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SEC Petition Evaluation Report

Petition SEC-00103

Report Rev #: Addendum Report Submittal Date: April 28, 2010

Subject Expert(s): Mike Mahathy, Robert Morris, Bryce Rich, Leo Faust, Sam Chu, Mel 

Chew

Site Expert(s): N/A

Petitioner Administrative Summary

Petition Under Evaluation 

Petition # Petition 

Type

Petition A 

Receipt Date DOE/AWE Facility Name

SEC-00103 83.13 March 4, 2008 Savannah River Site (SRS)

Class Evaluated by NIOSH

All construction workers who worked in any area at the Savannah River Site from January 1, 1953 through 

December 31, 1965.

NIOSH-Proposed Class(es) to be Added to the SEC

None. 

Related Petition Summary Information 

SEC Petition Tracking #(s) Petition Type DOE/AWE Facility Name Petition Status

NONE

Related Evaluation Report Information

Report Title DOE/AWE Facility Name

SEC Petition Evaluation Report, SEC-00103 Savannah River Site (SRS)

ORAU Lead Technical Evaluator: Mike Mahathy ORAU Review Completed By: Daniel Stempfley

Peer Review Completed By: [Signature on file] 5/3/2010 

Timothy Taulbee Date

SEC Petition Evaluation Reviewed By: [Signature on file] 5/4/2010 

J. W. Neton Date

SEC Evaluation Approved By: [Signature on file] 5/4/2010 

Stuart L. Hinnefeld Date
SEC-00103 Addendum 04-28-10 Savannah River Site

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SEC-00103 Addendum 04-28-10 Savannah River Site

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Addendum to Savannah River Site (SEC-00103) 

Special Exposure Cohort Evaluation Report

NIOSH presented a Special Exposure Cohort (SEC) evaluation report (NIOSH, 2008) regarding the 

Savannah River Site (SRS) to the Advisory Board on Radiation and Worker Health (Advisory Board) 

during the Advisory Board’s meeting held from December 16-18, 2008. In its report, NIOSH 

evaluated the feasibility of reconstructing radiation doses of construction workers who worked in any 

area at SRS during the time period of January 1, 1950 through December 31, 2007. The feasibility of 

reconstructing doses received from thorium exposure from the start-up of thorium operations in 1953 

through 1959 was reserved in the evaluation report while NIOSH continued to evaluate approaches for 

bounding doses from thorium exposures during that time period. This evaluation report addendum 

provides NIOSH’s evaluation of the reserved thorium work, thus completing its evaluation of the 

worker class for SEC-00103. 

NOTE: This Evaluation Report Addendum only addresses those sections in the Savannah River 

Site Evaluation Report that require discussion; therefore, the section numbering is not contiguous. 

The sections requiring additional thorium discussion begin below. 

Petition Evaluation Report Addendum Summary 

Class Evaluated by NIOSH (in this Addendum)

The feasibility of reconstructing doses received from thorium exposure from the start-up of thorium 

operations in 1953 through 1959 was reserved for further consideration in the original SEC-00103 

evaluation report. During the subsequent evaluation performed for this evaluation report and 

addendum, NIOSH has determined that similar thorium operations were conducted at SRS through 

1965; therefore, in this addendum NIOSH addresses the feasibility of bounding doses from thorium 

exposures received during the expanded time period of January 1, 1953 through December 31, 1965. 

NIOSH-Proposed Class(es) to be Added to the SEC 

NIOSH finds that potential radiation doses received from exposure to thorium at SRS from January 1, 

1953 through December 31, 1965 can be reconstructed with sufficient accuracy. NIOSH intends to 

use uranium bioassay data as a substitute for thorium bioassay for the reconstructions. The uranium 

bioassay data was statistically modeled as lognormal distributions. The 50th percentile excretion rate 

obtained for each year was used to model the daily intake rates of uranium, by mass. Based on the 

process and data comparisons presented in this Addendum, a one-to-one ratio of thorium to uranium 

was assumed and daily thorium mass intake rates were derived for 1953 through 1965. Therefore, 

NIOSH maintains its recommendation that no portion of the class evaluated in SEC-00103 be 

included in the SEC. 
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3.3 NIOSH-Proposed Class(es) to be Added to the SEC

Based on its research, NIOSH has obtained monitoring data, source term information, and process 

information that allow dose reconstructions to be performed with sufficient accuracy. Based on its 

analysis of these available resources, NIOSH found no part of the class under evaluation for which it 

cannot estimate radiation doses with sufficient accuracy.

4.0 Data Sources Reviewed by NIOSH to Evaluate the Class

ATTRIBUTION: Section 4.0 and its related subsections were completed by Mike Mahathy, Oak Ridge 

Associated Universities. These conclusions were peer-reviewed by the individuals listed on the cover 

page. The rationales for all conclusions in this document are explained in the associated text. 

NIOSH has obtained additional personal and area monitoring data for SRS since the initial evaluation 

report was published in November, 2008. Some of these data have been considered in the 

performance of this evaluation addendum and will be cited. NIOSH has also conducted additional 

interviews of former workers to obtain specific information on the use and monitoring of thorium. 

4.3 Facility Employees and Experts

NIOSH interviewed former SRS employees in order to learn about health physics practices, internal 

and external dosimetry programs, dose recording practices, and radiological incidents pertinent to 

thorium use from 1953 through 1965. 

• Personal Communication, 2009a, Personal Communication with Two Former SRS Staff Members, 

Interview by ORAU Team; December 17, 2008; SRDB Ref ID: 80280 

• Personal Communication, 2009b, Personal Communication with Two Former SRS Staff Members,

Interview by ORAU Team; December 17, 2008; SRDB Ref ID: 80281 

• Personal Communication, 2009c, Personal Communication with Former Nuclear Physicist, 

Telephone Interview by ORAU Team; June 11, 2009; SRDB Ref ID: 73085 

• Personal Communication, 2009d, Personal Communication with Former Radiation Safety 

Technician, Telephone Interview by ORAU Team; August 13, 2009; SRDB Ref ID: 73086 
SEC-00103 Addendum 04-28-10 Savannah River Site

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4.5 NIOSH Site Research Database

NIOSH has performed additional data captures at SRS since the initial evaluation report for the site 

was published in November 2008. As of August 2009, there were 3,677 documents in the Site 

Research Database (SRDB) pertaining to SRS; thus, approximately 1,400 additional documents have 

been captured, reviewed, and uploaded into the SRDB since that initial evaluation report. More than

100 documents pertained to thorium-processing, or to surface and air contamination conditions 

resulting from thorium. 

NIOSH has also obtained additional personal monitoring records for about 175 former SRS workers 

who worked in the area where thorium was processed through 1965 (Area 300M). SRDB documents 

evaluated for relevance to the thorium issue include historical background on thorium operations, 

radiological monitoring data (surface and air concentrations, personnel external and internal 

exposures), and information on the radiological controls program, monthly reports, and incident 

documentation. 

5.0 Radiological Operations Relevant to the Class Evaluated by 

NIOSH

The following subsections summarize SRS radiological operations involving thorium from January 1, 

1953 through December 31, 1965 as well as the information available to NIOSH for characterizing 

particular processes and radioactive source materials. From available resources, NIOSH has gathered 

process and source descriptions, information regarding the identity and quantities of each radionuclide 

of concern, and information describing both the processes through which radiation exposures to 

construction workers may have occurred and the physical environment in which they may have 

occurred. The information NIOSH has included within its initial evaluation report and the report’s 

addendum is intended only to be a summary of the available information. 

5.1 Savannah River Site Plant and Process Descriptions

ATTRIBUTION: Section 5.1 and its related subsections were completed by Mike Mahathy, Oak Ridge 

Associated Universities; and Robert Morris, Mel Chew and Associates, Inc. These conclusions were 

peer-reviewed by the individuals listed on the cover page. The rationales for all conclusions in this 

document are explained in the associated text.

5.1.6 300 M-Area Fabrication Facilities

Natural thorium processes at SRS are well-documented (300/M Area, 2006) and were conducted using 

the common buildings, equipment, and processing steps used to make natural uranium slugs. SRS 

canned thorium metal slugs for Hanford fuel tests in Buildings 313-M and 320-M. The first thorium 

canning campaign took place from January 1953 through March 1953; about 320 1-kg slugs were 

canned. In 1954, SRS began research and development into a small-scale production process using an 

AlSi bath to produce and encapsulate thorium metal slugs for inclusion in reactor fuel rods and 

subsequent irradiation in the SRS reactors; about 1785 slugs were canned in 1954 and 100 were 

canned in the first half of 1955. By mid-1955, the effort shifted to large-scale inspection and 
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acceptance testing of canned thorium slugs that were canned off-site by Sylvania Electric Products 

(SEP) using a hot-bonded process. The canned slugs were fabricated into fuel assemblies that were 

irradiated in various reactor charges. An air sampling log sheet documents an air sample collected in 

1955 in the Special Process Area of Building 313-M with the notation "welding 88 slugs [the code 

name for thorium slugs] and Y.C. [yellowcake uranium] about 2 feet from head of welding 

machine..." (Air Sample Log Sheets, 1955, pdf p. 60). 

