II. STATUS OF SOURCE TERM

A. CHEMICAL FORM OF RELEASED MATERIAL

Because of the importance of the chemical form of the uranium released on transport and uptake, the committee suggests that more detail be supplied on the physical and chemical characteristics of the materials released to the air and water. In addition, it would be beneficial to explain how these characteristics might influence the doses to the public.

B. PARTICLE SIZES

In the report, the authors use particle-size distributions from 1985 (the only year in which particle sizes were actually measured) generically, which seems appropriate given that no major changes in the processing occurred. While the pattern of the actual deposition of material does give some information about the particle-size distribution that existed in the atmosphere, this data, if it exists at all, will have limited usefulness. No other data exist for determining the effect of particle size on the source term and its subsequent effects on dispersion and on dry and wet deposition, although it is likely that there were some changes in the nature, types, and efficiencies of the air-cleaning equipment over time and improvements were probably incorporated when scrubbers and filters failed.

This approach might be appropriate, the actual analysis and interpretation of the observed and measured particle-size distributions are not justified. To illustrate this point, the committee examined the populations of data in Tables D1-D4 in the RAC report to determine whether they could be treated as lognormally distributed. This reexamination used the methodology of Waters and colleagues (Waters et al., 1991). The authors calculate a “ratiometric” to evaluate lognormality within the confidence limits of the data. In its evaluation, the committee used the < 2.5 μm and >20 μm sizes as presented. The data were tested and found to be lognormally distributed; the geometric means and standard deviations calculated by the committee are shown in Table 1. However, it does not appear that the



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DOSE RECONSTRUCTION FOR THE FERNALD NUCLEAR FACILITY: A REVIEW OFTASK 4 II. STATUS OF SOURCE TERM A. CHEMICAL FORM OF RELEASED MATERIAL Because of the importance of the chemical form of the uranium released on transport and uptake, the committee suggests that more detail be supplied on the physical and chemical characteristics of the materials released to the air and water. In addition, it would be beneficial to explain how these characteristics might influence the doses to the public. B. PARTICLE SIZES In the report, the authors use particle-size distributions from 1985 (the only year in which particle sizes were actually measured) generically, which seems appropriate given that no major changes in the processing occurred. While the pattern of the actual deposition of material does give some information about the particle-size distribution that existed in the atmosphere, this data, if it exists at all, will have limited usefulness. No other data exist for determining the effect of particle size on the source term and its subsequent effects on dispersion and on dry and wet deposition, although it is likely that there were some changes in the nature, types, and efficiencies of the air-cleaning equipment over time and improvements were probably incorporated when scrubbers and filters failed. This approach might be appropriate, the actual analysis and interpretation of the observed and measured particle-size distributions are not justified. To illustrate this point, the committee examined the populations of data in Tables D1-D4 in the RAC report to determine whether they could be treated as lognormally distributed. This reexamination used the methodology of Waters and colleagues (Waters et al., 1991). The authors calculate a “ratiometric” to evaluate lognormality within the confidence limits of the data. In its evaluation, the committee used the < 2.5 μm and >20 μm sizes as presented. The data were tested and found to be lognormally distributed; the geometric means and standard deviations calculated by the committee are shown in Table 1. However, it does not appear that the

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DOSE RECONSTRUCTION FOR THE FERNALD NUCLEAR FACILITY: A REVIEW OFTASK 4 RAC report used the data in this form. Because particle-size distribution is important for dispersion and deposition and for use in inhalation models, the committee recommends that the data be peer-reviewed by an expert in particle-size analysis and aerosol modeling. Although particle-size data collected by impaction instruments tends to fall off at both the low and high ends of the particle-size scale, this fall off does not significantly affect the observed particle-size distribution, which appears to be lognormally distributed. Because of this lognormality, the geometric mean and standard deviation are readily calculated for use in estimations of deposition with standard national and international lung models that assume a lognormal distribution. The mathematical analysis presented in the Task 4 report does not represent the state-of-the-art for conventional particle-size analysis; it should be revised accordingly. The derived means and standard deviations are not the necessary parameters for the models of the Task Group on Lung Dynamics and other groups. The geometric standard deviations of the data in Tables D-1 to D-4 are all around 2.0, which is what would be expected for such sampling. The calculated geometric means are very large; this implies that a considerable fraction of the particles would not be respirable, which indicates a relatively low dose per unit intake. Such large, dense particles also would be subject to substantial removal close to the point of release because of gravitational settling. C. DISPERSION MODELING In the report, the authors use a straightline Gaussian model modified to account for building wake effects to address dispersion of routine releases from site buildings. This seems appropriate in view of the difficulty of using a dynamic puff model–which requires meteorologic data that do not exist. Moreover, the model would be of dubious worth in this instance particularly because of the significance of near-field effects on dispersion and deposition. Episodic releases must be considered separately for dispersion modeling and for other evaluations. An assumption that roof vent releases predominated at all times requiring use of a wake model might not be valid for all of the major episodic releases in the early years. The actual mode of each major episodic release should be considered and a determination should be made of whether a puff model, a wake model, or perhaps a plume model is the most appropriate for a particular release.

