset strain) with relatively low strain-rate and temperature (20-90°C) sensitivity. High-burnup ZIRLO™ samples had 530-wppm hydrogen, a welldeveloped hydride rim, and only 140-wppm hydrogen within the inner two-thirds of the cladding wall. This ZIRLO™ also exhibited low strain-rate and temperature sensitivity. Cracking initiated in the hydride rim. Room-temperature (RT) offset strains were 7±1% for the three displacement rates. Offset strains increased from 7% to >10% with the 20-150°C increase in RCT temperature. High-burnup Zry-4 samples had 640-wppm hydrogen, a well-developed hydride rim, and 250-wppm hydrogen within the inner twothirds of the cladding wall. Based on maximum load, the material appeared to have low strain-rate sensitivity. However, offset strains were too low (<2%) to assess strain-rate and temperature (20-90°C) effects on ductility. Cracking within the outer half of the cladding wall occurred concurrently with plastic defor...

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Section: As-irradiated High-burnup Zirlomentioning

confidence: 99%

Used Fuel Disposition Campaign - Baseline Studies for Ring Compression Testing of High-Burnup Fuel Cladding

Billone

Burtseva

Liu

et al. 2012

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“…Both segments were sectioned from regions away from grid-spacer locations and within the uniform burnup region of the rod. Extensive characterization of sibling rods irradiated in the same lead test assembly was performed for the NRC-sponsored loss-of-coolant accident (LOCA) research program conducted by Argonne [14]. Based on sibling-rod characterization, the expected corrosion layer thickness (δ ox ) and hydrogen content (C H ) were: (a) 75 µm and 550 wppm for segment 605C6 and (b) 100 µm and 750 wppm for segment 605C2.…”

Section: Methodsmentioning

confidence: 99%

Ductile-to-Brittle Transition Temperature for High Burnup Zircaloy-4 and ZIRLO (TM) Cladding Alloys Exposed to Simulated Drying Storage Conditions.

Billone¹,

Burtseva²,

Yan³

2013

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EXECUTIVE SUMMARYStructural analyses of high-burnup fuel storage and transport casks require cladding mechanical properties and failure limits to assess fuel behavior. Properties and limits currently used are based on as-irradiated cladding samples from fuel rods discharged from reactors and stored in pools. Such cladding has reduced ductility due to irradiation effects and the presence of circumferential hydrides. However, as-irradiated cladding is not brittle. Pre-storage dryingtransfer operations and early stage storage subject cladding to higher temperatures and much higher pressure-induced tensile stresses than experienced in-reactor or during pool storage. If these are high enough, then radial hydrides could precipitate during pre-storage operations (slow cooling) and during dry-cask storage (very slow cooling). Radial hydrides represent an additional embrittlement mechanism that can reduce cladding failure limits during storage as the cladding temperature decreases below a ductile-to-brittle transition temperature (DBTT). As such, the effects of radial hydrides must be included in structural analyses when the cladding temperature is below or marginally above the DBTT.A test procedure was developed to simulate the effects of elevated temperatures, pressures and stresses during transfer-drying operations and early storage, as well as cooling slowly under decreasing pressures and stresses during both drying and storage. Pressurized and sealed rodlets were heated to the target temperature for a prescribed hold time and slow cooled at a computercontrolled linear temperature rate. The procedure was applied to both non-irradiated/prehydrided (PH) and high-burnup Zircaloy-4 (Zry-4) and ZIRLO™ using the NRC-recommended 400°C maximum temperature limit and a 5°C/h cooling rate. Following drying-storage simulation, samples sectioned from rodlets were subjected to ring-compression tests (RCTs). The RCT was used as a ductility screening test and to simulate pinch-type loading that would occur during cask transport. RCT load-displacement results were used to determine the DBTT for each cladding alloy as a function of the drying-storage hoop stress at 400°C. A strong correlation was found between the extent of radial hydride formation across the cladding wall and the extent of wall cracking during RCT loading.Prior to testing high-burnup cladding, a large number of tests were conducted with PH Zry-4 and ZIRLO™. It was observed that PH cladding with the same hydrogen content (350 to 650 wppm) was a poor surrogate for high-burnup cladding with respect to extent of radial-hydride precipitation and ductility reduction following simulated drying-storage. This was due to the uniform pre-test distribution of hydrides and the high-ductility metal matrix characteristic of PH cladding. However, test results for PH cladding were useful in defining a metric for the extent of radial hydride precipitation and in identifying the higher susceptibility of cladding with lower hydrogen contents (<300 wppm) to radial hydride precipitation.i...

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“…Despite the differences in the microstructure, it has been reported that oxidation kinetics, fracture behavior in the LOCA-simulated experiments, and postquench ductility in the ring compression tests are not so sensitive to alloy constituents. 2,6) Therefore, all the examined cladding alloys are not distinguished in the following evaluation.…”

Section: Postquench Ductilitymentioning

confidence: 99%

“…4,5) The tests have recently been performed with prehydrided nonirradiated cladding and high-burnup fuel cladding (70 GWd/t, <700 ppm) in order to confirm the safety of the high-burnup fuel and revise the criteria if necessary. [6][7][8][9][10][11] As a result, hydrogen produced the main burnup effect on embrittlement and the zero-ductility was seen at the oxidations much lower than the safety limit when the cladding absorbed hundreds of ppm of hydrogen, which is inconsistent with the results from the LOCA-simulated experiments.…”

Section: Introductionmentioning

confidence: 99%

Ring Compression Ductility of High-Burnup Fuel Cladding after Exposure to Simulated LOCA Conditions

Nagase

Chuto

Fuketa

2011

Journal of Nuclear Science and Technology

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Ring compression tests were conducted with specimens sampled from high-burnup PWR and BWR fuel cladding segments that had been ruptured, oxidized at 1,405-1,484 K, and quenched in LOCAsimulated experiments. The calculated oxidation amount for cladding thickness ranged from 11.3 to 25.3% and the hydrogen concentration ranged from 100 to 870 ppm in the ring specimens. The plastic strain to failure and maximum load measured in the ring compression tests decrease with increasing oxidation and hydrogen. Embrittlement of the cladding is seen when the hydrogen concentration is above 300-400 ppm. Although the examined fuel cladding segments did not fracture in the LOCA-simulated experiments, most of the specimens sampled from the segments exhibited a brittle nature in the ring compression tests. This obvious discrepancy between the fracture/no-fracture criterion and the embrittlement criterion is likely caused by a difference in the loading conditions in the two tests. The advantages and drawbacks of the test methodologies should be well considered on application of the test results to the regulatory judgment.

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Cladding embrittlement during postulated loss-of-coolant accidents.

Cited by 135 publications

References 16 publications

Used Fuel Disposition Campaign - Baseline Studies for Ring Compression Testing of High-Burnup Fuel Cladding

Used Fuel Disposition Campaign - Baseline Studies for Ring Compression Testing of High-Burnup Fuel Cladding

Ductile-to-Brittle Transition Temperature for High Burnup Zircaloy-4 and ZIRLO (TM) Cladding Alloys Exposed to Simulated Drying Storage Conditions.

Ring Compression Ductility of High-Burnup Fuel Cladding after Exposure to Simulated LOCA Conditions

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