Evaluation of the Potential for Internal 

Dose from Np-237 at the Rocky Flats
 

Plant After 1983
 

White Paper
 

Rev. 1
 

National Institute for Occupational
 

Safety and Health
 

January 8, 2015 

Dan Stempfley, Jim Bogard, and Chris Miles
 

Oak Ridge Associated Universities Team
 

-

Reviewed by LaVon Rutherford, CHP and James W. Neton, Ph.D., CHP
 

Division of Compensation Analysis and Support
 

Page 1 of 12 

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) 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. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution. 
 

 

 

 

 

 

 

 

White Paper: Evaluation of the Potential for Internal Dose from Np-237 at the Rocky Flats Plant After 1983 

INTRODUCTION 

In the Special Exposure Cohort Petition (SEC) Evaluation Report for Petition SEC-00192 

(SRDB 132777), NIOSH proposed the following class of workers to be added to the SEC: 

All employees of the Department of Energy, its predecessor agencies, and their contractors 

and subcontractors who worked at the Rocky Flats Plant in Golden, Colorado, from April 1, 

1952 through December 31, 1983, for a number of work days aggregating at least 250 work 

days, occurring either solely under this employment or in combination with work days within 

the parameters established for one or more other classes of employees included in the 

Special Exposure Cohort. 

This recommendation derived, in part, from NIOSH’s conclusion that neptunium processing at 

the Rocky Flats Plant (RFP) took place at least until 1983, and that available monitoring data are 

insufficient for estimating potential internal exposures to neptunium (Np). Subsequent to that 

evaluation report, NIOSH has identified evidence that operations involving neptunium may have 

taken place after 1983, perhaps as late as 1988. 

PURPOSE 

This white paper summarizes NIOSH’s extensive research on neptunium-237 (Np-237) 

processing at RFP after 1983 (the end of the current SEC period). It includes discussions of Np 

operations, inventories, available monitoring data, and an evaluation of the potential for internal 

exposure to Np-237 after 1983. 

NATURE OF Np-237 OPERATIONS 

A 1981 paper, Neptunium Processing at the Rocky Flats Plant (SRDB 24722, PDF p. 6), states 

that processing included preparation of pure neptunium oxide, metal, and metal alloys as well as 

Np-237 recovery from a variety of residues. Processes employed included dissolution, anion 

exchange, precipitation, filtration, calcination, conversion to fluoride, and reduction to metal. 

Fabrication steps such as casting and rolling were also sometimes performed for the production 

of high-purity metal shapes and foils. Neptunium was recovered from residual materials 

including sand, slag, crucibles, casting skulls, and various alloys containing plutonium, tin, 

uranium, or zirconium. This description of RFP neptunium operations is echoed in a 1984 

document, Actinide Processing at Rocky Flats (SRDB 24798, PDF p. 323). 

Page 2 of 12 

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) 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. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

White Paper: Evaluation of the Potential for Internal Dose from Np-237 at the Rocky Flats Plant After 1983 

Np-237 OPERATIONS FROM 1962 – 1983 

Neptunium was processed at Rocky Flats as early as 1962 (SRDB 24722, PDF p. 6). There is no 

evidence of continuous routine neptunium operations at Rocky Flats; rather, the evidence points 

to a series of discrete tasks performed from 1962 through 1983, involving a few grams to a few 

hundred grams, usually processed by request from other DOE laboratories. 

The first special-order request for neptunium processing at RFP came from Lawrence Radiation 

Laboratory, now known as Lawrence Livermore National Laboratory (LLNL), which required 

high-purity neptunium with gamma-emitting impurities removed. Techniques for purifying 

neptunium (including the removal of other actinides) were developed as a result of this project. 

The project also called for preparation of neptunium-plutonium (Pu) alloys, which were prepared 

by co-reducing Np and PuF4 mixtures with calcium metal; this effort led to a capability of 

producing pure Np metal that could be cast with Pu or uranium (U) to form alloys. The first 

Np-Pu alloy was produced in 1964, and several kilograms of Np metal were produced in 

subsequent years for preparation of U and Pu alloys. 

