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Title: Microbial Biofilm Growth on Irradiated, Spent Nuclear Fuel Cladding

Abstract

A fundamental criticism regarding the potential for microbial influenced corrosion in spent nuclear fuel cladding or storage containers concerns whether the required microorganisms can, in fact, survive radiation fields inherent in these materials. This study was performed to unequivocally answer this critique by addressing the potential for biofilm formation, the precursor to microbial-influenced corrosion, in radiation fields representative of spent nuclear fuel storage environments. This study involved the formation of a microbial biofilm on irradiated spent nuclear fuel cladding within a hot cell environment. This was accomplished by introducing 22 species of bacteria, in nutrient-rich media, to test vessels containing irradiated cladding sections and that was then surrounded by radioactive source material. The overall dose rate exceeded 2 Gy/h gamma/beta radiation with the total dose received by some of the bacteria reaching 5 × 103 Gy. This study provides evidence for the formation of biofilms on spent-fuel materials, and the implication of microbial influenced corrosion in the storage and permanent deposition of spent nuclear fuel in repository environments.

Authors:
Publication Date:
Research Org.:
Idaho National Laboratory (INL)
Sponsoring Org.:
DOE - NE
OSTI Identifier:
951634
Report Number(s):
INL/JOU-08-14560
Journal ID: ISSN 0022-3115; JNUMAM; TRN: US0902245
DOE Contract Number:
DE-AC07-99ID-13727
Resource Type:
Journal Article
Resource Relation:
Journal Name: Jounal of Nuclear Materials; Journal Volume: 384; Journal Issue: 2
Country of Publication:
United States
Language:
English
Subject:
12 MGMT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; BACTERIA; CONTAINERS; CORROSION; DEPOSITION; DOSE RATES; HOT CELLS; MICROORGANISMS; NUCLEAR FUELS; PRECURSOR; RADIATIONS; STORAGE; Microbial Biofilm Growth

