DISCLAIMER: This is a working document provided by the Centers for Disease Control and Prevention (CDC) 

technical support contractor, SC&A, for use in discussions with the National Institute for Occupational Safety and 

Health (NIOSH) and the Advisory Board on Radiation and Worker Health (ABRWH), including its Working Groups or 

Subcommittees. Documents produced by SC&A, such as memorandum, white paper, draft or working documents are not 

final NIOSH or ABRWH products or positions, unless specifically marked as such. This document prepared by SC&A 

represents its preliminary evaluation on technical issues.

NOTICE: This report has been reviewed to identify and redact any information that is protected by the 

Privacy Act 5 USC §552a and has been cleared for distribution. 

MEMORANDUM

TO: Advisory Board on Radiation and Worker Health, Work Group on Carborundum Company 

FROM: Robert Anigstein and John Mauro, SC&A 

DATE: June 30, 2017 

SUBJECT: Final Audit of NIOSH Response Paper and Example DRs

1 Background 

On March 2, 2017, Thomas Tomes (NIOSH/DCAS) issued a paper (Tomes 2017) in response to our 

findings on NIOSH’s use of surrogate data in performing dose reconstructions (DRs) for former 

Carborundum Company1 workers (Anigstein and Mauro 2016). Tomes also discussed the findings and 

observations in our review (Anigstein 2016) of the Carborundum Special Exposure Cohort (SEC) 

Petition-00223 and the NIOSH SEC Petition Evaluation Report (Jessen and Scalsky 2015). An interim 

status report of our review of Tomes’ report was issued on March 12 (Anigstein and Mauro 2017). A 

document titled “DR Examples 3-2-17,” containing summary results of two example DRs based on 

organ doses to two hypothetical Carborundum workers, along with 22 data files supporting these results, 

were issued via the DCAS restricted website on March 2, 2017. 

1 The Carborundum Company will be henceforth referred to as “Carborundum.”

The present memo presents an audit of the two example DRs.2

2 An earlier version of this audit was contained in a memorandum titled “Initial Audit of NIOSH Response Paper 

and Example DRs,” that was distributed to members of the Advisory Board on Radiation and Worker Health, Work Group on 

Carborundum Company, on March 20, 2017.

 

2 Example B1 

Example B1 was the case of a male worker with an unknown job who was employed at Carborundum 

from 1943 through 1980 and was diagnosed with cancer of the kidney on December 31, 1992. His 

period of employment spanned the two Atomic Weapons Employer (AWE) periods, the first residual 

period, and part of the second residual period. Because his job was unknown, NIOSH made the 

claimant-favorable decision to assign him doses to an operator, which is the job category with the 

highest radiation exposures. 

We first examined the annual external doses assigned to this worker. 

 
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2.1 External Exposure 

Because the kidney was not among the organs for which dose conversion factors (DCFs) for organ doses 

from external exposure were listed in OCAS-IG-001 (OCAS 2007), the liver was used as a surrogate 

organ for external dose calculations, as recommended by Siebert (2012). 

2.1.1 First AWE Period

NIOSH adopted as a source term for external exposure to penetrating radiation from uranium metal 

during the first AWE period the 10 uranium slugs that were shipped to Carborundum in 1943. NIOSH 

adopted a personal dose equivalent (Hp[10]) rate of 0.524 mrem/h to an operator, which is 10 times the 

dose rate from a single slug at a distance of 1 ft (30.48 cm) that was listed in TBD-6000 (Allen 2011, 

Table 6.1). NIOSH assigned this dose during the 119 days of the first AWE period—June 1 through 

September 27, 1943—assuming a 2,400-h work year, which is consistent with the pre-1951 exposure 

duration assumed by Allen that is discussed in section 2.1.2 of the present memo. NIOSH prorated the 

annual external exposures of a uranium machining operator to a contaminated floor and to submersion in 

uranium aerosols listed by Allen (2011, Table 6.4) to account for the duration of the first AWE period. 

Since these exposures were listed in roentgens, NIOSH multiplied the values by a factor of 1.42, the 

ratio of exposure-to-Hp(10) effective DCFs for the liver from 30–250 keV photons, and added these 

small doses to the dose from the 10 uranium slugs to obtain an Hp(10) dose of 0.210 rem. NIOSH 

multiplied this dose by the DCF for the liver for 30–250 keV photons to obtain an organ dose of 0.157 

rem, which was entered into the IREP (Interactive RadioEpidemiological Program) input file as the 

median of a lognormal distribution with a geometric standard deviation (GSD) of 5. 

We discussed and accepted the NIOSH source term in our previous memo (Anigstein and Mauro 2017). 

This source term was approved at the March 13, 2017, meeting of the Work Group on Carborundum 

Company, who voted to close the issue. 

2.1.2 First Residual Period

The first residual period extended from September 28, 1943 through December 31, 1958. To determine 

the external exposures during this period, NIOSH first calculated the areal uranium activity 

concentration on the contaminated floor. The starting point was an airborne activity concentration of 

5,480 dpm/m3, the geometric mean of the daily weighted average (DWA) of air sampling data from 

centerless grinding, the process employed at Carborundum, that was listed by Allen (2011, Table 7.5).3

3 Use of the DWA in the breathing zone of an operator leads to a bounding estimate of the contamination level of the 

floor, since the average air concentration in the room was most likely lower.

Assuming a settling rate of 0.00075 m/s and a settling time of 30 d, NIOSH obtained a concentration of 

1.07 x 107 dpm/m2

. It then calculated the external exposure rate during the remainder of 1943 (following 

the end of the first AWE period) and during 1944 by applying the photon DCF for surface 

contamination listed by Allen (2011, Table 3.10). NIOSH then calculated the airborne activity 

concentration during this same time period due to resuspension from the contaminated floor, obtaining a 

value of 106.53 dpm/m3. It calculated the external exposure rate from this source using the photon DCF 

for submersion in uranium-contaminated air listed by Allen (2011, Table 3.9). This exposure rate was 

added to that from the contaminated floor. NIOSH next calculated the annual exposures from these two 

 
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sources, assuming an exposure duration of 2,500 h/y. This is inconsistent with the 48-h workweek used 

by NIOSH to estimate external exposure during the first AWE period, which was based on the annual 

exposure durations assumed by Allen that are discussed below. 

