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Title: Examination of Hybrid Metal Coatings for Mitigation of Fission Product Release and Corrosion Protection of LWR SiC/SiC

Abstract

There is a need to increase the safety margins of current and future light water reactors (LWRs) due to the unfortunate events at Fukushima Daiichi Nuclear Plant. Safety is crucial to restore public confidence in nuclear energy, acknowledged as an economical, high-­density energy solution to climate change. The development of accident-­tolerant fuel (ATF) concepts is crucial to this endeavor. The objective of ATF is to delay the consequences of accident progression, being inset in high temperature steam and maintaining high thermomechanical strength for radionuclide retention. The use of advanced SiCf-­SiC composite as a substitute for zircaloy-­based cladding is being considered. However, at normal operations, SiC is vulnerable to the reactor coolant and may corrode at an unacceptable rate. As a ceramic-­matrix composite material, it is likely to undergo microcracking operation, which may compromise the ability to contain gaseous fission products. A proposed solution to both issues is the application of mitigation coatings for use in normal operations. At Oak Ridge National Laboratory (ORNL), three coating technologies have been investigated with industry collaborators and vendors. These are electrochemical deposition, cathodic arc physical vapor deposition (PVD hereafter) and vacuum plasma spray (VPS). The objective of this document is to summarize these processingmore » technologies, the resultant as-­processed microstructures and properties of the coatings. In all processes, substrate constraint resulted in substantial tensile stresses within the coating layer. Each technology must mitigate this tensile stress. Electrochemical coatings use chromium as the coolant facing material, and are deposited on a nickel or carbon “bond coat”. This is economical but suffers microcracking in the chromium layer. PVD-­based coatings use chromium and titanium in both metallic form and nitrides, and can be deposited defense-­in-­depth as multilayers. This vapor method eliminated tensile stress during processing and coatings were up to ~30 μm thick without microcracking. VPS produced coatings based on Zircaloy-2, which has a proven reactor-­compatibility. The tensile stresses appearred to be partially mitigated by annealing. Analysis showed that VPS coatings required further optimizations to prevent adverse reactions with the substrate and need a minimum thickness of ~50 μm. In addition, development of coatings are constrained by neutronic depletion analysis, which clearly indicated enrichment as an issue if the coating is too thick. Based on the present work, the cathodic arc PVD technology was considered ready for the extensive testing and evaluation on cladding materials due to their ability to mitigate the excessive tensile stresses and the reasonable coating quality achieved. The VPS Zircaloy-­2 coating technology required additional development toward mitigation of issues related to the substrate reaction and porosity. In the future, PVD and VPS will have be scaled upon successful development and demonstration. Electrochemical coatings, which are proven scalability, currently require development to mitigate issues related to the tensile stress after deposition.« less

Authors:
 [1];  [1];  [1];  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
1346647
Report Number(s):
ORNL/TM-2016/332
AF5810000; NEAF278
DOE Contract Number:
AC05-00OR22725
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS

