Release of fission products from pyrocarbon-coated HTGR fuel particles during postirradiation anneals

Abstract

2.4 Sources of Error in Experimental Measurements and Calculations 19 2.4.1 Possible Errors in Measurements 19 2.4.2 Possible Errors Involved in the Use of the Constant-Potential Equations 3. CHARACTERIZATION AND HISTORY OF MATERIALS USED 3.1 Characterization Procedures for Pyrocarbon Coatings. ... 3.2 Properties of Coated Particles Used in the Annealing Experiments 3.3 Bonded Fuel Pellets 3.4 Irradiation Data 3.5 Ceramographic Examination of Coated Particles 3.5.1 Group A Coated Particles 3.5.2 Groups C and F Coated Particles 4. EXPERIMENTAL RESULTS 4.1 Results of Early Experiments 4.2 Experimental Results on the Release of Cesium 4.2.1 Typical Graphs of Cesium Release vs Annealing Time 4.2.2 Measured and Calculated Parameters Relating to Cesium Release 4.3 Experimental Results on the Release of Barium, Strontium, and Cerium IV Page 4.3.1 Graphs of Fission Product Release vs Annealing Time 4.3.2 Coated-Particle Dimensions and Other Data DISCUSSION OF RESULTS 50 5.1 The Apparent Cesium Diffusion Coefficients 5.2 Evidence of a Concentration Limit in the Outer Coating. . 5.3 Evidence of a Trapped Fraction of Cesium 5.4 Abrupt Changes in Source Potential 5.5 Distribution of Fission Products in an Annealed Fuel Pellet 5.6 Barium, Strontium, and Cerium Results RECOMJ"[ENDATIONS 6.1 The Diffusion Coefficient 6.2 Limit of Cesium Concentration in the Coating 6.3 The Partition Coefficient 6.4 Trapped Fraction of Cesium 6.

HTGR fuels and core development program. Quarterly progress report for the period ending November 30, 1974

“…The release of cesium is further complicated by the occurrence of a trapped fraction (Ref. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], i.e., a fraction of the cesium in the kernel that is not released or released only slowly; the trapped fraction is apparently strongly dependent on bumup and temperature. The small release parameters (reduced diffusion coefficients) considered above presumably apply to release of the trapped fraction.…”

“…Since the UC" kernels are placed only in TRISO coated particles, which retain fission products quantitatively (Ref. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] when intact, the release of fission products from UC^ kernels is of interest only for failed particles, at least in regard to the primary circuit activity.…”

“…Extensive measurements (Refs. is not yet well enough understood (Ref,(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) to account for the variation introduced into the migration parameter but, apparently, some correction could be made for the effect of neutron fluence.…”

“…[9][10][11][12][13][14][15][16][17][18][19]. Samples that either failed to meet the TRISO coating design basis (Ref, [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] or had one or more coatings purposely designed to evaluate LHTGR fuel particle specification limits are not included.…”

“…[9][10][11][12][13][14][15][16][17][18][19]. Samples that either failed to meet the TRISO coating design basis (Ref, [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] or had one or more coatings purposely designed to evaluate LHTGR fuel particle specification limits are not included. The data were obtained from fuel capsules P13L, P13M, P13N, P13P, P13R, and P13S, Results from all unbonded particle samples in each test that satisfy the LHTGR TRISO UC" pressure vessel design basis are included in Table 9-22, as are results from all reference LHTGR TRISO UCfuel that has been irradiated in unbonded particle tests.…”