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4.4 GENERIC LIMITATIONS AND FINDINGS ASSOCIATED WITH THE USE OF 

MIVRLM DATA FOR URANIUM AND THORIUM DOSE ESTIMATES 

Sections 5.3.7 and 5.3.8 of FMPC TBD describe the Mobile In Vivo Radiation Monitoring 

Laboratory (MIVRML) that was used to monitor FMPC workers between 1968 and 1989. Data 

presented include the frequency by which individuals were selected for MIVRML analysis, 

radionuclide-specific MDA values, and assumptions regarding the method(s) employed for the 

interpretation/quantification of data. Presented below is a critical evaluation that challenges the 

credibility and usability of MIVRML data for the in vivo detection of uranium and thorium. 

Generic Design Limitations of the MIVRML

Not considered a finding by SC&A, a critical component of the MIVRML lung counting system, 

however, was the radiation detection system, which employed two very large sodium iodide 

detectors measuring 9 inches in diameter by 4 inches thick. While such large crystal detectors 

offer maximum counting efficiency that is highly desirable for whole-body counting of highenergy photons of fission/activation products (e.g., Cs-137, Co-60), the use in detecting lowenergy photons is severely compromised by their 4-inch thickness. 

This limitation in sensitivity is due to the fact that for large/thick crystals, the low-energy 

photons fall into that region of Compton-scattered photons that is maximal. For illustration, 

Figure 4.4-1 depicts a MIVRML gamma spectrum that is defined as “background.” 

The already high counts per channel at the left-site of the “background” spectrum are further 

enhanced by the presence of high-energy photons in the environment or within the person being 

chest counted. Figure 4.4-2 is an in vivo gamma spectrum from an “unexposed” or normal 

person. Note, one of the two peaks is due to Cs-137 (a weapon fallout product) and one is due to 

K-40. Their contribution to Compton-scattered photons diminishes the sensitivity of the system 

to detect the in vivo presence of low-energy photons associated with thorium. 

In order to improve the signal to noise ratio (or sensitivity) for the detection of low-energy 

photons, other DOE facilities during this time period employed NaI detectors with a nominal 

thickness of only 4 millimeters (or 1/25th) of the 4-inch thick crystals employed by the 

MIVRML system. 

Operator Inexperience

For the first 2 years of operation, the MIVRML was operated by Y-12 personnel. Starting in 

1970, the MIVRML was operated by FMPC personnel who had a limited understanding of the 

complexity of in vivo counting and the proper interpretation of results. In a letter to the DOE 

dated November 25, 1981, R.M. Spenceley, Manager at FMPC stated the following: 

. . . Many lung counts are made for screening purposes and are made under 

circumstances which require interpretation of the count results by someone 

familiar with vagaries of in vivo measurements. While all count data are retained 
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in the employees’ files, not all results are useful as an expression of the true lung 

burden.

In combination, these two factors raise concerns about the sensitivity as well as credibility of 

lung count data involving the MIVRML. 

Figure 4.4-1. Comparison of Background Radiation Levels inside Y-12 Iron Room 

and the MIVRML Iron Room 

Figure 4.4-2. Normal In Vivo Spectrum From an Unexposed Person 
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Finding 4.4-1: Limitations Regarding the Use of Th-234 and U-235 for Estimating Intakes 

of Uranium 

Section 5.3.7 of the FMPC TBD states that: 

. . . Uranium-235 was detected primarily by the emission of its 186 keV photon. 

Uranium-238 was calculated from measurement of the Th-234 progeny assumed 

to be in equilibrium with the U-238. 

Limitations regarding the use of Th-234 for estimating intakes of uranium by means of the 

MIVRML lung counter are two-fold: 

(1) Th-234 emits two very low-energy photons of 63 keV and 93 keV, which moreover also 

have very low yields of 3.5% and 4%, respectively. From the foregoing discussion, 

detection limits for Th-234 are compromised by the high background that characterizes 

the large detectors employed by the MIVRML. 

(2) While the surrogate use of Th-234 can provide quantitative data for estimating the 

presence of U-238, it provides no information regarding the presence of U-234, which 

may exist in equilibrium with U-238 or in various states of disequilibrium that reflect the 

use of depleted or variably enriched uranium. 

