Spent Nuclear Fuel Inventories at Commercial US Nuclear Plants

The Oak Ridge National Laboratory (ORNL) in Oak Ridge, TN, under the auspices of the National Technical Information Service published in 1994 its Integrated Database Report 1994 U.S. spent Nuclear Fuel and Radioactive Waste Inventories, Projections and Characteristics (revision 12).  In 1996, ORNL published its latest version of the Integrated Database, revision 13, which unfortunately, leaves out some of the important data published in previous editions.  In fact, 1996 represents the beginning of a period of high security and secrecy pertaining to nuclear information in the United States.  Many routine DOE and NRC radiation reports and surveillance activities have been curtailed since that date.  The most egregious example of information classification and restriction was the discontinuance of the journal Nuclear Safety, also published at Oak Ridge.  The waste inventories reprinted below are extracted from the 1994 report; this information is no longer available in the 1996 report and is probably no longer available on the DOE website, which reprints much, if not all, of the integrated database report.

The brief listing below is limited to the radioisotopes of most significant biological interest and is extracted from pages 258 - 265 of the 1994 database, Table A.2 Mass, radioactivity, and thermal power of nuclides in domestic commercial LWR spent nuclear fuel at the end of calendar year 1994. Only the inventory of radioactivity of selected isotopes is given below; the following summary does not include mass or thermal power of the isotopes of most concern as constituents of spent fuel.  For more information on characteristics of spent fuel, see excerpts from other EPA and DOE publications elsewhere in this website excerpted from A Review of Radiological Surveillance Reports.

There are presently 103 operating light water reactors in the United States, approximately two thirds of which are pressurized water reactors such as Maine Yankee and the other third are boiling water reactors.  The data reprinted below reflects cumulative radioactivity as of 1994.  Persons interested in determining the approximate quantity of biologically significant radioisotopes in spent fuel at their local nuclear reactor refer to the right hand column below.  The figures in this column represent 1/100th of the total inventory of these isotopes and constitute a handy guide to evaluate quantities of high-level waste to be sited at spent fuel waste storage facilities now under construction at sites such as Maine Yankee.

The dimensions of the nuclear waste debacle can be kept in mind by recalling the definition of a curie: 37 billion disintegrations per second.  A curie is therefore a very large quantity of radioactivity.  Even the safe storage of one curie of a long-lived radioactive substance poses substantial technological and financial challenges.

Biologically Significant Long-Lived Radioisotopes in Commercial Spent Fuel

Isotope Half-life* Decay mode daughter product 1994 inventory curic inventory
28.5 years
beta Yttrium-90 1.60E+09 Ci**
213,000 years
beta Ruthenium-99 3.45E+05 Ci
30.174 years
beta Barium-137 2.31E+09 Ci
2,140,000 years
alpha Protactinium-233 7.90E+03 Ci
2.35 days
beta Plutonium-239 3.35E+08 Ci
87.71 years
alpha Uranium-234 5.87E+07 Ci
24,131 years
alpha Uranium-235 9.00E+06 Ci
14.355 years
beta Americium-241 2.49E+09 Ci
432 years
alpha Neptunium-237 3.69E+07 Ci
162.76 days
alpha Plutonium-238 6.32E+07 Ci
*Half-life: the time it takes for one half of a quantity of radioactivity to decay.
**Ci = curie (see definition above)

Memorandum on biologically significant isotopes

Gamma detecting dosimeters are the most common type of equipment used to detect radiological contamination.  Contamination of the environment by spent fuel isotopes poses a special hazard.  As noted above, the principal long-lived isotopes with the greatest biological hazard once incorporated into living matter are first and foremost the alpha emitters, and secondly the beta emitters.  Alpha radiation cannot be detected with hand held dosimeters, evaluation of contaminated media must be done in the laboratory with time consuming spectroanalysis.  Alpha radiation consists of the nucleus of a helium atom; very large in size, it cannot penetrate a piece of paper.  A typical alpha disintegration (1 becquerel) will contain between 5 and 6 million volts of electromagnetic energy -- all dissipated within the area of one or two cells when incorporated into biological materials.  Beta radiation is slightly more penetrating and will be detectable through several feet of air.  Hand held dosimeters can provide some indication of contamination by beta emitters such as 137Cs.  Accurate determination of contamination by beta emitting isotopes must also be done in a laboratory.  Radioisotopes containing the more easy to detect gamma radiation do not constitute that portion of spent fuel which is of greatest concern with respect to storage of spent fuel over a long duration of time.

For additional information on biologically significant isotopes and their daughter products please refer to RAD4: Definitions and conversion factors.

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