Other specific projects involving Np-237 processing included the preparation of high-purity 

neptunium oxide for the Oak Ridge National Laboratory (ORNL) isotope pool, neptunium metal 

foils for the Savannah River Plant, and neptunium metal disks for use in the liquid-metal, 

fast-breeder reactor, neutron dosimeter program (SRDB 24722, PDF pp. 6-7). 

Based on reviews of numerous reports in the SRDB as well as reviews of classified documents, it 

is evident that only relatively small quantities of Np-237 were processed at RFP at any given 

time. The largest single operation appears to have been a special order in 1966 that involved just 

over 300 grams of neptunium (SRDB 126393). 

Np-237 OPERATIONS AFTER 1983 

The current SEC period ends on December 31, 1983, as recommended by NIOSH in the 

SEC-00192 Petition Evaluation Report (SRDB 132777). Since that report was issued, NIOSH 

has conducted an extensive search for evidence of Np processing after 1983. The result of this 

effort has been the identification of a single operation described in a 1987 document, 

Production-Scale Plutonium-Neptunium Separation and Residue Recovery at Rocky Flats Plant 

(SRDB 129512). This document does not make clear exactly when this operation took place, 

although it does indicate that the campaign lasted approximately one year. NIOSH interviewed 

one of the authors, who was also the Principal Engineer who designed the process and directed 

Page 3 of 12 

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) 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. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution 
 

 

 

 

 

 

 

 

 

White Paper: Evaluation of the Potential for Internal Dose from Np-237 at the Rocky Flats Plant After 1983 

the activities. He estimated that the operation began around January 1985 (SRDB 130877). This 

is the only post-1983 Np operation that NIOSH has been able to confirm. 

This 1985 operation involved the processing of plutonium scrap containing down to 0.5% (by 

weight) neptunium to separate and recover the two metals. The feed material for this process 

consisted of 63,728 grams of Pu containing 232 grams of Np. The separation process involved 

oxidizing the plutonium residue, passing Pu(III) through an anion exchange resin bed, and 

leaving Np(IV) behind for subsequent elution, evaporation, denitrification, and calcination to 

oxide (SRDB 129512, PDF p. 10). The authors reported completion of 24 separations over the 

course of a year using this process, resulting in the purification of 58,282 grams of plutonium by 

the removal of 222 grams of neptunium (~96% recovery). NIOSH re-interviewed the 

co-author/Principal Engineer who stated that project personnel consisted of five experimental 

operators who performed the glove box work and the Principal Engineer (SRDB 138682). 

The final purified Pu that resulted from this operation contained only 0.0069% Np. The 

“neptunium product” consisted of 1429 grams of Pu and 222 grams of Np, a Pu:Np mass ratio of 

6.4 (SRDB 129512, PDF p. 11). This operation involved no purified neptunium; the dose from 

any internal exposure would have been dominated by the overwhelming amount of plutonium in 

the mixture, making neptunium bioassay unnecessary. Given the much greater specific activity 

of Pu-239, Pu bioassay would account for all organ doses, of which Pu would be the dominant 

component. An evaluation of the relative dose contribution from Pu and Np resulting from an 

inhalation intake of the Pu-Np mixture is presented later in the section titled Potential for Np-237 

Exposures After 1983. 

According to the Principal Engineer and co-author of the 1987 report, separation of Pu and Np 

from alloys ended in 1987 (SRDB 130877, PDF p. 5). This statement is consistent with another 

reference that states that the neptunium program at RFP began in 1964 and was terminated in 

1988 (SRDB 33009, PDF p. 75). 

Np-237 INVENTORY TOTALS AND MEASURED QUANTITIES 

Documents captured by NIOSH and interviews conducted with former employees indicate that 

neptunium was present at RFP from 1962 to 2003. From 1963 through fiscal year 2003, 

neptunium quantities ranging between 29 grams and 1,318 grams are recorded in Material 

Balance Area accounts (SRDB 33009, PDF pp. 75-79; 126758; 131390). Neptunium-237 

inventory amounts at RFP from 1963-2003, obtained from the U.S. Department of Energy/U.S. 