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DOSE RECONSTRUCTION FOR THE FERNALD NUCLEAR FACILITY: A REVIEW OFTASK 4 Tables D-1 to D-4. Aerodynamics median diameters and geometric standard deviations calculated from the distributions for particle-size (mass median aerodynamic diameter, MMAD) analyses presented in Tables D-1 to D-4 of the RAC Report CDC-3 (RAC, 1993). Sample Identification Median Aerodynamic Diameter(μm) Geometric Standard Deviation Table D-1 Stack G4-2 8.7 1.85 Stack G4-5 6.6 2.20 Stack G4-12 7.9 1.71 Stack G4-14 8.3 1.97 Stack G5-249 6.5 2.06 Stack G5-250 7.7 2.05 Table D-2 Stack G4-2 7.5 1.70 Stack G4-5 5.8 2.05 Stack G4-12 9.2 1.67 Stack G4-14 12.5 1.55 Stack G5-249 9.5 1.74 Stack G5-250 13.3 1.53 Stack G5-253 8.1 1.88 Table D-3 Stack G5-254 5.5 1.88 Stack G5-256 5.4 1.96 Stack G5-261 6.7 1.82 Table D-4 Stack G5-254 7.0 2.05 Stack G5-256 7.9 1.74 Stack G5-260 6.9 1.84 Stack G5-261 10.1 1.79

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DOSE RECONSTRUCTION FOR THE FERNALD NUCLEAR FACILITY: A REVIEW OFTASK 4 It is noteworthy that the report advances the art of modeling building wake effects by using the work of Ramsdell (1990) as modified according to a 1993 memo from G. Killough (personal communication courtesy of John Till). Most analyses of this type rely on Nuclear Regulatory Commission regulatory guides, but the report addresses the specific characteristics of the Fernald site in its approach. The atmospheric dispersion of heavy metals at Fernald depends on these specific characteristics. To this extent, the RAC approach to modeling might not be generically applicable to other sites. Measurements were used for comparison with the estimates derived from the model, and the overall results are verified to be within a factor of 2. A plot of the predicted versus the observed results would be useful. The model tends to underestimate uranium depositions as previously predicted with gummed-film measurements, primarily because of assumptions about removal of large particles by deposition and therefore overestimates the uranium concentrations in air at distances from the facility. Uncertainties in meteorologic data, about the source term, and in air measurements themselves also contribute. Overall, the results of the comparison are a reasonable validation of the model predictions. The estimated deposition of uranium in the environment beyond the plant is 2 × 105 kg to 9 × 105 kg within a few kilometers (about 5 miles). The authors should describe more clearly how this estimate was derived and how it correlates with soil or gummed-film measurements. In Tables N-8 and N-9, the uranium releases are ascribed entirely to the old waste incinerator; however, the source-term document (Voillequé et al., 1991) reported much larger releases of uranium, which must have been in particulate form from other plant units. If those releases did happen and if the amounts released were large, the material should have appeared in onsite samples. In Appendix G of the RAC (1993) report, the

