White Paper, Rev. 0 Weldon Spring Thorium August 27, 2012 

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Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH

or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This

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White Paper

Weldon Spring Thorium Processing Investigations

Revision 0

August 27, 2012
White Paper, Rev. 0 Weldon Spring Thorium August 27, 2012 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its

Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH

or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This

document represents preliminary positions taken on technical issues prepared by NIOSH or its contractor.

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

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Background

The Uranium Division of the Mallinckrodt Chemical Works operated the Weldon Spring 

Chemical Plant (WS) for the U.S. Atomic Energy Commission (AEC) from 1957 to 1966. WS 

converted uranium ore concentrates and scrap to pure uranium trioxide, uranium tetrafluoride, 

and uranium metal. Wastes from plant operation are referred to as raffinate and include waste 

from extraction, and solids that result from neutralization. These wastes were pumped as slurry 

to four large pits (Raffinate Pits) that were constructed immediately adjacent to the plant. 

A concern has been raised that workers at WS may have worked with thorium recovered from a 

nuclear reactor, hereafter referred to as RTh, and that NIOSH has not appropriately addressed 

any potential exposures resulting from processing the RTh.

The word “recycled” has several different meanings in the nuclear industry, and at times has 

been used to describe reactor-recovered materials. These different uses of the term “recycled” 

have been a source of confusion that this paper will confront. 

When irradiated thorium is harvested from a nuclear reactor it is mixed with other nuclides that 

affect the potential worker exposures, which then change the dose assigned to workers. For 

example, if the WS work were with RTh, dose reconstructions would include actinides and 

fission product nuclides, but if the work was with natural thorium (ThNat) those additional 

nuclides are not included.
White Paper, Rev. 0 Weldon Spring Thorium August 27, 2012 

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Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH

or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This

document represents preliminary positions taken on technical issues prepared by NIOSH or its contractor.

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There is clear documentation of work with thorium at WS, but because of the impact irradiatedthorium has on the resulting dose, knowledge of the origin and if the thorium was previously 

irradiated is necessary to determine the dose appropriately. 

A petitioner, based on six documents made available through the Freedom of Information Act, 

raised the concern that WS work was performed with RTh. A summary of those documents is in 

Appendix-Petitioner Documents at the end of this paper. 

Discussion

NIOSH undertook two paths of investigation to determine if RTh could have been processed at 

WS. First, NIOSH researched WS inventory records again, searching for any indication of a 

source of thorium that could have included RTh. Then NIOSH researched records pertaining to 

the project to recover thorium from reactors looking for evidence of transfers of RTh to Fernald, 

since all thorium transfers to WS came via Fernald.

Which type of thorium did WS process?

Historical Nuclear Materials Balance Report for the Former AEC Owned WS Chemical Plant 

WS, MO (DOE, Jul1986) is a DOE report that identifies the quantities of nuclear material 

received and processed at WS. The report states that its accuracy was verified by comparison to 

audited performance-data reported to or generated by the AEC. The search for data in this report 

included: (1) two thorough searches of retired AEC/DOE files retained in Oak Ridge, TN, (2) an 

inspection of the files retained at WS, (3) contacts with the U. S. Government Records Center, 

St. Louis, MI, and (4) reviews of active DOE files.

In the Summary, the report states, “from June 1957 through December 1966, four (4) types of 

nuclear material were processed in the AEC-owned WS Chemical Plant”. These materials were:

(1) Natural uranium (UNat) (98% of WS throughput), 

(2) Depleted uranium (0.14% of WS throughput), 

(3) Slightly enriched uranium (UEn) (0.68% of WS throughput), and 

(4) ThNat (0.76% of WS throughput). 

The processing of these four materials is further described as “continuously throughout the life of 

the plant” for UNat, and the three remaining material types were “received and processed on an 

intermittent basis”. 
White Paper, Rev. 0 Weldon Spring Thorium August 27, 2012 

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Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH

or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This

document represents preliminary positions taken on technical issues prepared by NIOSH or its contractor.

