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Fission product retention in TRISCO coated UO sub 2 particle fuels subjected to HTR simulated core heating tests

Description: Results of the examination and analysis of 25,730 individual microspheres from spherical fuel elements HFR-K3/1 and HFR-K3/3 are reported. The parent spheres were irradiated in excess of end-of-life exposure and subsequently subjected to simulated core heating tests in a special high-temperature furnace at Forschungszentrum, Juelich, GmbH (KFA). Following the heating tests, the spheres were electrolytically deconsolidated to obtain unbonded fuel particles for Irradiated Microsphere Gamma Analyzer (IMGA) analysis. For sphere HFR-K3/1, which was heated for 500 h at 1600{degree}C, only four particles were identified as having released fission products. The remaining particles from the sphere showed no statistical evidence of fission product release. Scanning Electron Microscopy (SEM) examination showed that three of the defect particles had large sections of the TRISO coating missing, while the fourth appeared normal. For sphere HFR-K3/3, which was heated for 100 h at 1800{degree}C, the IMGA data revealed that fission product release (cesium) from individual particles was significant and that there was large particle-to-particle variation in retention capabilities. Individual particle release (cesium) averaged ten times the KFA-measured integral spherical fuel element release value. In addition, the bimodal distribution of the individual particle data indicated that two distinct modes of failure at fuel temperatures of 1800{degree}C and above may exist. 6 refs., 6 figs., 4 tabs.
Date: November 1, 1990
Creator: Baldwin, C.A. & Kania, M.J.
Partner: UNT Libraries Government Documents Department

Diffusion modeling of fission product release during depressurized core conduction cooldown conditions

Description: A simple model for diffusion through the silicon carbide layer of TRISO particles is applied to the data for accident condition testing of fuel spheres for the High-Temperature Reactor program of the Federal Republic of Germany (FRG). Categorization of sphere release of {sup 137}Cs based on fast neutron fluence permits predictions of release with an accuracy comparable to that of the US/FRG accident condition fuel performance model. Calculations are also performed for {sup 85}Kr, {sup 90}Sr, and {sup 110m}Ag. Diffusion of cesium through SiC suggests that models of fuel failure should consider fuel performance during repeated accident condition thermal cycling. Microstructural considerations in models in fission product release are discussed. The neutron-induced segregation of silicon within the SiC structure is postulated as a mechanism for enhanced fission product release during accident conditions. An oxygen-enhanced SiC decomposition mechanism is also discussed. 12 refs., 11 figs., 2 tabs.
Date: January 1, 1990
Creator: Martin, R.C.
Partner: UNT Libraries Government Documents Department

MHTGR product distinction

Description: Commercial power reactor operating experience and regulatory practice in the United States is dominated by Light Water Reactor (LWR) technology. This experience base and regulatory structure is a point of departure for the development of any future nuclear option, and must be understood and utilized as appropriate. This report discusses experience with current generation plants considered relevant to MHTGR development, as well as the fundamental differences between the MHTGR and LWR technology, and quantifies avoided business risks relative to current generation plants. It does not attempt to compare the MHTGR with other advanced nuclear options, LWR or other technologies, which are also under development and must relate to the historical framework in accordance with their own unique characteristics. 14 refs., 5 figs., 5 tabs.
Date: December 1, 1990
Creator: Available, Not
Partner: UNT Libraries Government Documents Department

IMGA [Irradiated Microsphere Gamma Analyzer] examination of the Set No. 4 fuel under project work statement FD-20

Description: Results of an examination of over 10,800 unbonded fuel particles from three irradiated spherical fuel elements by the Irradiated Microsphere Gamma Analyzer system are reported. The investigation was initiated to assess fission product behavior in LEU UO{sub 2} TRISO-coated fuel particles at elevated temperatures. Of the three spheres considered, one was reserved as a control and the other two were subjected to simulated accident-condition temperatures of 1600{degree}C and 1800{degree}C, respectively. For the control sphere and the sphere tested at 1600{degree}C, no statistical evidence of fission product release (cesium) from individual particles was observed. At fuel temperatures of 1800{degree}C, however, fission product release (cesium) from individual particles was significant and there was large particles-to-particle variation. At 1800{degree}C, individual particle release (cesium) was on average ten times the Kernforschungsanlage-measured integral spherical fuel element release value. Particle release data from the sphere tested at 1800{degree}C indicate that there may be two distinct modes of failure at fuel temperatures of 1800{degree}C and above. 5 refs., 9 figs., 9 tabs.
Date: March 1, 1990
Creator: Baldwin, C.A. & Kania, M.J.
Partner: UNT Libraries Government Documents Department

Capsule HRB-21 postirradiation examination plan

Description: Irradiation capsule HRB-21 is a test capsule designed to provide Modular High-Temperature Gas-Cooled Reactor (MHTGR) coated particle fuel performance data under test reactor conditions representative of normal MHTGR operation. The irradiated fuel will also be used for postirradiation heating in a controlled atmosphere allowing acquisition of fission product release data at sustained high temperatures. The in-reactor performance data, the postirradiation examination data, and the postirradiation heating data will be used for the validation of fuel performance models under normal and off-normal operating conditions. The accelerated irradiation is to take place in the High Flux Isotope Reactor (HFIR) at ORNL. This report identifies the procedures to be followed in carrying out the postirradiation disassembly and examination of HRB-21. Included is a description of the capsule, a detailed sequence of steps for disassembly of the capsule, a description of the postirradiation examination techniques to be employed, and specifications for the storage of capsule components and the reporting of results. 9 refs., 6 figs., 2 tabs.
Date: March 1, 1990
Creator: Packan, N.H.; Kania, M.J. & Shrader, L.G.
Partner: UNT Libraries Government Documents Department

Overall plant design specification Modular High Temperature Gas-cooled Reactor. Revision 9

Description: Revision 9 of the ``Overall Plant Design Specification Modular High Temperature Gas-Cooled Reactor,`` DOE-HTGR-86004 (OPDS) has been completed and is hereby distributed for use by the HTGR Program team members. This document, Revision 9 of the ``Overall Plant Design Specification`` (OPDS) reflects those changes in the MHTGR design requirements and configuration resulting form approved Design Change Proposals DCP BNI-003 and DCP BNI-004, involving the Nuclear Island Cooling and Spent Fuel Cooling Systems respectively.
Date: May 1, 1990
Partner: UNT Libraries Government Documents Department