Draft White Paper 

EVALUATION OF THE IMPACT OF RECYCLED THORIUM ON 

POTENTIAL WORKER EXPOSURES AT FERNALD – 

AN INTERIM REPORT 

Contract Number 200-2009-28555 

Prepared by 

 

John H. Stiver 

Robert Anigstein, PhD 

S. Cohen & Associates 

1608 Spring Hill Road, Suite 400 

Vienna, Virginia 22182 

February 2012 

Disclaimer 

This document is made available in accordance with the unanimous desire of the Advisory Board on 

Radiation and Worker Health (ABRWH) to maintain all possible openness in its deliberations. However, 

the ABRWH and its contractor, SC&A, caution the reader that at the time of its release, this report is predecisional and has not been reviewed by the Board for factual accuracy or applicability within the 

requirements of 42 CFR 82. This implies that once reviewed by the ABRWH, the Board’s position may 

differ from the report’s conclusions. Thus, the reader should be cautioned that this report is for 

information only and that premature interpretations regarding its conclusions are unwarranted.
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Document No. White Paper –

Impact of Recycled Thorium 

Effective Date: 

 Draft – February 8, 2012 

S. COHEN & ASSOCIATES: 

Technical Support for the Advisory Board on 

Radiation & Worker Health Review of 

NIOSH Dose Reconstruction Program Revision No. 

0 (Draft) 

Evaluation of the Impact of Recycled Thorium 

on Potential Worker Exposures at Fernald – 

An Interim Report 

Page 2 of 20 

Task Manager: 

________________________ Date:____________ 

John H. Stiver, MS, CHP 

Supersedes: 

N/A 

Project Manager: 

________________________ Date:____________ 

John H. Stiver, MS, CHP 

Peer Reviewer(s): 

 Robert Barton III 

 Joyce Lipsztein 

Record of Revisions 

Revision 

Number 

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from Peer Reviewer(s) on page 2. 
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TABLE OF CONTENTS 

1.0 Introduction..........................................................................................................................4 

2.0 Recycled Thorium Source Term..........................................................................................4 

3.0 External Exposure Potential.................................................................................................6 

4.0 Internal Exposure Potential..................................................................................................7 

5.0 Summary............................................................................................................................10 

6.0 References..........................................................................................................................11 

Attachment 1: SRDB Documents Relevant to Recycled Thorium Exposures at Fernald ............14 
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1.0 INTRODUCTION 

Recently an issue was raised regarding potential worker exposures (internal and external) from 

recycled (irradiated) thorium (referred to herein as RT) that was received and processed at 

Fernald. Thorium was fabricated into reactor fuel and targets that were irradiated in the 

production reactors to produce U-233. The U-233 that was created in the irradiated thorium fuel 

was chemically separated and extracted. Although the primary goal of the thorium programs 

was to produce U-233, the chemical process developmental work included thorium recovery for 

reuse. It is this recovered thorium that is of interest in this report. SC&A first became aware of 

receipts of RT at Fernald based on discussions that transpired during the Savannah River Site 

teleconference on August 12, 2011. SC&A’s previous investigations of thorium (Th-232) 

exposures at Fernald have focused on the proposed NIOSH internal dose coworker models based 

on air sampling and chest count data [Special Exposure Cohort (SEC) issue #6], as well as 

intakes of Th-230 from raffinates (SEC issue #4). Our concern regarding RT is principally 

related to unmonitored exposures to the uranium isotopes U-233, U-232, and to a lesser extent, 

Th-234, Pa-234m, Pa-233, and fission products during processing, handling, and storage of these 

materials.1 A review of documents in the Site Research Database (SRDB) has revealed that 

hundreds of metric tons of RT were received at Fernald from the mid-1960s through the late 

1970s. Recycled thorium was received at Fernald from Hanford and the Savannah River Site 

(SRS), predominately in the form of thorium nitrate tetrahydrate (TNT) solution, transported in 

trucks and rail tank cars. These materials were introduced into thorium processing campaigns, 

which took place mainly in the Pilot Plant and Plant 8 during this timeframe (Morris 2008). 

SC&A does not see RT as an SEC issue at Fernald, because we believe that, given a credible 

measure of thorium intake, both external and internal doses can be bounded based on the 

available data. Most SEC determinations are made on the basis of the ability to reconstruct 

internal dose. For RT, the internal dose is overwhelmingly from thorium. The principal 

contaminant radionuclides of concern in RT are isotopes of uranium. The impact of these 

isotopes on unmonitored dose is the subject of this report. 

