ML19350A409
| ML19350A409 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 03/03/1981 |
| From: | Dircks W NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Ahearne J NRC COMMISSION (OCM) |
| Shared Package | |
| ML19350A410 | List: |
| References | |
| NUDOCS 8103160089 | |
| Download: ML19350A409 (4) | |
Text
AfflC ga aseg UNITED STATES
[,Y > -c, ( ji NUCLEAR REGULATORY COMMISSION
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MAR 3 1981 b
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e-MEMORANDUM FOR:
Commissioner Ahearne g'g' 0 6 jggI A h)'
AE4 kd'ost/Q' FROM:
William J. Dircks, Executive Director for Operations o ^p
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SUBJECT:
EFFECTS OF TRITlUM In accordance with your memorandum of December 5, 1980, enclosed is a paper discussing the potential environmental impacts and health effects of tritium in general with specific examples of our anaivses around Three Mlle Island.
7Sgned)7. A.Rehm William J. Dircks, Executive Di rector y
for Operations
Enclosure:
Paper on the Effects of Tri ti um P
cc: Chairman Hendrie Commissioner Gilinsky Commissioner Bradford SECY PE GC
Contact:
W. Meinke, NRR ext: 27693 f
8108160C$1
EFFECTS OF TRITIUM Potential Impact of TMI Waste Tritium The options available for the TMI-2 cleanup do not eliminate tritium from the waste and therefore tritium may be released to the environment during the clear.up. Tritium is generally found throughout the environment, with contri-butions in the TMI area coming from natural cosmic-ray interacticas, fallout from atmospheric weapons testing, weapons production, anJ recer.cly from nuclear power reactors. In addition to this general " background" sr tritium, there are estimated to be about 2910 Ci of tritium present in the TM -2 waste in aqueous form.
If all of this'2910 Ci of tritium were released to the TMI environment through the air, the total dose to an individual at 1 mile would be about 0.8 mrad. If instead all the tritium were released as liquid ef fluent to tne Susquehanna River, the total dese to an individual at the nearest drinking water intake would be 0.01 mrad. These dose values can be compared with a dose value of about 0.01 mradlyr for non-nuclear related tritium and with the total annual background radiation dose from all natural sources of about 100 mrad for these same individ-uals in the TMI area. The dose commitment to the population within 50 miles of TMI associated with the release of 2910 Ci of tritium to the atmosphere or the river would cause 'less than one extra cancer death in the exposed population.
The recent Appendix I evaluction for TMI-1 estimates a total release of 1010 Ci/yr
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of tritium during normal operation, 500 Ci/yr to the Susquehanna River and l
510 Ci/yr to the atmosphere. These release values resulted in maximum calculated i
doses of about 0.1 mrad /yr from inhalation, vegetables and milk consumption, and l
about 0.01 mradlyr from water and fish consum-tfon. The following discussion adds perspective to this summary.
Physical Properties and b, ' ibution l
Tritium, the heaviest and only radioactive isotope of hydrogen, decays with a physical half life of 12.3 years by emitting a very weak beta particle with a maximum energy of 18 kev and an average energy of 5.7 kev. The wer1d inventory of natural tritium, due to cosmic-ray interactions, is estimated to be 70 mci (megacuries), corresponding to a production rate of 4 mci /yr. The world tritium inventory, due to weapons testing, reached a maximum of about 3100 mci in 1963 and is estimated to be at the 1110 mci level in 1981. Tritium is formed in roclear reactors by ternary fission and by activation of light elements such as boron and lithium. In 1981, the accumulated tritium contribution worldwide from nuclear power will be at the 2 Mri level.
In 1981 in the U.S., with 70 GWe in-stalled nuclear capacity, it is estimated that 1.2 mci of tritium will be produced by power reactors, of which about 0.03 mci will be released,10% to l
the atmosphere and 90% through liquid releases. For the year 1981, the calculated l
l
doses from these sources to humans residing in the northern hemisphere is esti-mated to be (in mrad): natural tritium: 0.001; fallout: 0.005; nuclear power:
0.0009; weapons production: 0.002; for a total of 0.009 mrad -- a small component of the annual total natural background radiation dose of about 100-125 mrad.
Biological Effects When humans are exposed to tritium as tritiated water by inhalation, ingestion, or skin absorption, the tritium is rapidly distributed to intracellular and extracellular water. The kinetics of tritium sovement throughout the body 1
l follow those of water. A small fraction (a few percent) of the intake becomes organically bound in two separate types of compounds. The effective half life of the tritium in free water in body tissue is 9.7 days compared to 30 days and 450 days for the bound components. There is no evidence for a significant con-centration process for tritium in either plants or animals.
The uptake by way of inhalation of tritiated water vapor is quite efiicient (i.e., 99% of that inhaled is taken it,to the 'sody water within seconds). Skin uptake is generally about equal to that of inhalation; ingested tritiated water is almost completely absorbed from the gastrointestinal tract and quickly appears in the venous blood. On the other hand, when humans inhale gaseous tritium, only a small fraction (hundredths of a percent) is converted to tritiated water and retained as free water. Thus the biological effect of tritium is highly dominated by tritium in the form of water.
Measurement The lower limit of detection for tritium in water with present day state-of-the-art, batch sampling and instrumentation is less than 1000 pCi/1. These measure-ment technicues are more than a thousand times more sensitiye than the maximum permissible concentration (MPC) of 3,000,000 pCi/1 (3 x 10-J uCi/ml) given in 10 CFR 20.106 and Column 2, Table II of 10 CFR 20, Appendix B, " Standards for Protection Against Radiation." Thus for the radioisotope tritium, our means of measurement are much more sensitive than the established limits for release of radioactivity in effluents to unrestricted areas.
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References:
1.
Tritium in the Environment, NCRP Report #62, March 1979,125 pp.
An excellent, concise survey publication. Tritium production from many sources, distribution and environmental kinetics, biological behavior, and the dosimetry of tritium are discussed.
2.
Bounds for Global Tritium Population Doses, R. D. Gentry and C. C. Travis, Health Physics, 40, 73-76 (1981). A recent discussion of models for worldwide tritium population doses.
3.
Behavior of Tritium in the Environment, Proceedings of an IAEA Symposium, IAEA, Vienna, 1979, 711 pp.
Contains the text of symposium papers in areas that include Distribution of Tritium, Evaluation of Future Discharges, Measurement of Tritium, Tritium in the Aqueous and Terrestrial Environments, Tritium in Man, and Monitoring of Tritium.
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