Citation Formats

Ang, Caen K., Burns, Joseph R., Terrani, Kurt A., and Katoh, Yutai. Examination of Hybrid Metal Coatings for Mitigation of Fission Product Release and Corrosion Protection of LWR SiC/SiC. United States: N. p., 2016. Web. doi:10.2172/1346647.
Ang, Caen K., Burns, Joseph R., Terrani, Kurt A., & Katoh, Yutai. Examination of Hybrid Metal Coatings for Mitigation of Fission Product Release and Corrosion Protection of LWR SiC/SiC. United States. doi:10.2172/1346647.
Ang, Caen K., Burns, Joseph R., Terrani, Kurt A., and Katoh, Yutai. 2016. "Examination of Hybrid Metal Coatings for Mitigation of Fission Product Release and Corrosion Protection of LWR SiC/SiC". United States. doi:10.2172/1346647. https://www.osti.gov/servlets/purl/1346647.
@article{osti_1346647,
title = {Examination of Hybrid Metal Coatings for Mitigation of Fission Product Release and Corrosion Protection of LWR SiC/SiC},
author = {Ang, Caen K. and Burns, Joseph R. and Terrani, Kurt A. and Katoh, Yutai},
abstractNote = {There is a need to increase the safety margins of current and future light water reactors (LWRs) due to the unfortunate events at Fukushima Daiichi Nuclear Plant. Safety is crucial to restore public confidence in nuclear energy, acknowledged as an economical, high-­density energy solution to climate change. The development of accident-­tolerant fuel (ATF) concepts is crucial to this endeavor. The objective of ATF is to delay the consequences of accident progression, being inset in high temperature steam and maintaining high thermomechanical strength for radionuclide retention. The use of advanced SiCf-­SiC composite as a substitute for zircaloy-­based cladding is being considered. However, at normal operations, SiC is vulnerable to the reactor coolant and may corrode at an unacceptable rate. As a ceramic-­matrix composite material, it is likely to undergo microcracking operation, which may compromise the ability to contain gaseous fission products. A proposed solution to both issues is the application of mitigation coatings for use in normal operations. At Oak Ridge National Laboratory (ORNL), three coating technologies have been investigated with industry collaborators and vendors. These are electrochemical deposition, cathodic arc physical vapor deposition (PVD hereafter) and vacuum plasma spray (VPS). The objective of this document is to summarize these processing technologies, the resultant as-­processed microstructures and properties of the coatings. In all processes, substrate constraint resulted in substantial tensile stresses within the coating layer. Each technology must mitigate this tensile stress. Electrochemical coatings use chromium as the coolant facing material, and are deposited on a nickel or carbon “bond coat”. This is economical but suffers microcracking in the chromium layer. PVD-­based coatings use chromium and titanium in both metallic form and nitrides, and can be deposited defense-­in-­depth as multilayers. This vapor method eliminated tensile stress during processing and coatings were up to ~30 μm thick without microcracking. VPS produced coatings based on Zircaloy-2, which has a proven reactor-­compatibility. The tensile stresses appearred to be partially mitigated by annealing. Analysis showed that VPS coatings required further optimizations to prevent adverse reactions with the substrate and need a minimum thickness of ~50 μm. In addition, development of coatings are constrained by neutronic depletion analysis, which clearly indicated enrichment as an issue if the coating is too thick. Based on the present work, the cathodic arc PVD technology was considered ready for the extensive testing and evaluation on cladding materials due to their ability to mitigate the excessive tensile stresses and the reasonable coating quality achieved. The VPS Zircaloy-­2 coating technology required additional development toward mitigation of issues related to the substrate reaction and porosity. In the future, PVD and VPS will have be scaled upon successful development and demonstration. Electrochemical coatings, which are proven scalability, currently require development to mitigate issues related to the tensile stress after deposition.},
doi = {10.2172/1346647},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 9
}

Technical Report:

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  • In order to estimate the level of air contamination to be expected in the vicinity of a critical using unclad U - Zr fuel, an experiment was designed to compare this unknown contamination level io the level in ihe vicinity of criticals using plastic fuel tape. Results indicate that the air activiiy in the vicinity of an operating critical using unclad metal fuel is lower by a factor of 100 than ihe air activity in the vicinity of an operating critical using plastic fuel. After shutdown, when the contamination level in the vicinity of the plastic fuel critical rises, themore » results predict a contaminaapproximately a factor of 1000. (auih) 53S Hafnium refining studies were conducted using a newly designed hot iop cell and a standard laboratory cold top cell, however, metal of adequate purity for use in assessment of these cells was not produced. Preparation of K/sub 2/HfF/sub 6/ for use as electrolyte is described. The softest metal produced in Hf electrorefining had a harchess of 42 Rockwell B; the average feed was 58 Rn. Cathode deposits of the metal were vacuum distilled io remove acherent salis, Data on the effects of voltage on the purity of refined yttrium are tabulated. (J.R.D.)« less
  • Rats and dogs were exposed to clouds of fission products released from the high temperature meltdown of reactor fuel element in the field. The primary goal of this biological program was attainment of good lung deposition values which could be used in the initial step of the biological counterpart of reactor hazards evaluation. There was a total of seven releases with biological participation three from aged and four from green fuel elements, and each under various conditions of lapse or inversion meteorological condition. The chief biological observations are summarized. In the early releases, even with the animal sacrifice occurring shortlymore » after exposure, the gastrointestinal (GI) tract values obtained were unrealistically high due primarily to licking. During the course of the Testing Program the GI tract-to-lung ratios in rats were reduced from > 30 to < 1 by altering such parameters as exposure, cage construction degree of consciousness of animals during exposure, methods of sacrifice, and time of entry into the field for pickup and sacrifice. In both rats and dogs the median deposition of fission products in the lower respiratory tract appears to be between 30 and 35% of that amount of material breathed, and the estimated total deposition appears to be at least 70%. The fission products released from green fuel elements may be deposited in the lower respiratory tract somewhat more readily than those from aged elements. Limited metabolism data from dogs indicate a short effective half-time of elimination of fission products from the green elements via the urine, and also via the feces for the early period post-release. At later times the effeetive half-time of elimination of fission products from the lung increases and consequently the rate of fecal excretion decreases. The use of fall-out measurements for estimation of body uptake (lung deposition) can give misleading results unless the individual isotopes are well characterized. The external contamination-to-lung ratios for rats exposed to green releases (iodine) are 10 times the ratios of those exposed to aged releases (cesium). (auth)« less