2.0 RECYCLED THORIUM SOURCE TERM 

Attachment 1 provides a listing of SRDB documents that comprise the basis for SC&A’s 

estimate of the RT source term at Fernald. As stated in the “Introduction,” hundreds of metric 

tons of RT were received at Fernald, principally from SRS and Hanford, from about 1967 

through the late 1970s. SC&A’s analysis demonstrates that internal doses from RT constituent 

radionuclides can be bounded, based on thorium intake measurements and knowledge of the 

relative activity concentrations and radiological properties of the constituent radionuclides in the 

source material. If it is determined that changes to the NIOSH technical basis documents 

(TBDs) are in order, it will be incumbent on NIOSH to develop a more detailed spatial and 

temporal accounting of the RT receipts at Fernald and/or develop credible simplifying 

assumptions regarding worker exposure potential. 

1

 Non-uranium constituents are of lesser concern, because the RT solutions were “held up” for periods of 

time following U-233 recovery to allow for radiological decay of these short-lived isotopes (Quigley 1967). 
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Quigley (1967) contains results of an analysis of samples of thorium nitrate solution from 

irradiated thorium oxide processed at SRS. The samples were collected to determine whether it 

was feasible to handle and process RT at Fernald. The samples were collected early in 1966 

from six tank cars of thorium nitrate solution, but it is not evident from the reference how long 

after separation the samples were taken. According to Quigley (1967), thorium concentrations 

for individual carloads ranged up to 565 g/L. One gram of thorium is indicated to yield 5 × 

105

 d/m, of which 2.5 × 105 d/m are from Th-232.2 Table 1 (replicated from Table II of Quigley 

1967) gives the activity of the various nuclides and the ratios of these activities to the Th-232 

activity in the thorium nitrate solution. The tabulated values represent the highest constituent 

concentrations relative to thorium from among the tank cars and can, therefore, be assumed 

bounding. 

Table 1. Constituent Concentrations in SRS TNT 

Nuclide Activity in Th(NO3)4

Solution [dpm/ml] Activity Ratio Ratio Air MPC Ratio Water MPC 

Th-232 1.4E+05 1 1.0 1.0 

Th-234 3.7E+08 2.6E+03 1.5E+04 20 

Pa-233 2.5E+07 1.8E+02 1.0E+05 100 

Zr-95 1.6E+06 11 1.5E+04 60 

Ru-108a 9.9E+05 7.1 3.0E+03 10 

U-233 3.0E+04 0.21 50 30 

a

 This is a typo in the original document. Ruthenium-108 has a half-life of 4.55 min—there are no MPCs listed for 

this nuclide. Most likely, the nuclide is Ru-106, which had the correct ratio of MPCs in air, based on 10 CFR 20 

App. B (January 1, 1995), although the ratio for water was 100. Ruthenium-106 has a half-life of 374 d and is 

produced by fission. 

Source: Quigley 1967, Table II 

Although the age (post-separation) of the TNT solution is not provided, it was most likely newly 

separated based on the tabulated activities, the half-lives of the short-lived constituents (27 days 

for Pa-233 and 24.1 days for Th-234), and the following excerpt from page 3: 

...because of the short radioactive half-lives for these materials, decay for periods 

of eight to nine months prior to processing will result in a reduction of the Th-234 

and Pa-233 activities by a factor of 103

... 

Based on the results of the analysis reported in Quigley (1967), National Lead of Ohio (NLO), the 

M&O contractor for Fernald at the time, indicated in March 1966 that they could handle the 

recycled thorium nitrate in existing equipment without a problem. 

Uranium-232 was a concern in RT, due to its high specific activity and the external exposure 

potential posed by its gamma-emitting progeny, as discussed in Section 3.0. SC&A did not 

locate direct measurements of the U-232 content of the TNT received at Fernald. However, 

Prout and Symonds (1967) and Ellett (1964) reveal an awareness of the undesirable side 

 2

 Our independent calculations indicate that the specific activity of Th-232 = 2.43 × 10 5 d/m. 
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reactions that led to U-232 buildup during Th-232 irradiation and measures that were employed 

to limit its concentration, in accordance with Atomic Energy Commission (AEC) requirements. 

Uranium-232 levels were controlled principally by special placement of the Th-232 target 

elements in the reactor lattice during irradiation and by controlling the irradiation period. Prout 

and Symonds (1967) indicates that the U-232 formed primarily by the sequence starting with the 

(n,2n) reaction of high-energy neutrons with Th-232 was controlled to <6.5 ppm with the proper 

reactor lattice placement. Ellett (1964) indicates U-232 was similarly controlled to 50 and 

500 ppm U-233 in accordance with AEC specifications. 

3.0 EXTERNAL EXPOSURE POTENTIAL 

As noted in the introduction, as well as in Section 4.0 which follows, the principal constituent 

radionuclides of concern for RT are isotopes of uranium. Uranium-233 decays by alpha 

emission and produces weak photon radiation. Its daughter product is Th-229, which builds up 

very slowly, due to its 7,340-y half-life. Furthermore, it is also a relatively weak photon emitter. 