Limitations regarding the use of the 186 keV photon emitted by U-235 in part parallel the 

limitations defined for the use of Th-234. While the 186 keV photon emitted by U-235 has a 

higher energy as well as yield, its detection is compromised by the fact that this photon energy 

coincides with the 180° backscatter energies of more energetic gammas such as Cs-137, K-40, 

etc. 

Equally, a quantitative estimate for the presence of U-235 provides limited information regarding 

the presence of U-238 and U-234 for the aforementioned reasons. Thus, in the absence of 

definitive information regarding the isotopic composition of the source material(s) to which a 

worker was exposed, interpretation of MIVRML data poses serious limitations and uncertainties. 

Finding 4.4-2: Use of Surrogate Daughter Products and Unsupported Assumptions for 

Thorium Exposure 

Thorium isotopes of concern at FMPC include Th-232, which is the parent isotope of the 4 η

thorium series, and Th-228, which is a radioactive daughter within the decay chain. 

Exhibit 4.4-2 identifies crucial information regarding the thorium decay series that are relevant 

to SC&A’s concerns. 

Inspection of Exhibit 4.4-2 points to the fact that Th-232 does not emit photon(s) and can, 

therefore, not be directly detected by a lung counter; and Th-228 emits two low-energy photons 

with very low yields that limit their use in lung counting for reasons discussed above. 
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EXHIBIT 4.4-2 

In behalf of these limitations, Section 5.3.7 of the FMPC TBD and Section 6.1 of the ER provide 

the following statements relative to the use of MIVRML data for thorium: 

. . . Thorium-232 and Th-228 activities were determined based on equilibrium 

assumptions and detection of their progeny, most likely Ac-228 for Th-232, but 

Pb-212 may have been used for assessment of both Th isotopes. [Emphasis 

added.] 
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At FMPC, thorium existed in various physical and chemical forms that included thorium ores, 

crushed thoria, (powdery thorium dioxide) pellets, thorium oxalate, thorium hydroxide, thorium 

tetrafluoride purified thorium metal, etc. Based on the relative half-lives of decay chain 

members and/or their chemical properties, NIOSH’s basic assumptions of equilibrium conditions 

between (1) Th-232 and Th-228, (2) Th-232 and Ac-228, and (3) Th-232/Th-228 and Pb-212 are 

technically incorrect and unsupported as explained below. 

Even if thorium ores that served as a primary feedstock can be assumed to have contained all 

members of the decay chain in full equilibrium, disequilibrium would first occur at time of 

chemical separation of Th-232 and Th-228 from all other decay chain members. 

At the time of thorium extraction, Ra-228 (and its short-lived daughter Ac-228) would, therefore, 

not be present. The slow rate of ingrowth of Ra-228 (and Ac-228) in chemically extracted 

thorium products is governed by the 6.7-year half-life of Ra-228 and the 1.9-year half-life of 

Th-228. Thus, the relative activity of Th-228 to Th-232 is governed by three factors that include: 

(1) The starting activities of Th-232 and Th-228 in the ore 

(2) The age of the thorium material, which determines the loss of Th-228 by radioactive 

decay 

(3) The age of the thorium material, which determines the ingrowth of Ra-228 that in turn 

gives rise to Th-228 

From this brief discussion, it must be emphasized that assumptions of equilibrium among 

Th-232, Ac-228, Th-228, and Pb-212 for all thorium materials and all time periods are 

technically incorrect. Correspondingly, the surrogate use of Ac-228 and/or Pb-212 for 

estimating lung burdens of Th-232 and Th-228 is technically flawed and would consistently lead 

to results that are claimant unfavorable. As an extreme case, consider a worker who is exposed 

to a freshly isolated thorium extract or a purified thorium metal. Since the thorium would not 

contain any significant amounts of Ra-228/Ac-228, a chest count would imply a false negative 

result. 

A most puzzling set of data pertaining to MIVRML lung counts is contained in Table 6.2 of 

NIOSH’s SEC Evaluation Report. As summarized above, Section 6.1 of the ER specifically 

identifies the use of Ac-228 and/or Pb-212 as the potential surrogate radionuclides for estimating 

the lung burden of Th-232 and/or Th-228. These two isotopes are specifically cited in Table 6.2 

of the ER. Thus, for example, Table 6.2 identifies that in 1971, only three lung counts were 

performed for Pb-212 and two lung counts were performed for Ac-228. Yet, Column 4 of 

Table 6.2 identifies a total of 680 lung counts for “thorium” (along with 686 lung counts for U235 and uranium). 
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SC&A interprets these data to represent the following: 

(1) Column #4 of Table 6.2 and identified as “Thorium” is, in fact, a reference to Th-234. 