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Section 5.1.4 shows the annualized ThNat balances for the entire ten-year WS operating life. 

There is an entry for a trivial amount (44 kg) at the start of WS operations in 1958, but that 

amount remained static until 1962. There is a similar case for UEn. These materials appear to be 

concentrates “stored at the site prior to the start of the processing” as identified in Section 2.0. 

However, significant receipt and processing of ThNat is shown to start in FY1964. 

The material balances shown in the Historical Nuclear Materials Balance Report (referenced 

above) are corroborated by a separate balance report generated by the plant owners 

(Mallinckrodt), and presented in Weldon Spring Plant Nuclear Material Balances Final Report 

Summary by Year and Annual Material Balances, Appendix A (Mallinckrodt, Jan1986). In it, 

Mallinckrodt similarly reports receiving 44 kg of ThNat in 1958, in a section of the report labeled 

“other materials” whose quantities remained static. Those same 44 kg remain on their balance 

until 1962 when 39 kg were shipped off site. The Mallinckrodt report remains in agreement with 

the DOE report and shows WS receiving the first significant quantity (13,111 kg) of ThNat after 

July 1, 1963. This report also shows ThNat processing started after July 1, 1963 by showing 

additions to Raffinate Pit 3 at that time. 

Reports that show waste (Raffinate) generation can also be used to determine when processing 

occurred. Material processing at WS generated significant quantities of waste; ~ 2 lbs. of waste 

generated for each 1 lb. of material processed. Sections 2.1.4 and 5.1.4 of Historical Nuclear 

Materials Balance Report for the Former AEC-Owned Weldon Spring Chemical Plant, Weldon 

Spring, Missouri (DOE, Jul1986) indicate that ThNat was received in a nitrate or oxide form, 

batch processed in the refinery and wastes were sent to the Raffinate Pit. Section 2.3.1 of 

Interim Work Plan for the Weldon Spring Site Remedial Action Project (WSSRAP) (DOE,

Jun1986) states that Th232 Raffinates were sent to the Pit between July 1, 1963 and December 16,

1966 (Note: ThNat is, by mass, virtually all Th232). To summarize this: (1) processing generates

waste, (2) all waste was sent to Pits 3 and 4, and (3) Pits 3 and 4 received this waste from July 1, 

1963 to December 16, 1966. 

There was some processing at WS of some extremely pure thorium nitrate tetrafluoride for the 

production of thorium oxide documented (Bonfer, 1988; Thorium, 1965-1967). This material 

was shipped from Fernald to WS starting in November 1963 until December 1966, and was 

concentrated ThNat not RTh.

Where was the RTh prior to the 1966 WS closure?

The figure, Flow of Materials through the Nuclear Weapons Complex (DOE, 1997) shows the 

typical flow of nuclear materials in the mid 1960’s, and for WS to receive RTh from a reactor 

site (i.e. SRS or Hanford) it would first have to be processed at Fernald. Fernald could not have 

shipped RTh to WS, because they did not receive any until after AEC operations ceased at WS in

1966. 
White Paper, Rev. 0 Weldon Spring Thorium August 27, 2012 

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Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH

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document represents preliminary positions taken on technical issues prepared by NIOSH or its contractor.

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SRS records indicate the first Thorex campaign (1964-1965) did not recover the thorium during 

the separation of U-233. It was not until the second campaign (1965-1966) that they recovered 

the thorium in nitrate form and shipped it to Fernald. The document, By-Product Thorium Nitrate 

Solution Handling and Storage (Hobert, 1965) discusses a meeting held “on November 15, 1965, 

to inform interested persons on the plans for handling and storage of the thorium nitrate solution 

that will be produced in 221H building during the Uranium -233, Thorex program”. A schedule 

in this memo indicates the first loading of thorium nitrate would begin later in the November 

1965 and continue through the beginning of 1966. Then the material would be aged in the tank 

cars for a year before shipping. This is the earliest shipment of significant quantities of RTh to 

Fernald from the reactor sites which based on the schedule, could not have occurred prior to 

November 1966. 