Consequently, any U-233 present in RT will not make any significant contribution to doses from 

external exposure. 

The other significant uranium isotope in RT is U-232. This nuclide also decays by alpha 

emission and, by itself, is a very weak photon emitter. However, its daughter product is Th-228, 

which has a half-life of about 1.9 years. This nuclide grows in over a period of years, reaching 

50% of full equilibrium after one half-life. Thorium-228 rapidly achieves full equilibrium with 

its short-lived progeny, which includes several powerful gamma emitters, most notably Tl-208, 

which emits a 2.6 MeV gamma. As shown in Table 2 in Section 4, the maximum likely activity 

concentration of U-232 in TNT solution is about 25% of the Th-232 concentration. The decay 

chain of Th-232 also includes Th-228 and its progeny, as shown below: 

232Th α → 228Ra t1⁄2 = 5.75 y

ß → 228Ac t1⁄2 = 6.15 h ß → 228Th t1⁄2 = 1.9 y

Freshly purified Th-232 potentially contains large amounts of Th-228, due to the chemical 

similarity of these two isotopes and the fact that they will usually be found together in the natural 

environment. However, it will be separated from its Ra-228 daughter during purification. In 

time, however, the Th-228 will decay, and, being an unsupported progeny, will only grow in 

after the ingrowth of Ra-228. This latter nuclide grows in more slowly, due to its 5.75-y halflife. After prolonged storage, equilibrium with the entire Th-232 decay chain will be reestablished. Given that Fernald stored very large quantities of Th-232, which would be in at 

least partial equilibrium with its progeny, the potential radiation exposure from the trace 

quantities of U-232 would be subsumed by the exposures to stored Th-232. In any case, any 

external exposures to photon radiation would be monitored by the dosimeters worn by Fernald 

workers. 

The other exposure pathway concerns neutron radiation. Since for much of the operational 

period, workers at Fernald were not effectively monitored for neutron exposure, all sources of 

neutron exposure need to be considered in the dose evaluations. One source of neutron radiation 

is spontaneous fission; however, for the nuclides in question, this is an extremely rare event. 
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Thorium-232 undergoes spontaneous fission in less than one in 5 × 1010 disintegrations, while 

the ratio for U-233 is even smaller. Uranium-232 does not undergo spontaneous fission. 

The other source of neutrons is the (α,n) reaction, in which an energetic α particle impinges on a 

nucleus of a light element and produces a heavier nucleus, which may emit one or more neutrons 

as well as photons. The main nonradioactive constituent of TNT is water. Hydrogen does not 

undergo an (α,n) reaction; neither does O-16, the most common isotope of oxygen. Oxygen-17 

and 18 have very large (α,n) reaction cross-sections and can, therefore, potentially contribute to 

neutron emission. However, since these isotopes constitute only 0.038% and 0.205%, 

respectively, of natural oxygen, oxygen is not a powerful source of neutrons via the (α,n) 

reaction. Of the materials that are found at Fernald, UF4 and UF6 are among the strongest 

sources of neutron emission, and have high neutron-to-photon (n:p) ratios. The n:p ratio for 

TNT, and for RT in general, would be lower than that for UF4. 

In summary, the presence of RT at Fernald does not significantly contribute to external 

exposures. 

4.0 INTERNAL EXPOSURE POTENTIAL 

As noted in the introduction, the principal constituent radionuclides of concern for RT are 

isotopes of uranium. The problem is therefore one of determining if these isotopes contribute 

appreciably to internal dose, and if so, determining sufficiently accurate and bounding “default” 

levels of U-233 and U-232 to be included in a Th-232 intake. Those bounding activity 

concentrations relative to Th-232 are provided in Table 2. Table 2 provides activity ratios for 

U-233 and U-232 relative to Th-232, based on the values reported for the six cars of TNT 

sampled in 1966 and reported in Table 1, and the range of U-232/U-233 mass ratios of 7, 50, and 

500 parts per million (ppm) reported in Prout and Symonds (1967) and Ellett (1964). 

Table 2. U-232 and U-233 Activity Ratios 

Nuclide Activity in Th(NO3)4

Solution [dpm/ml] Activity Ratio 

Th-232 1.40E+05 1 

U-233 3.00E+04 0.21 

500 3.29E+04 0.249 

U-232* 50 3.29E+03 0.025 

7 4.61E+02 0.0035 

*ppm on U-233 mass basis 

A worker’s organ doses from intakes of U-232 and U-233 in RT can be determined by applying 

the appropriate ICRP dose conversion factors (ICRP 1994) to the applicable “default” intakes of 

U-232 and U-233, as based on Th-232 source term data in Table 2. 

