MONITORING AND SURVEILLANCE OF DECOMMISSIONED NUCLEAR WASTE REPOSITORIES (RADIOACTIVE, SEQUENTIAL ANALYSIS, POISSON DISTRIBUTION, TREND ANALYSIS, GROUNDWATER).

摘要

High-level nuclear wastes must be isolated from human exposure because of the health hazards they create. In the United States, the most likely disposal method will involve permanent emplacement in repositories in deep geological formations. After these repositories are decommissioned, a set of stresses on the waste isolation system can conceivably lead to groundwater migration and release of radionuclides to the biosphere in about 500-600 years. These releases could have serious consequences if they occur. Even if these scenarios are considered scientifically implausible, the public reassurance offered by potential detection and correction of waste isolation system failures could be the principal justification for including monitoring and surveillance systems as part of waste disposal system design.;An original data acquisition protocol is proposed for detecting changes in background values of monitored parameters. This protocol includes detection system design (instrumentation and detector spatial distribution) and management (sample scheduling).;A theoretical approach to interpretation of sequentially acquired data is developed based on the sequential probability ratio test (SPRT) applied to two simple hypotheses: the data represent background values, or the data represent a specific value greater than background. An extension to the SPRT is developed for testing trends in data. Statistical decision theory is used to evaluate erroneous acceptance of each of the above hypotheses. Based on monetary loss functions and the SPRT statistics, original risk functions are developed. The formulae are developed assuming Poisson-distributed frequency counts on monitored radioactivity.;The theory is applied to a case study of groundwater radioactivity migration at Hanford Reservation, Washington. Decisions on actual data are assumed erroneous to evaluate their risks. Idealized plume lobe geometry and one-dimensional transport models are used to compute aquifer flux and biosphere entry concentrations, which are compared to maximum permissible concentrations. Groundwater contamination mitigative technologies are detailed, as well as standardized unit monitoring and mitigation costs.;A monitoring and surveillance system is developed that could detect short-term failures, assess the consequences of biosphere releases, and compute the risks of erroneous decisions on the existence of radiocontaminants in groundwater.;The applicability of these techniques to monitoring and surveillance of hazardous waste repositories is discussed.