In September 1956, SRS received a request to irradiate five tons (~5000 slugs) of thorium to produce 

U-233 (Monthly Report, September 1956). The plan was to produce material that would then be 

shipped to the Oak Ridge National Laboratory (ORNL) in 0.75-ton batches with minimal cooling time 

(less than 30 days after discharge) to enable testing of radiation damage to extraction solvents and to 

determine radiation levels during various stages of the extraction process (Monthly Report, February 

1957). Sylvania-Corning Nuclear Corporation (Sylcor) canned these thorium slugs (Monthly Report, 

September 1956). A total of 5200 canned slugs were to be faced, welded, bond-tested, and autoclavetested at SRS. This fuel was planned for inclusion in the reactor loads R-9, R-10 (Monthly Report, 

January 1957), R-11, and R-12 (Monthly Report, February 1957). By July 1957, eight shipping casks 

containing irradiated thorium fuel had been shipped to ORNL (Monthly Report, July 1957).

In October 1961, Sylcor was authorized to extrude and can 600 hollow thorium metal slugs for use in 

the Mark IV fuel (Monthly Report, October 1961). In 1962, Bridgeport Brass Company extruded 

43,000 kg of thorium metal that was machined and canned at Sylcor. That work resulted in 14,000 

Mark VII-T thorium slugs being delivered to SRS for inspection and use in the L-8 Mar VI-B charge 

(Plant History, 1974, pdf p. 108). Essentially, all of the irradiated thorium fuel was processed off site 

(usually at ORNL). This work continued sporadically at varying levels of production through 1963. 

In 1964, SRS installed vibratory-compaction equipment in 313-M to facilitate the production of 

thorium oxide (thoria) slugs. Subsequently, the use of off-site vendors was discontinued. [Note: The 

year 1965 was included in the class period under evaluation to allow time for removal of scrap 

material.]
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Figure 5-1 presents a graphical timeline showing the start-ups of uranium operations, thorium 

operations, and uranium bioassay. 

(a) Construction History, 1957

(b) Monthly Report, January 1953; Monthly Report, February 1953; Monthly Report, March 1953

(c) Monthly Report, January 1954; Monthly Report, February 1954; Monthly Report, March 1954; Monthly Report, April 

1954; Monthly Report, May 1954; Monthly Report, June 1954; Monthly Report, July 1954; Monthly Report, August 

1954

(d) Monthly Report, January 1955; Monthly Report, February 1955; Monthly Report, March 1955; Monthly Report, April 

1955; Monthly Report, May 1955; Monthly Report, August 1955; Monthly Report, September 1955; Monthly Report, 

November 1955

(e) Monthly Report, January 1957; Monthly Report, February 1957; Monthly Report, March 1957; Plant History, 1974

(f) Health Physics Monthly, Nov. 1953

(g) Handbook 52, 1953

(h) Operating Procedure, 1961

Figure 5-1: Start-ups of SRS Uranium Operations, Thorium Operations, and Uranium Bioassay
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Only a small number of thorium slugs were handled at SRS compared to the number of uranium slugs. 

Differences are shown in Table 5-1 for the years 1953 through 1964. 

Table 5-1: Uranium vs. Thorium Slugs at SRS

Year Number of 

Uranium Slugs

Number of 

Thorium Slugs

Thorium 

Fraction (%)

Notes

1953 200,000 321 0.16 Uranium estimate based partly on 90,109 

canned from November 1952 to July 

1952. 

1954 500,000 1,726 0.36 Thorium canning development work at 

SRS.

1955 1,200,000 26,618 2.22 Thorium canned at Sylcor Electric 

Products (SEP) finished at SRS

1956 2,700,000 0 0.00

1957 751,000 5,200 0.69 Thorium canned at Sylcor Electric 

Products (SEP) finished at SRS

1958 840,000 0 0.00 ---

1959 1,600,000 0 0.00 ---

1960 1,106,500 0 0.00 ---

1961 725,100 417 0.06 Thorium canned at Sylcor Electric 

Products (SEP) finished at SRS

1962 955,000 14,000 1.47 Thorium canned at Sylcor Electric 

Products (SEP) finished at SRS

1963 404,825 16,500 4.08 Thorium canned at Sylcor Electric 

Products (SEP) finished at SRS

1964 286,900 9,600 3.35 Thorium canned at Sylcor Electric 

Products (SEP) finished at SRS

6.0 Pedigree of Savannah River Site Data

The following statements apply to the thorium exposure analysis in this evaluation report addendum: 

• All air monitoring data used in this analysis came from official SRS primary source documents 

(i.e., handwritten logs) obtained during NIOSH data captures. 

• All bioassay data used in this analysis came from official SRS bioassay record books. Uranium 

bioassay data recorded in the books through 1965 were entered into spreadsheets for use in the 

statistical analyses.

• All other documents and data used in this analysis were addressed in the original data pedigree 

analysis provided in SEC Petition Evaluation Report for Savannah River Site (NIOSH, 2008). 
SEC-00103 Addendum 04-28-10 Savannah River Site

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7.1 Evaluation of Bounding Internal Radiation Doses at Savannah River Site

ATTRIBUTION: Section 7.1 and its related subsections were completed by Mike Mahathy, Oak Ridge 

Associated Universities; Sam Chu, Mel Chew and Associates, Inc.; Billy Smith, Mel Chew and 

Associates, Inc.; and Robert Morris, Mel Chew and Associates, Inc. These conclusions were peerreviewed by the individuals listed on the cover page. The rationales for all conclusions in this 

document are explained in the associated text. 

In its SRS evaluation report (NIOSH, 2008), NIOSH reserved for future consideration the feasibility

determination for thorium exposures from January 1, 1950 through December 31, 1959. Since the 

publication of the SRS report, NIOSH has evaluated and quantified thorium operations conducted at 

SRS from 1950 through 1959. During that evaluation, NIOSH determined that the period of thorium 

metal work for which a common feasibility decision should be applied extended through 1965. This 

section provides further discussion of thorium operations by year and presents a methodology for 

bounding potential exposures from thorium metal and thoron. Comparisons of the uranium and 

thorium processes and data are also provided. 

7.1.1.8 Thorium (Th-228, Th-232)

Building 313-M was declared an exclusion area in August 1952; uranium was introduced to the 

building in September 1952 (Construction History, 1957). The first thorium canning campaign took 

place in 313-M from January through March 1953, during which about 320 1-kg slugs were canned. 

In August 1954, Test Authorization Number 3-138, "DPSOX-00530, AlSi Canning Thorium Slugs" in 

Building 313-M was approved. That authorization identified goals, processes (the same as used for 

uranium slug canning), responsibilities, and safety controls. The safety controls included: a 

precaution regarding alpha and gamma radiation; a requirement to use hand and shoe counters; a 

requirement to run air sampling in thorium-handling areas; an air concentration control limit of 

1 x 10-11 μCi/cm3, at which point respiratory protection would be imposed; and a requirement to cover 

potentially-contaminated surfaces with paper and dispose of the paper as radioactive waste each day.

By November 1954, four quatrefoil fuel assemblies had been produced and were included in the L-2 

reactor loading for irradiation testing (Monthly Report, January 1956; Monthly Report, November 

1954). A maximum permissible concentration in air for Th-232 of 2 x 10-12 μCi/cm3 (2 pCi/m3) was 

adopted in June 1955 (Health Physics Logbook, 1955).

Early in 1955, SEP was contracted to produce 11,000 hot-press-bonded thorium slugs due to SEP’s 

demonstrated capability for producing uranium slugs using that process as compared to the low yields 

from the competing AlSi hot-dip process at SRS. The SRS portion of the effort included process 

research and metallurgy on un-irradiated samples, inspection of the canned slugs and subsequent 

welding and fabrication into fuel rods. A second order for 15,000 canned thorium slugs was largely 

fulfilled in August 1955 (Monthly Report, August 1955, pdf pp. 19-20, 32-34). The SEP thorium fuel 

was used for the R-7 1

 

1 The R-nn and L-nn designations represent the particular reactor and an operating cycle. 

full-core reactor loading (Monthly Report, August 1955). In September 1955, 

the SEP thorium program was reviewed, which resulted in a plan to dispose of the unused inventory 

by stripping the cans and returning the metal to the Fernald Feed Materials Production Center (FMPC) 

(Monthly Report, September 1955).
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In September 1956, SRS received a request to irradiate five tons (~5000 slugs) of thorium to produce 

U-233 (Monthly Report, September 1956); the plan was to produce material that would then be 

shipped to ORNL in 0.75-ton batches with minimal cooling time (less than thirty days after discharge) 

to enable testing of radiation damage to extraction solvents and to determine radiation levels during 

various stages of the extraction process (Monthly Report, February 1957). Sylcor commenced 

canning the thorium slugs (Monthly Report, September 1956). About 5,200 canned slugs were to be 

faced, welded, bond-tested, and tested by autoclave at SRS. The resulting fuel was to be included in 

reactor loads R-9, R-10 (Monthly Report, January 1957), R-11, and R-12 (Monthly Report, February 

1957). By July 1957, eight shipping casks containing irradiated thorium fuel had been shipped to 

ORNL (Monthly Report, July 1957).

Several SRS reactor loadings included thorium. L-2 included four thorium quatrefoils; R-5 included 

252 thorium slugs. Following their 67-day irradiation, these materials were examined for dimensional 

changes in the 100-R Area Hot Laboratory (Monthly Report, September 1955), then shipped to ORNL 

in February 1956. R-6 included uranium-thorium quatrefoils (Monthly Report, September 1955) 

containing 1680 thorium slugs (Monthly Report, January 1956). Those quatrefoils were cooled until 

January 1956. The R-6 material was shipped to ORNL between January and March 1956 (Monthly 

Report, January 1956; Monthly Report, February 1956; Monthly Report, March 1956). R-7 was a full 

thorium load (Monthly Report, August 1955). R-8 included two tubular elements containing enriched 

uranium and thorium (Monthly Report, November 1955). Loadings R-9, R-10, R-11, and R-12 

included material to support testing at ORNL.

