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The following documents In t h e NUREG series are available for purchase from t h e Government Printing Office:formal NRC staff and contractor reports, NRC-sponsored conference proceedings, international agreement reports, grantee reports, and NRC booklets and brochures. Also available a r e regulatory guides, NRC regulatlons In t h e Code of Federal Regulations, and Nuclear Regulatory Commission Issuances. Documents available from t h e National Technical Information Service include NUREG-series reports and technlcal reports prepared by other Federal agencies and reports prepared by t h e Atomic Energy Commission, forerunner agency to t h e Nuclear Regulatory Commission. Documents available from public and special technical libraries include all open literature items, such as books, Journal artlcles. and transactions. Federal Register notices. Federal and S t a t e legislation, and congressional reports can usually b e obtained from these libraries.Documents such as theses, dissertations, foreign reports and translations, and non-NRC conference proceedings are available for purchase from the organization sponsoring the publication cited.

The Nuclear Regulatory Commission stipulates in 10 CFR 61 that disposed lowlevel radioactive waste (LLW) be stabilized. To provide guidance to disposal vendors and nuclear station waste generators for implementing those requirements, the NRC developed the Technical Position on Waste Form, Revision 1. That document details a specified set of recommended testing procedures and criteria, including several tests for determining the biodegradation properties of waste forms. Cement has been widely used to solidify LLW; however, the resulting waste forms are sometimes susceptible to failure due to the actions of waste constituents, stress, and environment. The purpose of this research program is to develop modified microbial degradation test procedures that will be more appropriate than the existing procedures for evaluating the effects of microbiologically influenced chemical attack on cement-solidified LLW. Groups of microorganisms indigenous to LLW disposal sites are being employed that can metabolically convert organic and inorganic substrates into organic and mineral acids. Such acids aggressively react with cement and can ultimately lead to structural failure. Results over the past year on the application of mechanisms inherent in microbially influenced degradation of cement-based material are the focus of this annual report. Data-validated evidence of the potential for microbially influenced deterioration of cement-solidified LLW and subsequent release of radionuclides has been developed during this study.