Allen (2011, Table 6.4) presented a matrix of annual doses to workers with various job titles from 

external exposures to six sources for each of six uranium-metal-working processes. There are three sets 

of such matrix elements corresponding to three time periods: pre-1951, 1951–1955, post-1955. 

Comparing the individual values to data for the various pathways presented earlier in this document, one 

can infer that the annual exposure durations in these time periods are 2,400, 2,200, and 2,000 h, 

respectively. This conclusion is further confirmed by the annual inhaled and ingested intakes of uranium 

dust listed by Allen (2011, Tables 7.8 and 7.9), which are broken down into the same three date ranges. 

This conclusion is consistent with external exposures listed by Allen (2011, Tables 6.2 and 6.3), which 

are based on 48-h, 44-h, and 40-h workweeks, if it is assumed that the workers work 50 weeks per year, 

with 2 weeks off. 

To calculate the external exposures during 1945–1958, the remainder of the first residual period, NIOSH 

applied the depletion factors listed by Sharfi (2012, Table 4-2) to the 1944 exposure rates, which were 

based on an annual exposure duration of 2,500 hours. This is inconsistent with Allen’s (2011) assumed 

work hours during the three time periods spanned by the first residual period. 

The organ doses were calculated by applying the effective exposure-to-organ DCFs for 30–250 keV 

photons listed by OCAS (2007) and were entered in the IREP input file as the median values of 

lognormal distributions with a GSD of 5. However, in referring to the DCFs for exposure to a uraniumcontaminated floor, Allen (2011) stated: 

For this particular conversion factor, 71.8% of the exposure is associated with photons 

with energies below 30 keV; 17.8% is from photons with energies between 30 keV and 

250 keV, and the remaining 10.4% is for photons with energies greater than 250 keV. 

Similarly, in referring to the DCFs for submersion in uranium-contaminated air, Allen (2011) stated: 

For this particular conversion factor, 50.5% of the exposure is associated with photons 

with energies below 30 keV; 28.5% is from photons with energies between 30 keV and 

250 keV, and the remaining 21.0% is for photons with energies greater than 250 keV. 
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To demonstrate the effect of NIOSH’s assuming that all the photons were in the 30–250 keV, we 

calculated the total dose to the kidneys from exposure to a uranium-contaminated floor using the method 

employed by NIOSH, and compared the results to those obtained by employing the photon energies 

provided by Allen (2011). In both cases, we used a total worker exposure to a contaminated floor of 

0.0500 R during the first and second residual periods,4

4 The external exposures during the second residual period are discussed later in the present memo.

 which is the sum of the year-by-year external 

exposures listed in the worksheet [Example DR external dose calculations.xlsx]Kidney!, found on the 

restricted DCAS website.5

5 This value includes the contribution from air submersion; however, this contribution accounts for only 0.006% of 

the total exposure rate and thus has no effect on the listed results.

 Table 1 shows a comparison of the median dose to the kidneys calculated by 

both methods. 

Table 1. Calculation of Doses to Kidneys From External Exposure to Uranium-Contaminated Floor 

E

(keV)

DCF–livera

(rem/R)

Fraction Dose (rem)

NIOSHb TBD-6000c NIOSH TBD-6000d

0-30 0.106 0% 71.8% 0 0.0038

30-250 1.064 100% 17.8% 0.0532 0.0095

>250 0.845 0% 10.4% 0 0.0044

Total 0.0532 0.0177

a OCAS 2007

b Example DR 

c Allen 2011

d Calculated using the energy distribution in the fourth column

The table shows that the method used in the example DR produces a 3-fold overestimate of the dose 

from this source. This is in addition to the overestimate resulting from the assumption of an annual 

exposure duration of 2,500 h, as discussed earlier. Although the total median dose from this source in 

calculated by NIOSH in the present example is only 53 mrem, NIOSH should be consistent in applying 

Allen’s (2011) guidance. 

2.1.3 Second AWE Period

The second AWE period spanned 1959–1967. The sources of external exposure during this period 

comprised uranium operations and x-ray diffraction (XRD) analyses during the entire period, and the 

fabrication of uranium-plutonium carbide fuel pellets during 1961–1967. Since these operations were 

performed in separate locations, a claimant should be assigned to the location resulting in the highest 

doses from external exposures. 

Early Years: 1959–1960 

For the years 1959–1960, NIOSH adopted a limiting external exposure scenario based on the exposure 

of an operator to a flat uranium plate, using the dose rate at 30.48 cm listed by Allen (2011, Table 6.1). 

The organ dose was calculated using the DCF for the liver from 30–250 keV photons listed by OCAS 

(2007), yielding a dose rate of 0.173 rem/y, which was entered into the IREP input file as a constant 

 
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distribution. This is inconsistent with the guidance of Allen (2011, section 6.4), who stated: “Each 

annual dose value is assumed to be the geometric mean of a lognormal distribution with a GSD of 5.” It 

is also inconsistent with the distribution of doses from external exposure to uranium metal that was 

assigned to the same hypothetical worker during the first AWE period, which does follow Allen’s 

guidance. 

We confirmed that the exposure of an operator to a flat uranium plate produced higher doses than the 

exposure of an XRD operator to stray radiation from that apparatus; we therefore agree with NIOSH’s 

selection of the limiting external exposure scenario during 1959–1960. This conclusion is not affected 

by our finding regarding the radiation exposure from the XRD apparatus, which was presented as 

Issue 1 in our previous memo (Anigstein and Mauro 2017). 

Later Years: 1961–1967 

The limiting external exposure scenario during the remainder of the second AWE period (1961–1967) 

was an operator exposed to uranium-plutonium carbide pellets in a glovebox. The Hp(10) photon and 

neutron doses were calculated by NIOSH, using the MCNP6 radiation transport code. As discussed in 

our previous memo (Anigstein and Mauro 2017), we had several concerns over the MCNP6 model that 

was the basis of the NIOSH analyses. These issues notwithstanding, we wished to determine if the 

MCNP6 results were correctly implemented in the example DRs.