In December 1958, ORNL proposed that pellets of mixed 4% enriched UO2 and ThO2 be irradiated at 

SRS. Each pellet was to be 0.26 inches in diameter and 3.5 inches long and was to be clad in stainless 

steel, aluminum, or Zircalloy (Monthly Report, December 1958). In June 1959, a procedure was 

tested for making a final arc weld on aluminum-canned hot-press-bonded slugs containing powdered 

and compacted thorium oxide. Ten slugs were welded and evaluated (Monthly Report, June 1959).

The use of a cation resin column to remove thorium in the Plant Special Products process was 

reported in October 1960, and an analytical procedure for thorium to routinely check column feed and 

product effluent was evaluated for routine use (Monthly Report, October 1960). In October 1961, 

irradiated metal waste, including thorium and uranium with 8400 curies of fission products, was 

shipped from the SRS high-level caves to Building 643-G. The waste was encased in concrete before 

being shipped to the burial ground (Monthly Report, October 1961).

In October 1961, Sylcor was given authorization to extrude and can 600 hollow thorium metal slugs 

for use in the Mark IV fuel (Monthly Report, October 1961). The Sylcor cladding process was to be 

qualified by destructive examination of slugs at SRS. All of the Sylcor pieces were expected for 

delivery by November 1961 (Monthly Report, October 1961). In 1962, Bridgeport Brass Company 

extruded 43,000 kg of thorium metal that was machined and canned at Sylcor; this resulted in 14,000 

Mark VII-T thorium slugs being delivered to SRS for inspection and use in the L-8 Mar VI-B charge 

(Plant History, 1974, pdf p. 108). 

In February 1963, 6000 Mark VII-T canned thorium slugs were finished at SRS for use in the L-1 

charge. In November 1963, 10,500 more thorium slugs were finished for use in the L-2 charge. All 

10,500 thorium slugs used in the L-2 charge were examined by radiography (Plant History, 1974, pdf 

p.116). In 1964, Sylcor made 9600 Mark VII-TS solid thorium metal slugs for two Mark V-E blanket 

charges but the core quality was reported as poor. Those slugs had been produced from scrap that had 
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been recycled several times from earlier campaigns (Plant History, 1974, pdf p. 126). Five 

thorium-enriched uranium alloy tubes clad with zirconium were extruded over April and May 1964 as 

part of research into developing fuel for the Heavy Water Components Test Reactor (HWCTR) on 

short notice (Monthly Report, April 1964, pdf p. 184). SRS records show that thorium was 

transferred within the site in 1964 (Surveys, 1964). 

Natural thorium processes at SRS were conducted using the common buildings, equipment, and 

processing steps used to make natural uranium slugs and were sometimes conducted concurrently. 

Based on the relative fraction of thorium-to-uranium handled at SRS (as shown in Table 5-1), the 

mass balance of thorium-to-uranium would have been less than one-to-one. However, the use of a 

one-to-one mass balance provides for a bounding assumption. 

Using Uranium Bioassay as a Substitute for Thorium Bioassay

NIOSH has identified the results of 224 thorium bioassay samples collected in 1956. All results were 

reported to be less than the detection level limit of 0.5 dpm per 1500 ml sample of urine. NIOSH has 

discussed the limitations of those thorium bioassay data (NIOSH, 2008). NIOSH has not found 

additional thorium bioassay for SRS workers. However, NIOSH has obtained the results of uranium 

urinalyses performed from late 1953 through 1965. As presented in this section of the report, uranium 

and thorium operational processes were radiologically similar. Therefore, NIOSH intends to use the 

uranium bioassay as a substitute for thorium bioassay to support its ability to bound thorium internal 

doses for the time period under evaluation. This substitute data internal dose reconstruction approach 

is described later in this section.

Area and air monitoring of uranium were performed by the SRS Health Physics group upon start-up. 

In March 1953, the National Bureau of Standards published Maximum Permissible Amounts of 

Radioisotopes in the Human Body and Maximum Permissible Concentrations in Air and Water

(Handbook 52, 1953). In Handbook 52, the Subcommittee on Permissible Internal Dose of the 

National Committee on Radiation Protection (NCRP) stated that all unnecessary exposure to 

radioisotopes should be avoided but that such avoidance “was often impractical, if not impossible.” 

Therefore, the subcommittee established levels of maximum permissible exposure to serve as guides 

to “safe operation and upper levels of exposure.” As a means of detecting levels of uranium exposure, 

SRS Health Physics implemented a routine uranium bioassay within months of the release of 

Handbook 52, which is referenced in SRS’s document, Radiation & Contamination Control

(Operating Procedure, 1961). The SRS Health Physics Monthly Report for September 1953 states 

that uranium bioassay had been taken for Technical Division staff in Building 678-G, and that a 

procedure for sampling other areas for uranium urinalysis was worked out with the aid of Methods 

and Standards and would be put into operation as soon as possible (Health Physics Monthly, Sept. 

1953, pdf p. 11). SRS implemented routine bioassay sampling of uranium for 300 Area staff in 

November 1953 (Health Physics Monthly, Nov. 1953; Health Physics Monthly, Dec. 1953). The first 

routine samples for uranium were obtained in the 300 Area on November 23, 1953 (Monitoring Log, 

1953-1954, pdf p. 22; SRP History, 1954, pdf p. 7). As discussed in Section 7.1.1.8, the routine 

uranium bioassay program overlapped with thorium operations. 

NIOSH evaluated the 1956 SRS thorium bioassay data and limitations of these data in its SRS 

evaluation report (NIOSH, 2008). NIOSH has not found additional thorium bioassay for SRS 

workers. NIOSH has obtained all SRS uranium urinalysis data record books (Monitoring Log, 1953-
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1954; Uranium Record Book, 1954-55; Uranium Record Book, 1955; Uranium Record Book, 1955-

56; Uranium Record Book, 1956a; Uranium Record Book, 1956b; Uranium Record Book, 1956-57; 

Uranium Record Book, 1957-58; Uranium Record Book, 1959-60; Uranium Record Book, 1960-62; 

Uranium Record Book, 1962-64; Uranium Record Book, 1964-65). 

The data in the record books for workers in the M Area were entered in spreadsheets suitable for 

statistical analyses. A discussion of the statistical treatment of the uranium record data is provided in 

Appendix B. The number of workers assigned to M area from 1953 through 1965 is shown in Table 

7-1. Also included in this table is the total number of workers used in the statistical analysis, the 

number of non-censored results, and the number of people monitored as a percentage of the total 

headcount assigned to the 300 Area. The percentage monitored of the assigned M Area headcount 

could exceed 100% of the listed workforce due to turnover and because additional workers unassigned 

to the 300 Area were sometimes brought into the area and monitored. 

Table 7-1: M Area Assigned Headcount vs. Bioassay Monitoring Count

Month Year

Manufacturing Headcount

Assigned to M Area

(minus Security personnel)

Bioassay

WS LW WK Total Total 

Monitored

Non-Censored 

Results

% Monitored 

of Assigned 

Headcount* 

December 1953 35 190 --- 225 32 32 14.2

June 1954 42 218 --- 260 519 514 *199.6

June 1955 80 248 35 363 486 486 *133.9

June 1956 111 449 51 611 722 694 *118.2

May 1957 125 371 49 545 295 45 54.1

June 1958 116 322 44 482 417 92 86.5

June 1959 98 254 36 388 269 70 69.3

May 1960 87 260 38 385 456 58 *118.4

June 1961 92 212 31 335 253 20 75.5

June 1962 83 233 28 344 191 27 55.5

June 1963 77 222 31 330 298 196 90.3

June 1964 75 199 31 305 225 178 73.8

June 1965 62 137 27 226 198 141 87.6

WS = Wilmington Salary wage group

LW = Local Wage group

WK = Weekly wage group

* Values could exceed 100% of the listed workforce due to turnover and because additional workers unassigned to the 300 

Area were sometimes brought into the area and monitored.
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Feasibility of Bounding Thorium Doses

As stated, NIOSH has a large quantity of uranium bioassay data. NIOSH has demonstrated in this 

evaluation report addendum that under the conditions of use of natural thorium metal at SRS, these 

uranium data can be used to support thorium intake modeling. Chronic intakes of natural uranium 

were modeled using the available uranium data. Annual intakes of Th-232 were derived by assuming 

a 1:1 mass balance with natural uranium and the specific activities of thorium (Th-232) to natural 

uranium. Based on the relative fraction of thorium-to-uranium handled at SRS as shown in this 

report’s addendum, the mass balance of thorium-to-uranium would have been less than one-to-one. 

However, the use of a one-to-one mass balance provides for a bounding assumption. 

Using the 50th percentile value of each yearly co-worker uranium excretion rate, daily intake rates of 

Th-232 were modeled for solubility types M and S and are shown in Table 7-2. The modeling

resulted in different daily intake rates for the time periods of 1953, 1954, 1955 through 1956, 1957 

through 1962, and 1963 through 1965, respectively. To ensure a bounding assessment, the thorium 

activity is assumed to be fully-equilibrated among Th-232, Th-228, and Ra-228. Therefore, intake 

rates of Th-228 and Ra-228 equal to those of Th-232 for each time period for each class were added to 

the intake model. 

