2006 Nuclear Utility REMP Conference Isotopes Of Concern
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Transcript of 2006 Nuclear Utility REMP Conference Isotopes Of Concern
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2006 Nuclear Utility REMP Conference Isotopes Of Concern
General Engineering Laboratories, LLC
Environmental Levels And Methods For Monitoring H-3. C-14. Sr-90, Fe-55, Tc-99. Ni-63
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Today We Will Review
• H-3 Levels in US ground water, surface water and drinking water “Pick Your Background Level”
• Compare NRC and EPA limits
• Look at H-3, C-14, Sr-90, Tc-99, Ni-63 analytical methods and typical detection limits
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Tritium
• Naturally occurring in rainwater at 40-150 pCi/L
• The Tritium Unit (TU) is defined as:– 1 TU = 3.2 pCi
• Concentration varies as a function of upper atmospheric conditions, solar conditions, and age of the ground water
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Environmental H-3 Levels In The United States
(USGS Ground Water)• USGS Lists 5 types of H-3 Ground Water Levels Based
on age of recharge from surface water • Less Than 0.8 TU (2.6 pCi/l) “Submodern” Prior to 1952.
Analytically we call this dead water• 0.8TU(2.6 pCi/l) To 4 TU(13pCi/l) “Mixture between
submodern and recent recharge• 5TU(16pCi/l) to 15 TU(50pCi/l) Modern Less than 5 years
to 10 Years• Greater Than 30 TU(100pCi/l) Considerable Component
of Recharge from 1960 to 1970’s• Greater Than 50(162pCi/l) TU Dominantly 1960 recharge
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Environmental H-3 Levels In The United States
(EPA Surface Water Testing 1994 to 2000)• EPA testing of H-3 in drinking water taken from
locations away from nuclear instillations list US H-3 levels ranging from 100 to 300 pCi/l
• EPA testing of H-3 in surface water taken downstream from operating nuclear facilities ranges from 100 to 2,900 pCi/l (most locations tested had results less than 300 pCi/l)
• A few of the sites that stand out are: 2,300 pCi/l (Savannah River ) and 2,900 pCi/l (Lake Robinson), 2,200 (North Anna River)
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So What is The H-3 Background In The US
• USGS Data Shows Environmental H-3 ranging from 3 pCi/l to a high of 160pCi/l [GW]
• EPA H-3 Drinking Water Results dating January 1994 – March 1994 range from 100 to 300 pCi/l [SW]
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I Think Its Safe To Say We Have More Than One H-3 Background
Level• H-3 in ground water “aquifer” is less than
160pCi/l
• H-3 in drinking water ranges from 100 to 300pCi/l
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Can You Write Off H-3 At Low Levels As Environmental Only?
• Is your H-3 level above 160 pCi/l • Do you have a good understanding of the hydro-
geology of your site• Can you have a radiological leak to the ground • Is it time to look harder• What To Do: Additional site wells, hydro-
geology study of your site, and start looking for other isotopes (C-14, Sr-90, Tc-99, Ni-63)
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NRC 10CFR20 Table 2 Effluent Values
EPA MCL ValuesEPA MCL• H-3 20,000 pCi/l• C-14 2,000 pCi/l• Sr-90 8 pCi/l• Tc-99 900 pCi/l• Ni-63 50 pCi/l
NRC Values• H-3 1E6 pCi/l• C-14 3E4 pCi/l• Sr-90 5E3 pCi/l• Tc-99 6E4 pCi/l• Ni-63 1E5 pCi/l
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Analytical Methods for H-3
• H-3 decays by -, Emax 0.018 MeV• Liquid Scintillation • Typical MDA without sample enrichment runs
about 500 pCi/l and with extended 4 hr counts you can push this down to 200 pCi/l (but the uncertainty at this level is about 100% relative to the actual measurement)
• Typical MDA with sample enrichment runs about 3 pCi/l
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H-3 Beta Spectrum
H-3 in Water
0
2
4
6
8
10
1 101 201 301 401 501 601 701 801 901
Channel
Co
un
ts
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Analytical Methods For Very Low Tritium Detection
• For H-3 Analysis at levels less than 200 pCi/l the gold standard is H-3 sample enrichment
• Process takes 4 to 6 weeks• Samples go through an electrolytic enrichment
step • Typical MDA is 0.1 TU or 0.3 pCi/l• Tritium Laboratory University of Miami (305)
361-4100
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Analytical Methods for C-14
• C-14 Decays by -, Emax 0.160 MeV
• Liquid Scintillation
• Acid Digested to remove all carbon as CO2
• The CO2 is collected on a chemical trap and determined using liquid scintillation counting
• Typical MDAs for this test are 50 pCi/l
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C-14 Beta Spectrum
S P E C T R U M P L O TUSER 17 - C-14
0
5
10
15
20
25
0 100 200 300 400 500 600 700 800 900 1000
Channel Number (Log)
Cou
nts
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Analytical Methods for Sr-90
• Sr-90 in secular equilibrium with Y-90
• Both decay by -, Emax 0.546Sr and 2.3Y MeV
• Gas Flow Proportional Counting
• Sr-90 is removed via EPA method 905.0 “Drinking Water Method”
• Typical MDA is 2 pCi/l for Sr-90
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Analytical Methods for Tc-99
• Tc-99 Decays by -, Emax 0.294 MeV
• Liquid Scintillation
• The sample is oxidized to pertechnetate and removed via resin extraction
• Typical MDA is 50 pCi/l
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Tc-99 Beta Spectrum
Tc-99 Beta Spectrum
0
50
100
150
200
250
1 101 201 301 401 501 601 701 801 901
Channel
Co
un
ts
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Analytical Methods for Ni-63
• Ni-63 Decays by -, Emax 0.067 MeV
• Liquid Scintillation
• Analytical Chemistry to take all the nickel to nickel – DMG – precipitate. The precipitate is taken to a liquid phase via nitric acid
• Typical MDA is 50 pCi/l
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Ni-63 Beta Spectrum
Ni-63
05
1015
20253035
1 101 201 301 401 501 601 701 801 901
Channel
Co
un
ts