Rocky Flats Plant 

Special Exposure Cohort Petition 

Evaluation Report Rev. 1

LaVon B. Rutherford, CHP

National Institute for Occupational Safety and Health

Division of Compensation Analysis and Support

October 2013

Westminster, CO 
Background

 September 5, 2012 - SEC-00192 Evaluation Report 

(ER) Rev. 0 for Rocky Flats Plant (RFP) issued 

 September 18, 2012 - NIOSH presented ER at the 

Advisory Board meeting in Denver, CO

• NIOSH’s recommendation was not to add a class

• Advisory Board concluded follow-up required, including 

classified interviews and classified document review
Background–cont.

 Since the ER presentation, NIOSH conducted a variety of 

follow-up efforts that identified additional issues

 Three work group meetings held in 2013 to discuss 

these issues (Feb. 20, July 8, and Sept. 12)

 NIOSH revised the ER to incorporate the new findings

 September 30, 2013 - DCAS sent the revised ER to the 

Advisory Board

 October, 4, 2013 ER cleared Authorized Derivative 

Classifier (ADC ) review, sent revised ER to petitioner 
Follow-up Efforts

 Additional Data Captures (classified and 

unclassified) – Los Alamos National Laboratory, 

Office of Scientific and Technical Information, 

Environmental Management Consolidated Business 

Center, and Department of Energy (DOE)-Legacy 

Management

 Secure Discussions

 Secure Interviews and other interviews (19)

 Additional dose reconstruction modeling
Post Evaluation Issues

 Follow-up efforts on RFP Tritium Issues

 Evaluation of petitioner concerns about data 

falsification and/or data Invalidation

 U-233/Thorium Strikes 

 Neptunium 

 Other Thorium Activities – evaluation included in ER
Issues that Resulted in Evaluation 

Report Revision

 U-233/Thorium Strikes 

• Classified interviews indicated the number of strikes 

were greater than previously evaluated in SEC-00030

• Hanford infeasibility associated with U-233 

 Neptunium

• Not clearly evaluated under SEC 0030

• Hanford infeasibility associated with Neptunium

 Other Thorium Activities

• Classified review indicated there may have been 

additional work with thorium not previously evaluated
Tritium

 Follow-up Efforts on SEC-00192 RFP Tritium Issues

• Issued whitepaper on June 25, 2013

– Concluded tritium dose reconstruction feasible 

• Provided to the work group on June 26, 2013 and the 

petitioners on July 3, 2013 (after ADC review)

• Presented to the work group and petitioners on July 8, 2013 

during the RFP work group meeting

– Preliminary follow-up questions identified by the work group and 

Sanford Cohen and Associates (SC&A) 

• Work Group and SC&A discussed paper during the work group 

meeting on September 12, 2013
Tritium–cont.

 Tritium Related Operations

• Tritium contaminated materials from returned units

• Neutron Generator Targets

– Sealed units

– Maintenance performed by factory authorized reps

 Potential for the production of tritium from various 

radioactive materials present onsite

• Determined not to be a significant source or contributor to 

exposure 
Tritium–cont.

 Additional Data Captures and Interviews:

• Identified and confirmed potential for tritium exposure 

from contaminated shipping containers

• Supported our previous finding that all known incidents 

involving a tritium release were below the release levels 

from 1973 incident

• Did not identify any other sources of tritium exposure 

beyond previously evaluated other than from the 

shipping containers
Tritium–cont.

 Tritium exposure time periods evaluated:

• From 1959 through 1972

• During 1973 

• Post 1973 
Tritium Exposure 1959 - 1972

 Based on interviews and document review, NIOSH 

believes the most likely chronic exposure scenario 

from opening and working with shipping containers 

that contained units returned from other sites

 Exposure scenario developed from August 30, 1974 

incident where 1.5 curies of tritium released from a 

shipping container
Tritium Exposure 1959 – 1972–cont.

 Basis for using 1974 incident:

• Background levels prior to the incident were being 

measured and were dosimetrically insignificant prior to 

the release

• Quantity released was probably more typical of a release 

from a shipping container

• Tritium was released to the workplace environment and 

not in a glovebox
Tritium Exposure 1959 – 1972-cont.

 Basis for using 1974 incident:

• The release involved elemental tritium and not tritium 

oxide

• The incident occurred close enough to the 1973 incident 

that work place controls were likely similar to prior to 

1973

– SC&A questions the basis for believing this is a reasonably 

bounding scenario
Tritium Exposure 1959 - 1972–cont.

 Monitoring Data from 1974 incident:

• Air samples from June through September 1973

– Average concentration prior to Aug. 30, 1974 were 5343 + or -

4518 pCi/m3

– Concentration Aug. 30 was 37, 676, 609 pCi/m3 

• Bioassay samples taken indicated a high result of 32, 320 

pCi/L

• Work Areas Smears were taken (>200)
Tritium Exposure 1959 – 1972–cont.