Nuclear Regulatory Commission Nuclear Materials Management & Safeguards System 

(NMMSS), are shown in Table 1. The neptunium program was reportedly terminated in 1988 

Page 4 of 12 

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) 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. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution 


 

 

 

 

 

 

 

 

 

 

White Paper: Evaluation of the Potential for Internal Dose from Np-237 at the Rocky Flats Plant After 1983 

INTERNAL DOSE MONITORING 

Captured documents contain only two reported neptunium bioassays. A urinalysis result in July 

1966 was “Below Significant Level” (SRDB 24691, PDF p. 74; 26259, PDF p. 3). A urinalysis 

result in August 1966 reported 0.9 dpm/24h; a follow-up body count showed no detectable 

uptake (SRDB 24691, PDF p. 78; 26259, PDF p. 5). 

WORKPLACE AIR MONITORING 

NIOSH has found no neptunium-specific workplace air monitoring. 

CONTAINMENT MEASURES EMPLOYED DURING Np-237 OPERATIONS 

The neptunium processing descriptions described in the 1981 document, Neptunium Processing 

at the Rocky Flats Plant (SRDB 24722) supports NIOSH’s understanding that, by 1983, all Np 

operations were being performed in glove box facilities. For example, the document states: 

A typical glove box for aqueous Np processing consisted of a “wet” section (for aqueous 

processes) and a “dry” section (for calcining precipitates and weighing powders) separated 

by an air lock. Each section had separate air inlet and exhaust filters. A door in the air lock 

was used to pass equipment and material between the wet and dry sections. A 1⁄8-inch-thick 

lead sheet was bonded to the stainless steel portion of the glove box and 1⁄4-inch leaded glass 

was placed over the glove box windows as a shield against gamma radiation from the 

neptunium and its impurities (SRDB 24722, PDF pp. 7-8). 

The single neptunium processing operation identified by NIOSH after 1983 involved the 

separation of neptunium from plutonium residues (see Np-237 Operations After 1983). 

According to the Principal Engineer who designed the process and directed activities, this 

operation was performed in glove boxes and tanks. The tanks contained feed material (plutonium 

and neptunium nitrate solution) that was piped directly into the glove boxes (SRDB: 138682). 

WORKPLACE INCIDENTS 

No radiological incidents at RFP involving neptunium have been identified. 

Page 7 of 12 

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) 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. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution 


 

 

 

 

 

 

 

 

 

White Paper: Evaluation of the Potential for Internal Dose from Np-237 at the Rocky Flats Plant After 1983 

The previous discussion also noted that this single post-1983 operation did not involve purified 

Np, but rather Pu with Np as a contaminant. Even the most highly-concentrated Np product 

produced by this separation process was still mostly Pu, with a Pu:Np mass ratio of 6.4. Since 

the specific activity of Pu-239 is about 90 times greater than that of Np-237, the activity ratio of 

this Pu:Np mixture is greater than 500. As a result, all organ doses resulting from an intake from 

such a mixture would be dominated by the Pu component. The Np dose component would 

comprise only about 0.1% for Type M Pu for most organs, and only about 1% for Type S Pu 

(SRDB 137075). 

As mentioned previously, NIOSH conducted two interviews with the Principal Engineer/ 

co-author of the 1987 document, Production-Scale Plutonium-Neptunium Separation and 

Residue Recovery at Rocky Flats Plant (SRDB 129512). As Principal Engineer, he was closely 

involved with the 1985 Pu-Np separation operation under discussion. During those interviews, 

he stated that everyone who worked in a hot building had a urinalysis every few months as well 

as annual whole body counts (SRDB 130877; 138682). If this individual or any of his coworkers had received Np intakes from this operation, the resulting organ doses would be 

adequately accounted for by the Pu bioassay program. Pu bioassay data are readily available for 

RFP claimants. 

