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Radioactive NESHAP Stack Sampling

Stack Sampling Program

Radioactive materials are an integral part of many activities at the Laboratory. Some operations involving these materials may vent emissions to the environment through a stack. We evaluate these operations to determine impacts on the public and the environment. If this evaluation shows that emissions from a stack may potentially result in a member of the public receiving 0.1 mrem or more in a year, this stack must be sampled in accordance with 40 CFR 61, Subpart H, "National Emission Standards for Emissions of Radionuclides Other than Radon from Department of Energy Facilities" (EPA 1989). As of the end of 1998, we have identified 28 stacks as meeting this criterion. An additional three sampling systems were in place to meet DOE requirements for nuclear facilities. Where sampling is not required, emissions are estimated using engineering calculations and radionuclide materials usage information.

Radioactive Materials Usage Survey for Point Sources

The Radioactive Materials Usage Survey for Point Sources is an annual report compiled by ENV-EAQ. As required by 40 CFR 61, Subpart H, LANL must monitor any point source with the potential to contribute a PEDE of 0.1 mrem/yr or greater to any member of the public. The regulation further requires that LANL perform periodic confirmatory measurements to verify the low emissions from unmonitored point sources. LANL uses data from its this survey to determine whether a point source exceeds the monitoring levels.

Sampling Methodology

As of the end of 1998, LANL was continuously sampling 31 stacks (28 of which are required as noted above) for the emission of radioactive material to the ambient air. LANL has categorized its radioactive stack emissions into four areas: (1) particulate matter, (2) vaporous activation products (VAP), (3) tritium, and (4) gaseous/mixed air activation products (G/MAP). For each of these emission types, the Laboratory employs an appropriate sampling method, as described below.

We sample emissions of radioactive particulate matter, generated by operations at facilities such as the Chemistry and Metallurgy Research Building (CMR) and TA-55, using a glass-fiber filter. A continuous sample of stack air is pulled through the filter, where small particles of radioactive material are captured. These samples are analyzed weekly using gross alpha/beta counting and gamma spectroscopy to identify any increase in emissions and to identify short-lived radioactive materials. Every six months, ENV-EAQ composites these samples for analysis at an off-site laboratory. These composited samples are analyzed to determine the total activity of materials such as ²³⁴U, ²³⁵U, ²³⁸U; ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu; and ²⁴¹Am. We then use these data to calculate emissions.

VAP emissions, generated by LANSCE operations and by hot-cell activities at CMR and TA-48, are sampled using a charcoal filter or canister. A continuous sample of stack air is pulled through a charcoal filter where vaporous emissions of radionuclides are adsorbed. Gamma spectroscopy determines the amount and identity of the radionuclide(s) present on the filter.

We measure tritium emissions from the Laboratory's tritium facilities using a collection device known as a bubbler. This device enables the Laboratory to determine not only the total amount of tritium released but also whether it is in the elemental (i.e., HT) or oxide (i.e., HTO) form. The bubbler operates by pulling a continuous sample of air from the stack, which is then "bubbled" through three sequential vials containing ethylene glycol. The ethylene glycol collects the water vapor from the sample of air, including any tritium that may be part of a water molecule (HTO). "Bubbling" through these three vials essentially removes all HTO from the air, leaving only elemental tritium. The sample containing the elemental tritium is then passed through a palladium catalyst, which converts the elemental tritium to HTO. The sample is then pulled through three additional vials containing ethylene glycol, which collects the newly formed HTO. The amounts of HTO and HT are determined by analyzing the ethylene glycol for the presence of tritium using liquid scintillation counting (LSC).

Tritium emissions from LANSCE are determined using a silica gel sampler. A sample of stack air is pulled through a cartridge containing silica gel. The silica gel collects the water vapor from the air, including any HTO. The water is distilled from the sample, and the amount of HTO is determined by analyzing the water using LSC. Because the primary source for tritium is activated water, sampling for only HTO is appropriate>

G/MAP emissions resulting from activities at LANSCE are measured using real-time monitoring data. A sample of stack air is pulled through an ionization chamber, which measures the total amount of radioactivity in the sample. Gamma spectroscopy and decay curves identify specific radioisotopes.