It is clear that any determination of internal dose from RT constituents is predicated on the 

ability to derive a bounding and sufficiently accurate Th-232 intake. As a cautionary note, at the 

time that this report was prepared, it is the ability to reconstruct Th-232 intakes post-1968 that 
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poses the greatest obstacle to assessing dose from RT constituent radionuclides. The Fernald 

Work Group has agreed that breathing zone air sampling data in the form of daily weighted 

exposures (DWEs) can be used to reconstruct Th-232 intakes for the period from 1953–1967. 

Beginning in 1968, however, Fernald phased out the DWE-based intake assessments in favor of 

individual in-vivo chest counts using the Mobile In-Vivo Radiation Monitoring Laboratory 

(MIVRML). Chest count data were used to monitor thorium and uranium intakes from 1968–

1989. Because the source data for these determinations are not available for 1968–1978, the 

issue of whether the chest count data for that period are sufficiently accurate to reconstruct 

Th-232 intakes in an SEC context remains open. If it is determined that the in-vivo thorium 

results are not sufficiently accurate for use in a coworker model, then the issue of RT 

constituents is rendered moot for that period of time. 

 

It is evident from Table 2 that the estimated U-232/Th-232 activity ratio in TNT, as derived from 

the highest reported U-232 concentration of 500 ppm on a U-233 mass basis, is about 0.25; just 

slightly higher than the value of 0.21 reported for U-233. To put the potential dose impact of 

U-232 and U-233 relative to thorium in RT in perspective, Table 3 provides activity-adjusted 

ratios of 50-year inhalation organ dose coefficients for U-232 and U-233 relative to Th-232 for a 

single inhalation intake of absorption Types M and S.3

Table 3. 50-year Dose Coefficients Ratios (U/Th) for RT 

Organ 0.249 (U-232/Th-232) 0.21 (U-233/ Th-232) 

Type M Type S Type M Type S 

Adrenals 0.034 0.061 0.005 0.005 

Bladder Wall 0.034 0.060 0.005 0.005 

Bone Surface 0.008 0.036 0.000 0.001 

Brain 0.034 0.060 0.005 0.005 

Breast 0.034 0.061 0.005 0.005 

Esophagus 0.034 0.061 0.005 0.005 

St Wall 0.034 0.061 0.005 0.005 

SI Wall 0.034 0.060 0.005 0.006 

ULI Wall 0.036 0.075 0.005 0.008 

LLI Wall 0.040 0.098 0.005 0.014 

Colon 0.038 0.083 0.005 0.011 

Kidneys 0.031 0.070 0.009 0.010 

Liver 0.036 0.095 0.003 0.004 

Muscle 0.034 0.060 0.005 0.005 

Ovaries 0.015 0.040 0.002 0.002 

Pancreas 0.034 0.061 0.005 0.005 

Red Marrow 0.018 0.065 0.001 0.001 

ET Airways 0.398 0.633 0.182 0.145 

Lungs 0.420 0.484 0.223 0.115 

Skin 0.034 0.061 0.005 0.005 

Spleen 0.034 0.060 0.005 0.005 

Testes 0.015 0.040 0.002 0.002 

Thymus 0.034 0.061 0.005 0.005 

Thyroid 0.034 0.060 0.005 0.005 

Uterus 0.034 0.060 0.005 0.005 

 3

 TNT is Type M and is most representative of the RT received at Fernald. Type S materials were also 

present as the result of processing the TNT into oxide, ThF4, and thorium metal. 
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Table 3. 50-year Dose Coefficients Ratios (U/Th) for RT 

Organ 0.249 (U-232/Th-232) 0.21 (U-233/ Th-232) 

Type M Type S Type M Type S 

Remainder 0.035 N/A 0.005 N/A 

Effective Dose 0.041 0.539 0.016 0.121 

It is evident from Table 3 that the dose potential from thorium far outweighs that from uranium 

constituents at the bounding activity concentrations reported in Table 2. 

Unusually high dose ratios were observed for the remainder organs for inhaled U-232 and 

U-233, 5 micron, Class S. SC&A found that the remainder dose is incorrectly calculated in the 

ICRP CD Ver. 2.01 (Eckerman et al. 2001) and recalculated the 50-year remainder dose, based 

on the average of 10 tissues, and obtained 1.6 E-7 and 2.0 E-8 for U-232 and U-233, 

respectively, instead of 1.4E-4 and 3.8E-5. Because there appears to be an error in the remainder 

dose coefficients as calculated in the ICRP CD Ver. 2.01, those ratios are omitted from the 

comparison in Table 3. 

The intakes of U-232 and U-233 will comprise some fraction of the total intake of RT. From a 

practical dose reconstruction standpoint, it is important to determine whether the dose increments 

from U-232 and U-233 in RT comprise a significant contribution to the total dose. If so, an 

adjustment to the internal dose TBD (ORAUT 2004) may be in order. 