The MCNP6 input and output files are found on the restricted DCAS website; a report of the MCNP6 

analyses was presented in Attachment 1 to “Carborundum DR Methodology: July 23, 2015” in the same 

location.6

 In the course of our previous review (Anigstein 2016), we audited the MCNP6 analyses and 

confirmed that they correctly embodied the assumptions presented in that report. We also inspected the 

Hp(10) tally results for photons and neutrons in the various energy ranges that were listed in Tables 7–9 

of the attachment and confirmed that they were correctly copied from the MCNP6 output files. 

6 This document will henceforth be referred to as “DR Methodology.”

The MCNP6 tallies were compiled in units of pSv/s and comprised doses from a single fuel pellet. 

Tomes (2017, Table 4) listed annual external doses from photons and neutrons in the same energy 

ranges to four categories of workers. The source was assumed to be a batch of fuel pellets that contained 

100 g of elemental plutonium, the maximum amount of plutonium that could be handled in the glovebox 

at any one time, according to safety regulations in place at Carborundum at that time. To derive the dose 

rates to an operator, we need to determine the number of pellets in such a batch. The first step is to 

determine the mass fraction of plutonium in the fuel—this calculation is shown in Table 2. 

Table 2. Determination of Plutonium Mass Fraction in Fuel Pellet

Nuclide Atomic number

density AW Atomic massdensity Pu mass fraction

C-12 3.05E+22 12 3.66E+23 –

C-13 3.30E+20 13.00335 4.29E+21 –

Pu-239 5.76E+21 239.0522 1.38E+24 1.79E-01

Pu-240 3.62E+20 240.0538 8.69E+22 1.13E-02

Pu-241 3.51E+19 241.0569 8.46E+21 1.10E-03

Am-241 1.83E+18 241.0568 4.41E+20 –

 
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Nuclide Atomic number

density AW Atomic massdensity Pu mass fraction

U-234 1.25E+17 234.041 2.93E+19 –

U-235 9.23E+19 235.0439 2.17E+22 –

U-238 2.45E+22 238.0508 5.83E+24 –

Total 7.70E+24 1.91E-01

The table lists the atomic number density, in atoms/cm3, of each nuclide in the fuel pellet that was 

copied from GloveBox.Pu_U_Carbide.photon.R00.i, one of the MCNP6 input files. This value was 

multiplied by the atomic weight to yield the atomic mass density of each nuclide. Dividing the atomic 

mass density of each plutonium isotope by the total atomic mass density of all constituents of the fuel 

pellet yields the mass fraction of each isotope. The sum of these mass fractions is 0.191, the mass 

fraction of plutonium in the fuel pellet. This analysis shows that the maximum batch of fuel that can be 

handled at any one time was 523 g (100 g ÷ 0.191 ≈ 523 g). GloveBox.Pu_U_Carbide.photon.R00.o, 

one of the MCNP6 output files, listed the mass of one pellet as 1.33355 g, which means that one batch 

could contain ≈ 392 pellets (523 g ÷ 1.33355 g/pellet ≈ 392 pellets). 

We used the Hp(10) tally results at 35 cm for photons and neutrons in the various energy ranges that 

were listed in Tables 7–9 of Attachment 1 to “DR Methodology” to derive annual external doses to an 

operator. We first converted the tally results, listed in pSv/s per pellet, to mrem/h, then multiplied these 

results by the number of pellets in one batch to obtain the hourly dose rate from a batch of pellets. The 

operator was assumed to spend 50% of his time at the glovebox. Assuming a 2,000-h work year, the 

operator would have been exposed for 1,000 h/y. We compared our results to the annual doses to an 

operator listed by Tomes (2017, Table 4). The results are shown in Table 3 of this memo. 

Table 3. Annual Hp(10) Doses to Glovebox Operators (rem) 

Energy range NIOSHa SC&A Δb

Photons

<30 keV 1.074 1.108 -3.1%

30-250 keV 2.166 2.235 -3.1%

>250 keV 1.258 1.298 -3.1%

Neutrons

10-100 keV 0.001 0.001 ─

0.1-2 MeV 0.109 0.113 -3.5%

2-20 MeV 0.183 0.189 -3.0%

a Tomes (2017, Table 4)

b NIOSH ÷ SC&A - 1 

As shown in the table, all the NIOSH doses are approximately 3% lower than the doses calculated by 

SC&A. Since both analyses utilized the same MCNP6 results, and since the differences are consistent, 

given the number of significant figures displayed by Tomes (2017, Table 4), we surmise that the 

difference is due to a difference in the assumed number of fuel pellets in the glovebox. It would be 

helpful if NIOSH were to present its derivation of the dose rates based on the MCNP6 results so that this 

discrepancy could be resolved. 

NIOSH converted the Hp(10) photon dose rates in the <30–keV energy range to organ doses by applying 

the DCFs for plutonium listed by Allen (2011, Table 4.1a). (We note that Allen displayed two tables, 

both numbered 4.1a. The DCFs in question were listed in the first of these tables.) Since these DCFs had 
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fixed values, the resulting organ doses were entered into the IREP input file as constant distributions. 

The Hp(10) doses from photons in the 30–250 keV and >250-keV energy ranges were multiplied by the 

minimum, effective, and maximum DCFs for each energy range. The resulting triplets of doses were 

entered into the IREP input file as the minima, modes, and maxima of triangular distributions. 

A similar procedure was followed for the neutron doses from the pellets. Although six energy ranges 

were included in the analyses, only doses from neutrons in the 10–100 keV, 0.1–2 MeV, and 2–20 MeV 

ranges resulted in dose rates of ~1 mrem/y or greater, so only these three ranges were included in the 

dose assessment. In each case, a triplet of doses were calculated in the same manner as for the photon 

doses discussed above and entered into the IREP input file as the parameters of triangular distributions.

We confirmed that the NIOSH Hp(10) doses listed in Table 3 of this memo were correctly converted to 

organ doses, notwithstanding the discrepancies in the Hp(10) dose calculations.