NIOSH has not identified any specific operations involving neptunium other than the 1985 

operation. If other operations of a similar nature (i.e., Np associated with Pu) did take place, Pu 

bioassay would have similarly accounted for any doses due to Np. 

CONCLUSIONS 

In conclusion, NIOSH finds no evidence that Np-237 intakes occurred at RFP after December 

31, 1983. If intakes had occurred during this period from the single identified Np operation, the 

resulting organ doses would be adequately accounted for by the available Pu bioassay data. 

A recent interviewee provided to NIOSH additional names of individuals who may be 

knowledgeable about RFP Np operations (SRDB 138666). NIOSH will follow-up on these 

individuals and continue to evaluate any new information that becomes available regarding Np 

operations after 1983. If such information suggests that intakes of purified Np may have 

occurred during this time, NIOSH will reconsider its position, as appropriate. For the 1962 

through 1983 period, NIOSH maintains its existing conclusion, as stated in the SEC-00192 

Petition Evaluation Report (SRDB 132777), that unmonitored Np intakes may have occurred and 

insufficient data are available for estimating resulting doses. 

Page 10 of 12 

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) 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. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution 
 

 

 

 

 

White Paper: Evaluation of the Potential for Internal Dose from Np-237 at the Rocky Flats Plant After 1983 

REFERENCES 

SRDB 24691: Status Reports: Industrial Hygiene & Bio-Assay – June and July, 1966 

SRDB 24722: Neptunium Processing at the Rocky Flats Plant 

SRDB 24798: Actinide Processing at Rocky Flats; Chapter 15: Neptunium Recovery Process 

SRDB 26259: Special Analyses Logbook 

SRDB 30013: Technical Basis Document: Rocky Flats Plant – Site Description 

SRDB 33009: Summary of Rocky Flats Plant Waste Buried in the Subsurface Disposal Area: 

Section 10. Special-Order Work 

SRDB 104511: Validation of the Rocky Flats Plant Radionuclide Inventory in the Historic Data 

Task Using SWEPP Assay Data, Volume 1 

SRDB 126393: Research and Development Quarterly Progress Report for October, November, 

and December 1966 – Chemistry and Physics 

SRDB 126758: RFP MT82 Inventories Export to Excel 

SRDB 129484: Fiscal Year 2012, Historical Tables, Budget of the U.S. Government 

SRDB 129510: Documented Communication with [name redacted] on Neptunium Inventory 

Values at Rocky Flats 

SRDB 129512: Production-Scale Plutonium-Neptunium Separation and Residue Recovery at 

Rocky Flats Plant 

SRDB 130877: Documented Communication SEC-00192 with [name redacted] on Neptunium 

Handling at Rocky Flats 

SRDB 131225: Documented Communication SEC-00192 with [name redacted] on Neptunium 

Handling at Rocky Flats 

SRDB 131384: RIS Code ARF Np Shipments and Receipts 1983 to 1988 

Page 11 of 12 

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) 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. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution 
 

 

 

 

White Paper: Evaluation of the Potential for Internal Dose from Np-237 at the Rocky Flats Plant After 1983 

SRDB 131387: RIS Codes ARFH Np Shipments and Receipts January 31, 1983 

SRDB 131388: RIS Code ORF Np Shipments and Receipts 1990 to 2003 

SRDB 131389: RIS Code ORW Np Shipments and Receipts 2002 to 2003 

SRDB 131390: Np Inventory 1989 to 2003, All RIS Codes 

SRDB 132777: SEC Petition Evaluation Report for Petition SEC-00192, Rocky Flats Plant 

SRDB 137075: PDF of Excel Spreadsheet Calculations from [name redacted] SEC-00192 Rocky 

Flats Neptunium 

SRDB 138530: Validation of the Rocky Flats Plant Radionuclide Inventory in the Historic Data 

Task Using SWEPP Assay Data, Volume 2 

SRDB 138666: Interview on Neptunium with [name redacted] 

SRDB 138682: Documented Communication SEC-00192 Re-interview with [name redacted] on 

Neptunium at Rocky Flats 

Page 12 of 12 

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) 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. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution