Environmental Impact of Yucca Mountain Repository in the Case of Canister Failure

Mathematical models and a computation code have been developed for total release of transuranic (TRU) and fission product radionuclides from waste packages in the Yucca Mountain Repository (YMR) into the surrounding geosphere in the case of simultaneous package failure. The total amount of these radionuclides in the geosphere, which is called the environmental impact in this paper, has been expressed in terms of radiotoxicity. Inventory abstraction has been made, based on the data provided in the Final Environmental Impact Statement published by the U.S. Department of Energy. Various types of waste packages in the YMR have been abstracted into commercial spent nuclear fuel (CSNF) and defense waste. For defense waste, co-disposal and naval spent fuel have been abstracted separately. Numerical results show that within the total environmental impact, contribution from the defense waste packages is about 10%, which is close to the fraction of the repository capacity allocated for defense waste. Impacts due to isotopes of TRU and their decay daughters are dominant, compared with those from fission product nuclides. If the mass of TRU nuclides to be disposed of in the repository were reduced by a factor of 100, the impact from CSNF would become smaller than that from defense waste.