Robert D. Rogers

Radiocolloids in leachate from the NRC field lysimeter investigations

An investigation of colloidal particles has been completed on leachate samples collected from sand and soil-filled lysimeters (of the Field Lysimeter Investigation: Low-Level Waste Data Base Development Program) in which low-level radioactive waste forms were buried. An array of analytical techniques including: gamma spectroscopy, liquid scintillation spectrometry, gross alpha and beta particle proportional counting, energy dispersive X-ray analysis (EDX), neutron activation analysis (NAA), X-ray fluorescence analysis (XRF), proton induced X-ray emission analysis (PIXE), gravimetric analysis, and scanning electron microscopy (SEM), were performed on samples thought to contain colloidal particles to determine particle composition and the nature of their association with radioactive material. Several different types of particles ranging in size from 0.02 to 20 μm were identified within the leachate including crystalline calcium hydroxide particles, rounded siliceous grains, angular weathered soil, and spherical particles apparently composed of an organic polymer. The primary radioactive material associated with these particles was Sr-90. About 2% of the total Sr-90 activity in the leachate is associated with colloidal particles. This information indicates that colloidal particles play a role in radioactive material transport through lysimeter soils.

Performance verification of solidified radioactive waste using lysimeters

Abstract Accurate data on the long-term performance of the radioactive wastes in disposal systems is becoming a necessity in part because of restrictive federal and state regulations which are being promulgated. A method which provides data on the performance of buried radioactive waste forms is comprised of lysimeters. They are ideal instruments for obtaining actual field test data because when properly designed and operated they can be used to isolate and then study soil/waste systems under actual environmental conditions. The complexity of interactions under such conditions can never be completely duplicated by standard laboratory testing. This paper provides data from two instrumented, operational lysimeter arrays containing waste forms fabricated with highly loaded exchange resin materials. The lysimeters have been in operation for three years and provide both meteorological data and radionuclide content of percolating water. This paper provides data obtained from the lysimeters and discusses how these data can be used as a database for input into codes used to verify performance of buried radioactive waste forms.

Evaluation of Microbially Influenced Degradation as a Method for the Decontamination of Radio Actively Contaminated Concrete

Because there are literally square kilometers of radioactively contaminated concrete surfaces within the US Department of Energy (DOE) complex, the task (both scope and cost) of decontamination is staggering. Complex-wide cleanup using conventional methodology does not appear to be feasible for every facility because of prioritization, cost, and manual effort required. The authors are investigating the feasibility of using microbially influenced degradation (MID) of concrete as a unique, innovative approach for the decontamination of concrete. Currently, work is being conducted to determine the practicality and cost effectiveness of using this environmentally acceptable method for decontamination of large surface concrete structures. Under laboratory conditions, the biodecontamination process has successfully been used to remove 2 mm of the surface of concrete slabs. Subsequently, initial field application data from an ongoing pilot-scale demonstration have shown that an average of 2 mm of surface can be removed from meter-square areas of contaminated concrete. The cost for the process has been estimated as

Microbially influenced degradation of concrete structures

1.29/m{sup 2}. Methodologies for field application of the process are being developed and will be tested. This paper provides information on the MID process, laboratory evaluation of its use for decontamination, and results from the pilot field application.

A preliminary investigation of the existence of radiocolloids in leachate from the NRC field lysimeter investigations

Steel reinforced concrete is the most widely used construction material in the world. The economic costs of repair or replacement of environmentally damaged concrete structures is astronomical. For example, half of the concrete bridges in the Federal Department of Transportation highway system are in need of major repairs. Microbially influenced degradation of concrete (MID) is one of the recognized degradative processes known to adversely affect concrete integrity. It is not possible to assign a specific percent of effect to any of these processes. However, MID has been shown to be as aggressive as any of the physical/chemical phenomena. In addition, the possibility exists that there is a synergism which results in cumulative effects from all the processes. Three groups of bacteria are known to promote MID. Of these, sulfur-oxidizing bacteria (SOB) are the most aggressive. Much is known about the nutritional needs of these bacteria. However, there has not been a biological linkage established between the presence of environmental, polluting sulfur sources and the degradation of concrete structures. It has been shown that the environmental pollutants sulfur dioxide and sulfite can be utilized by active SOB for the biological production of sulfuric acid. Therefore, it is not a reach of reality to assume that SOB exposed to these pollutants could have a major impact on the degradation of concrete structures. But, until the environment sulfur loop is closed it will not be possible to calculate how important SOB activity is in initiating and promoting damage.

