Lively, J. W. | Search NASA

DOE OSTI2012

Method for Implementing Subsurface Solid Derived Concentration Guideline Levels (DCGL) - 12331

The U.S. Nuclear Regulatory Commission (NRC) and other federal agencies currently approve the Multi-Agency Radiation Site Survey and Investigation Manual (MARSSIM) as guidance for licensees who are conducting final radiological status surveys in support of decommissioning. MARSSIM provides a method to demonstrate compliance with the applicable regulation by comparing residual radioactivity in surface soils with derived concentration guideline levels (DCGLs), but specifically discounts its applicability to subsurface soils. Many sites and facilities undergoing decommissioning contain subsurface soils that are potentially impacted by radiological constituents. In the absence of specific guidance designed to address the derivation of subsurface soil DCGLs and compliance demonstration, decommissioning facilities have attempted to apply DCGLs and final status survey techniques designed specifically for surface soils to subsurface soils. The decision to apply surface soil limits and surface soil compliance metrics to subsurface soils typically results in significant over-excavation with associated cost escalation. MACTEC, Inc. has developed the overarching concepts and principles found in recent NRC decommissioning guidance in NUREG 1757 to establish a functional method to derive dose-based subsurface soil DCGLs. The subsurface soil method developed by MACTEC also establishes a rigorous set of criterion-based data evaluation metrics (with analogs to the MARSSIM methodology) that can be used to demonstrate compliance with the developed subsurface soil DCGLs. The method establishes a continuum of volume factors that relate the size and depth of a volume of subsurface soil having elevated concentrations of residual radioactivity with its ability to produce dose. The method integrates the subsurface soil sampling regime with the derivation of the subsurface soil DCGL such that a self-regulating optimization is naturally sought by both the responsible party and regulator. This paper describes the concepts and basis used by MACTEC to develop the dose-based subsurface soil DCGL method. The paper will show how MACTEC's method can be used to demonstrate that higher concentrations of residual radioactivity in subsurface soils (as compared with surface soils) can meet the NRC's dose-based regulations. MACTEC's method has been used successfully to obtain the NRC's radiological release at a site with known radiological impacts to subsurface soils exceeding the surface soil DCGL, saving both time and cost. Having considered the current NRC guidance for consideration of residual radioactivity in subsurface soils during decommissioning, MACTEC has developed a technically based approach to the derivation of and demonstration of compliance with subsurface soil DCGLs for radionuclides. In fact, the process uses the already accepted concepts and metrics approved for surface soils as the foundation for deriving scaling factors used to calculate subsurface soil DCGLs that are at least equally protective of the decommissioning annual dose standard. Each of the elements identified for consideration in the current NRC guidance is addressed in this proposed method. Additionally, there is considerable conservatism built into the assumptions and techniques used to arrive at subsurface soil scaling factors and DCGLs. The degree of conservatism embodied in the approach used is such that risk managers and decision makers approving and using subsurface soil DCGLs derived in accordance with this method can be confident that the future exposures will be well below permissible and safe levels. The technical basis for the method can be applied to a broad variety of sites with residual radioactivity in subsurface soils. Given the costly nature of soil surveys, excavation, and disposal of soils as low-level radioactive waste, MACTEC's method for deriving and demonstrating compliance with subsurface soil DCGLs offers the possibility of significant cost savings over the traditional approach of applying surface soil DCGLs to subsurface soils. Furthermore, while yet untested, MACTEC believes that the concepts and methods embodied in this approach could readily be applied to other types of contamination found in subsurface soils. (author)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2012

Environmental Remediation Activities in Japan Following the Fukushima Dai-ichi Reactor Incident - 12603

In March 2011, the Fukushima Dai-ichi reactor power plant was crippled by the Great Pacific earthquake and subsequent tsunami. Much of the focus in the news was on the reactor site itself as the utility company (TEPCO), the Japanese government, and experts from around the world worked to bring the damaged plants into a safe shutdown condition and stem the release of radioactivity to the environment. Most of the radioactivity released was carried out to sea with the prevailing winds. Still, as weather patterns changed and winds shifted, a significant plume of radioactive materials released from the plant deposited in the environment surrounding the plant, contaminating large land areas of the Fukushima Prefecture. The magnitude of the radiological impact to the surrounding environmental is so large that the Japanese government has had to reevaluate the meaning of 'acceptably clean'. In many respects, 'acceptably clean' cannot be a one-size-fits-all standard. The economics costs of such an approach would make impossible what is already an enormous and costly environmental response and remediation task. Thus, the Japanese government has embarked upon an approach that is both situation-specific and reasonably achievable. For example, the determination of acceptably clean for a nursery school or kindergarten play yard may be different from that for a parking lot. The acceptably clean level of residual radioactivity in the surface soil of a rice paddy is different from that in a forested area. The recognized exposure situation (scenario) thus plays a large role in the decision process. While sometimes complicated to grasp or implement, such an approach does prioritize national resources to address environment remediation based upon immediate and significant risks. In addition, the Japanese government is testing means and methods, including advanced or promising technologies, that could be proven to be effective in reducing the amount of radioactivity in the environment beyond a fixed, concentration based limit. Essentially, the definition of acceptably clean includes the concept of reasonably achievable, given the available technology, means and methods, and the cost to implement such. The Japanese government recently issued three technology demonstration contracts expressly designed to test and evaluate the available technologies, means, and methods, which, if implemented, might produce the greatest risk reduction from environmental contamination for the best value. One of the Japanese contract holders, Obayashi JV, has teamed with AMEC to demonstrate the applicability and capabilities of the Orion ScanPlot{sup SM} and ScanSort{sup SM} technologies in radiologically impacted towns both inside and immediately outside the 20 km restricted zone. This presentation provides some unique images and informative insight into the environmental radioactive impacts in and around the exclusion zone. It will provide a look at one element of the Japanese government?s efforts to achieve the greatest risk reduction that is reasonably achievable. The Orion ScanPlot{sup SM} and ScanSort{sup SM} are being used with success on the Japan Town Demonstration Project to assess pre-remedial action contamination levels, document the post-remedial action contamination levels and to precisely measure and segregate excavated soils based on their radioactive content and the prescribed segregation limits (DCS). Initial results suggest that these technologies could provide capabilities to the remedial action efforts that would result in considerable improvements in field data certainty and compliance with remedial objectives while reducing overall costs. (authors)

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