 Dose Assessment from 1974 incident:

• The largest reported urine sample was 32, 320 pCi/L with 

a start date of August 30, 1974

• Using IMBA, the resulting dose was < 1 mrem (0.15 

mrem)

• Assuming 1 incident per day for 250 per year results in 

37.5 mrem/year

 Therefore, all unmonitored workers for tritium will 

be assigned 37.5 mrem for all years prior to 1973
Tritium Exposure 1973 

 Annual Dose Assigned based 1973 incident:

• The incident occurred April 9 through April 25, 1973 when 

a shipment of scrap plutonium from LLNL was processed 

at RFP in bldg. 779A

• The incident was not immediately identified so individual 

monitoring did not begin until September 1973

• Approximately 250 people were bioassayed for tritium

– Initially 19 people were identified with elevated tritium

– Upon recheck only 5 were above 10,000 pCi/L action level
Tritium Exposure 1973–cont.

 The five cases (Case A, B, C, D, and H) exceeding 

10,000 pCi/L were reviewed from the final incident 

report:

• All cases were modeled to determine the best fist for the 

urine data which then would give the most likely dose

• Case H best fit exposure scenario resulted in the highest 

dose of 84 mrem

– Limited information therefore assumed acute intake first day of 

event

 Tritium doses will be assigned to all unmonitored 

workers
Tritium Exposure post 1973 

 Co-worker analysis was performed using 1974 and 1975 

tritium bioassay data

• 38 individuals with tritium data 1974

• 37 individuals with tritium data 1975

 Because tritium was only present as a potential 

contaminant, groups of individuals were not placed on 

routine bioassay for tritium

 One-tenth of the urine samples collected for plutonium 

were analyzed for tritium

 Also, samples were required when there was a concern
Tritium Exposure post 1973–cont.

 Dose Assessment for 1974 and 1975:

• It was assumed each worker had potential for exposure 

throughout the year

• The 95th percentile was used because only one-tenth of 

the population was sampled

 The co-worker study for 1974-1975 period yielded 

doses of 0 mrem for everyone

 For post 1974 the same dose will be assigned for 

unmonitored workers based on the limited bioassay 

data being consistent with the 1974 and 1975 data
Thorium

 In SEC-0030 evaluation the NIOSH position was that 

documents supported that Thorium quantities present 

at Rocky Flats were not in high enough quantities to 

contribute significantly to internal dose potential

 As stated in NIOSH’s original SEC-0030 evaluation, 

beginning in 1952, Thorium was used on site in 

quantities small enough that effluents were not 

routinely analyzed for Th. Thorium quantities varied 

from as little as none to as much as 238 kilograms (kg) 

in a given month
Thorium–cont.

 Thorium was used in a variety of processes including:

• Fabrication of metal parts from natural thorium or thorium 

alloys

• Use of oxide (“thoria”) as a mold-coating compound

• Numerous analytical procedures and research and 

development

• As a substitute for U or Pu components in research and 

development

• Removal of Th-228 from U-233

• Mg-Th alloy work (This is still being evaluated) 
Thorium–cont.

 Most of the work associated with Thorium during 

the SEC-0030 evaluation was focused on specific 

activities that occurred in the 1960s

 Based on interviews and document review, NIOSH 

decided to re-evaluate the Thorium issue
Thorium–cont.

 During NIOSH’s review documents supported that:

• Activities involving thorium occurred as far back as 1952

• A concern with exposure or the need to monitor personnel as far 

back as 1954 

 Changing Inventories in these early years supported that 

work with Thorium was occurring during this period

• Activities and processes involving Thorium were not well 

documented in the early years nor was the throughput 

 Based on NIOSH’s review of the NMMS database, no 

significant inventories of Thorium existed at Rocky Flats after 

1971

• Documents do indicate that thorium solutions (thorium nitrate) 

existed up through 1974
Thorium–cont.

Personnel and Area Monitoring Data

 RFP developing personnel monitoring approach for thorium 

through the 1950s into the 1960s

 No routine monitoring for thorium existed at RFP

• Personnel and area air samples from 1960, but no activity results

• Two bioassay samples in 1966

• Some Thorium Specific Personnel and Area monitoring data
Thorium–cont.

Surrogate Data

 During review of SEC-00030 NIOSH used surrogate data air 

samples for the thorium ingot operation in 1960

• This was vetted in 2007 before surrogate data criteria (IG-004) was 

established in 2008

• Data was from a study conducted at the Albany Research Center. 

This was a one-time operation conducted under experimental 

laboratory conditions 
Thorium–cont.

Feasibility Determination

 Activities involving thorium in the 1950s and early 1960s 

were not well defined

 Lack sufficient personnel and area monitoring

 Surrogate data used does not meet the criteria for using 

surrogate data established in IG-004
Thorium–cont.

Feasibility Determination-cont.