Table 7-2: Daily Intake Rates

Years Th-232

(pCi/d)

Ra-228

(pCi/d)

Th-228

(pCi/d)

Solubility Type M

1953 11.1 11.1 11.1

1954 3.73 3.73 3.73

1955-1956 2.69 2.69 2.69

1957-1962 0.16 0.16 0.16

1963-1965 1.18 1.18 1.18

Solubility Type S

1953 347 347 347

1954 175 175 175

1955-1956 80.4 80.4 80.4

1957-1962 4.77 4.77 4.77

1963-1965 27.0 27.0 27.0

 

Comparison of Uranium and Thorium Air Sampling Results

SRS records show that the Health Physics organization performed common monitoring steps for 

uranium and thorium (Air Sample Log Sheets, 1955; Health Physics Logbook, 1955; Shipment 

Records, 1955; Surveys, 1955a; Surveys, 1955b; Surveys, 1955c; Surveys, 1955d; Surveys, 1956; 

Surveys, 1962; Surveys, 1963; Surveys, 1964a; Surveys, 1964b; Surveys, 1964c). The same MPC 

was used for both radionuclides through June 1955 (a maximum permissible concentration for Th-232 
SEC-00103 Addendum 04-28-10 Savannah River Site

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of 2 x 10-12 μCi/cm3 (2 pCi/m3) was adopted in June 1955 [Health Physics Logbook, 1955]). In 1954 

and 1955, SRS performed air monitoring for uranium and thorium using the same equipment and 

procedure. An interview with a former Health Physics Technician on August 13, 2009 (Personal 

Communication, 2009d) provided insight into the thorium operations. The former Health Physics 

technician stated: 

The routine samples...were representative of the breathing zone of the worker. They were 

located where the operators were standing and were not mounted on a wall.

Air sample results were recorded on Air Sample Log Sheets. Air sample records were considered 

workplace monitoring records as opposed to intake monitoring records. Air sample records were 

associated with each facility separately and were stored as facility records (ORAUT-TKBS-0003, pdf 

p. 75). 

In order to demonstrate how uranium operations compared to thorium operations, NIOSH analyzed air 

monitoring data obtained from each operation. NIOSH obtained thirty air results for air monitoring of 

thorium metal operations in 313-M and 320-M in 1954 and 1955 (Air Sample Log Sheets, 1953; Air 

Sample Log Sheets, 1954a; Air Sample Log Sheets, 1954b; Air Sample Log Sheets, 1955); these are 

shown in Appendix A, Table A-1. NIOSH selected 33 uranium air sample results from available 

uranium air monitoring data to test the hypothesis that the mean of the thorium air results was less 

than or equal to the mean of the uranium results. Uranium air sample results selected for the NIOSH 

analysis were for air monitoring collected on the same dates, and from the same buildings as the 

thorium air sample results (Appendix A, Table A-2). The building and location where each sample 

was collected are included in the table. While uranium and thorium samples were taken in common 

locations, the distance from the source term sometimes differed. Sampling of uranium processes 

tended to be from the general work areas (e.g., north of canning line, recovery, process control, and 

metal labs) so that results would have a slight low bias relative to breathing zone concentrations. 

Thorium samples were collected closer to the source term, with one sample collected within one foot 

of the welding head (Air Sample Log Sheets, 1955, pdf p. 59) so that results may be biased high. 

Sampling was performed using Staplex2 high-volume and other vacuum-cleaner-type devices with 

flow rates ranging from 5.9 to 10.5 ft3

/min. Sampling times ranged from thirty to two hundred 

minutes. Filter papers were used as the collecting media. Air concentrations (pCi/m3) of total 

thorium were calculated using the raw data available in the data sheets (gross counts due to counting 

uncertainties) and assumptions regarding: (1) alpha counting efficiency [30% under 2 • geometry for 

a calibration source3

 

2 Attribution: Bryce Rich, Mel Chew and Associates, Inc.

]; (2) particle collection efficiency of the sampling media (95%3) and (3) sample 

self-absorption (50%3). Th-232 was assumed to be in equilibrium with Th-228 and Ra-228; therefore, 

concentrations of total thorium were divided by 3 to obtain the concentrations of Th-232. Th-232 

mass concentrations were derived using a specific activity of 0.111 pCi/μg; uranium mass 

concentrations were derived using a specific activity of 0.672 pCi/μg. The mass concentrations 

(μg/m3) for Th-232 and natural uranium are included in Appendix A, Tables A-1 and A-2 

respectively. 

3 Attribution: Robert Morris, Mel Chew and Associates, Inc. These assumptions are based on extensive experience with

alpha counter and air sampling equipment. Several of these assumptions can be substantiated in the Air Force Institute of 

Operational Health consultative letter, Alpha Correction Factor for New Bioenvironmental Engineering Radiological Air 

Sampling Equipment – RADeCO® Model H-809VII (Correction Factor, 2005).
SEC-00103 Addendum 04-28-10 Savannah River Site

Page 15 of 43 

Descriptive statistics were generated for the thorium dataset and the uranium dataset using mass 

concentrations; these are shown in Table 7-3. 

Table 7-3: Description Statistics for SRS Thorium and Uranium Data

Statistic Th-232 Uranium

number of samples 30 33

minimum (μg/m3) 0.49 0.35

first quartile (μg/m3) 2.02 2.29

mean (μg/m3) 6.40 4.48

median (μg/m3) 3.86 4.71

standard deviation 6.17 3.10

third quartile (μg/m3) 8.22 6.26

maximum (μg/m3) 25.5 16.21

geometric mean (μg/m3) 4.00 3.36

The descriptive statistics were used to generate the box-and-whisker plots in Figure 7-1. When two 

box-and-whisker plots are displayed on the same scale, as in Figure 7-1, key features of the data can 

be graphically compared. The minimum values of both distributions are as close to zero as can be 

measured with the selected technology. The box portion of the plot is bounded by the lower quartile 

and upper quartile values and the median is between those two values (represented by the horizontal 

solid line inside the box). The box defines the range of the middle 50% of the data, which is also 

called the interquartile distance. Whiskers on each side of the box represent the 10th and 90th

percentiles; the black dots represent the 5th and 95th percentiles. The conclusion drawn from this 

figure is that the thorium distribution median values are generally less than the uranium distribution. 

Thus, the plots support the hypothesis that the thorium concentrations are in the same airborne 

concentration range (by mass) as the uranium values and the internal exposure profiles for uranium 

and thorium are similar.
SEC-00103 Addendum 04-28-10 Savannah River Site

Page 16 of 43 

Figure 7-1: Comparison of SRS Thorium and Uranium Air Sample Data

NIOSH performed a one-tail t-Test analysis (two-sample assuming unequal variances) to test the 

hypothesis that the mean of the natural log of the mass concentrations of thorium was less than or 

equal to the mean of the natural log of the mass concentrations obtained for uranium using • = 0.05 

(H0 : μt = μu) with the alternate hypothesis H1 : μt > μu  In order for the hypothesis to be true, t

tcritical must be true. Results of the hypothesis test are shown in Table 7-4. 

Table 7-4: t-Test Analysis

(Data values used in the analysis are log transformations of the mass concentrations) 

Thorium Uranium

mean 1.39 1.21

variance 1.11 0.78

observations 30 33

hypothesized mean difference 0 ---

degrees of freedom 57 ---

• 0.05 ---

t 0.717 ---

p value one-tail 0.238 ---

t-critical one-tail 2.00 ---

With a p value of 0.238, there is not sufficient statistical evidence to reject the null hypothesis (μt = 

μu) in favor of the alternate hypothesis (μt > μu).
SEC-00103 Addendum 04-28-10 Savannah River Site

Page 17 of 43 

Plausibility of Intakes Derived Using Uranium Bioassay

In order to check the plausibility of intakes derived using the uranium urinalysis data, NIOSH 

estimated intakes of thorium using: (1) the air monitoring data displayed in Appendix A, Table A-1; 

and (2) the 1956 thorium bioassay data (NIOSH, 2008). 

Thorium intake rates were estimated using the air monitoring data provided in Appendix A, Table 

A-1. The geometric mean of the thorium air concentrations by mass was 6.4 μg/m3, which equals

0.715 pCi/m3 using the specific activity for Th-232 of 0.111 pCi/μg. The geometric mean of 0.715 

pCi/m3

 is less than the 1954 Th-232 MPC of 10 pCi/m3 and less than the Th-232 MPC of 2 pCi/m3 in 

use from 1956 through 1965. Therefore, NIOSH used an air concentration for Th-232 of 2 pCi/m3

(the latter MPC) to derive a comparative intake rate. Using a breathing rate of 1.2 m3/hr applied over 

an 8-hour work day yields a daily intake of 19.2 pCi (Type S material assumed). The intake rate is on 

the same order of magnitude as the average daily intake rate obtained using the uranium bioassay data, 

which supports the use of those substitute data. 

All thorium bioassay data for 1956 were reported as less than the Th-232 detection limit of 0.5 dpm 

per 1500 mL. Therefore, NIOSH estimated chronic inhalation using the Th-232 detection limit and 

evaluated the result. The resulting annual inhalation intake rate of 650 pCi per day was derived; that 

rate was assumed to be constant through 1965. Although this value is higher than the intake rates 

using the uranium data, such an intake rate would equate to a constant air concentration for Th-232 of 

34 pCi/m3 which is significantly higher than the Th-232 maximum permissible concentration 

averaged over the entire span of time from 1953 through 1965. Given this information, NIOSH does 

not find that employing the Th-232 limit of detection provides a plausible analysis of potential 

thorium intakes in light of the available air sampling data and the known rates of thorium metal 

processing.

Bounding of Doses from Intakes of Thoron

Exposures to radon-220 (thoron) and its short-lived progeny cannot be discounted during the time 

period when thorium metal was processed at SRS (1953-1965). NIOSH has found no air sampling 

collected to measure concentrations of thoron. However, applying conservative assumptions, NIOSH 

used data from Appendix A, Table A-1, where samples were counted at least twice, to estimate an 

upper bound for thoron air concentration. The extrapolation from long-lived air sample data to thoron 

concentration in air was made using the following assumptions: 

• The Pb-212 half-life of 10.64 hours was used to extrapolate the initial airborne alpha count rate 

between sample collection and the first count.