To estimate the relative impact of the U-232/U-233 dose increment from measured intakes of 

Th-232, SC&A reviewed the records for a select group of thorium workers (chemical operators) 

at Fernald. For illustrative purposes, the results for one of these workers are presented in 

Table 4. Note that the veracity of thorium results reported in mg from 1968–1978 is an SEC 

issue for the Fernald Work Group. The use of mg thorium values in this illustrative example is 

for convenience only and does not imply an implicit acceptance of their use in dose 

reconstruction. 

Table 4. Chest Measurement of Thorium 

Measurement Date Th-232 (mg) 

Case 1 April 1968 Negative (0) 

July 1969 9.1 

The following hypothetical calculations using Case #1 in Table 4 provide a first-order 

comparison of the 50-year dose commitment one might expect from intakes of U-233 and U-232 

in RT relative to Th-232, assuming that all of the Th-232 was from RT. 

 

Case 1: U-232 and U-233 dose increment from RT intake assuming all of the inhaled thorium in 

the year was from RT. Type M thorium is assumed (thorium nitrate). 

In order to calculate the U-232 and U-233 intakes, it is necessary to estimate the Th-232 intake 

that resulted in a chest burden of 9.1 mg. For this particular worker, the only available 

monitoring results are indicated in Table 4. The first one gave a negative result, indicating that 
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thorium exposures occurred between April 1968 and July 1969. There is no information on the 

period of time the worker was exposed. For this illustrative example, a 30-day exposure period 

was assumed. This 1-month exposure could have taken place during any month between April 

1968 and July 1969. For this example, the following dates of exposures are assumed: 

1.a July 1968 (in-vivo monitoring done 335 days after last day of exposure) 

Th-232 U-233 U-232 

Intake (Bq/d) 282 60 71 

Bone Surface Committed Equivalent Dose (Sv) 14.7 5 E-3 9.8 E-2 

Lung Committed Equivalent Dose (Sv) 1.3 3 E-2 5.7 E-2 

1.b February 1969 (in-vivo monitoring done 150 days after last day of exposure) 

Th-232 U-233 U-232 

Intake (Bq/d) 94 20 24 

Bone Surface Committed Equivalent Dose (Sv) 5.0 1.8 E-3 3.3 E-2 

Lung Committed Equivalent Dose (Sv) 0.4 1.0 E-2 1.9 E-2 

1.c June 1969 (in-vivo monitoring done 30 days after last day of exposure) 

Th-232 U-233 U-232 

Intake (Bq/d) 38 8 9.4 

Bone Surface Committed Equivalent Dose (Sv) 2 7 E-4 1.3 E-2 

Lung Committed Equivalent Dose (Sv) 0.2 4 E-3 7.6 E-3 

Although this simple calculation reflects only three hypothetical exposure scenarios among 

many, it does suggest that U-232 and U-233 in the concentrations reported in RT TNT solutions 

result in modest dose increments for most organs in comparison to thorium doses. The 

hypothetical RT dose is also based on the maximizing assumptions that all Th-232 was from RT, 

and that U-232 existed in the highest reported concentration of 500 PPM U-233. 

5.0 SUMMARY 

SC&A’s investigations into potential dose from RT indicate that the presence of RT at Fernald 

does not significantly contribute to unmonitored external exposures. Internal exposures from RT 

are predominantly from thorium. However, as illustrated in the three exposure scenarios 

presented in Section 4, U-232 and U-233 intakes at the indicated levels can still result in rem 

level organ doses. Thus, NIOSH may wish to further investigate the impact of uranium 

contaminants in RT when assigning internal dose commitments from intakes of thorium at 

Fernald. 
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6.0 REFERENCES 

10 CFR 20, 1991. Title 10, Part 20: Standards for Protection Against Radiation. Appendix B 

January1, 1995. 

Audia, S.F., 1977. U-233 as a Contaminant in Hanford Thorium Nitrate Solution. National Lead 

Company of Ohio. Cincinnati, Ohio. May 19, 1977. REF ID: 43563. 

Chapman, C.R., 1971. Possible Sources of Feed for Thorium Metals by Commercial Vendors. 

National Lead Company of Ohio. Cincinnati, Ohio. June 25, 1971. REF ID: 28982. 

Dunaway, D.L., 1968. Disposition of Thorium Waste Solution Containing U-233. National 

Lead Company of Ohio. Cincinnati, Ohio. December 20, 1968. REF ID: 43165. 

Earle, G.W., 1966. Calculated Radiation Levels from Recovered Thorium. E.I. du Pont de 

Nemours & Company – Savannah River Plant. Aiken, South Carolina. March 11, 1966. REF ID: 

49906 

Eckerman, K.F., et al. 2001. ICRP Database of Dose Coefficients for Workers and Members of 

the Public, Version 2.01, International Commission on Radiological Protection, 2001. 