2.1.4 Second Residual Period

The uranium operations during the first and second AWE periods were most likely carried out in 

separate areas of the Carborundum plant. In the present example, the worker was assigned external 

doses from the residual contamination from the first AWE period during the years 1968–1980, which 

end with the termination of his employment. We confirmed that the exposure rates were calculated by 

applying Sharfi’s (2012, Table 4-2) depletion factors to the initial exposure rate during the first residual 

period. The resulting exposures are higher than those resulting from the residual contamination from the 

second AWE period; therefore, assigning external doses from the residual contamination from the first 

AWE period was correct and claimant favorable. The external doses to the kidneys were calculated in 

the same manner as the doses during the first residual period and entered into the IREP input file as the 

median values of lognormal distributions with a GSD of 5. As shown in Table 1 of this memo, these 

doses do not account for the energy distributions of photons from uranium-contaminated air and surfaces 

listed by Allen (2011), and also reflect the erroneous assumption of an exposure duration of 2,500 h/y, 

instead of 2,000 h/y that was assumed by Allen for this time period. However, all the median annual 

doses during the second residual period are <0.04 mrem and consequently do not need to be considered 

in the DR.

2.2 Exposure to Medical X Rays

The dose from medical x rays was assigned for each year of employment during the two AWE periods 

as a normal distribution with a mean of 0.025 rem. This is the dose to organs such as the urinary bladder, 

listed by Thomas (2011, Table A-7), rather than the dose to the liver, the surrogate organ for external 

exposure to the kidneys, which was used in assigning doses to the kidneys from other sources of external 

photon radiation. An examination of the anatomical drawing presented by Thomas (2011, Fig. 2) shows 

that the kidneys are just below the liver and are much closer to the x-ray beam used to examine the lungs 

than is the bladder, which is much lower in the body and thus further from the collimated beam. The 

dose to the liver was listed as 0.0902 rem in Table A-7. The standard deviation (σD) assigned to this 

distribution was 0.0075 rem, which corresponds to an uncertainty of ±30% in the mean dose, consistent 

with the guidance of Thomas (2011). Since σD was calculated on the basis the incorrect mean dose, both 

the mean dose and σD need to be corrected.
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2.3 Internal Exposure

2.3.1 Intakes

First AWE Period

NIOSH assigned the worker an inhaled intake of natural uranium aerosols of 43,632 dpm per calendar 

day during the first AWE period, which is the same as the value of 19,654 pCi/d listed by Allen (2011, 

Table 7.8) for a uranium machining operator prior to 1951. NIOSH likewise assigned an ingestion rate 

of 895 dpm per calendar day to the worker during this period, which is the same as the rate of 403 pCi/d 

listed by Allen (2011, Table 7.9) for the same exposure scenario. 

First Residual Period

NIOSH used the areal activity concentrations during the first residual period, discussed in section 2.1.2 

of this memo, to calculate the uranium aerosol concentrations by assuming a resuspension factor of 

1 x 10-5 m-1. NIOSH then calculated the inhaled intake per calendar day, assuming an exposure duration 

of 2,500 h/y. As stated earlier, this is inconsistent with the assumption of 2,400 h/y used for external 

exposure during the first AWE period, and with Allen’s (2011) assumptions of annual exposure 

durations of 2,200 h in 1951–1955 and 2,000 h after 1955. NIOSH assigned an ingestion rate of 

895 dpm/d to the worker during the first year of the residual period and reduced the rate using the 

depletion factors listed by Sharfi (2012, Table 4-2), but again failed to adjust for the shorter exposure 

durations after 1950.

We confirmed that the intakes listed by Tomes (2017, Tables 8–9) were consistent with the methodology 

described above. The worker in the present example was assigned these intakes during the first AWE 

period and during the first residual period. The post-1950 intakes were elevated due to the incorrect 

annual exposure durations. 

Second AWE Period—Early Years: 1959–1960

NIOSH based the uranium intakes during 1959–1960, the first two years of the second AWE period, on 

aerosol activity concentrations measured during two surveys performed by the Health and Safety 

Laboratory (HASL) of the Atomic Energy Commission in 1959 and 1961 (HASL n/d). Using the 

regression of order statistics (ROS) method prescribed by Brackett (2005), NIOSH derived a 95th

percentile activity concentration of 7.384 dpm/m3. This resulted in an inhaled intake rate of 48.55 dpm 

per calendar day by a worker in the general labor category. Twice that value (97.10 dpm/d) was assigned 

to an operator, which is consistent with the default ratio of intakes by an operator to those of a general 

laborer specified by Allen (2011). We confirmed that these inhaled intakes, which were listed by Tomes 

(2017, Table 10), are consistent with the methodology described by NIOSH. Tomes also listed the 

ingestion rates of the operator and general laborer as 1.94 and 0.971 dpm per calendar day, respectively. 

As shown in the DCAS file Carborundum dose calculations_draft 3-2-17.xlsx, these values were 

derived by multiplying the inhaled intakes per calendar day by a factor of 0.02. This calculation is 

inconsistent with the guidance of Neton (2004), who stated: “The amount of activity ingested on a daily 

basis can be approximated by assuming it to be 0.2 times the activity per cubic meter of air.” Applying 

that methodology to the activity concentrations cited above results in ingested intake rates of 1.01 dpm 
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per calendar day by the general laborer and 2.02 dpm/d by the operator, approximately 4% higher than 

Tomes’ values.

The uranium intakes were assumed to include contaminants found in recycled uranium, as listed by 

Allen (2011, Table 3.2). This assumption is consistent with Allen’s guidance that uranium processed 

after 1953 might include such contaminants. The uranium activity concentrations were derived from the 

HASL sample analyses, while the activity concentrations of the contaminants were calculated by 

multiplying the uranium activities by the factors listed by Allen and reproduced by Tomes (2017, 

Table 11). Since the uranium activity was derived from air dust samples that were presumably assayed 

for total alpha, which might have included the alpha-emitting contaminants, this might appear to be 

double accounting, since 234U was assigned a multiplier of 1 and the activities of the other radionuclides 

were added to the mix. However, since it is not known whether the other nuclides were in fact present, 

and since some of these nuclides may have lower DCFs than 234U for certain organs, such double 

accounting is prudent and claimant favorable. 