• The filter paper contained both long-lived activity and short-lived activity.

• The build-up of thoron on the filter paper during sampling should be approximated. 

• The decay that occurred between the end of the sampling and the first count should be calculated.
SEC-00103 Addendum 04-28-10 Savannah River Site

Page 18 of 43 

Using the methodology described in Appendix C, the thoron concentrations were derived and are 

shown in Table 7-5. Intakes in pCi/day of thoron were calculated by assuming a breathing rate of 1.2 

l m3

/hour for 8 hours, and using an overall counting and collection efficiency of 0.29. 

Table 7-5: Results of SRS Thoron Assessment

Date Total 

Sample 

Collection 

Time (hrs)

Time Between 

Collection and 

Start of First 

Count (hrs)

Initial 

cpm

Decayed

cpm

Hours After 

First Count 

Until Decayed 

Count

Flow 

Rate 

(ft

3

/min)

Thoron 

pCi/m3

4/15/55 1.00 5.58 29.8 3.8 67.00 7.9 4.56

7/9/54 1.92 4.00 182.6 8.0 72.00 7.9 16.8

7/9/54 1.67 4.25 108.5 26.1 72.00 7.9 8.06

7/30/54 1.58 0.33 214.3 28.0 67.00 7.9 14.8

6/29/54 1.92 4.08 76.9 44.0 8.67 7.9 10.7

7/8/54 1.00 4.48 120.0 37.3 24.00 7.9 18.4

7/7/54 1.00 4.10 128.7 55.3 24.50 7.9 15.8 

5/3/55 1.00 1.07 256.7 12.9 24.00 10.5 30.4

The concentrations were fit to a lognormal distribution with the following parameters: GM = 13.1 

pCi/ m3

; GSD = 1.78; arithmetic mean = 14.9 pCi/m3; and 95th percentile = 26.2 pCi/ m3. The daily 

intake of thoron is bounded by the product of the geometric mean (13.1 pCi/ m3) with the breathing 

rate of 9.6 m3 of air per 8-hour work shift which gives 126 pCi. 

7.4.5 Bounding of Doses from Intake of Thorium

NIOSH has established in Section 7.1.1.8 that internal doses resulting from potential exposures to 

thorium can be plausibly bounded for SRS construction workers using uranium bioassay as a 

substitute data set. 

7.5 Summary of Feasibility Findings for Petition SEC-00103

This addendum to the Savannah River Site Evaluation Report (SEC-00103) evaluates the feasibility of 

estimating with sufficient accuracy the dose received from potential exposures to thorium for all 

construction workers who worked in any area at the Savannah River Site during the period from 

January 1, 1953 through December 31, 1965. 

NIOSH determined that it has sufficient personal monitoring data, source term information, and 

workplace monitoring data for thorium to allow adequate bounding of the total potential internal 

exposures at the site during this time period. Consequently, NIOSH finds that it is feasible to estimate 

with sufficient accuracy the radiation doses resulting from internal thorium exposures received by 

members of this class.
SEC-00103 Addendum 04-28-10 Savannah River Site

Page 19 of 43 

NIOSH has documented herein that it can complete the dose reconstructions related to this addendum 

(i.e., doses resulting from exposure to thorium from January 1, 1953 through December 31, 1965). 

The basis of this finding is specified in this addendum, which demonstrates that NIOSH has access to 

sufficient information to estimate with sufficient accuracy either the maximum radiation dose incurred 

by any member of the class or to estimate such radiation doses more precisely than a maximum dose 

estimate.

NIOSH has documented in its original SEC-00103 Evaluation Report (NIOSH, 2008), and in this 

addendum, that it can complete dose reconstructions for exposure to all site occupational radiation 

sources for all construction workers who worked in any area at the Savannah River Site during the 

time period from January 1, 1950 through December 31, 2007. 

Note: An Appendix follows the References section.
SEC-00103 Addendum 04-28-10 Savannah River Site

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SEC-00103 Addendum 04-28-10 Savannah River Site

Page 21 of 43 

References for This Addendum 

300/M Area, 2006, 300/M Area, Fuel and Target Fabrication, Savannah River Site Cold War Historic 

Property Documentation, Westinghouse Savannah River Company; November 27, 2006; SRDB Ref 

ID: 71618 

Air Sample Log Sheets, 1953, Air Sample Log Sheets for the 300 Area, Savannah River Plant; various 

dates in 1953; SRDB Ref ID: 75469 

Air Sample Log Sheets, 1954a, Air Sample Log Sheets for October-December 1954, Savannah River 

Site; various dates in October-December 1954; SRDB Ref ID: 70018 

Air Sample Log Sheets, 1954b, Air Sample Log Sheets for June-September 1954, Savannah River 

Site; various dates in June-September 1954; SRDB Ref ID: 70026 

Air Sample Log Sheets, 1955, Air Sample Log Sheets for various dates in 1955, Savannah River Site; 

various dates in 1955; SRDB Ref ID: 70003 

Construction History, 1957, Savannah River Plant Construction History, Volume IV of IV; 

Construction 300-M, 400-D, 700-A and 500/600/900-G Areas, Engineering Department, E. I. Du Pont 

Nemours & Co., Inc.; January 1957; SRDB Ref ID: 50153 

Handbook 52, 1953, Maximum Permissible Amounts of Radioisotopes in the Human Body and 

Maximum Permissible Concentrations in Air and Water, National Bureau of Standards Handbook 52; 

March 20, 1953; SRDB Ref ID: 12332 

Health Physics Logbook, 1955, Health Physics Log Book (March-August 1955), 300/700 Area 

Survey Group, Savannah River Site; log started 01-19-54; pages 24-84 for March-August 1955; 

SRDB Ref ID: 70793, pdf p. 36 

Health Physics Monthly, Sept. 1953, Health Physics Monthly Report - September 1953, Savannah 

River Site Health Physics Group, September 1953; SRDB Ref ID: 56550 

Health Physics Monthly, Nov. 1953, Health Physics Monthly Report - November 1953, Savannah 

River Site Health Physics Group, November 1953; SRDB Ref ID: 56599, pdf p. 49 

Health Physics Monthly, Dec. 1953, Health Physics Monthly Report - December 1953, Savannah 

River Site Health Physics Group, December 1953; SRDB Ref ID: 56599, pdf p. 3 

Monitoring Log, 1953-1954, Startup to 12-14-1954; handwritten monitoring log with entries from 

July 29, 1953 to December 8, 1954 (207 pages); author unknown; SRDB Ref ID: 48929 

Monthly Report, January 1953, Monthly Progress Report for January 1953, DPSP-53-1-1; Works 

Technical Department; February 6, 1953; SRDB Ref ID: 11419 
SEC-00103 Addendum 04-28-10 Savannah River Site

Page 22 of 43 

Monthly Report, February 1953, Monthly Progress Report for February 1953, DPSP-53-1-2; Works 

Technical Department; March 9, 1953; SRDB Ref ID: 11421 

Monthly Report, March 1953, Monthly Progress Report for March 1953, DPSP-53-1-3; Works 

Technical Department; April 6, 1953; SRDB Ref ID: 11422 

Monthly Report, January 1954, Monthly Progress Report for January 1954, DPSP-54-1-1; Works 

Technical Department; February 8, 1954; SRDB Ref ID: 11444 

Monthly Report, February 1954, Monthly Progress Report for February 1954, DPSP-54-1-2; Works 

Technical Department; March 1954; SRDB Ref ID: 11445 

Monthly Report, March 1954, Monthly Progress Report for March 1954, DPSP-54-1-3; Works 

Technical Department; April 5, 1954; SRDB Ref ID: 11446 

Monthly Report, April 1954, Monthly Progress Report for April 1954, DPSP-54-1-4; Works 

Technical Department; May 4, 1954; SRDB Ref ID: 11447 

Monthly Report, May 1954, Monthly Progress Report for May 1954, DPSP-54-1-5; Works Technical 

Department; June 4, 1954; SRDB Ref ID: 11448 

Monthly Report, June 1954, Monthly Progress Report for June 1954, DPSP-54-1-6; Works Technical 

Department; July 1954; SRDB Ref ID: 11449 

Monthly Report, July 1954, Monthly Progress Report for July 1954, DPSP-54-1-7; Works Technical 

Department; August 19, 1954; SRDB Ref ID: 16851 

Monthly Report, August 1954, Monthly Progress Report for August 1954, DPSP-54-1-8-DV; Works 

Technical Department; September 15, 1954; SRDB Ref ID: 17106 

Monthly Report, October 1954, Monthly Progress Report for October 1954, DPSP 54-1-10; Works 

Technical Department; October 1954; SRDB Ref ID: 11458 

Monthly Report, November 1954, Monthly Progress Report for November 1954, DPSP-54-1-11; 

Works Technical Department; December 20, 1954; SRDB Ref ID: 11459 

Monthly Report, December 1954, Monthly Progress Report for December 1954, DPSP-54-1-12; 

Works Technical Department; January 19, 1955; SRDB Ref ID: 11461 

Monthly Report, January 1955, Monthly Progress Report for January 1955, DPSP-55-1-1; Works 

Technical Department; February 22, 1955; SRDB Ref ID: 11464 

Monthly Report, February 1955, Monthly Progress Report for February 1955, DPSP-55-1-2; Works 