Ellett, J.D., 1964. Technical Data Summary – Chemical Processing of Irradiated Thorium. E.I. 

Du Pont De Nemours and Company. Aiken, South Carolina. January 10, 1964. REF ID: 49524 

Gessiness, B., 1978. NMC Report on the Thoria Gel Process – May 1977 Through June 30, 

1978. National Lead Company of Ohio. Cincinnati, Ohio. August 21, 1978. REF ID: 43178. 

Gibbs, A., 1994. Uranium, Thorium, and TRU Inventories at SRS (U). Westinghouse Savannah 

River Company – Solid Waste & Environmental Restoration – Solid Waste Engineering. Aiken, 

South Carolina. Document #WSRC-TR-940255. May 1994. REF ID: 49576. 

Harmon, L.H. 1977. Material Type Code Lot Marking of Thoria Gel. National Lead Company 

of Ohio. Cincinnati, Ohio. October 10, 1977. REF ID: 43180. 

ICRP (International Commission on Radiological Protection) 1994. Dose Coefficients for 

Intakes of Radionuclides by Workers, ICRP Publication 68, Annals of the ICRP Volume 24/4, 

Elsevier. July 1994. 

Jenkins, W.A., 1955. Radioactivity of the U-233 Product and Recovered Thorium. E.I. Du Pont 

De Nemours and Company – Explosives Department. Wilmington, Delaware. February 18, 

1955. REF ID: 49518. 

Monier, J.A. Jr., 1967. Thorium Tank Car Requirements. E.I. du Pont de Nemours & Company 

– Savannah River Plant. Aiken, South Carolina. October 17, 1967. REF ID: 58561. 
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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.

Morris, R.M., 2008. FMPC Thorium Timeline with Attribution and Annotation. National 

Institute of Occupational Safety and Health (NIOSH). February 29, 2008. SRDB REF ID: 

42940. 

Nelson, M.S., 1970. Specifications for Thorium Nitrate Produced for Tennessee Nuclear 

Specialties, Inc. And Nuclear Chemicals and Metals Corporation. National Lead Company of 

Ohio. Cincinnati, Ohio. November 25, 1970. REF ID: 28958. 

NLO Undated. Thorium Accountability Documents, 1965-1967. National Lead Company of 

Ohio. Cincinnati, Ohio. REF ID: 43017. 

NLO 1975. Environmental Assessment of the Processing of Reactor Recycle Materials 

Containing Transuranium Elements. National Lead Company of Ohio – Health and Safety 

Division. Document #: NLCO-1130. Cincinnati, Ohio. November 17, 1975. Ref ID: 17333. 

Noyes, J.H., 1969. Shipment of Thorium Nitrate Solution to NFS (H-038). National Lead 

Company of Ohio. Cincinnati, Ohio. June 2, 1969. REF ID: 43177. 

ORAUT 2004. Technical Basis Document for the Fernald Environmental Management Project 

(FEMP) – Occupational Internal Dose. Oak Ridge Associated Universities Team – NIOSH 

Dose Reconstruction Project. ORAUT-TKBS-0017-5 Rev. 00. May 28, 2004. 

Orth, D.A., 1978. SRP Thorium Processing Experience. E.I. du Pont de Nemours and Company 

– Savannah River Plant. Aiken, South Carolina. June 1978. REF ID: unavailable. 

Prout, W.E., and A.E. Symonds, 1967. Recovery of Thorium and Uranium-233 from irradiated 

Thorium Oxide and Metal. Savannah River Laboratory. Aiken, South Carolina. January 1967. 

REF ID: 49306. 

Quigley, J.A., 1967. Analysis of Health Problem in Processing Recycle Thorium. National Lead 

Company of Ohio. Cincinnati, Ohio. April 10, 1967. REF ID: 29545. 

Radford, L., 1992. Major Thorium Campaigns at FMPC NLO/Fernald 33266-0001-6. Kirkland 

and Ellis. June 18, 1992. REF ID: 41375. 

St. John, D.S., and E.C. Toops, 1958. Formation of U-232 during Irradiation of Thorium. E.I. 

du Pont de Nemours & Co. – Savannah River Laboratory – Atomic Energy Technical Division. 

Aiken, South Carolina. April 1958. SRDB REF ID: 76140. 

Stoddard, D.H., 1963. Hard Gamma Dose Rates from U-233 Enriched Natural Thorium 

Assemblies. Savannah River Laboratory – Technical Division. Aiken, South Carolina. 

December 23, 1963. REF ID: 49520. 