The possibility for microbially influenced degradation of cement solidified low-level radioactive waste forms

Abstract Leachate samples collected from sand and soil-filled lysimeters (of the Field Lysimeter Investigation: Low-Level Waste Data Base Development Program) were examined to determine if radiocolloid particles were present. Radiometric analyses were performed on 1.0 1 volumes of leachate. Samples of these leachates were passed through polycarbonate filters with pore diameters from 0.01 μm to 0.40 μm. One set of filters was analyzed to determine if radioactive material was trapped on their surfaces. A second set of filters was analyzed with a scanning electron microscope and energy dispersive x-ray analysis. Three radionuclides, Sr-90, Cs-137, and Co-60, were measured at 33.7 33.7 ± 0.52, 0.20 ± 0.03, and 0.13 ± 0.03 Bq/L, respectively, in the sand filled lysimeter leachate. Only Sr-90 at a concentration of 8.58 ± 0.37 Bq/l was measured in the soil filled lysimeter leachate. Amorphous particles μ m in diameter were observed on the filters used with the sand filled lysimeter leachate. X-ray dispersive analysis was used to quantify the fractions of high atomic number materials present in these particles. Although stoichiometrically appropriate quantities of oxygen and perhaps carbon are also present, x-ray dispersive analysis indicated that these particles were composed of Si (9%), Ca (87%), and Mg (4%). Amorphous particles ⩽ 0.20 μ m in diameter composed primarily of Si, and spherical particles about 0.2 μm in diameter composed of low atomic number material, were observed on the filters used with the soil filled lysimeter leachate. Beta radiation emitting radioactive material was detected on the filters. The relative activity of beta emiting radionuclides detected on the filters was observed to increase as filter pore sizes decreased. This observation provides evidence of the presence of radiocolloids. It also indicates that a minor radiocolloid transport mechanism may be occurring within these lysimeters.

Biodegradation testing of radioactive waste forms.

The Nuclear Regulatory Commission (NRC) regulations 10 CFR Part 61, “Licensing Requirements for Land Disposal of Radioactive Waste”, regulate the disposal of radioactive waste and provide, among other stipulations, that class B and C low-level radioactive waste (LLW) must be stabilised. This is intended to ensure that solidified waste does not structurally degrade and cause subsidence in the disposal unit’s cover system. It is reasoned that deterioration of the waste form could adversely affect the stability of the burial site and lead to the release of radionuclides to the environment. Because of its apparent structural integrity, cement has been widely used as a binder to solidify LLW. However, the resulting preparations called pozzolanic cements are susceptible to failure due to the actions of stress and environment.

Field Testing of Waste Forms Using Lysimeters

Biodegradation tests were conducted on solidified waste forms containing ion exchange resins contaminated with high levels of radioactive nuclides. These tests were part of a program to test waste forms in accordance with the U.S. NRC Branch Technical Position on Waste Forms. Small waste forms were manufactured using two different solidification agents, Portland Type I–II cement and vinyl ester-styrene (VES). Ion exchange material was taken from a filter system which had been used to remove radionuclides from highly contaminated water. As specified by NRC, the waste forms were evaluated for their resistance to biological degradation using the G21 and G22 procedures of the American Society for Testing Materials (ASTM). Results showed that microbial growth can be supported by the VES waste forms. The particular organisms used in the tests did not grow in the presence of the cement waste forms. It is also shown that the ASTM tests specified in the Technical Position are not suitable for the use intended. A different testing methodology is recommended which would provide direct verification of waste form integrity.

Encapsulation method for maintaining biodecontamination activity

This paper describes field testing and gives preliminary findings. Solidified ion exchange resin materials from EPICOR-II prefilters used in the cleanup of the Three Mile Island Nuclear Power Station are being field tested to develop a low-level waste data base and obtain information on survivability of waste forms composed of ion exchange media loaded with radionuclides and solidified in martices of cement and Dow polymer. Emphasis is placed on obtaining data on performance of waste in a disposal environment using lysimeter arrays at Oak Ridge National Laboratory and Argonne National Laboratory in Illinois. 6 refs., 9 figs., 5 tabs.