Technical Department; March 18, 1955; SRDB Ref ID: 11465 

Monthly Report, March 1955, Monthly Progress Report for March 1955, DPSP-55-1-3; Works 

Technical Department; April 22, 1955; SRDB Ref ID: 11466 
SEC-00103 Addendum 04-28-10 Savannah River Site

Page 23 of 43 

Monthly Report, April 1955, Monthly Progress Report for April 1955, DPSP-55-1-4; Works 

Technical Department; May 18, 1955; SRDB Ref ID: 11467 

Monthly Report, May 1955, Monthly Progress Report for May 1955, DPSP-55-1-5-DV; Works 

Technical Department; June 17, 1955; SRDB Ref ID: 11471 

Monthly Report, August 1955, Monthly Progress Report for August 1955, DPSP-55-1-8-DV; Works 

Technical Department; September 19, 1955; SRDB Ref ID: 11473 

Monthly Report, September 1955, Monthly Progress Report for September 1955, DPSP-55-1-9-DV; 

Works Technical Department; October 21, 1955; SRDB Ref ID: 11476 

Monthly Report, November 1955, Monthly Progress Report for November 1955, DPSP-55-1-11-DV; 

Works Technical Department; December 21, 1955; SRDB Ref ID: 11477 

Monthly Report, January 1956, Monthly Progress Report for January 1956, DPSP-56-1-1; Works 

Technical Department; February 20, 1956; SRDB Ref ID: 11478 

Monthly Report, February 1956, Monthly Progress Report for February 1956, DPSP-56-1-2; Works 

Technical Department; March 16, 1956; SRDB Ref ID: 11480 

Monthly Report, March 1956, Monthly Progress Report for March 1956, DPSP-56-1-3; Works 

Technical Department; April 18, 1956; SRDB Ref ID: 11482 

Monthly Report, September 1956, Monthly Progress Report for September 1956, DPSP-56-1-9; 

Works Technical Department; October 18, 1956; SRDB Ref ID: 16859 

Monthly Report, January 1957, Monthly Progress Report for January 1957, DPSP-57-1-1; Works 

Technical Department; February 18, 1957; SRDB Ref ID: 11575 

Monthly Report, February 1957, Monthly Progress Report for February 1957, DPSP-57-1-2; Works 

Technical Department; March 20, 1957; SRDB Ref ID: 11576 

Monthly Report, March 1957, Monthly Progress Report for March 1957, DPSP-57-1-3; Works 

Technical Department; March 20, 1957; SRDB Ref ID: 68248 

Monthly Report, July 1957, Monthly Progress Report for July 1957, DPSP-57-1-7; Works Technical 

Department; August 19, 1957; SRDB Ref ID: 11601 

Monthly Report, August 1957, Monthly Progress Report for August 1957, DPSP-57-1-8; Works 

Technical Department; September 19, 1957; SRDB Ref ID: 11602 

Monthly Report, September 1957, Monthly Progress Report for September 1957, DPSP-57-1-9; 

Works Technical Department; October 18, 1957; SRDB Ref ID: 11603 

Monthly Report, December 1958, Monthly Progress Report for December 1958, DPSP-58-1-12-DV; 

Works Technical Department; January 23, 1959; SRDB Ref ID: 11615 
SEC-00103 Addendum 04-28-10 Savannah River Site

Page 24 of 43 

Monthly Report, June 1959, Progress Report for June 1959; DPSP-59-1-6; Works Technical 

Department; July 21, 1959; SRDB Ref ID: 11628 

Monthly Report, October 1960, Progress Report for October 1960; DPSP 60-1-10-DV; Works 

Technical Department; November 17, 1960; SRDB Ref ID: 11786 

Monthly Report, October 1961, Progress Report for October 1961, DPSP-61-1-10-DV; Works 

Technical Department; November 20, 1961; SRDB Ref ID: 11796 

Monthly Report, December 1963, Progress Report for December 1963, DPSP-63-1-12; Works 

Technical Department; December 1963; SRDB Ref ID: 68451 

Monthly Report, April 1964, Progress Report for April 1964, DPSP-64-1-4; Works Technical 

Department; May 25, 1964; SRDB Ref ID: 12286 

NIOSH, 2008, SEC Petition Evaluation Report for Savannah River Site, National Institute for 

Occupational Safety and Health (NIOSH); November 14, 2008; SRDB Ref ID: 

www.cdc.gov/niosh/ocas/pdfs/sec/srs/srser.pdf 

Operating Procedure, 1961, Operating Procedure for Radiation and Contamination Control, Rev. 6; 

Technical Procedures Office, E. I. du Pont de Nemours and Company, Explosives Department, 

Atomic Energy Division, Savannah River Plant; DPSOP 40; July 1961; SRDB Ref ID: 52806, pdf p. 

39 

ORAUT-OTIB-0075, Use of Claimant Datasets for Coworker Modeling, Rev. 00, Oak Ridge 

Associated Universities; May 25, 2009; SRDB Ref ID: 67223 

ORAUT-PROC-0095, Generating Summary Statistics for Coworker Bioassay Data, Rev. 00, Oak 

Ridge Associated Universities; June 5, 2006; SRDB Ref ID: 73397 

ORAUT-RPRT-0044, Analysis of Bioassay Data with a Significant Fraction of Less-Than Results, 

Rev. 00, Oak Ridge Associated Universities; August 7, 2009; SRDB Ref ID: 73398 

ORAUT-TKBS-0003, Savannah River Site, Rev. 03, Oak Ridge Associated Universities; April 5, 

2005; SRDB Ref ID: 20176 

Personal Communication, 2009a, Personal Communication with Two Former SRS Staff Members, 

Interview by ORAU Team; December 17, 2008; SRDB Ref ID: 90280 

Personal Communication, 2009b, Personal Communication with Two Former SRS Staff Members,

Interview by ORAU Team; December 17, 2008; SRDB Ref ID: 80281 

Personal Communication, 2009c, Personal Communication with Former Nuclear Physicist, 

Telephone Interview by ORAU Team; June 11, 2009; SRDB Ref ID: 73085 

Personal Communication, 2009d, Personal Communication with Former Radiation Safety Technician, 

Telephone Interview by ORAU Team; August 13, 2009; SRDB Ref ID: 73086 
SEC-00103 Addendum 04-28-10 Savannah River Site

Page 25 of 43 

Plant History, 1974, Savannah River Plant History: Raw Materials Area, July 1954 through 

December 1972, E. I. du Pont de Nemours and Company; February 1974; SRDB Ref ID: 48563 

Shipment Records, 1955, Radioactive Shipment Records, Savannah River Plant; various dates in 

1955; SRDB Ref ID: 69969 

Surveys, 1955a, Radiation Survey Log Sheets for the 300/700 Area, Savannah River Plant; various 

dates in January 1955; SRDB Ref ID: 70821, pdf p. 15 

SRP History, 1954, Savannah River Plant History, Volume 2, Health Physics Section, Savannah River 

Plant, July 1953 – June 1954; SRDB Ref ID: 51620 

Surveys, 1955b, Radiation Survey Log Sheets for the 300/700 Area, Savannah River Plant; various 

dates in January 1955; SRDB Ref ID: 70803, pdf pp. 4, 6, and 8 

Surveys, 1955c, Radiation Survey Log Sheets for the 300/700 Area, Savannah River Plant; various 

dates in May-June 1955; SRDB Ref ID: 70805 

Surveys, 1955d, Radiation Survey Log Sheets for the 300/700 Area, Savannah River Plant; various 

dates in March-April 1955; SRDB Ref ID: 70818 

Surveys, 1956, Radiation Survey Log Sheets for 221F Area, Savannah River Plant; various dates in 

December 1956; SRDB Ref ID: 67958 

Surveys, 1962, Radiation Survey Log Sheets for the 300/700 Area, Savannah River Plant; various 

dates in August 1962; SRDB Ref ID: 70262 

Surveys, 1963, Radiation Survey Log Sheets for the 300/700 Area, Savannah River Plant; various 

dates in November-December 1963; SRDB Ref ID: 70876, pdf p. 3 

Surveys, 1964a, Radiation Survey Log Sheets for the 300/700 Area, Savannah River Plant; April-May 

1964; SRDB Ref ID: 70891 

Surveys, 1964b, Radiation Survey Log Sheets for the 300/700 Area, Savannah River Plant; FebruaryMarch 1964; SRDB Ref ID: 70875, pdf pages 2, 9, 10, and 11 

Surveys, 1964c, Radiation Survey Log Sheets for the 300/700 Area, Savannah River Plant; MarchApril 1964; SRDB Ref ID: 70881 

Uranium Record Book, 1954-55, Uranium Record Book, 9-8-1954 thru 3-23-1955, Savannah River 

Site; handwritten log book; various dates in 1954-1955; SRDB Ref ID: 49592 

Uranium Record Book, 1955, Uranium Record Book, 4-15-1955 thru 9-28-1955, Savannah River 

Site; handwritten log book; various dates in 1955; SRDB Ref ID: 49591 

Uranium Record Book, 1955-56, Uranium Record Book, 10-5-1955 thru 4-30-1956, Savannah River 

Site; handwritten log book; various dates in 1955-1956; SRDB Ref ID: 48925 
SEC-00103 Addendum 04-28-10 Savannah River Site

Page 26 of 43 

Uranium Record Book, 1956a, Uranium Record Book, 3-19-1956 thru 6-11-1956, Savannah River 

Site; handwritten log book; various dates in 1956; SRDB Ref ID: 49605 

Uranium Record Book, 1956b, Uranium Record Book, 5-4-1956 thru 9-28-1956, Savannah River 