Various Authors 1968. Letters Concerning Th Disposition in 1968 Accounting. National Lead 

Company of Ohio. Cincinnati, Ohio. 1968. REF ID: 44392. 
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NOTICE:

Various Authors 1977. Shipping Papers for Th from Hanford to Fernald 1977. National Lead 

Company of Ohio. Cincinnati, Ohio. 1977. REF ID: 43558.
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ATTACHMENT 1: SRDB DOCUMENTS RELEVANT TO RECYCLED THORIUM EXPOSURES 

SRDB Source Dates Quantity Chemical/Physical Form and Containment Potential Exposure Pa

17333

(NLO 1975) 

1975 report Thorium nitrate 

tetrahydrate (TNT) solution. 

Recycle thorium will probably be for purification in the Pilot Plant sthis system, thorium is extracted fdiamylamyl phosphonate-solvesso extracted from the organic phase iwater solution. The resulting purinitrate may be shipped, or it may bthorium compound or to metal. 

41375

(Radford 1992) 

Impure TNT from various places; residues from Hanford and France 

1964–1976 940 tons TNT solution. Page 5: Pilot Plant–solvent extrac

43177

(Noyes 1969) 

Richland Office 

FY 1969 46 tons Oxide. Page 18: Preparation for shipping 

truck cars, but not established. 

FMPC process residues 

1/31/69 190 gal in 4 

55-gal drums 

Raffinate. Page 20: Thorium content of 438 

U-233 about 22.5% for a total of aRetained in isolated storage area o

SRS 1970 40 tons TNT solution. Page 13: Tank cars. SRS 1971 40 tons TNT solution. Page 13: Tank cars. 

Pages 4–9: Process flow diagram

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SRDB Source Dates Chemical/Physical Form Quantity Potential Exposure Pa

and Containment 

43017

(NLO undated) 

French thorium nitrate 

1965–1967 Various: 

100–200 tons 

TNT solution or crystals (contaminated with ionium page 47: high = > 2.7 ppm) 

Material procured and/or available breeder (LWB) reactor program. New Jersey, purified at Fernald anliquid TNT. Page 35: Thorium purification on suggests the following course of aat 1 ton/d. "supplement the feed sumaterials, such as thorium metal, Lrecycled ThO2." Page 49, item b: "1/2 ton per day solution when poor feed is used (pdefined, but was used during most of being thorium feed high in uranPages 22–24: Describes the transfMiddelsex to NLO. Last shipmenMiddlesex closed in 1966. Pages 72–74: Flow diagrams of ddenitration process. 

43165

(Dunaway 1968) 

Process residues 

1968 190 gal in 4 

55-gal drums 

Raffinate. See 43177, line 2. 

Beginning of the document talks acontaining a lot of U-233. Page 4 been separated from Hanford recythrough the Pilot Plant Y solvent ePage 21: Problems of cross contain several reports, but this appears in processing streams and not RT. Page 48: Discusses Richland operNuclear fuel requirements, and "h

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SRDB Source Dates Chemical/Physical Form Quantity Potential Exposure Pa

and Containment 

43178

(Gessiness 1978) 

Hanford (Richland Office) 

May 1977–June 1978 

Tables on pages 4 (June 1978) and 7 (Sep. 1978) have quantitative information on U-233 content. 

TNT solution. Pages 2–3: 20 tank cars processed

Page 3: About 93% to 95% U-23thoria gel processing. Pages 6-8: Total of 28 tank cars fTable 1: Mass balances and partitPage 8: Displays the receipts in ksolution received from Hanford (sSeptember 1978) Page 13: Lists "returns from PZAdesignated as French Source." 

43180

(Harmon 1977) 

Hanford (Richland Office) 

1977 Page 3: 

Quantitative information on U-233 mass and concentration in 8 tank cars 

TNT solution. Thoria Gel Process – May (Startup

1977. Page 3: "The NMC Department cRichfield Hanford Company, Rich24, 1977, and requested that they thorium nitrate solution having higuntil the latter part of the campaigTable 1, page 5: 94% U-233 retai

43558

(Various authors 

1977) 

Hanford 1977 Tank cars of 

TNT 

TNT solution. Contains shipping receipts for tho

containing "unseparated U-233" frPage 26: U-233 assay 5.7 ppm Th

43563 

(Audia 1977) 

Hanford 1977 33 rail car 

shipments over 2 years beginning March 1977. 2 cars per month 

TNT solution. U-233 content about 130 grams/ca

Pages 2–3: Storage configuration 2000 g total “trigger” value to be d

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SRDB Source Dates Chemical/Physical Form Quantity Potential Exposure Pa

and Containment 

28958

(Nelson 1970) 

NLO (FMPC) Nov. 25 1970 NA TNT. November 1970: "The major sour

stream are now as follows: 1. Refrom Savannah River, 2 - Thorium NLO Recovery Plant oxalate camfrom Middlesex Depot produced bRecycled thorium nitrate solution equivalent to French TNT except 

44392

(Various authors 

1968) 

FMPC Process residues 

1968 190 gal in 4 

55-gal drums 

Raffinate. See 43177, line 2. 