Th-234, the daughter of U-238, however, has no relationship to Th-232 and Th-228, 

which are the thorium isotopes of concern in the SEC petition. 

(2) Based on Table 6.2, the total number of in vivo bioassays for Th-232/Th-228 for the 

period of 1965 to 1977 was fewer than 15. 

(3) In vivo assessments for Th-232/Th-228 only began in earnest in 1979. 

(4) The value of conducting thorium-specific lung counts after 1979, however, is 

questionable. According to Table 5-13 of the FMPC TBD, all thorium production lung 

counts would principally assess the inhalation of Th-232/Th-228 associated with the 

repackaging and shipping operations of thorium products. 

(5) Since inhalation of even insoluble forms of thorium (i.e., Type S) can be expected to 

remain in the lung for a finite time, the use of lung counts in the post-1979 era has limited 

value for workers exposed during the production years that predate 1979. 

Finding 4.4-3: Worker Selection Criteria and Infrequent Use of MIVRML 

Section 5.3.7 of the FMPC TBD states that: 

Lung counting became available to FEMP in 1968 in the form of the Mobile In 

Vivo Radiation Monitoring Laboratory [MIVRML]. The mobile van visited the 

Fernald plant on a routine schedule and counted the workers on a schedule based 

on their internal exposure potential and their urine sampling results. 

[Emphasis added.] 

In a Health Protection Appraisal Report for NLO dated September 1968, the following 

statements were noted regarding the use of air monitoring data as the selection criteria of 

workers for MIVRML evaluation: 

Recent in vivo monitoring of NLO employees utilizing the IVRML indicated eight 

employees apparently sustaining 70 to 100% of a permissible lung burden of 

uranium . . . A serious question has been raised regarding the validity of the job 

weighted air dust sampling approach long used by NLO since that data would not 

suggest lung exposures for these employees at the in vivo indicated level. 

[Emphasis added.] 

Two years later in another NOL Health Protection Appraisal Report dated September 1970, the 

following concerns were noted regarding the frequency/completeness of the MIVRML program: 

The IVRML visited NLO on two occasions during CY 1970. It was on site for two 

weeks, beginning March 30, and again from early July through the end of 
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September. During the first counting period, about 24 employees were counted 

and during the second period 103 employees (including the 24 previously 

counted) were monitored . . . It is estimated that about 200 employees are 

currently working in production areas and have a generally comparable potential 

for uranium lung exposures. It is therefore noted with concern that only about 

half of those potentially subject to exposure have been monitored by IVRML 

during this year. It is further noted that a substantial fraction (approximately 20-

24 percent) of the production workforce has not received at least one IVRML 

count since the counter first went to NLO in 1968. [Emphasis added.] 

These statements support two concerns that SC&A has raised elsewhere in this report. The first 

concern is the apparent lack of correlation between air sampling data (used to identify workers 

with the highest potential for exposure) and the workers’ measured lung burdens as assessed by 

the MIVRML. The failed correlation between air sampling data and lung counts may imply 

errors and uncertainties associated with either or both air sampling and lung counting. 

Use of air sampling data, for selection of a subpopulation of workers to be monitored by lung 

counting, poses yet a second concern. The lack of reported correlation between air sampling 

data and lung count data suggests that persons monitored by lung counts may not represent the 

higher exposed worker group(s) and conversely, that maximally exposed workers may not ever 

have been lung counted. 

Finding 4.4-4: The Improper Correlation of MIVRML Thorium Lung Count Data with 

Thorium Air Sampling Data as Proposed by NIOSH 

As suggested in Exhibit 4.3-1 above, for thorium intakes, NIOSH intends to correlate the results 

of “. . . 6000 in vivo results for thorium (Ac-228 and Pb-212) . . . with 2000–4000 thorium air 

sample results.” 

