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Title: Radioactive Fission Product Release from Defective Light Water Reactor Fuel Elements

Abstract

Results are provided of the experimental investigation of radioactive fission product (RFP) release, i.e., krypton, xenon, and iodine radionuclides from fuel elements with initial defects during long-term (3 to 5 yr) irradiation under low linear power (5 to 12 kW/m) and during special experiments in the VK-50 vessel-type boiling water reactor.The calculation model for the RFP release from the fuel-to-cladding gap of the defective fuel element into coolant was developed. It takes into account the convective transport in the fuel-to-cladding gap and RFP sorption on the internal cladding surface and is in good agreement with the available experimental data. An approximate analytical solution of the transport equation is given. The calculation dependencies of the RFP release coefficients on the main parameters such as defect size, fuel-to-cladding gap, temperature of the internal cladding surface, and radioactive decay constant were analyzed.It is shown that the change of the RFP release from the fuel elements with the initial defects during long-term irradiation is, mainly, caused by fuel swelling followed by reduction of the fuel-to-cladding gap and the fuel temperature. The calculation model for the RFP release from defective fuel elements applicable to light water reactors (LWRs) was developed. It takes into account themore » change of the defective fuel element parameters during long-term irradiation. The calculation error according to the program does not exceed 30% over all the linear power change range of the LWR fuel elements (from 5 to 26 kW/m)« less

Authors:
;  [1]
  1. State Scientific Centre of Russian Federation-Research Institute of Atomic Reactors (Russian Federation)
Publication Date:
OSTI Identifier:
20826742
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nuclear Technology; Journal Volume: 138; Journal Issue: 1; Other Information: Copyright (c) 2006 American Nuclear Society (ANS), United States, All rights reserved. http://epubs.ans.org/; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; ANALYTICAL SOLUTION; BWR TYPE REACTORS; FISSION PRODUCT RELEASE; FISSION PRODUCTS; FUEL ELEMENTS; IODINE; KRYPTON; NUCLEAR DECAY; RADIOISOTOPES; SURFACES; SWELLING; TRANSPORT THEORY; XENON

Citation Formats

Konyashov, Vadim V., and Krasnov, Alexander M.. Radioactive Fission Product Release from Defective Light Water Reactor Fuel Elements. United States: N. p., 2002. Web.
Konyashov, Vadim V., & Krasnov, Alexander M.. Radioactive Fission Product Release from Defective Light Water Reactor Fuel Elements. United States.
Konyashov, Vadim V., and Krasnov, Alexander M.. Mon . "Radioactive Fission Product Release from Defective Light Water Reactor Fuel Elements". United States. doi:.
@article{osti_20826742,
title = {Radioactive Fission Product Release from Defective Light Water Reactor Fuel Elements},
author = {Konyashov, Vadim V. and Krasnov, Alexander M.},
abstractNote = {Results are provided of the experimental investigation of radioactive fission product (RFP) release, i.e., krypton, xenon, and iodine radionuclides from fuel elements with initial defects during long-term (3 to 5 yr) irradiation under low linear power (5 to 12 kW/m) and during special experiments in the VK-50 vessel-type boiling water reactor.The calculation model for the RFP release from the fuel-to-cladding gap of the defective fuel element into coolant was developed. It takes into account the convective transport in the fuel-to-cladding gap and RFP sorption on the internal cladding surface and is in good agreement with the available experimental data. An approximate analytical solution of the transport equation is given. The calculation dependencies of the RFP release coefficients on the main parameters such as defect size, fuel-to-cladding gap, temperature of the internal cladding surface, and radioactive decay constant were analyzed.It is shown that the change of the RFP release from the fuel elements with the initial defects during long-term irradiation is, mainly, caused by fuel swelling followed by reduction of the fuel-to-cladding gap and the fuel temperature. The calculation model for the RFP release from defective fuel elements applicable to light water reactors (LWRs) was developed. It takes into account the change of the defective fuel element parameters during long-term irradiation. The calculation error according to the program does not exceed 30% over all the linear power change range of the LWR fuel elements (from 5 to 26 kW/m)},
doi = {},
journal = {Nuclear Technology},
number = 1,
volume = 138,
place = {United States},
year = {Mon Apr 15 00:00:00 EDT 2002},
month = {Mon Apr 15 00:00:00 EDT 2002}
}
  • The emission of fission gases and iodines by a pressurized water reactor fuel rod containing a defect when it is initially put in the reactor is studied experimentally using a pressurized water loop in the Siloe reactor at Grenoble. The initial leakage is simulated by making a small hole near the upper end of the rod. The rare gases and iodines are continuously analyzed, and the source terms of fission products are expressed as the ratio of the release rate of a given isotope from the defective fuel rod to the birth rate of this isotope. The release fractions ofmore » rare gases and iodines have been determined in different conditions: steady power level between 120 and 700 W . cm/sup -1/, power cycling in the range of 200 to 400 W . cm/sup -1/, and in the range 120 to 400 W . cm/sup -1/. At steady power level, the amounts of radioactive gases escaped from the rod are 100 times higher than those emitted by a sound fuel submitted to a similar power level. The power cycling favors the emission of all iodines whose release rate is 10 to 20 times higher than at the maximum steady power level.« less
  • Fission product release from fully irradiated light water reactor fuel under accident conditions and the chemical forms and behavior of the released material have been studied at high temperatures. This work has emphasized release from commercial fuels, but tracer-level tests using specific fission product species have been used in efforts to clarify chemical behavior. The specimens were heated in an induction furnace in flowing steam at temperatures of 1700 to 2300 K. The fractional releases of krypton, iodine, and cesium increased with temperature, reaching maxima of nearly 60% in 20 min. The release of tellurium varied strongly with the extentmore » of cladding oxidation and approached that of cesium for completely oxidized cladding. In addition to some structural material, the major chemical forms in the furnace effluent appeared to include CsI, CsOH, silver, antimony, and tellurides of cesium and tin. The fractional releases of the volatile fission products correlated with the amount of fuel porosity, and the masses of aerosol collected increased with test temperature and oxidation. Comparison of our results with several fission product release models showed agreement ranging from good to poor.« less
  • A simplified semi-empirical model predicting fission gas release form UO{sub 2+x} fuel to the fuel rod plenum as a function of stoichiometry excess (x) is developed to apply to the fuel of a defective LWR fuel rod in operation. The effect of fuel oxidation in enhancing gas diffusion is included as a parabolic dependence of the stoichiometry excess. The increase of fission gas release in a defective BWR fuel rod is at the most 3 times higher than in an intact fuel rod because of small extent of UO{sub 2} oxidation. The major enhancement contributor in fission gas release ofmore » UO{sub 2+x} fuel is the increased diffusivity due to stoichiometry excess rather than the higher temperature caused by degraded fuel thermal conductivity.« less
  • Data from a reactor operating with a single defective fuel element were used to develop a physically based model for describing the increased release of iodine to the primary coolant following reactor shutdown. Transport of iodine from the fuel-to-sheath gap of the element to the primary coolant is described by a diffusion process. The model has been used to predict the timing of the increased release.