Site; handwritten log book; various dates in 1956; SRDB Ref ID: 49604 

Uranium Record Book, 1956-57, Uranium Record Book, 10-1-1956 thru 1-16-1957, Savannah River 

Site; handwritten log book; various dates in 1956-1957; SRDB Ref ID: 49594 

Uranium Record Book, 1957-58, DPSPN 682, Uranium, 1-17-1957 thru 1-9-1958, Savannah River 

Site; handwritten log book; various dates in 1957-1958; SRDB Ref ID: 49643 

Uranium Record Book, 1959-60, Uranium Record Book, 8-7-1959 thru 12-8-1960, Savannah River 

Site; handwritten log book; various dates in 1959-1960; SRDB Ref ID: 48923 

Uranium Record Book, 1960-62, Uranium Record Book, 12-20-1960 thru 9-20-1962, Savannah River 

Site; handwritten log book; various dates in 1960-1962; SRDB Ref ID: 48910 

Uranium Record Book, 1962-64, Uranium Record Book, 9-25-1962 thru 4-8-1964, Savannah River 

Site; handwritten log book; various dates in 1962-1964; SRDB Ref ID: 48907 

Uranium Record Book, 1964-65, Uranium Record Book, 4-9-1964 thru 11-17-1965, Savannah River 

Site; handwritten log book; various dates in 1964-1965; SRDB Ref ID: 48908 
SEC-00103 Addendum 04-28-10 Savannah River Site

Page 27 of 43 

Appendix A

Table A-1: SRS Thorium Samples

Sampled for Building Location Comment Collection 

Date cpm

Derived

Concentration

Th-232

(pCi/m3) 

Mass/volume

Th-232

(μg/m3)

†

thorium 320M Lathe Room Cutting and 

machining rods 6/22/1954 14.3 0.37 3.37

thorium 320M Lathe Room Cutting and 

machining rods 6/22/1954 12.0 0.30 2.74

thorium 320M Lathe Room Cutting and 

machining rods 6/23/1954 28.0 0.69 6.26

thorium 320M Lathe Room Cutting and 

machining rods 6/23/1954 56.7 1.34 12.03

thorium 320M Lathe Room Cutting and 

machining rods 6/25/1954 4.0 0.07 0.64

thorium 320M Lathe Room Cutting and 

machining rods 6/25/1954 7.7 0.16 1.41

thorium 320M Lathe Room Cutting and

machining rods 6/25/1954 36.3 0.47 4.28

thorium 320M Lathe Room Cutting and 

machining rods 6/28/1954 31.0 0.37 3.29

thorium 320M Lathe Room Cutting and 

machining rods 6/29/1954 44.0 0.90 8.12

thorium 320M Lathe Room Cutting and 

machining rods 6/29/1954 42.8 0.92 8.25

thorium 320M Lathe Room Cutting and 

machining rods 6/29/1954 38.3 0.62 5.60

thorium 320M Lathe Room Cutting and 

machining rods 6/30/1954 35.0 0.78 7.07

thorium 320M Lathe Room Cutting and 

machining rods 6/30/1954 30.0 2.83 25.46

thorium 320M Lathe Room Cutting and 

machining rods 7/1/1954 10.0 0.26 2.36

thorium 320M Lathe Room Cutting and 

machining rods 7/2/1954 4.7 0.10 0.87

thorium 320M Lathe Room Cutting and 

machining rods 7/2/1954 3.7 0.32 2.88

thorium 320M Lathe Room Cutting and 

machining rods 7/6/1954 46.6 1.83 16.48

thorium 320M Lathe Room Cutting and 

machining rods 7/7/1954 55.3 2.17 19.55

thorium 320M Lathe Room Cutting and 

machining rods 7/8/1954 37.3 1.46 13.19

thorium 320M Lathe Room Cutting and 

machining rods 7/9/1954 8.0 0.19 1.70

thorium 320M Lathe Room Cutting and 

machining rods 7/9/1954 26.1 0.61 5.54

thorium 320M Spectro-Chem 

Lab Grinding 7/30/1954 28.0 1.10 9.90
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Table A-1: SRS Thorium Samples

Sampled for Building Location Comment Collection 

Date cpm

Derived

Concentration

Th-232

(pCi/m3) 

Mass/volume

Th-232

(μg/m3)

†

thorium 320M Swagging 

Area

Swagging of 

rods 8/11/1954 9.0 0.21 1.91

thorium 320M Swagging 

Area

Swagging of 

rods 8/12/1954 3.0 0.05 0.49

thorium 313M North of 

Canning Line

Normal 

Operation 8/30/1954 28.9 0.73 6.60

thorium 313M North of 

Canning Line Canning Slugs 12/22/1954 70.0 1.46 13.15

thorium 313M Special 

Process

Handling 

Thorium 4/15/1955 3.8 0.15 1.34

thorium 313M Special 

Process

One foot from 

welding of slugs 4/15/1955 2.6 0.08 0.69

thorium 313M Special 

Process

Two feet from 

welding of slugs 4/15/1955 3.6 0.38 3.41

thorium 313M Special 

Process Thorium in room 5/3/1955 12.9 0.38 3.43

† Thorium mass based on specific activity of Th-232.
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Table A-2: SRS Uranium Samples

Sampled for Building Location Comment Collection Date cpm

Derived

Concentration

U-nat

(pCi/m3) 

Mass/volume

U-nat

(μg/m3)

†

uranium 320M Process 

Control

Normal 

operation 6/22/1954 29.3 4.30 6.40 

uranium 320M Metal Labs Normal 

operation 6/23/1954 27.6 2.37 3.53

uranium 320M Process 

Control

Normal 

operation 6/29/1954 26.7 3.31 4.93

uranium 320M Metal Labs Normal 

operation 6/30/1954 27.5 3.41 5.08

uranium 320M Metal 

Polishing Lab

Cutting 

and 

polishing 

metal

7/8/1954 28.0 2.60 3.88

uranium 320M Metal Labs Normal 

operation 7/28/1954 25.0 4.65 6.92

uranium 320M Metal Labs Normal 

operation 7/28/1954 27.0 4.31 6.41

uranium 320M Spectro-Chem 

Lab Grinding 8/3/1954 33.0 2.22 3.30 

uranium 320M Metal Labs Normal 

operation 8/4/1954 28.9 3.58 5.33

uranium 320M Metal Labs

Unusual 

amount of 

slugs 

8/10/1954 25.1 4.67 6.95

uranium 320M Process 

Control

Normal 

operation 8/10/1954 27.0 5.02 7.47

uranium 320M Process 

Control

Normal 

operation 8/17/1954 25.6 4.08 6.07

uranium 320M Metal Labs Normal 

operation 8/18/1954 26.4 4.21 6.26

uranium 313M Recovery --- 8/30/1954 27.9 2.16 3.22

uranium 313M Storage Normal 

operation 8/30/1954 33.6 3.17 4.71

uranium 313M North of 

Canning Line

Normal 

operation 8/30/1954 40.7 3.83 5.71

uranium 313M Lathe Room Stripping 

from cans 8/30/1954 114.2 10.9 16.29

uranium 313M Recovery

Normal 

operation; 

some 

spillage

8/30/1954 32.9 1.77 2.64

uranium 313M North of 

Canning Line

Normal 

operation 12/22/1954 44.8 3.18 4.72

uranium 313M North of 

Canning Line

Normal 

operation 12/22/1954 33.6 3.17 4.71
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Table A-2: SRS Uranium Samples

Sampled for Building Location Comment Collection Date cpm

Derived

Concentration

U-nat

(pCi/m3) 

Mass/volume

U-nat

(μg/m3)

†

uranium 313M Final Storage

Cleaning 

canned 

Slugs

12/22/1954 20.8 1.47 2.19

uranium 313M Recovery Cleaning 12/22/1954 61.6 5.80 8.64

uranium 313M X-ray

Normal 

operation

12/22/1954 49.6 4.67 6.95

uranium 313M Cleaning Cleaning 4/15/1955 12.1 1.14 1.70 

uranium 313M North of 

Canning Line

Normal 

operation 4/15/1955 9.4 0.89 1.32

uranium 313M Recovery Normal 

operation 4/15/1955 21.7 1.54 2.29

uranium 313M Recovery Normal 

operation 4/15/1955 31.0 2.20 3.27

uranium 313M North of 

Canning Line

Normal 

operation 4/15/1955 31.0 2.20 3.27

uranium 313M North of 

Canning Line

Normal 

operation 5/3/1955 6.1 0.57 0.86

uranium 313M Recovery Cleaning 5/3/1955 3.3 0.23 0.35 

uranium 313M South of 

Canning Line

Normal 

operation 5/3/1955 14.2 1.01 1.50 

uranium 313M North of 

Canning Line

Normal 

operation 5/3/1955 4.3 0.41 0.60 

uranium 313M Recovery Normal 

operation 5/3/1955 4.1 0.29 0.43

† Uranium mass based on specific activity of natural uranium.
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Appendix B 

The SRS uranium-mass-in-urine data from the logbooks were supplied in an Excel file. The 

worksheet was converted to a comma separated value (csv) file and read into the R analysis tool. The 

uranium concentration in each urine sample was calculated from the fluorimetry results using the 

following equation (Uranium Record Book, 1954-55):

 , 

Where: 

U = Concentration of uranium in urine (μg/L)

R = Mean of three fluorimetry readings from the sample

Rs = Mean of two fluorimetry readings from a known spike 

The concentration U calculated above was used for the co-worker models unless the fluorimetry 

readings were missing or the concentration was equal to zero. If the fluorimetry readings were 

missing, the reported concentration (which may have been censored) was used. If U was equal to zero 

the result was censored, with the censoring level (CL in the plots) being set equal to the minimum 

non-zero concentration reported for that year. 