Second AWE Period—Later Years: 1961–1967 

To determine the source term for internal exposure during the later years of the second AWE period 

(1961–1967), NIOSH compared the doses from uranium intakes derived from the analyses of HASL 

samples collected on 11/9/1959 and 4/5/1961 to doses from intakes of plutonium derived from HASL 

samples collected on 4/5/1961 and 6/7/1961. Tomes (2017, Table 12) listed the intakes of plutonium by 

workers in the various job categories; he listed the isotopic composition of the plutonium aerosols in 

Table 13. NIOSH found that the uranium intakes resulted in higher doses to the kidneys and therefore 

assigned only those intakes in the example DR. We performed scoping calculations in which we 

multiplied the listed intakes of uranium and plutonium by the respective equivalent dose coefficients for 

the kidneys at various times after an acute intake, extracted from ICRP (2001). We found that the 

uranium intakes resulted in doses to the kidneys that were at least 3-fold higher than those from the 

plutonium intakes, thus confirming the NIOSH finding.

However, we find that it is illogical to assume that the worker was externally exposed to the fabrication 

of uranium-plutonium pellets, but that his intakes consisted only of uranium aerosols. He clearly would 

have been exposed to airborne plutonium in the course of his work. However, he may also have been 

exposed to intakes of uranium. The fact that the fuel pellets contained approximately 80% uranium and 

20% plutonium shows that the two materials were handled simultaneously. 

According to the NIOSH report of an interview with a former Carborundum workers, , cited 

in our previous review (Anigstein 2016): 

When the work was first started people were not familiar with the dangers of working 

with any of the material. There were 50-80 pounds (estimate) of uranium powder in a 

metal cage. The uranium oxide powder was screened and people had to wipe it off the 

desks. (ORAUT 2015) 

This clearly indicates that uranium contamination was present in various areas of the facility. We also 

note that the HASL surveys performed on 4/5/1961 measured both uranium and plutonium—the 

samples analyzed for uranium were collected 20 minutes after the collection of the last sample for 

plutonium analysis; however, the locations of these samples were not clearly identifiable on the survey 
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reports (HASL n/d). The plutonium sample sheet has the notation: α – count + chemistry (the last word 

is only partly legible). This indicates that the plutonium was assayed after chemical separation, so 

uranium might have been part of the original sample. It is therefore not possible to rule out intakes of 

both radionuclides by the same worker. As stated in our previous review (Anigstein 2016, section 5.2.2), 

we recommend that NIOSH assign intakes of both uranium and plutonium in calculating internal doses. 

Anticipating the use of plutonium intake data in future DRs, we reviewed the plutonium intake rates 

listed by Tomes (2017, Table 12). NIOSH correctly derived the plutonium aerosol activity 

concentrations by applying the ROS method, obtaining a value of 1.163 dpm/m3, as shown in the DCAS 

file Carborundum dose calculations_draft 3-2-17.xlsx. Tomes used this value to correctly derive the 

inhalation rate of 7.65 dpm per calendar day listed in Table 12. The plutonium ingestion rates were 

derived by multiplying the inhaled intakes per calendar day by a factor of 0.02, which, as stated earlier, 

is inconsistent with the guidance of Neton (2004): The ingested intakes per calendar day should be equal 

to 20% of the activity in 1 m3 of air.

We also reviewed the assumed isotopic ratios of plutonium and americium in the plutonium aerosols 

listed by Tomes (2017, Table 13). This table was copied from a table titled “Plutonium Mixture Isotopic 

to Total Alpha Activity Ratios” in “DR Methodology.” In our previous review (Anigstein 2016, section 

5.2.2), we stated that 

“DR Methodology” assigns isotopic ratios to plutonium based on a preliminary planning 

report (Taylor 1960) that was issued prior to the actual start of plutonium operations, 

which listed the composition of plutonium obtained from the Dow Chemical Company. . . 

However, according to Strasser and Taylor (1962 . . .), during the period of 

September 15, 1961 to December 31, 1961, fuel pellets were produced from powder 

prepared by Hanford Atomic Products Operations. 

We found that use of the Hanford fuel isotopic ratios was consistent with the historical record and was 

also claimant favorable, since intakes with the isotopic composition of either fresh or 5-y-old Hanford 

fuel led to higher effective doses than those in the plutonium from Dow (Anigstein 2016, Table 1). We 

had previously recommended that NIOSH adopt either the fresh or the 5-y-old Hanford fuel isotopic mix 

as the source for both internal and external doses, whichever produces the highest total dose. 

Second Residual Period

During the second residual period, residual uranium contamination levels from uranium operations 

during the first AWE period were higher than those from the second AWE period. In the present 

example, the worker was assigned intakes from the residual uranium contamination from the first AWE 

period during the years 1968–1980, which end with the termination of his employment. In this case, it 

was not necessary to assign intakes from residual plutonium contamination, since such intakes, even 

combined with intakes of uranium residues from the second AWE period, would lead to lower doses 

than from intakes of uranium residues from the first AWE period. Since the plutonium contamination 

was most likely confined to the plutonium production areas, it would not have been present in areas used 

for uranium operations during the first AWE period. As was the case with the intakes during the first 

residual period, NIOSH calculated these inhaled intakes by applying Sharfi’s (2012, Table 4-2) 

depletion factors to the calculated intake during the first year of the first residual period, which 

incorporated the erroneous assumption of 2,500 work hours per year. Similarly, NIOSH calculated the 
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ingested intakes by applying the depletion factors to the pre-1951 ingestion rates, which were based on a 

2,400-h work year, but failed to account for a 2,000-h year after 1955. 

