Fluctuations And Transport In Fusion Plasma Progress Report October 1 1989 September 30 1990

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Download or read book Plasma physics and fusion progress report for the period 1st October, 1979 to 30th September, 1980 written by and published by . This book was released on 1981 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: A simple empirical model of activity and crud transport in the candu hts has been developed and its utility illustrated using station data. the model emphasizes the fundamental role played by the out-of-core deposits. the input parameters required by the model can be obtained from data from station artefact characterizations, radiation field measurements and oxi-probe measurements and single-tube decontaminations. the details of the model are illustrated using the "simple" example of 95zr transport, which is transported mainly as particles. the more challenging case of 60co transport is then used to highlight additional aspects of the model and to point out some of the areas where further work is required. the model provides insights into the effectiveness of the candu purification system. it has allowed order of magnitude estimates to be made of the effective deposition half-lives for radionuclide removal by the hts deposits; in particular: ? t1/2 (95zr) = 10 - 98 h ? t1/2 (60co) = 7 -62 min typical candu purification half-lives range from 50 minutes to several hours. this is short enough to compete effectively with hts surfaces for 95zr removal. at the highest flow rates, the one-hour half-life is short enough to have a measurable impact on 60co deposition; at longer purification half-lives, the impact on 60co deposition is likely small. it should be noted that 95zr is transported and deposited mainly as particles, while 60co is deposited mainly as a dissolved species. further work is required to determine if these half-lives can be generalized to all particulate and dissolved species. the model leads to an estimate for the efficiency of the main hts system for the removal of the different radionuclides from the circulating coolant. for 60co, this removal efficiency is in the range 0.28 to 2.5%. in most discussions of the purification system effectiveness, an implicit assumption has been that the hts deposits were highly efficient in removing dissolved species from the coolant. these values illustrate the error of that assumption. while the purification system receives only a very small flow compared to the steam generators (on the order of 0.1%), it is highly efficient (95 -100%). the main hts loop receives 99.9% of the flow, but is inefficient (on the order of 1%). the net result is that the two removal mechanisms are more closely matched than previously assumed. the pseudo-efficiency provides a link between this model and more mechanistic treatments of activity deposition. the hts deposit "full flow purification system" can be broken into components: outlet feeders, steam generators, inlet feeders. the utility of this sub-division has been demonstrated by calculating the effect of removing the steam generator deposits by decontamination on reactor face fields in the year immediately following the decontamination. the predicted factor of 3.0 increase in 60co deposition at the reactor face compares favourably with the increase observed at gentilly-2 after the siva-blast of a factor of 2.8. refinements to the model should enable the pseudo-efficiencies to be linked to hts parameters such as the iron deposition profile, information on the affinity of radionuclides for magnetite and for the outlet end-fittings, feeders and hot leg of the steam generator tubes where the deposits are much thinner, plus various geometric considerations (surface areas, diameters, fluid velocities) via more mechanistic models. some deficiencies in the existing station data were identified during the application of the model to 95zr and 60co. a series of measurements is recommended to obtain the data required to assess the model; in particular: ? develop a good set of deposition constants for all radionuclides of interest (especially 60co, 124sb and 95zr/95nb) including the contributions of dissolved and particulate species. ? develop a good set of purification system removal constants for all radionuclides of interest, including the contributions from dissolved and particulate species ? determine c, the coolant concentration, for all species of interest, including dissolved and particulate species.