nureg/cr-6700 - Oak Ridge National Laboratory

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Radiation Shielding Section 5 Figure 19 Neutron source from 1 metric tonne (t) of PWR fuel; 60 GWd/t (from Ref. 17) Figure 19 Neutron source from 1 metric tonne (t) of PWR fuel; 60 GWd/t (from Ref. 17) 40
Section 5 Radiation Shielding The neutron source was further evaluated to identify the major actinides that contribute to the spontaneousfission neutron source. The relative contributions of the dominant actinides are shown in Figures 20 and 21. A common feature for all cooling times investigated is the dominance of 244 Cm at high burnup and the significant increase in the relative contribution of 244 Cm (and 246 Cm) and the decreasing relative importance of the Pu isotopes to the dose rate with increasing burnup. At lower burnups the contribution from 240 Pu is significant (particularly at 100-years cooling, where it is the dominant nuclide) although its relative importance diminishes rapidly with increasing burnup as the curium isotopes build up. These results demonstrate the high relative importance of neutrons, specifically the spontaneous fission neutrons, to cask shielding studies for high-burnup fuel and cooling times greater than 5 years. For shorter cooling times the fission products represent the higher fraction of the dose. However, neutrons only become a dominant fraction of the total dose rate for the steel and lead cask designs analyzed in this study, which were less effective than concrete in shielding neutrons. The concrete storage cask has the smallest neutron dose rate component (60% after 100-years cooling). 5.2 Radionuclide Rankings The fractional contribution of individual radionuclides to the total dose rate for the three different cask designs was calculated for the enrichment and burnup combinations and cooling-time ranges of interest to obtain the importances used in the ranking process. A review of the dominant nuclides for each of the application regimes (cask design, fuel enrichment, burnup and cooling time) found that the majority of the dose rate was attributed to relatively few nuclides for all regimes studied. The nuclides listed in Table 10 (11 actinides, 8 fission products, and 1 activation product) account for more than 99% of the total dose rate for all cask designs and fuel regimes (enrichments and burnup) analyzed. Table 10 Most important nuclides in cask shielding calculations U-238 Pu-242 Cm-246 Y-90 Ba-137m Pu-238 Am-241 Cm-248 Rh-106 Eu-152 Pu-239 Cm-242 Cf-252 Ag-110m Eu-154 Pu-240 Cm-244 Co-60 Cs-134 Pr-144 The nuclide importance, expressed as the fractional contribution of each nuclide to the total dose rate at the cask surface, is illustrated in Figures 22 and 23 (steel cask), Figures 24 and 25 (concrete cask), and Figures 26 and 27 (lead cask) for 5-wt % PWR spent fuel. The results are presented as a function of increasing burnup and for cooling times of 5 years and 100 years. The fractional contributions and ranking for the dominant radionuclides (>1%) are listed in Table 11 for moderate- and extended-enrichment and high-burnup PWR fuel (5-wt % and 70-GWd/t) for 5- and 100-year cooling times. The lower-burnup results (3-wt % and 20-GWd/t) are included for comparison and as verification with previous calculations in Ref. 9. A comparison of the dominant nuclides and their contributions to the total dose rate for the lower-enrichment and low-burnup fuel is consistent with previous ranking studies that assessed more conventional-burnup fuel. 41
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NUREG/CR-6700 ORNL/TM-2000/284 Nucl
Page 3: NUREG/CR-6700 ORNL/TM-2000/284 Nucl
Page 7: CONTENTS ABSTRACT..................
Page 10 and 11: LIST OF FIGURES (continued) Figure
Page 12 and 13: LIST OF TABLES (continued) Table Pa
Page 14 and 15: xii
Page 16 and 17: Introduction Section 1 Finally, sev
Page 18 and 19: Analysis Approach Section 2 70000 6
Page 20 and 21: Analysis Approach Section 2 Table 2
Page 22 and 23: Analysis Approach Section 2 using t
Page 24 and 25: Criticality Safety Section 3 1 Abso
Page 26 and 27: Criticality Safety Section 3 Absorp
Page 28 and 29: Criticality Safety Section 3 Absorp
Page 30 and 31: Criticality Safety Section 3 Table
Page 36 and 37: Criticality Safety Section 3 The fi
Page 38 and 39: Decay Heat Section 4 10000 Decay He
Page 40 and 41: Decay Heat Section 4 4.1 Decay-Heat
Page 42 and 43: Decay Heat Section 4 1 Fraction of
Page 44 and 45: Decay Heat Section 4 Table 9 Radion
Page 46 and 47: Radiation Shielding Section 5 0.025
Page 48 and 49: Radiation Shielding Section 5 0.16
Page 50 and 51: Radiation Shielding Section 5 1 0.9
Page 52 and 53: Radiation Shielding Section 5 Neutr
Page 56 and 57: Radiation Shielding Section 5 1 Rel
Page 58 and 59: Radiation Shielding Section 5 Fract
Page 64 and 65: Radiation Shielding Section 5 Table
Page 66 and 67: Radiation Shielding Section 5 Table
Page 68 and 69: Summary Section 6 Table 13 Summary
Page 70 and 71: Summary Section 6 56
Page 72 and 73: Conclusions and Recommendations Sec
Page 74 and 75: References Section 8 13. S. M. Bowm
Page 77 and 78: APPENDIX A COMPUTER CODE INPUT AND
Page 79 and 80: Appendix A Computer Code Input and
Page 99 and 100: NUREG/CR-6700 ORNL/TM-2000/284 INTE
Page 101: 90. H. Okuno, Japan Atomic Energy R
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