2.3.2 Remote-Handled Transuranic Waste Radioactivity Inventory

Table 2.2 (see above) shows that the activity of RH-TRU waste currently in storage is approximately 660,000 curies. DOE calculated the total activity of the RH-TRU (stored plus projected) waste inventory to be approximately 1 million curies (DOE-CAO, 1996a; Appendix BIR). According to this estimate, the amount of RH-TRU curies to be emplaced in WIPP is about 20 percent of the total amount of curies from RH-TRU waste allowed by the Land Withdrawal Act (5.1 million curies). For comparison, the total activity to be emplaced in WIPP from CH- and RH-TRU waste is estimated to be 7.4 million curies, of which 6.4 million come from CH-TRU waste (DOE-CAO, 1996c; Appendix BIR).

Table 2.3 shows a comparison between the principal TRU and non-TRU radionuclides in CH and RH-TRU waste to be emplaced in WIPP. In 1995, the total activity of RH-TRU waste represented approximately 14 percent of the total activity of the TRU inventory (from CH-TRU and RH-TRU waste). However, the activity due to TRU radionuclides in RH-TRU waste corresponds only to 0.5 percent of the total TRU activity expected in WIPP. Table 2.3 also shows a comparison of the isotopic characteristics of CH- and RH-TRU waste expected inventories in WIPP. The total curie inventory in RH-TRU waste represents roughly 16 percent of the total curie inventory in CH-TRU waste but the number of TRU curies in the latter is two orders of magnitude higher than in RH-TRU waste. Only TRU radionuclides (i.e., radionuclides with a half-life greater than 20 years) have an impact on the long-term9 performance of WIPP since non-TRU radio

TABLE 2.3 Principal TRU and Non-TRU Radionuclides in WIPP Disposal Inventory

Radionuclide (half-life)

CH-TRU Waste (total curies)

RH-TRU Waste (total curies)

Ratio RH/CH

Plutonium-238 (87.7 years)

2,610,000

1,000

0.0004

Plutonium-239 (24,100 years)

785,000

10,000

0.013

Plutonium-240 (6,560 years)

210,000

5,000

0.024

Plutonium-241 (14.4 years)

2,310,000

142,000

0.061

Americium-241 (433 years)

442,000

6,000

0.014

Cesium-137 (30.2 years)

8,000

216,000

27

Barium-137m (2.6 minutes)

8,000

204,000

25.5

Cobalt-60 (5.3 years)

0

10,000

N/A

Strontium-90 (29.1 years)

7,000

209,000

30

Yttrium-90 (64 hours)

7,000

209,000

30

Total TRU curies (>20 years)

4,048,000

22,000

0.005

Total curies (TRU and non-TRU)

6,390,000

1,012,200

0.158

NOTE: Activities for RH- and CH-TRU waste were estimated in 1995, the year of inventory compilation. Activities decrease very rapidly for RH-TRU waste because of the short half-lives of its radionuclides. Total curies calculated assuming a volume of 7,080 cubic meters for RH-TRU waste and 168,500 cubic meters of CH-TRU waste. TRU radionuclides, by definition, have a half-life greater than 20 years.

SOURCE: Appendix BIR, Table 3–1 in TWBIR Rev 3. Supplemental Disposal Inventory Information, June (DOE, 1996c).

9  

Long-term refers to the 10,000 years of regulatory compliance with radionuclide release limits established by the EPA in Title 40 Code of Federal Regulations Part 191 (see Chapter 3).



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