2.3.2 Internal Doses

First AWE Period and First Residual Period

We audited the internal doses to the kidneys from the source terms described above by performing 

independent calculations using integrated doses derived from the DCAL (Dose and Risk Calculation) 

computer code (ORNL 2010). This totally independent methodology allows us to audit the doses using 

the same International Commission on Radiological Protection (ICRP) models and parameters that are 

employed by IMBA (Integrated Modules for Bioassay Analysis). We first compared the internal doses

to the kidneys in the years 1943–1992 from intakes of uranium during the first AWE period and the first 

residual period listed by Tomes (2017, Table 9). These doses were listed in entries 75–124 in the DCAS 

file IREP input Carborundum Example_kidney_3-2-17.xls. We found very good agreement between the 

two sets of calculations. We next calculated the doses from the intakes during the same period, corrected 

for shorter exposure durations in the years following 1950: The annual NIOSH doses were up to 3% 

higher than our values. 

Second AWE Period

We also performed independent assessments of the doses to the kidneys resulting from intakes of 

uranium during the second AWE period, which were listed in entries 125–158 in IREP input 

Carborundum Example_kidney_3-2-17.xls. In order to verify the NIOSH calculations, we based our 

analyses on the uranium intake rates discussed in section 2.3.1 of this memo, omitting contributions 

from plutonium intakes that we found should be included in the assessment. We obtained very good 

agreement with the NIOSH calculations, despite the discrepancy in the ingestion rate. Because the 

ingested intake is a small fraction of the total intake and the DCF for the kidneys by the ingestion 

pathway is smaller than that for inhalation, the ingested intakes have only a minor impact on the doses in 

this case. 

We recommend that NIOSH correct the ingestion rate in the interest of consistency. More important, 

doses from intakes of plutonium, using a revised isotopic mixture, should be added to those from 

uranium. 

Second Residual Period

We performed independent assessments of the doses to the kidneys resulting from intakes of uranium 

during the years 1968–1980, part of the second residual period, which were listed in entries 176–200 in 

IREP input Carborundum Example_kidney_3-2-17.xls. As expected, the NIOSH values are almost 25% 

higher than those we calculated, due to the incorrect annual work hours during this period. However, the 

total median dose from these intakes calculated by NIOSH is ~10 mrem, so the error has little 

significance in the present example.
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3 Example B2 

Example B2 was the case of a male maintenance worker who was employed at Carborundum from 1953 

through 1980 and was diagnosed with cancer of the lung on December 31, 1992. His period of 

employment spanned the second AWE period and parts of the two residual periods. Because of his job 

description, NIOSH assigned him doses to a general laborer.

We first examined the external annual doses assigned to this worker. 

3.1 External Doses

3.1.1 First Residual Period

NIOSH calculated the external doses to the lungs during 1953–1958 from exposures to a uraniumcontaminated floor and submersion in uranium-contaminated air, as discussed in section 2.1.2 of this 

memo. The same issues that were noted previously apply in this case: 

• NIOSH assumed all photons to be in the 30–250 keV energy range instead of using the energy 

distributions specified by Allen (2011), cited in section 2.1.2. 

• NIOSH assumed an annual exposure duration of 2,500 hours, instead of using a 2,200-h work 

year during 1953–1955 and a 2,000-h year after 1955, as assumed by Allen (2011). 

As was the case with example B1, we were able to replicate the NIOSH dose calculations.

3.1.2 Second AWE Period

Early Years: 1959–1960 

In the present example, the limiting external exposure scenario during 1959–1960 for a worker in the 

general labor category was a technician operating the XRD apparatus. As discussed in our previous 

memo (Anigstein and Mauro 2017), NIOSH assigned an annual exposure of 0.167 R to a worker from 

this scenario. Our memo discussed the issues we found with the NIOSH assessment of this scenario. In 

the present example, NIOSH calculated the lung dose using the DCF for the lungs for 30–250 keV 

photons of 0.986 rem/R to obtain a dose rate of 0.165 rem/y, which was entered into the IREP input file 

as a constant distribution. We were able to replicate the NIOSH calculation.

As described in our memo (Anigstein and Mauro 2017), we derived an exposure rate of 1.033 R/y in this 

scenario. Given a photon energy of ~8 keV, the appropriate effective DCF for the lungs for the <30 keV 

range, listed by OCAS (2007), is 0.100 rem/R. This results in an annual dose to the lungs of 0.103 rem, 

less than the dose calculated by NIOSH.

We compared this dose to the alternate exposure scenario during this time period: a general laborer 

exposed to a flat uranium plate. As listed in the DCAS worksheet [Carborundum dose 

calculations_draft 3-2-17.xlsx]External-U Operations!, the deep dose rate from this scenario is 

27.8 mrem/y. Assuming a 30–250 keV energy range, we obtained a lung dose of 19.3 mrem/y. We 

therefore agree with NIOSH’s selection of the exposure to the XRD apparatus as the limiting external 

exposure scenario during 1959–1960. 
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Later Years: 1961–1967 

The limiting external exposure during the remainder of the second AWE period, 1961–1967, was that of 

a general laborer exposed to uranium-plutonium carbide pellets in a glovebox. The issues raised in the 

discussion of the doses to an operator in this scenario, presented in section 2.1.3 of this memo, apply in 

the present instance. Furthermore, we found an additional discrepancy in two of the hourly photon dose 

rates to the laborer listed by Tomes (2017, Table 4). These dose rates, from <30-keV and >250-keV 

photons, were listed in “DR Methodology,” as 0.120 and 0.154 mrem/h, respectively, while the values 

listed by Tomes and used in the example DR calculations were 0.127 and 0.149, 6% greater and 3% 

lower, respectively, than the “DR Methodology” values. 

We used the Hp(10) tally results at 100 cm for photons and neutrons from a single pellet in the various 

energy ranges, listed in Tables 7–9 of Attachment 1 to “DR Methodology,” to derive annual external 

doses to a laborer in a manner similar to that used to calculate external doses to the glovebox operator. 

We compared our results to the annual doses to a laborer listed by Tomes (2017, Table 4). The results 

are shown in Table 4 of this memo. As shown in the table, the NIOSH doses range from approximately 

6% lower to 3% higher than the doses calculated by SC&A. However, when we compared our results to 

those listed in “DR Methodology,” we found that the latter results were approximately 3% lower, similar 

to the comparison of doses to the glovebox operator displayed in Table 3. This reinforces our hypothesis 

that the differences between our results and those in “DR Methodology” are due to differences in the 

calculated number of fuel pellets in the glovebox, while the additional differences between our results 

and Tomes’ results for <30-keV and >250-keV photons are due to an error in transcribing the “DR 

Methodology” values. 