As documented in Interim Work Plan for the Weldon Spring Site Remedial Action Project

(WSSRAP), Fernald conducted a feasibility study, starting in January 1966 and finished in March 

1966, to determine the safe handling of RTh (DOE, June 1986). This study examines possible 

future handling of RTh and refers to six rail carloads of RTh generated as part of the Savannah 

River Site’s (SRS) Thorex campaign. 

Fernald conducted another feasibility study in March 1967 to determine, among other things, 

waste disposition options for their thorium hydroxide production. This process utilized RTh 

from the SRS Thorex campaign and is documented in Radium and Ruthenium in Effluent from 

the Production of Thorium Hydroxide (Ross, 1967). 

Conclusion

The results obtained during this two-pronged NIOSH investigation show the WS processed ThNat

from 1963 to 1966 inclusive, and WS did not process RTh.

Inventory records were extensively searched and closely examined, and no evidence was 

discovered that show WS possessed any thorium types other than ThNat.

Materials recovered from reactors operated as part of the nuclear weapons complex were 

positively controlled and well documented during this period. These documents clearly show the 

majority of the RTh at Fernald was not received until after 1967 and into the 1970s, and therefore 

were not available to WS prior to the end of AEC operations there in 1966. 
White Paper, Rev. 0 Weldon Spring Thorium August 27, 2012 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its

Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH

or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This

document represents preliminary positions taken on technical issues prepared by NIOSH or its contractor.

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

Page 6 of 8 

References

Bonfer, 1988, Thorium-A Search of Available Records at the FMPC, PO(DCB)88-012; D. C. 

Bonfer; November 15, 1988; SRDB Ref ID: 9012 

DOE, Jun1986, Interim Work Plan for the Weldon Spring Site Remedial Action Project 

(WSSRAP), select pages, DOE/OR-869; Department of Energy (DOE); June 1986; SRDB Ref 

ID: 3645, pdf pp. 311-317 

DOE, Jul1986, Historical Nuclear Materials Balance Report for the Former AEC-Owned 

Weldon Spring Chemical Plant, Weldon Spring, Missouri, DOE/OR-872; Department of Energy 

(DOE); July 1986; SRDB Ref ID: 3645, pdf pp. 130-160 

DOE, 1997, Flow of Materials through the Nuclear Weapons Complex, diagram from page 122 

of Linking Legacies document; Department of Energy (DOE); January 1997; SRDB Ref ID:

3645, pdf p. 2 

Heatherton, 1967, Analysis of Health Problems in Processing Recycle Thorium, correspondence 

to J. A. Quigley; R. C. Heatherton; April 10, 1967; SRDB Ref ID: 29545 

Hobert, 1965, By-Product Thorium Nitrate Solution Handling and Storage; R. H. Hobert; 

November 19, 1965; SRDB Ref ID: 58541 

Kleeschulte, unspecified, Compilation and Preliminary Interpretation of Hydrologic Data for the 

Weldon Spring Radioactive Waste-Disposal Sites, St. Charles County, Missouri—a Progress 

Report; Michael J. Kleeschulte and Leo F. Emmett; unspecified date; SRDB Ref ID: 3645, pdf 

pp. 254-263 

Mallinckrodt, Jan1986, Weldon Spring Plant Nuclear Material Balances Final Report Summary 

by Year and Annual Material Balances, Appendix A; Mallinckrodt; January 13, 1986; SRDB 

Ref ID: 3645, pdf pp. 265-272 

Ross, 1967, Radium and Ruthenium in Effluent from the Production of Thorium Hydroxide, 

correspondence to R. H. Starkey; K. N. Ross; March 13, 1967; SRDB Ref ID: 42850 

Thorium, 1965-1967, Transfer of Thoria/Thorium Nitrate to Weldon Spring, various memos; 

authors include J. H. Cavendish, J. H. Noyes, C. L. Karl, and George Rennich; various dates 

from September 21, 1965 through April 19, 1967; SRDB Ref ID: pdf pp. 15-19, 32-36, 41-42, 

and 48-55 
White Paper, Rev. 0 Weldon Spring Thorium August 27, 2012 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its

Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH

or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This

document represents preliminary positions taken on technical issues prepared by NIOSH or its contractor.