Based on data presented in Table 6-2 of the SEC-00046 Evaluation Report and reproduced 

herein as Table 4.4-1, it is SC&A’s understanding that NIOSH intends to establish a correlation 

between BZ air sampling data that may have been taken as early as the 1950s with MIVRML 

data for thorium that only began in earnest in 1979. Important to note is that thorium production 

had ceased by 1979, as acknowledged in Section 5.2.3 of ORAUT-TKBS-0017-5, which states: 

Thorium processing was completed in 1979, with exposure from that time being 

limited to repackaging and shipping operations. [Emphasis added.] 

Based on the relative time periods, it is inconceivable how lung burdens of thorium measured 

post-1979 (and corresponding to “repackaging and shipping”) can be correlated to BZ air 

samples taken decades earlier when thorium was processed. 
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Table 4.4-1. Number of In-vivo Measurements Performed Annually at the FMPC 

(as reported in MIVRML) 

Year Uranium-235 Uranium Thorium Lead-212 Actinium-228 

1965 2 2 0 2 2 

1968 306 362 310 2 1 

1969 107 108 107 0 0 

1970 168 168 164 0 0 

1971 686 686 680 3 2 

1972 277 277 274 1 0 

1973 235 235 233 2 1 

1974 324 324 321 1 1 

1975 277 277 275 0 0 

1976 267 267 262 1 1 

1977 219 218 217 3 3 

1978 212 214 161 40 41 

1979 216 224 26 198 197 

1980 232 239 5 214 219 

1981 171 176 3 166 170 

1982 209 215 3 204 210 

1983 212 217 4 195 200 

1984 410 419 4 408 415 

1985 426 418 3 405 407 

1986 506 507 10 467 467 

1987 577 576 12 570 566 

1988 229 228 3 111 107 

1989 6 6 0 1 1 

It is, therefore, concluded that NIOSH’s proposed method for linking air monitoring data with 

MIVRML lung count data for estimating thorium intakes prior to 1979 is without scientific 

merit. 

Finding 4.4-5: The Inappropriate Use of ORAUT-OTIB-0002 for FMPC Claims

In a presentation to the Advisory Board on February 8, 2007, in Mason, Ohio, NIOSH presented 

summary data regarding the number of claims that had been completed as of that date. 

Attachment 4.4-5 is a reproduction of viewgraph #7 presented to the Board. It shows that 90% 

or a total of 619 dose reconstructions had been completed. 

While SC&A has access to individual claims, no analysis of the types of DR methods used in the 

619 claims that have been completed is available. But a review of some randomly selected 

claims shows that many FMPC claims that were denied on the basis of a maximized dose 

reconstruction that employed ORAUT-OTIB-0002. 

SC&A regards the use of OTIB-0002 inappropriate of all FMPC claims, as explained below. 

Section 2.0 of OTIB-0002 explains the regulatory basis for its use as an efficiency measure in 

which a dose is determined using worst-case assumptions that substitute for further research and 
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analyses. Worst-case is defined as “the highest reasonable value based on reliable science, 

documented experience, and relevant data . . .” 

Section 3.0 (Implausible Undiscovered Intakes) further explains the technical basis and 

justification for its use by providing the following: 

For claims where it is considered likely that the covered employee had no 

significant internal radiation exposure, a method to expedite claims has been 

developed in accordance with 42 CFR 82.10(k)(2). This method assumes the 

“largest reasonably possible value” of the source term comprised of 

radionuclides that are/were typically the more significant radionuclides (by either 

preponderance or by internal dose significance) on a site. For this “worst-case” 

estimate of internal dose, it is assumed that on the first day of the first year of 

employment, the covered employee had an acute inhalation intake of each of the 

radionuclides in the source term, in the amounts listed below. 

Based on historical data, it is believed to be highly unlikely that such an intake 

could have occurred without being detected by workplace monitoring at the 

time. It is also believed that this is a significant overestimate of internal dose for 

an unmonitored covered employee or a covered employee with no internal 

monitoring above detection thresholds. [Emphasis added.] 

Given the limitations and deficiencies of internal monitoring as described in Sections 4.1, 4.2, 

4.3, and 4.4 of this report, SC&A concludes that the use of OTIB-0002 for any FMPC claimant 

is inappropriate and unjustified. 