Table 4. Annual Hp(10) Doses to Laborer Exposed to Glovebox Operations (rem) 

Energy range NIOSHa SC&A Δb 

Photons

<30 keV 0.127 0.124 2.7%

30-250 keV 0.256 0.265 -3.5%

>250 keV 0.149 0.159 -6.2%

Neutrons

10-100 keV 0.0001 0.0001 ─

0.1-2 MeV 0.0134 0.0139 -3.5%

2-20 MeV 0.0225 0.0231 -2.7%

a Tomes 2017, Table 4

b NIOSH ÷ SC&A - 1 

3.1.3 Second Residual Period

As was discussed in section 2.1.4, the external exposures during the second residual period from residual 

contamination from the first AWE period were higher than those from residual contamination from the 

uranium operations during the second AWE period. As in the previous example, the worker was 

assigned doses from the area with the higher exposures, which end with the termination of his 

employment.

The external doses to the lungs were calculated in the same manner as the doses during the first residual 

period and entered into the IREP input file as the median values of lognormal distributions with a GSD 
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of 5. As shown in Table 1 of this memo, these doses do not account for the energy distributions of 

photons from uranium-contaminated air and surfaces listed by Allen (2011), and also reflect the 

erroneous assumption of an exposure duration of 2,500 h/y, instead of 2,000 h/y, which is appropriate 

for this time period. However, all the median annual doses during the second residual period are <0.03 

mrem and consequently do not need to be considered in the DR.

3.1.4 Doses From Medical X Rays

Doses from medical x rays were assigned for each year of employment during the second AWE period 

as a normal distribution with a mean of 0.0838 rem, which was the dose listed by Thomas (2011, 

Table A-7) for the lungs, and σD = 0.01675 rem, which corresponds to an uncertainty of ±20%. This is 

inconsistent with the guidance of Thomas (2011, section 8.0), who recommended an uncertainty 

of ±30%. This discrepancy needs to be corrected.

3.2 Internal Exposure

3.2.1 Intakes

First Residual Period

NIOSH assigned intakes of uranium dust during 1953–1958 to the worker in the present example that 

were the same as those described in section 2.3.1 of this memo. As discussed previously, these intakes 

were elevated because NIOSH incorrectly assumed an exposure duration of 2,500 h/y, which is 

inconsistent with Allen’s (2011) assumption of a 2,200-h work year in 1951–1955 and a 2,000-h year 

after 1955. 

Second AWE Period—Early Years: 1959–1960

As described in section 2.3.1 of this memo, NIOSH used uranium aerosol activity concentrations 

measured by HASL to derive a 95th percentile activity concentration of 7.384 dpm/m3. This resulted in 

an inhaled intake rate of 48.55 dpm per calendar day by a worker in the general labor category (Tomes 

2017, Table 10). Tomes also listed the ingestion rate of the general laborer as 0.971 dpm per calendar 

day which, as discussed previously, is inconsistent with the guidance of Neton (2004): The ingested 

intakes per calendar day should be equal to 20% of the activity in 1 m3 of air. Applying that 

methodology to the activity concentrations cited above results in an ingested intake rate of 1.01 dpm 

calendar day by the general laborer. As in the previous example, the uranium intakes were assumed to 

include contaminants found in recycled uranium.

Second AWE Period—Later Years: 1961–1967

As in the previous example, NIOSH concluded that intakes from uranium operations during the later 

years of the second AWE period (1961–1967) produced higher doses to the lungs than intakes of 

plutonium. We performed scoping calculations in which we multiplied the listed intakes of uranium and 

plutonium by the respective equivalent dose coefficients for the lungs at various times after an acute 

intake, extracted from ICRP (2001). We found that the uranium intakes resulted in doses to the lungs 

that were more than 10-fold higher than those from the plutonium intakes. thus confirming the NIOSH 

conclusion. However, as discussed in section 2.3.1 of this memo, we find that it is illogical to assume 
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that the worker was externally exposed to the fabrication of uranium-plutonium pellets, but that his 

intakes consisted only of uranium aerosols. We recommend that NIOSH assign intakes of both uranium 

and plutonium in calculating internal doses from this scenario. 

Second Residual Period

As was discussed in section 2.1.4, the contamination levels during the second residual period from 

residual contamination from the first AWE period were higher than those from residual contamination 

from the uranium operations during the second AWE period. As in the previous example, the worker 

was assigned intakes from the area with the higher exposures during the years 1968–1980, which end 

with the termination of his employment. As was discussed previously, these inhaled intakes incorporated 

the erroneous assumption of 2,500 work hours per year. Similarly, the ingested intakes were based on a 

2,400-h work year. The assigned intakes via both pathways failed to account for the 2,000-h work year 

after 1955 assumed by Allen (2011).

3.2.2 Internal Doses

First Residual Period

We audited internal doses to the lungs from the source terms described above by performing 

independent calculations, as described in section 2.3.2. We compared the internal doses to the lungs in 

the years 1953–1992 from intakes of uranium during the first residual period, corrected for shorter 

exposure durations in the years following 1950, to the doses calculated by NIOSH that were listed in 

entries 64–103 in the DCAS file IREP input Carborundum Example_lung 3-2-17.xls. These differences 

resulted in annual NIOSH doses that were 13%–20% higher than our values. 

Second AWE Period

We also performed independent assessments of the doses to the lungs resulting from intakes of uranium 

during the second AWE period, which were listed in entries 104–137 in IREP input Carborundum 

Example_ lung 3-2-17.xls. We based our analyses on the uranium intake rates discussed in section 2.3.1 

of this memo, again omitting contributions from plutonium intakes that we found should be included in 

the assessment. We found that all but one of the annual doses calculated by NIOSH were 99% higher 

than our values. Inspecting the DCAS workbook [CAD_222224_lung U 1959-1967.xls]222224!, we 

found that NIOSH had erroneously assigned this worker an inhaled intake rate of 97.10 dpm per 

calendar day, which, according to Tomes (2017, Table 10), is the intake rate of an operator, rather than 

the 48.55 dpm/d intake rate of a laborer. In like manner, the worker was assigned an ingested intake rate 

of 1.94 dpm/d, which Tomes listed as the intake rate of an operator. 