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

Page 7 of 8 

Appendix-Petitioner Documents

This Appendix includes select statements and information from documents provided by the 

petitioner through an email to SC&A, dated March 20, 2012. The petitioner supplied the 

following documents: 

• Occupational Exposures of Workers to Chemicals during Uranium Processing 1942-1966

Figure III-3, on page 8 (pdf p. 14) of Occupational Exposures of Workers to Chemicals during 

Uranium Processing 1942-1966, is a table showing potential exposures; the last line shows that 

Thorium (ThO2) processing was conducted during 1964-1966 and is consistent with figure III2. The line labeled "Raffinate Chemicals++" that shows potential exposures to chemical agents 

in the raffinate is true because the chemicals were also used in the uranium separation process. 

The ++ footnote to this table lists the raffinate chemicals and states, "Th-230 was recovered" for 

the period 1947-1966. This is not consistent with Figure III-1 and III-2, which does not show 

raffinate processing at WS. This 1984 document was a chemical exposure study, and as such did 

not appear to concentrate on the radioactive details of the materials.

The last paragraph on page 9 and 1st paragraph on page 10, states that solid residues (raffinate) 

were processed for recovery of ionium (thorium-230). "During some periods (after 1947)...” 

This statement is true for Plant 7E for 1955~1958, as verified in Figures III-1 and III-2, but does 

not appear to apply to WS from the information in this document. 

• Process Development Quarterly Report - Part I Laboratory Work, April 1, 1958 

Process Development Quarterly Report - Part I Laboratory Work discusses the demonstration

of a process for the recovery of nitrate values from raffinate on a laboratory scale, and states that 

thorium concentrations must be considered if this method is used, especially if high-thorium 

Canadian refinery feed is used. 

• Weldon Spring Site Background Report

Pages 26 and 27 state that WS processed uranium ore concentrates and recycled scrap and that 

"some processing of thorium residues was also performed.” 

• Engineering Evaluation of Alternatives for the Disposition of the Weldon Spring Raffinate

Pits Site

The Executive Summary on page 1, (pdf 4), discusses the types of waste at the pits site, to 

include "neutralized raffinates from uranium refining operations, washed slag residues from 

uranium metal production operations, and raffinate solids from the processing of thorium recycle 

materials.” 
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Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH

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document represents preliminary positions taken on technical issues prepared by NIOSH or its contractor.

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In May of 1983, Bechtel National Inc. (BNI) analyzed sludge from the four Raffinate Pits and 

calculated the following:

Thorium (total tons) Th-230 (pCi/g) Th-232 (pCi/g)

Pit 1 4 24000 ± 1000 100 ± 20

Pit 2 6 24000 ± 1000 120 ± 20

Pit 3 40 14000 ± 1000 120 ± 20

Pit 4 15 1600 ± 100 120 ± 20

Source: Table 3.1, page 15 (pdf 10) and Table 3.2, page 17 (pdf 12) of Engineering Evaluation

of Alternatives for the Disposition of the Weldon Spring Raffinate Pits Site

• Raffinate Pit Sampling Plan, May 27, 1988 

The Raffinate Pit Sampling Plan states that the pits contain "... raffinate solids from the 

processing of thorium recycle materials." 

• EPA Environmental Impact Statement, September 1989 

The EPA Environmental Impact Statement states that Pits 1 and 2 contain residues and waste 

from uranium mining operations and washed slag residue from uranium metal production, while 

Pits 3 and 4 contained "...similar waste plus thorium-contaminated raffinate solids from 

processing thorium recycled products.”

Evaluating these documents as a whole indicates that the term "thorium recycled materials" or 

“products/residues” refers to the Th-232 production process that took place during 1963-1966, 

not to the recycling of pit raffinate material for the recovery of thorium (Th-230). The one 

article describes the processing of raffinate material on a lab scale, and points out that

thorium needs to be concentrated if this process was used.