Embrittlement of Zircaloy-Clad Fuel Rods by Steam During Loca Transients.

Hobson, D.O.; Rittenhouse, P.L.

doi:10.2172/4670175

Cited by 34 publications

(11 citation statements)

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“…Hobson [16] and Hobson and Rittenhouse [17] performed low-and high-strain-rate ring compression tests, respectively, using two-sided oxidized Zry-4 cladding samples over a wide range of temperatures. The results of the low-strain-rate tests interpolated to ≈135ºC (275ºF) were used to formulate the 1204ºC (2200ºF) peak cladding temperature and 17% maximum oxidation level (Baker-Just ECR [12]).…”

Section: Ductility Determination Using Ring-compression Testsmentioning

confidence: 99%

Cladding embrittlement during postulated loss-of-coolant accidents.

Billone¹,

Yan²,

Burtseva³

et al. 2008

137

105

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The effect of fuel burnup on the embrittlement of various cladding alloys was examined with laboratory tests conducted under conditions relevant to loss-of-coolant accidents (LOCAs). The cladding materials tested were Zircaloy-4, Zircaloy-2, ZIRLO, M5, and E110. Tests were performed with specimens sectioned from as-fabricated cladding, from prehydrided (surrogate for high-burnup) cladding, and from high-burnup fuel rods which had been irradiated in commercial reactors. The tests were designed to determine for each cladding material the ductile-to-brittle transition as a function of steam oxidation temperature, weight gain due to oxidation, hydrogen content, pre-transient cladding thickness, and pre-transient corrosion-layer thickness. For short, defueled cladding specimens oxidized at 1000-1200ºC, ring compression tests were performed to determine post-quench ductility at ≤135ºC. The effect of breakaway oxidation on embrittlement was also examined for short specimens oxidized at 800-1000ºC. Among other findings, embrittlement was found to be sensitive to fabrication processes -especially surface finish -but insensitive to alloy constituents for these dilute zirconium alloys used as cladding materials. It was also demonstrated that burnup effects on embrittlement are largely due to hydrogen that is absorbed in the cladding during normal operation. Some tests were also performed with longer, fueledand-pressurized cladding segments subjected to LOCA-relevant heating and cooling rates. Recommendations are given for types of tests that would identify LOCA conditions under which embrittlement would occur. ForewordFuel rod cladding is the first barrier for retention of fission products, and the structural integrity of the cladding ensures coolable core geometry. In the early 1990s, new data from foreign research programs showed degraded cladding behavior for high-burnup fuel compared with low-burnup fuel in tests designed to simulate postulated accidents. Interim actions were taken, but it became clear that extrapolation from a low-burnup data base needed to be reassessed more carefully for regulatory purposes.One of NRC's central regulations used in plant licensing deals with postulated loss-of-coolant accidents (LOCAs). A portion of that regulation in 10 CFR 50.46(b) specifies criteria that were derived from tests with unirradiated Zircaloy cladding, and these criteria limit the peak cladding temperature and the maximum cladding oxidation during the accident. These two limits are known as embrittlement criteria. Their purpose is to prevent cladding embrittlement during a LOCA, thus ensuring that the general core geometry will be maintained and be coolable.In the mid-1990s, NRC sponsored a cooperative research program at Argonne National Laboratory to reassess these limits for the possible effects of fuel burnup. The program's industry partners included the Electric Power Research Institute, Framatome ANP (now AREVA), Westinghouse, and Global Nuclear Fuel; in general, the industry partners were responsible fo...

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Section: Ductility Determination Using Ring-compression Testsmentioning

confidence: 99%

Cladding embrittlement during postulated loss-of-coolant accidents.

Billone¹,

Yan²,

Burtseva³

et al. 2008

137

105

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“…Item (3) cited above would indicate that the ductility loss undergone by the cladding is not determined by absorbed hydrogen alone: The microstructure of the cladding and the absorbed oxygen must also be considered to play some part in the loss of ductility. Nevertheless, it is evident from the other two items (1) and (2) that it is the absorbed hydrogen ,&phase grain boundary. A large number of fine precipitates are observed in the dark region of photograph (d).…”

Section: Causal Relation Between Cladding Embrittlement and Inner Surmentioning

confidence: 99%

Zircaloy-4 cladding embrittlement due to inner surface oxidation under simulated loss-of-coolant condition.

Uetsuka

Furuta

Kawasaki

1981

J. Nucl. Sci. Technol.

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Embrittlement of Zircaloy-4 cladding by oxidation of the inner surface occurring in an L WR loss-of-coolant accident was studied using simulated fuel containing of Al.Oa pellets sheathed in Zircaloy-4 specimen cladding, filled with Ar gas, and sealed. This simulated fuel rod was heated from outside until the isothermal oxidation temperature between 880 and 1,167"C was obtained after the cladding burst. This exposed the inner surface of the cladding to the environmental atmosphere, provided by steam flowing at a constant rate in the range of 0.13-1.6g/cm 2 ·min. The embrittlement of the specimen due to inner surface oxidation is influenced primarily by the amount of hydrogen absorbed by the Zircaloy-4. Ring compression tests conducted at 100"C on test pieces constituted of sliced sections of oxidized specimen showed that Zircaloy containing more than 200-300 wt.ppm of absorbed hydrogen became brittle when oxidized at temperatures above 1,000"C. In the range of oxidation temperature 932 to 972"C, brittleness did not appear below 500-750 wt.ppm absorbed hydrogen. Hydrogen absorbed by the Zircaloy precipitated in the form of fine hydride crystals formed along previous ,9-phase grain boundaries. Peaks were found in the distribution of hydrogen absorbed on the inner surface, at a distance of 15-45 mm upward and downward of the rupture opening. Within this range, the distance was influenced by the oxidation temperature and steam flow rate.

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“…However the integral tests carried out by Fumihisha et al [7] of cladding rupture indicated a high fracture threshold value of 56% ECR for both non-hydrided and pre-hydrided axially unrestrained cladding. A fractional thickness, the ratio of oxide þ a-Zr(O) phase to initial clad thickness, below which the cladding was reported to be safe by Hobson and Rittenhouse [1] was 0.44 so far as the thermal shock failure was concerned. Considering the clad thickness (0.68 mm) used in their investigation, the combined thickness of ZrO 2 and a-Zr(O) comes to 0.3 mm or 300 mm.…”

Section: Discussionmentioning

confidence: 99%