Second Residual Period

We performed independent assessments of the doses to the lungs resulting from intakes of uranium 

during the years 1968–1980, part of the second residual period, which were listed in entries 172–196 in 

IREP input Carborundum Example lung_3-2-17.xls. As expected, the NIOSH values were about 25% 

higher than those we calculated, due to the incorrect annual work hours during this period. 

NIOSH should correct the discrepancies in the intakes used in this example DR.
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4 Results and Conclusions

Based on our audit, we found that we understood the methods used by NIOSH and that we could 

replicate the NIOSH dose calculations with reasonable accuracy. However, we found several instances 

of errors and inconsistent assumptions in the example DRs.

4.1 Findings

4.1.1 Inconsistent Annual Exposure Durations

The inhaled intakes and external exposures to uranium-contaminated air and surfaces during the first and 

second residual periods were based on an annual exposure duration of 2,500 h. This is inconsistent with 

the pre-1951, 1951–1955, and post-1955 exposure durations of 2,400, 2,200, and 2,000 h, respectively, 

that were assumed by Allen (2011) and that were used by NIOSH to calculate doses during the first and 

second AWE periods. The ingested intakes during the first residual period after 1950 and during the 

second residual period were incorrectly based on the pre-1951 exposure durations of 2,400 h/y, failing to 

account for the shorter durations in subsequent years. 

4.1.2 Incorrect Probability Distributions of Doses from External Exposure to Uranium Metal

The doses from uranium-handling operations during 1959–1960 in Example B1 were entered into IREP 

as constant values. This is inconsistent with the use of a lognormal distribution with a GSD of 5, as 

prescribed by Allen (2011, section 6.4), and with the distribution of doses from external exposure to 

uranium metal that was assigned to the same hypothetical worker during the first AWE period, which 

does follow Allen’s guidance. 

4.1.3 Incorrect Source Term and Glovebox Model Used in MCNP6 Dose Analysis

Anigstein (2016, Appendix B) presented a critical discussion of the glovebox model and the uraniumplutonium-americium source term used in the MCNP6 assessment of external doses from uraniumplutonium fuel pellets handled in a glovebox. In the context of reviewing the NIOSH SEC petition 

evaluation report, this issue did not rise to the level of a finding: We determined that NIOSH was 

capable of performing such an assessment and, in fact, furnished an alternative MCNP analysis with 

revised input data which could provide the basis for such an assessment. As an issue for present and 

future DRs, however, this does constitute a finding, since our analysis yielded photon dose rates to the 

operator that were approximately 50% higher than the NIOSH results. 

4.1.4 Incorrect Doses from Medical X Rays

In Example B1, doses to the kidneys from medical x rays were based on doses to organs such as the 

urinary bladder, rather than the dose to the liver, the surrogate organ for external exposure of the 

kidneys. In Example B2, doses from medical x rays were assigned an uncertainty of ±20% rather than 

the uncertainty of ±30% recommended by Thomas (2011). 
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4.1.5 Workers Externally Exposed to Glovebox Operations Should be Assigned Intakes of both 

Uranium and Plutonium

We find it to be illogical to assume that a worker who was externally exposed to the fabrication of 

uranium-plutonium pellets would be assigned intakes that consisted only of uranium aerosols. Anigstein 

(2016, section 5.2.2) recommended that NIOSH assign intakes of both uranium and plutonium in 

calculating internal doses. In the context of reviewing the NIOSH SEC petition evaluation report, this 

issue did not rise to the level of a finding: We determined that NIOSH had the data necessary to perform 

such an assessment. As an issue for present and future DRs, this does constitute a finding, since intakes 

of plutonium can make significant contributions to internal doses. 

4.1.6 Incorrect Uranium Intakes by Laborer During Second AWE Period

NIOSH incorrectly used intakes of uranium dust assigned to an operator during the second AWE period 

to calculate the internal doses to a worker classified as a laborer in Example B2, which approximately

doubled the doses. 

4.2 Observations 

We have observations on two aspects of dose assessments that have minor impacts on the doses in the 

present examples, but that are inconsistent with guidance in other NIOSH technical documents. 

4.2.1 Energy Distributions of Photons from Uranium-Contaminated Air and Surfaces

NIOSH calculated the doses from external exposure to a uranium-contaminated surface, and the much 

smaller exposure from submersion in uranium-contaminated air, using fixed values of the exposure-toorgan-dose DCFs for 30–250 keV photons. This is inconsistent with the energy distributions of photons 

from these two sources cited by Allen (2011), who noted that most of the exposures from both sources 

are due to photons with energies <30 keV. As shown in Table 1 of this memo, using this method in 

Example B1 results in a 3-fold increase in the dose to the kidney. NIOSH should either explicitly 

incorporate Allen’s energy distributions in its dose assessment, or discuss why the method used in the 

example DR represents an acceptable, claimant-favorable simplification. Although this has but a small 

impact on the total dose in Example B1—an increase of 35 mrem in a total dose of ~35 rem—and an

even smaller impact in Example B2, NIOSH should ensure that such an approach, if it were to be used, 

is applied uniformly in fairness to claimants from other sites.

4.2.2 Estimates of Ingestion Rates Based on Air Concentrations 

The ingestion rates in the example DRs during the second AWE period were derived by multiplying the 

inhaled intakes per calendar day by a factor of 0.02. This is inconsistent with the guidance of Neton 

(2004): The ingested intakes per calendar day should be equal to 20% of the activity in 1 m3of air. The 

ingestion rates during the second AWE period are approximately 4% lower than those derived according 

to Neton. This has a very small impact on the total doses, since the intakes by ingestion are much lower 

than by inhalation, and since the DCFs in most cases are lower for the ingestion pathway. Nevertheless, 

we recommend that NIOSH be consistent in its intake calculations.
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