188 Table 15.5. Volume of water (in m3) potentially contaminated to radioactivity concentration guide values for ingestion in unrestricted areas (10CFR20, Table 11, column 2) by solidified high-levelwaste resulting from 33,000 MWd of exposure of enriched 235U, 239Pa,and 233U fuels
2.0 X 10' m3 = volume of water required to reduce ingestion hazard of the corresponding amount of uranium ore (0.17%U). 1.1 X lo7 m3 = volume of water that results from dissolving the salt required to store waste equivalent to 33,000 MWd exposure to a terminal concentration of 500 ppm. 1.07 X lo6 m3 = approximate volume of water required to reduce ingestion hazard potential of the corresponding amount of earth containing naturally occurring uranium plus thorium in equilibrium with their daughters at the average concentration in the earth's crust. Age of waste (Years)
1.26 X 2.24 X 2.00 x 1.55 X 6.53 X 4.26 X 2.44 X 2.14 X
30 100 300 1,000 3,000 10,000 30,000
1,000,000 3,000,000 10,000,000 30,000,000
10" (90Sr) 10" ("Sr) IO' ( 9 0 ~ r ) lo7 (241Am) lo6 (243Am) lo6 (239Pu) lo6 (239Pu) 10' ("'Ra) 10" (226Ra)
1.58 x io6 ( 1 2 9 ~ ) 9.93 x io5 ( 1 2 9 ~ ) 5.28 x lo5 ( 1 2 9 ~ ) 2.57 x io5 ( 1 2 9 ~ )
7.22 X 1.32 X 3.93 X 1.09 x 2.24 X 1.26 X 6.88 X 5.74 X
10" (90Sr) 10" (90Sr) 10' (241Am) 10' (241Am) lo7 (243Am) lo7 (243Am) lo6 (239Pu) lo6 (226Ra)
2.03 x io6 (1291) 9.53 x lo5 ( 1 2 9 ~ ) 4.88 x io5 (1291) 2.38 x io5 (129.~)
2.11 x 10" ( 9 0 ~ r ) 3.75 x 10'0 ( 9 0 ~ r ) 3.76 X 10' (90Sr) 4.72 X 10' (223Ra and 228Ra) 5.06 X lo6 (223Ra and 22'Ra) 9.34 x lo6 (226Ra) 2.2 X lo' (226Ra) 4.45 X lo7 ("'Ra) 4.68 x lo7 (226Ra) 9.42 X 10' (226Ra) 1.80 X lo6 (228Ra) 1.56 X 10' (228Ra) 1.20 X lo6 (228Ra)
=Reference PWR fueled with 3.3%enriched uranium, operated at a specific power of 30 MW per metric ton of heavy metal charged to reactor. Processing losses of '4%of uranium and plutonium to waste are assumed. bAI reference oxide LMFBR mixed core and blankets fueled with LWR discharge plutonium and diffusion plant tails. Average specific power of blend is 58.2 MW per metric ton of heavy metal charged to reactor. Processing losses of y%of uranium and plutonium to waste are assumed. CReference MSBR with continuous protactinium isolation on a tenday cycle and rare-earth removal by the metal transfer process. Thorium is discarded on a 420Way cycle, and '4%of the uranium inventory in the reactor is assumed to be lost to waste over a 30-year plant Life.
million years or more have a greater ingestion hazard associated with them than other waste types, principally as the result of radioactivity from 3 2 Th daughters. Both of these problems can be alleviated by making more efficient use of thorium in the fuel cycle, which is, at present, utilized with an efficiency of only 13.7%. We are investigating processing schemes that can increase the thorium utilization to greater than 90% and thus eliminate these problems. The study also revealed that a greater ingestion hazard is associated with MSBR wastes during the period 30,000 to 1 million years as the result of the presence
of 226Ra, a daughter of 238Pu. The isotope "'PU exists in MSBR wastes in substantial concentrations as a result of the long removal time for neptunium and the short removal time for plutonium in the present processing scheme. The amount of 38Puin the MSBR wastes could be reduced by removing neptunium more efficiently or by use of a processing scheme that would allow plutonium to remain in the fuel salt and be consumed by neutron capture. Both of these possibilities are being considered as improvements to the present processing flowsheet.