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DOSE RECONSTRUCTION FOR THE FERNALD NUCLEAR FACILITY: A REVIEW OFTASK 4 importance of the Plant 8 scrubbers is emphasized, but the authors seem to assume that only gaseous material and small droplets escaped. Because early releases were mainly episodic, the low uranium concentrations in soil (Stevenson and Hardy, 1993) could be used to argue in favor of surface runoff into Paddy's Run for most of that material if the deposition occurred as dust on a relatively dry surface. If verified, this assumption would need to be incorporated into the surface water source term. At the very least, the authors should discuss reasons why their report's source term is 100 times the results of Stevenson and Hardy. Soil measurements might have little bearing on validation of the airborne model, particularly if soil was disturbed, and they could be of questionable value if wake effects predominated. Appendix G illustrates the committee's concern regarding the utility of soil measurements for validation. In this appendix, the authors oscillate between gravitational settling for coarse particles from a steady plume (Fig. G-3) and a dry-deposition velocity for very fine particles from a plume (Eq. G-3). The discussion is well done, but it leaves open the question of source depletion of coarse particles on the site from puff releases for low release points, which could have been the source of the largest release fraction during episodic events. This is confirmed on page F-11, but it needs to be developed further. The importance of the source depletion is illustrated by Stevenson and Hardy (1993). The comparison of the modeling estimates of deposition of radionuclides with data gathered from gummed-film collectors could also indicate two other inaccuracies. One is that the aerosol component of the source term used has too high a value. The other is that the effects of gravitational settling and precipitation have been underestimated. This could increase the scatter of points and could perhaps be used to adjust the source term particle-size distribution for the incinerator and for times when the scrubbers and filters failed.

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DOSE RECONSTRUCTION FOR THE FERNALD NUCLEAR FACILITY: A REVIEW OFTASK 4 D. VALIDATION AND UNCERTAINTY The uncertainty analysis in different parts of the report is inconsistent and is expressed in different terms (e.g., in Table O-1 it is standard deviation, in Table Q-9 it is an average of uncertainties both positive and negative, and in Table RS-3 it is standard deviation obtained with Crystal BallTM). A consistent procedure should be outlined for propagating these uncertainties and, in particular, for taking into account the substantial systematic errors in many of the early sampling and analysis data. There also will be an appreciable uncertainty associated with estimates of early episodic releases, and it will be important to conduct a sensitivity analysis to eliminate minor, but highly uncertain, contributions to the total dose. Although the techniques of dealing with data distributions for the Cincinnati climate were most useful and helpful to the approach to determining dispersion input parameters, many of the assumed distributions seem arbitrary. The use of assumed data distributions in a Monte Carlo calculation does not make the calculated distribution correct. Even though the analysis appears rigorous and thorough, the resulting distribution is no more credible than are the data distributions used as input. The only way to solve this dilemma appears to be to ensure that the distributions of the input parameters are valid. Because the data are as much as 40 years old and the conditions under which they were taken are not certain, a best estimate with a clear expression of uncertainty might be all that can be expected. E. RADON The importance of the radon source term associated with the K-65 silos is difficult to establish, primarily because the silos have been modified several times over the years. If the head space has been adequately sampled, the silos' inventory could be modeled for release (assuming no retardation by the cap, which has been sealed to various degrees over the years) as a worst-case endpoint. It is reasonable to separate the calculations into

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DOSE RECONSTRUCTION FOR THE FERNALD NUCLEAR FACILITY: A REVIEW OFTASK 4 daytime and nighttime dispersion, because the dispersion figures would certainly differ. However, no justification is given for the release terms of 140 Ci/yr continuous or 810 Ci/yr during the daytime only. It also might be a reasonable refinement to have transition periods in between. No correlation is presented for the radium vs. radon inventory in the stored waste and airborne releases. It is also not clear whether a separate source-term-and-release scenario was adopted for conditions before and after the dome was sealed. RAC appears to have used monitoring measurements that deal only with radon seepage after the cracks in the dome were sealed. These might have little bearing on previous release conditions and their radon progeny equilibrium. If it is argued that merely the magnitude of the radon release was changed by sealing the cracks, then this should be stated and justified. The low (predicted concentration of 222Rn divided by the measured (net) concentration of 222Rn) P/O ratios in Table P-6 are noteworthy; the model probably overestimates radon concentrations because it ignores precipitation effects. Thus, the source-inventory-to-release term appears to be consistently underestimated. Regardless of their uncertainty, the estimates of radon emissions from the K-65 silos are probably important. However, a major difficulty in determining the study endpoint (projected lung-cancer incidence) will be the broad distribution of radon background exposure estimated for individual homes.