Sampling and Analysis

We chose analytical methods for compliance with EPA requirements (40 CFR 61, Appendix B, [EPA 19] Method 114). These methods were selected during 1995, as part of the development of quality assurance project plans for tritium, particulate, and vapor sampling. General discussions on the sampling and analysis methods for each of LANL's emissions follow.

Particulate Matter Emissions

Glass-fiber filters that sample facilities with significant potential for radioactive particulate emissions were generally removed and replaced weekly and transported to the Health Physics Analysis Laboratory (HPAL). Before screening the samples for the presence of alpha and beta activity, the HPAL allowed approximately 72 hours for the short-lived progeny of radon to decay. These initial screening analyses ensured that potential emissions were within normal values. Final analyses were performed after the sample had been allowed to decay for approximately one week. In addition to alpha and beta analyses, the HPAL, using gamma spectroscopy, identified gamma-emitting isotopes in the samples by determining the energy of the gamma photon(s) emitted during radioactive decay. Because the energy of decay is specific to a given radioactive isotope, the HPAL could determine the identity of any isotopes gamma spectroscopy detected. The amount, or activity, of an isotope could then be found by noting the number of photons detected during analysis. Glass-fiber filters from LANSCE were analyzed using only gamma spectroscopy.

Because gross alpha/beta counting cannot identify specific radionuclides, the glass-fiber filters were periodically composited for radiochemical analysis at a commercial laboratory. This program was added in 1995. During 1998, we continued with changes to our composite analyses that were implemented in 1997. Specifically, rather than using isotopic data only to identify radionuclides as was done in the past, these data also quantified these emissions. We consider this method an improvement in sample analysis and in emissions determination. To ensure that the analyses requested (e.g., ²³⁴U, ²³⁵U, ²³⁸U, ²³⁸Pu and ²³⁹Pu, etc.) identify any significant activity in the composites, ENV-EAQ compares the results of the isotopic analysis to gross activity measurements.

P/VAP Emissions

Charcoal canisters that sampled facilities with the potential for significant VAP emissions were generally removed and replaced weekly. These samples were transported to the HPAL where gamma spectroscopy, as described above, identified and quantified the presence of vaporous radioactive isotopes.

Tritium Emissions

Tritium bubbler samples that sampled facilities with the potential for significant elemental and oxide tritium emissions were generally collected and transported to the HPAL on a weekly basis. The HPAL added an aliquot of each sample to the appropriate amount of liquid scintillation cocktail and determined the amount of tritium in each vial by LSC.

Silica gel samples sampled facilities with the potential for significant tritium emissions in the oxide form only. These samples were transported to the Inorganic Trace Analysis Group (CST-9), where the water was distilled from the silica gel, and the amount of tritium in the sample was determined using LSC.

G/MAP Emissions

We used continuous monitoring to record and report G/MAP emissions for two reasons. First, the nature of the emissions is such that standard filter paper and charcoal filters will not collect the radionuclides of interest. Second, the half-lives of these radionuclides are so short that the activity would decay away before any sample could be analyzed off line. The G/MAP monitoring system includes a flow-through ionization chamber in series with a gamma spectroscopy system. Total G/MAP emissions were measured with the ionization chamber. The real-time current measured by this ionization chamber was recorded on a strip chart, and the total amount of charge collected in the chamber over the entire beam operating cycle was integrated on a daily basis. The gamma spectroscopy system analyzed the composition of these G/MAP emissions. Using decay curves and energy spectra to identify the various radionuclides, LANSCE personnel determined the relative composition of the emissions. Decay curves were typically taken one to three times per week based on accelerator operational parameters. When major ventilation configuration changes were made at LANSCE, new decay curves and energy spectra were recorded.

Data & Documents

Public Notices

Review of November 2008 Groundwater Data