Citation Formats

S.M. Frank. Microbial Biofilm Growth on Irradiated, Spent Nuclear Fuel Cladding. United States: N. p., 2009. Web.
S.M. Frank. Microbial Biofilm Growth on Irradiated, Spent Nuclear Fuel Cladding. United States.
S.M. Frank. 2009. "Microbial Biofilm Growth on Irradiated, Spent Nuclear Fuel Cladding". United States. doi:.
@article{osti_951634,
title = {Microbial Biofilm Growth on Irradiated, Spent Nuclear Fuel Cladding},
author = {S.M. Frank},
abstractNote = {A fundamental criticism regarding the potential for microbial influenced corrosion in spent nuclear fuel cladding or storage containers concerns whether the required microorganisms can, in fact, survive radiation fields inherent in these materials. This study was performed to unequivocally answer this critique by addressing the potential for biofilm formation, the precursor to microbial-influenced corrosion, in radiation fields representative of spent nuclear fuel storage environments. This study involved the formation of a microbial biofilm on irradiated spent nuclear fuel cladding within a hot cell environment. This was accomplished by introducing 22 species of bacteria, in nutrient-rich media, to test vessels containing irradiated cladding sections and that was then surrounded by radioactive source material. The overall dose rate exceeded 2 Gy/h gamma/beta radiation with the total dose received by some of the bacteria reaching 5 × 103 Gy. This study provides evidence for the formation of biofilms on spent-fuel materials, and the implication of microbial influenced corrosion in the storage and permanent deposition of spent nuclear fuel in repository environments.},
doi = {},
journal = {Jounal of Nuclear Materials},
number = 2,
volume = 384,
place = {United States},
year = 2009,
month = 2
}
  • This work describes experiments and computational simulations to analyze single-chamber, air-cathode microbial fuel cell (MFC) performance and cathodic limitations in terms of current generation, power output, mass transport, biomass competition, and biofilm growth. Steady-state and transient cathode models were developed and experimentally validated. Two cathode gas mixtures were used to explore oxygen transport in the cathode: the MFCs exposed to a helium-oxygen mixture (heliox) produced higher current and power output than the group of MFCs exposed to air or a nitrogen-oxygen mixture (nitrox), indicating a dependence on gas-phase transport in the cathode. Multi-substance transport, biological reactions, and electrochemical reactions inmore » a multi-layer and multi-biomass cathode biofilm were also simulated in a transient model. The transient model described biofilm growth over 15 days while providing insight into mass transport and cathodic dissolved species concentration profiles during biofilm growth. Lastly, simulation results predict that the dissolved oxygen content and diffusion in the cathode are key parameters affecting the power output of the air-cathode MFC system, with greater oxygen content in the cathode resulting in increased power output and fully-matured biomass.« less
  • Galvanic corrosion is a concern during wet storage of spent nuclear fuels when aluminum alloys used as cladding for nuclear fuel rods become coupled to stainless steel alloys used as materials for construction of fuel rod hangers and containment equipment. A larger galvanic current density was observed between coupled UNS A96061 and UNS S30400 electrodes submerged in autoclave-sterilized makeup water. The differences were attributed to the development of a discontinuous bacterial biofilm on the couples submerged in as-received makeup water, which was not evident on the control couples that contained several orders of magnitude lower densities of bacteria. While pittingmore » corrosion was observed on the UNS A96061 electrodes containing high or low densities of bacteria, maximum pit depth on the electrodes with high bacterial densities was twice that measured on electrodes with low bacterial densities.« less
  • The feasibility of decontaminating spent fuel cladding hulls using hydrofluoric acid (HF) was investigated as part of the Global Energy Nuclear Partnership (GNEP) Separations Campaign. The concentrations of the fission product and transuranic (TRU) isotopes in the decontaminated hulls were compared to the limits for determining the low level waste (LLW) classification in the United States (US). The {sup 90}Sr and {sup 137}Cs concentrations met the disposal criteria for a Class C LLW; although, in a number of experiments the criteria for disposal as a Class B LLW were met. The TRU concentration in the hulls generally exceeded the Classmore » C LLW limit by at least an order of magnitude. The concentration decreased sharply as the initial 30-40 {micro}m of the cladding hull surface were removed. At depths beyond this point, the TRU activity remained relatively constant, well above the Class C limit. Reprocessing of spent nuclear fuel generates a cladding waste which would likely require disposal as a Greater than Class C LLW in the US. If the cladding hulls could be treated to remove a majority of the actinide and fission product contamination, the hulls could potentially meet acceptance criteria for disposal as a LLW or allow recycle of the Zr metal. Discard of the hulls as a LLW would result in significant cost savings compared to disposal as a Greater than Class C waste which currently has no disposition path. During fuel irradiation and reprocessing, radioactive materials are produced and deposited in the Zircaloy cladding. Due to short depths of penetration, the majority of the fission products and actinide elements are located in the ZrO{sub 2} layer which forms on the surface of the cladding during fuel irradiation. Therefore, if the oxide layer is removed, the majority of the contamination should also be removed. It is very difficult, if not impossible to remove all of the activity from spent fuel cladding since traces of U and Th in the unirradiated Zircaloy adsorb neutrons generating higher actinides in the bulk material. During fuel irradiation, {sup 92}Zr is also converted to radioactive {sup 93}Zr by neutron adsorption. Methods for decontaminating and conditioning irradiated Zircaloy cladding hulls have been investigated in Europe, Japan, and the US during the last 35 years; however, a method to decontaminate the hulls to an activity level which meets US acceptance criteria for disposal as a LLW was not deployed on a commercial scale. The feasibility of decontaminating spent fuel cladding hulls was investigated as part of the GNEP Separations Campaign. Small-scale experiments were used to demonstrate the removal of the ZrO{sub 2} layer from Zircaloy coupons using dilute solutions ({le}1.0 M) of HF. The most effective conditions resulted in dissolution rates which were less than approximately 2 mg/cm{sup 2}-min. With dissolution rates in this range, uniform removal of the oxide layer was obtained and a minimal amount of Zircaloy metal was dissolved. To test the HF decontamination process, experiments were subsequently performed using actual spent fuel cladding hulls. Decontamination experiments were performed to measure the fission product and actinide concentrations as a function of the depth of the surface removed from the cladding hull. The experimental methods used to perform these experiments and a discussion of the results and observations are presented in the following sections.« less
  • As part of the spent fuel treatment program at the Idaho National Laboratory, a vacuum distillation process is being employed for the recovery of actinide products following an electrorefining process. Separation of the actinide products from a molten salt electrolyte and cadmium is achieved by a batch operation called cathode processing. A cathode processor has been designed and developed to efficiently remove the process chemicals and consolidate the actinide products for further processing. This paper describes the fundamentals of cathode processing, the evolution of the equipment design, the operation and efficiency of the equipment, and recent developments at the cathodemore » processor. In addition, challenges encountered during the processing of irradiated spent nuclear fuel in the cathode processor will be discussed.« less