Uranium Decay Calculator - HELP
(last updated 12 Nov 2000)
Contents:
This calculator performs radioactive decay calculations for uranium.
The calculator considers the uranium-isotopes U-238, U-235, and U-234 and all their decay products. In case of uranium recycled from spent fuel, also U-236 and U-232 and their decay products are considered.
The parameters used for the calculation can be set in the Material Input table. These parameters show reasonable initial values which can be modified as needed. There are no other hidden parameters used in the calculation. Any assumptions made for the calculations are described on this page.
The results are presented in 2 resp. 4 charts showing the stacked activities of the nuclides of each uranium series considered. For calculation time constraints, not the complete series are calculated, but each series is truncated after some long-lived member (designated by a "+" suffix), assuming secular equilibrium with its short-lived decay products. This truncation introduces negligible errors.
See special instructions for offline use of this calculator.
See also the Universal Decay Calculator:
- for decay calculations of other nuclides, or
- for other nuclide mixes than covered by this calculator, or
- if truncation is not wanted, or
- if numerical output is required, or
- if a logarithmic vertical scale without stacking is required (Vers. B only).
- Input
- enter number (mandatory!) and select appropriate unit.
- If the checkbox "U in/as" is checked in combination with a mass unit, then the input means the uranium contents of the material selected, otherwise it means the mass of the material selected.
- If the unit "Bq U-238 in" is checked, the input mass is determined from the uranium-238 activity contained.
- If the unit "Bq Unat in" is checked, the input mass is determined from the combined activities of the natural uranium isotopes U-238, U-234, and U-235.
- If the unit "Bq Ra-226 in" is checked, the input mass is determined from the radium-226 activity contained (this is in particular useful for mill tailings). It is assumed that Ra-226 is in secular equilibrium with its parent nuclide Th-230 and with all of its decay products.
- Type
- select appropriate type
- Parameters: ore grade [% U] (used for types "ore" and "mill tailings")
- Weight-percent of uranium contained in the ore removed from the ore body for processing in the mill. Other units used are % U3O8, among others (see also Unit Conversion). Ore grades being processed at present cover a wide range of 0.026% U (Rössing, Namibia) to 1.1% U (Key Lake, Canada). New uranium mining projects under develepment even have ore grades of up to 12.7% U (McArthur River Project, Canada).
Note: this parameter can also be used to assess the exposures to waste rock, by entering the appropriate uranium concentration.
- Parameters: mill loss [%] (used for type "mill tailings")
- Not all of the uranium contained in the ore is recovered in the milling process. The extraction losses are depending on the grade of the ore processed. Upon entry of an ore grade value, the calculator presents an estimated value for the Mill Extraction Losses. If you want to use another value for the losses, you can overwrite it.
- Parameters: natural uranium (used for types U ... U3O8)
- uranium obtained from natural sources. The U-238 and U-235 decay series are considered.
- in equilibrium with progeny (used for natural uranium)
- uranium of natural isotope composition, in secular equilibrium with its decay products (U-238 and U-235 series)
- pure (used for natural uranium)
- pure uranium of natural isotope composition, without decay products. (0.71 weight-% U-235; U-234 in equilibrium with U-238).
- enriched to ... wt% U-235 (used for natural uranium)
- pure uranium with U-235 contents enriched to level higher than natural. Values for use in pressurized water reactors (PWR) range between 3.6% and 4.1 wt-% (weight-percent), and for use in boiling water reactors (BWR) between 3.0% and 3.2%.
- depleted to ... wt% U-235 (used for natural uranium)
- Pure uranium with U-235 contents depleted to lower than natural level. Typical values range between 0.2% and 0.3%. This tails assay can be selected according to economic feasibilty. Since the concentration of U-234 in depleted uranium is depending on the product assay obtained in the enrichment process, an input is also required for this figure.
- Parameters: recycled uranium (used for types U ... U3O8)
- uranium obtained from recycling of spent fuel. The U-236 and U-232 decay series are considered in addition to the U-238 and U-235 series. The U-237 and U-233 decay series are neglected for their insignificant dose contributions. Fission products and transuranics are not considered.
The composition of the uranium isotopes is determined according to the selection from the "burnup / initial enrichment" pick list, based on [Neghabian1991]. The burnup unit GWd/tHM stands for Giga-Watt-days per metric tonne heavy metal. A 5 year storage time after reactor unload is assumed.
- as is (used for recycled uranium)
- uranium as is recycled from spent fuel
- re-enriched to initial U-235 equivalent (used for recycled uranium)
- recycled uranium re-enriched to initial U-235 equivalent; the actual U-235 concentration is higher to compensate for the presence of U-236.
- depleted to 0.2 wt% U-235 (used for recycled uranium)
- recycled uranium depleted to 0.2 wt% U-235
[Neghabian1991] Verwendung von wiederaufgearbeitetem Uran und von abgereichertem Uran, von A.R. Neghabian, H.J. Becker, A. Baran, H.-W. Binzel, Der Bundesminister für Umwelt, Naturschutz und Reaktorsicherheit 
(Hg.), Schriftenreihe Reaktorsicherheit und Strahlenschutz, BMU-1992-332, November 1991, 186 S.