ICP-MS measurement of iodine diffusion in IG-110 graphite for HTGR/VHTR

Abstract

Graphite functions as a structural material and as a barrier to fission product release in HTGR/VHTR designs, and elucidation of transport parameters for fission products in reactor-grade graphite is thus required for reactor source terms calculations. We measured iodine diffusion in spheres of IG-110 graphite using a release method based on Fickain diffusion kinetics. Two sources of iodine were loaded into the graphite spheres; molecular iodine (I 2) and cesium iodide (CsI).Measurements of the diffusion coefficient were made over a temperature range of 873-1293 K. We have obtained the following Arrhenius expressions for iodine diffusion: ,

Estimation of Routine Discharge of Radionuclides on Power Reactor Experimental Rde

“…There is a significant retention of the fission products in the kernel itself. The fuel kernel and the SiC coating are the major barriers for fission products release from the fuel particle [6,[13][14]16] . The graphitic materials do not retain fission gases and iodine, but operation experience indicates that fission metals like strontium and cesium are strongly retained in these materials.…”

“…The reactor source terms are determined from its inventories and radionuclide fractions released from the fuel to the cooling system and other reactor systems until stack. The released fractions used were obtained from a reference parameter [1,[6][7]16] . nuclides of TRISO [6][7] Removable fission products parameters from pebble and the four layers to the environment are calculated using removable fractions and diffusion processes in the scheme of Fig.…”

“…nuclides of TRISO [6][7] Removable fission products parameters from pebble and the four layers to the environment are calculated using removable fractions and diffusion processes in the scheme of Fig. 2-3 and assumptions of parameters [1,[6][7]16] . Defective particles and fuel diffusion from the kernel to the outside part of the pebble in Fig.…”

“…Based on Fig. 2 assumed that the Removable Fraction (FL) through defective particles is 8x10 -4 , diffusion through intact coatings is 5x10 -4 , transport through degraded coatings Inservice is 5x10 -5 , and release of fission products from fuel particles is 5x10 -3 [1,[6][7]16] . Figure 3 shows the transport mechanism of fuel nuclides into the environment.…”

“…Figure 3 shows the transport mechanism of fuel nuclides into the environment. Assumptions for fission products release from fuel particles is 5 x 10 -3 ; fission products release from fuel quality specification on contamination is 6 x 10 -5 ; and fission product release from Heavy metal contamination is 5 x 10 -5 [1,[6][7]16] . On the circulating system, activity in primary coolant is assumed to be 1 % for the nuclides of I and H-3, and 10 % for other nuclides.…”