Metal fission products

Bramman, J. I. Sharpe, R. M. Thom, D. Yates, G. "Metallic Fission-Product Inclusions in Irradiated Oxide Fuels. Jour. Of Nuclear Materials 1968.25.201. 

SEPARATION AND UTLISATION OF RARE METAL FISSION PRODUCTS IN NUCLEAR FUEL CYCLE AS FOR HYDROGEN PRODUCTION CATALYSTS ... 

Fig. 3-5 Accumulated metallic fission product release fraction from a spherical fuel element in the 170 MW(th) process heat HTR-MODUL, from [55]... 

High bumup of fissile material leads to a high fission product cont t in the fuel elements resulting in the formation of seminoble metal fission product alloys, which are insoluble in boiling nitric acid. The insoluble material ccmsists of mm sized metal particles of Ru, Rh, Tc, Mo, and Pd. These metal particles usually contain negligible amounts of uranium and plutonium and can be filtered as high level solid waste, HLSW. 

Provide a secondary barrier to metallic fission product release through adsorption mechanisms. 

A fuel performance analysis was conducted to predict the core temperature distributions, fuel particle failure, and gaseous and metallic fission product release under normal operating conditions at full power. The calculated fission product releases were then compared with the radionuclide design criteria, summarized In Section 4.2.3 and presented In detail In Section 11.1 to determine the adequacy of the fuel and core designs with regard to the radionuclide control requirements. 

The fuel rod matrix is rather porous and provides little holdup of the fission gases which are released from the fuel particles. However, the matrix is a composite material which has a hi content of amorphous carbon, and this constituent of the matrix is highly sorptive of metallic fission products, especially Sr. While the matrix is highly sorptive of metals, it provides little diffusional resistance to the release of fission metals because of its high interconnected porosity. 

TRAFIC (Ref. 6) A core-survey code for calculating the full-core release of metallic fission products. TEIAFIC is a finite-difference solution to the transient diffusion equation for the multihole fuel element geometry with a convective boundary condition at the coolant surface. The temperature and failure distributions required as input are supplied by an automatic interface with the SURVEY/PERFOR code. 

The reference fuel design, quality, performance models, and methods discussed in Section 4.2.5.2.2.3 were used to calculate the fuel particle failure and the gaseous and metallic fission product releases as a function of time. The key attributes for fuel quality are summarized in Table 4.2-4 and the design is in Table 4.2-16. The following fuel particle failure mechanisms were considered in the analysis ... 

Alberstein, D., P. D. Smith, and M. J. Haire. Metallic Fission Product Release from the HTGR Core. GA Report GA-A13258, May 15, 1975. 

Smith, P. D. TRAFIC, A Computer Program for Calculating The Release of Metallic Fission Products from an HTGR Core, USDOE Report, GA-A14721, General Atomic, February 1978. 

The report on the disassembly and postoperative examination of the ARE pointed to the ease of removal of the noble gases and the deposition of certain noble metal fission products on metallic surfaces. It was also learned that because of the evolution of chemistry that occurs during radioactive decay, it is important to account for the kinetics of noble gas removal from the salt. 

A 140-page summary report describing the behavior of fission products in the MSRE is the most complete source of information on fission product behavior in molten fluorides. In all instances, the evidence confirms what basic thermodynamics tells us only the noble gases (Xe, Kr) and tritium are released from the salt. All of the alkali (eg., Cs), alkaline earth (e.g., SrX rare earth (e.g., Y, Ln), and most metallic fission products (e g., Zr) are dissolved in the salt as fluorides and are relatively nonvolatile. A few of the metallic fission products (the noble group Ag, Pd, Ru, Mo, Tc, Rh, Sb) are not dissolved (or are partially dissolved), but remain as metallic species and tend to deposit on the colder metallic surfaces. 

The release of metallic fission products, e.g., Ba , Cs , and Sr , tends to be by surface diffusion rather than by pore diffusion, as in the case of noble gases. Work done by the Dragon project (/, 42) has... 

Hulls, noble metal fission products Most fission products ... 

The liquid fuel of MSRs allows fission product gases such as xenon and krypton to be released from the liquid. Along with xenon and krypton, noble metal fission products may entrain and exit as a fine particulate smoke (ORNL 4865,1975). Iodine tends to form a stable iodide within the liquid salt but a fraction is expected to entrain as well. Finally, while alkali, alkaline, and lanthanide fission products will bind to fluorine to form salt-stable fluorides when bom within the salt, there are many unstable isotopes of xenon and krypton that after leaving the salt subsequently decay to daughter isotopes including i37Cs (30 year) and (2.3 million year) along with numerous other isotopes of Ba, La, Ce, Rb, and Sr. 

Noble metal fission products will not form stable fluorides in the fuel salt but will tend to plate out on surfaces in the primary loop. The main complication that arises from this is in terms of the primary heat exchangers. Work with the MSRE indicated that upward of 40% of noble metals plated-out on the walls of heat exchanger. If shell and tube designs are proposed, then the heat generation by noble metals attached to tube surfaces can be a concern if both primary and secondary salts are drained from the heat exchangers, a rare but plausible event. ORNL determined this a manageable but concerning situation (ORNL TM-3145,1971). 

Some of the metallic fission products are plated out to a large extent onto the outer surfaces of the fuel rod claddings in the immediate vicinity of the defect this means that only small fractions of them are transported into the coolant. This is true in particular for tellurium, probably due to an electrochemical reaction on the Zircaloy surface resulting in the formation of the compound SnTe. The rather long-lived Te (halflife 76.3 h) decays there under the production and continuous release of its daughter to the coolant this mechanism is assumed to be the reason for the specific release behavior of this radionuclide, which is markedly different from that of the other iodine isotopes, both during constant load operation and during transients. 

The release of metal fission products from pyrocarbon-coated UO2 particles was... 

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