Page 7: "On November 15, the th(DWY) remaining from the purifi(1,155 tons) of recycled thorium ffour stainless steel 55-gallon drumimpurity separated from this recycthis "waste" solution." 

29545

(Quigley 1967) 

Hanford or SRS (likely SRS based on context relative to other memos) 

1967 Six carloads of 

thorium nitrate solution 

TNT solution. This is likely the first RT to arrive at FMPC. 

Page 3: (Source term info): "Refinformation for six carloads of thoThorium concentrations for indivi[illegible] to 565 g/l. For this anaconcentration of thorium was chosyields 5×105 d/m, of which 2.5×10Page 5: Table 2 contains contami

28982

(Chapman 1971) 

SRS 1971 Not specified TNT solution. “During the last thorium metal cam

considerable amount of Savannah solution directly without purificatiprocesses." 

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SRDB Source Dates Chemical/Physical Form Quantity Potential Exposure Pa

and Containment 

49306

(Prout and 

Symonds 1967) 

SRS 1967 Not specified Recovery of Thorium and Uranium

Thorium Oxide. Page 10: The U-232, formed primstarting with the (n,2n) reaction of Th-232, was controlled to <6.5 pplattice. Page 12: Figures 1 and 2 outline iproducts and activity in irradiated 3: relative gamma activity in sepaprocessing. Important for externa

49518 

(Jenkins 1955) 

SRS 1955 NA Mostly provides 

calculated dose rates for U-233 and recovered Th-232 metal products as either billets or rods. This might be useful for determining the dose rates from thorium metal produced at FMPC from RT. 

Page 4: Table II gives radioactivithorium billets after many cycles tpre-separation cooling times. Page 6: Diagram of important reaactivity in the recovered thorium eseparations plant. Pages 9-10: First order dose estimrequirements. Split lag processing and intensity metal after multiple irradiations. APPENDIX II Induced Th-228 in Th-232. The cTh-228 in Th-232 are calculated fcycle with the following schedule for the first cycle. Page 22, Figure 1: Recovered tho

49520

(Stoddard 1963) 

SRS 1963 NA Hard gamma dose rates 

from U-333-enriched natural thorium assemblies. 

Page 3: The calculated dose rates million parts U-233 at equilibrium separation) are shown in Table I. content may be made by multiplyithe part per million U-232 in U-23

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SRDB Source Dates Chemical/Physical Form Quantity Potential Exposure Pa

and Containment 

49524

(Ellett 1964) 

SRS 1963 NA Page 3: Identifies acceptance crite

To fulfill the AEC’s request for 90 than 500 ppm U-232 and for 30 kg 50 ppm U-232, the thorium is beinzones of the reactors. The two urasegregated during chemical proce

49576

(Gibbs 1994)

SRS 1994 NA Th-232 was used to make targets f

using the Th-232 (n, γ) Th-233 (βreactions. This program was com

49906

(Earle 1966) 

SRS 1966 NA Thorium nitrate in railroad 

tank cars. Dose rates calculated. 

Page 4. "Dose rate calculations inthorium reprocessing should not b400 days after reactor discharge (gand Th-228 decay curves).” Thorium recovered from the U-23stored as thorium nitrate in railroalocation for radioactive decay of Tits Pa-234 daughters. At some futdenitrated, converted to high densrecycle. Page 5: Mass concentrations of Uratios of U-232/U-233. Based upon all of this informationmade to determine radiation dose filled with Th(NO3)4, a 1 ft2 area thoria slug. Pages 5–18: Presents some source recovered thorium. Pages 19–36: Presents the sample analysis. 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Work

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Health for factual accuracy or applicability within the requirements of 42 CFR 82.

NOTICE

wever, th

SRDB Source Dates Quantity Chemical/Physical Form and Containment Potential Exposure Pa

58561

(Monier 1967) 

SRS 1967 NA Thorium nitrate in railroad 

tank cars. 

Page 2: "The Thorium II campaigArea in April 1968 will require a tClass I and one Class II, by June 1thorium nitrate solution. At the pron the Plant three Class I tank carempty. There are also available thpresent time are loaded with thoriuSRP and one is at NLO." 

76140

(St. John and 

Toops 1958) 

SRS 1958 NA Formation of U-232 during the Irr

Technical report discussing the foheterogeneous reactor, along with calculations to predict the formati

CP17E

(Orth 1978) 

SRS 1978 NA Page 3: In the five separate thoriu

conducted at SRS, thorium was prfacilities that had been converted ienriched uranium. Two different flow sheets were usapproximately 240 tons of thorium processed. In these two initial camconditions for the thorium metal r40 to 50 ppm and 200 ppm U-232 product uranium.