All uranium-in-urine concentrations were converted to μg/1.5 L, grouped by year, and the highest 

result for each individual in a given year was selected. The urine data for 1953 though 1956 were

satisfactorily fit with a single lognormal distribution using a maximum likelihood method (the data 

had multiple censoring levels so a regression on the order statistics could not be done). 

The parameters given in the plots for 1953-1956 include the geometric mean (GM), geometric 

standard deviation (GSD), total number of results (N), number of uncensored results (n), and the 

coefficient of determination (R2). For this application, R2

 is defined to be the square of the correlation 

coefficient between the log observed uncensored data and the log predicted uncensored data : 

For a linear relationship such as the line of best fit in the plots, this definition of R2 is numerically 

equal to the standard definition for R2: 
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Statistics derived using these methods are summarized in Table B-1. 

Table B-1: Derived Statistics Used for Intake Modeling

Year GM GSD 84th

1953 5.557 1.386 7.70

1954 2.805 1.847 5.18

1955 1.97 1.724 3.40

1956 1.555 1.698 2.64

1957 0.152 3.01 0.46

1958 0.185 3.49 0.65

1959 0.205 3.77 0.77

1960 0.146 2.92 0.43

1961 0.127 2.51 0.32

1962 0.169 3.43 0.58

1963 0.559 4.19 2.34

1964 0.923 3.57 3.30

1965 0.571 3.77 2.15

Figure B-1 shows a box-and-whisker plot depicting the change in fitted uranium urine concentration 

over time. The lower and upper dots for each year represent the 5th and 95th percentiles, while the 

lower and upper whiskers represent the 10th and 90th percentiles. The traditional box represents the 

inner 50th percentile; thus, the lower limit of the box is equal to the 25th percentile while the upper 

portion represents the 75th percentile. The solid line in the middle of the box represents the 50th

percentile or the geometric mean of the fitted uranium urine concentration whereas the dotted line is 

the arithmetic mean. This figure illustrates that from 1953 through 1957, there was a steady decrease 

in the uranium urine concentration among workers in the 300 Area. From 1957 through 1962, the 

urine concentration remained relatively low with a geometric mean typically less than 0.2 ug/d. From

1963 through 1965, there was an increase in the urine concentration among the 300 Area workers.
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Figure B-1: Derived Statistics Used for Intake Modeling
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Plots for each of the years 1953 through 1965 are presented in Figures B-2 through B-14. 

-2 -1 0 1 2

4 6 8 10 12

SRS Uranium Mass 1953

Standard Normal Quantiles

Uranium in Urine (ug/1.5L)

GM = 5.557

GSD = 1.386

N = 32

n = 32

R2 = 0.966

Figure B-2: SRS Uranium Mass Statistical Fit for 1953

-2 -1 0 1 2 3

0.5 1.0 2.0 5.0 10.0 20.0

SRS Uranium Mass 1954

Standard Normal Quantiles

Uranium in Urine (ug/1.5L)

GM = 2.805

GSD = 1.847

N = 519

n = 514

R2 = 0.969

Figure B-3: SRS Uranium Mass Statistical Fit for 1954 
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-3 -2 -1 0 1 2 3

1 2 5 10 20

SRS Uranium Mass 1955

Standard Normal Quantiles

Uranium in Urine (ug/1.5L)

GM = 1.97

GSD = 1.724

N = 486

n = 486

R2 = 0.954

Figure B-4: SRS Uranium Mass Statistical Fit for 1955

-2 -1 0 1 2 3

0.5 1.0 2.0 5.0 10.0 20.0 50.0 100.0 200.0

SRS Uranium Mass 1956

Standard Normal Quantiles

Uranium in Urine (ug/1.5L)

GM = 1.555

GSD = 1.698

N = 722

n = 694

R2 = 0.715

Figure B-5: SRS Uranium Mass Statistical Fit for 1956
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For the years 1957-1965, the data were fit with a sum of two lognormal distributions using the 

maximum likelihood methods described in ORAUT-RPRT-0044 to give an effective fit to the data. 

Note that the analytical background for the uranium urine data is lognormal rather than normal as 

described in ORAUT-RPRT-0044. The geometric mean and geometric standard deviation of the 

lognormal distribution below the censoring level (i.e., the analytical background) was selected to give 

the highest coefficient of determination (R2

) for the fit to the uncensored data. Using this criterion, a

GM value of 0.1 and a GSD value of 1.75 were selected for the analytical background for 1957-1965. 

Given the above analytical background, the GM and GSD for the “exposed” distribution are

calculated along with the fraction of the population estimated to be analytical background. For 

example, for the exposed distribution in 1957 the GM = 2.54 and the GSD = 1.68. The fraction of the 

population that comprises analytical background is 0.8699, which means that the exposed fraction 

makes up 1 – 0.8699 = 0.1301 of the population. The dashed line in the plot is the best fit to the data 

using the two lognormal distributions. The sigmoid-shape of the curve is a result of plotting two 

independent distributions on the same probability plot. The “effective” fit to the data is a single 

lognormal distribution (GM=0.152, GSD=3.01) represented by the solid line. The GM and GSD from 

the effective fit are used in the co-worker model.

-4 -2 0 2 4

0.02 0.05 0.10 0.20 0.50 1.00 2.00 5.00

SRS Uranium Mass 1957

Standard Normal Quantiles

Uranium in Urine (ug/1.5L)
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-4 -2 0 2 4

0.02 0.05 0.10 0.20 0.50 1.00 2.00 5.00

SRS Uranium Mass 1958

Standard Normal Quantiles

Uranium in Urine (ug/1.5L)
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-4 -2 0 2 4

0.02 0.05 0.20 0.50 2.00 5.00 20.00

SRS Uranium Mass 1960

Standard Normal Quantiles

Uranium in Urine (ug/1.5L)
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-4 -2 0 2 4

0.02 0.05 0.20 0.50 2.00 5.00 20.00

SRS Uranium Mass 1962

Standard Normal Quantiles

Uranium in Urine (ug/1.5L)
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-4 -2 0 2 4

0.02 0.05 0.10 0.20 0.50 1.00 2.00 5.00

SRS Uranium Mass 1964

Standard Normal Quantiles

Uranium in Urine (ug/1.5L)
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The statistical parameters given in Table B-1 were used to model the daily intake rate of natural uranium. The modeled 

data resulted in different daily intake rates for the time periods of 1953, 1954, 1955 through 1956, 1957 through 1962, 

and 1963 through 1965, respectively. To obtain daily intake rates of Th-232, a mass balance of one-to-one of natural 

uranium to Th-232 was assumed, giving the same mass intake rate for each year. To ensure a bounding assessment, the 

thorium activity is assumed to be fully-equilibrated among Th-232, Th-228, and Ra-228. Therefore, intake rates of 

Th-228 and Ra-228 equal to those of Th-232 were added to the intake model for each time period for each class. Derived 

intake rates are given in Table B-2. 

Table B-2: Thorium, Daily Intake Rates

Years U 

(pCi/day)

U:Th 

Mass 

Ratio

Th-232: 

Ra-228 

Activity Ratio

Th-232: 

Th-228 

Activity Ratio

Th-232 (pCi/day) Ra-228 (pCi/day) Th-228 (pCi/day)

Type M

1953 67.1 1 1 1 11.1 11.1 11.1

1954 22.6 1 1 1 3.73 3.73 3.73

1955-1956 16.3 1 1 1 2.69 2.69 2.69

1957-1962 0.97 1 1 1 0.16 0.16 0.16

1963-1965 7.15 1 1 1 1.18 1.18 1.18

Type S

1953 2100 1 --- 1 347 347 347

1954 1060 1 --- 1 175 175 175

1955-1956 487 1 --- 1 80.4 80.4 80.4

1957-1962 28.9 1 --- 1 4.77 4.77 4.77

1963-1965 163 1 --- 1 27.0 27.0 27.0

 

 
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Appendix C

The thoron concentrations in Table 7-5 were calculated using the following methodology. 

A1 = AL + AT1

A2 = AL + AT2 

AT2 = AT1 e(-• * T2)

Where:

A1 and A2 = Filter activity during the first and second count 

AL = Long-lived activity on the filter paper

AT1 and AT2 = Thoron activity on the filter during the first and second count 

ATF = Thoron activity on the filter paper at the end of the sampling 

TS = Sample time (time the sample ran)

T1 = Time between the end of sampling and the first count 

T2 = Time between the first and second counts 

• = Pb-212 • = (ln(2)/10.64 hours) 

Step 1: 

Solve these three equations for AT1 as follows: 

AT1 = (A1-A2)/(1-e(-• * T2)) 

Since AT1 is the thoron activity on the filter paper during the first count, it must now be corrected 

for the decay that occurred between the end of the sampling and the first count. 

ATF=AT1 * e(• * T1}

(Note: this is a positive exponent) 

Step 2: 

To arrive at the concentration of thoron in the air, the build-up of thoron on the filter during 

sampling must be considered. This can be expressed as: 

ATF = CT*R/• * (1-e(-• * TS)) 

Where:

CT = Thoron concentration in the air

R = Sampling rate (volume per time)

This can be rearranged to:

CT = ATF * •/R/(1-e(-• * TS)) 

Combining this with the previous equations gives: 

CT = [ {(A1-A2)/(1-e(-• * T2))} * e{• * T1) ]* •/R * {1/(1-e(-• * TS))}

The underlined part represents ATF (Step 1) and the remainder is the build-up correction.