 

ATTACHMENT 4.4-5 
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4.5 FINDINGS ASSOCIATED WITH EXTERNAL EXPOSURE MONITORING AT 

FMPC 

Finding 4.5-1: Absence of Performance Standards/Quality Assurance for Personnel 

Dosimeters 

Throughout the period of facility operation, workers were monitored for external radiation by 

means of film dosimeters and TLDs, and extremity exposures were monitored with wrist 

film/TLD badges starting in 1970. Although SC&A is not generically questioning the merits of 

external dose data, the credibility of external dosimetry data has to be viewed in context with 

several limitations, as described in a document entitled Response to Dosimetry Assessment Fact 

Sheet, September 11, 1981. In this response (to a DOE inquiry), the following statements were 

made (see Attachment 4.5-1): 

(1) All dosimeter evaluations were “in house” except for approximately the first 12 months 

of operation when film badges were processed by DOE’s Health and Safety Laboratory... 

(2) No procedure is available [for the processing/evaluation of personnel dosimeters]. 

(3) Test dosimeters [i.e., control badges] are not routinely processed. [Emphasis added.] 

(4) Initially, heat damage from leaving badges in cars during hot weather was a problem. 

However, this has not been a real problem for many years. Leaving badges in desks, 

cars, etc. did not have a significant impact on the overall external dosimetry program. 

(5) There were no specific training requirements for the film badge technicians when this 

program began in 1951. The technician received on-the-job training. The technician 

now performing [i.e., in 1981] all film badge process began this work in 1952 and has 

been only technician doing this task since 1959. [Emphasis added.] 

In summary, while it appears that FMPC monitored workers for external exposures, there are 

concerns about the quality and accuracy of these data due to the absence/unavailability of 

standard operating procedures, quality control measures, and formal training of dosimetry 

technician(s). 
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ATTACHMENT 4.5-1 
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Attachment 4.5-1 (Continued) 
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Attachment 4.5-1 (Continued) 
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Attachment 4.5-1 (Continued) 
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Attachment 4.5-1 (Continued) 
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Attachment 4.5-1 (Continued) 
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Finding 4.5-2: Unaccounted Doses to Extremities

Radioactive daughter products of the U-238 and Th-232 decay chains emit both beta and gamma 

radiation. Of particular concern is the high-energy beta emitted by Pa-234. For select processes 

such as the reduction of uranium and thorium to produce derbies or their remelting/casting, 

causes a separation of daughter impurities not only to concentrate on the surface of the derbies 

and ingots, but also the volatilization of these impurities. 

Statements contained in Attachment 4.5-2A indicate that the ratio of recorded skin dose (beta 

and gamma) to deep dose (gamma only) varied significantly with time, as given in the following 

statement: 

The highest skin exposure for 1963 was reported as 22.9 rem which includes 

4.4 rem of penetrating radiation. The beta plus gamma to gamma ratio for the 

plant population has decreased significantly since 1960 when the ratio was 20.7 

to 1 as compared to a ratio of 5.4 to 1 for 1963. [Emphasis added.] 

SC&A interprets these data to reflect monitoring data as recorded by the whole-body 

dosimeters normally worn on the chest area of the body. 

Considerably high skin exposures involved extremities of the body as acknowledged in a 1970 

Health Protection Appraisal Report (see Attachment 4.5-2B), which states the following: 

NLO has performed a study of exposure to the forearms of some Plant 5 

employees. The results of this study showed projected annual forearm exposure 

from about 14,000 to 46,000 mrem. According to NLO estimates, about 300 

employees would require extremity monitoring because of potential exposure to 

the hands. It appears necessary that further attention by given by NLO to this 

matter. Extremity dosimeters should be provided as appropriate and an 

evaluation of involved operations should be made . . . 

 The study does not indicate the level of hand exposure for these employees. From 

previous experience at other uranium facilities, it would be expected that the 

hand exposure could be 2-3 times the wrist exposure. [Emphasis added.] 

From these statements, SC&A concludes the following: 

(1) The ratio of recorded “skin dose” to deep dose was highly variable over time as measured 

by the whole-body dosimeter. 

(2) Shallow doses to extremities were likely several times higher, but were not monitored for 

a large fraction of FMPC’s operating period. 

(3) Potential extrapolation and use of the measured shallow dose (as recorded by the wholebody dosimeter) for deriving extremity doses to the forearms/hands poses serious