 Therefore, NIOSH finds it’s not feasible to reconstruct 

thorium exposure from 1952 through 1966

 NIOSH intends to use any relevant internal monitoring data 

that may become available for individual claims
U-233/Thorium Strikes

 Exposure during U-233/Thorium strikes was originally 

evaluated under the SEC -0030 evaluation

• Re-opened under SEC-0192 after indications this may have occurred 

more than the two times (1965 and 1967) previously identified

 U-233 was being evaluated for its use in the weapons 

program

 Problems with U-233 was a contaminant U-232

• U-232 progeny pose a significant external hazard

 A chemical process called a “Thorium strike” was used to 

remove the Th-228 and its progeny
U-233/Thorium Strikes–cont.

 SEC-0030 assumed U-233 exposure covered with 

uranium bioassay

 During the deliberation of SEC-0030 the bounding 

Thorium dose was based on air sampling taken 

during the strike in 1965

• This strike was considered bounding because it had the 

highest concentration of U-232 of the two strikes

• No credit was taken for ventilation, hoods or time limits
U-233/Thorium Strikes–cont.

 Interviews and documents indicated additional strikes 

occurred other than the two previously evaluated

• Were the potential exposures from other strikes bounded by 

the 1965 exposure analysis? 

 Other questions came up based on recent addition of a 

class at Hanford based on inability to reconstruct doses 

to U-233

• Were the activities similar?

• Were the material quantities similar?

• How much monitoring data do we have in comparison?
U-233/Thorium Strikes–cont.

Reasons to believe 1965 Strike is still bounding for 

Thorium

 Most documents indicate the U-233 was to be processed or 

shipped off site prior to the 90 day period to prevent the 

hazard from the ingrowth and therefore a strike would not 

be required

 Documents indicate the concentration of U-232 did not 

exceed 8 ppm after 1965

 Although NIOSH determined the 1965 exposure was still 

bounding, it’s not clear how this would be applied if 

additional strikes are assumed
U-233/Thorium Strikes–cont.

Determining U-233 exposures

 The quantity of U-233 on site at RFP varied from 1964 to the 

end of U-233 operations in 1983

 Estimates from available documents indicate quantities 

could have been from 1 kg up to 150 kg from 1965 through 

1983

• Highest quantities from 1965 through 1968

 Bioassay data for uranium exists and a uranium co-worker 

model exists for the period of concern
U-233/Thorium Strikes–cont.

Determining U-233 exposures

 Initial idea was to give a corrected uranium dose to all workers 

with uranium bioassay

• Assumption based on all workers who worked on U-233 activities would 

have uranium bioassay

 A review was conducted to determine if any of the Operators 

(46) listed in logbook for U-233 operations were existing 

claimants in NOCTS

• There were 18 of the 46 who are claimants

• Of the 18 claimants, 17 had uranium bioassay; no clear reason why this 

claimant did not have bioassay
U-233/Thorium Strikes–cont.

Determining U-233 exposures

 NIOSH cannot assume all workers working on U-233 operations 

necessarily had uranium bioassay

 NIOSH cannot identify all workers who worked with U-233 

through the years of operations

 If NIOSH used the uranium co-worker, NIOSH would have to 

assume all workers could have been exposed and a correction 

factor for exposures to U-233/U-232 and progeny applied

• Factor could vary significantly depending on mass based analysis or 

activity based

 U-233 Specific Activity is approx. 140 times U-235

• U-233 operations would have been handled differently than other 

uranium operations. Therefore, using the uranium co-worker would not 

necessarily have been indicative of U-233 exposures. 
U-233/Thorium Strikes–cont.

Personnel and Area Monitoring Data

 No U-233 specific bioassay data

 No Th-228 specific bioassay data

 One set of U-233 specific air samples in 1965 (Highest RCG 

39%)

 Uranium co-worker cannot be used 
U-233/Thorium Strikes–cont.

Feasibility Determination

 NIOSH finds it’s not possible to completely reconstruct 

internal U-233, U-232, and Th-228 radiation dose for the 

period from 1964 through 1983

 NIOSH intends to use any related internal monitoring data 

that may become available for individual claims
Neptunium

 General conclusion under SEC-0030 was Neptunium 

was used in small quantities for research type work 

and had limited exposure potential compared to 

Uranium and Thorium

 A determination was made to re-explore this 

exposure situation based on interviews and recent 

determination associated with Neptunium at 

Hanford
Neptunium

 Records indicate that Neptunium was processed at 

Rocky Flats as early as 1962 and inventories existed 

until 1988

 Neptunium was processed to produce pure 

Neptunium oxide, metal, and metal alloys

 Processes employed included dissolution, anion 

exchange, precipitation, filtration, calcination, 

conversion to fluoride, and reduction to metal
Neptunium–cont.

 Fabrication steps such as casting and rolling were 

performed to produce metal shapes and foils

 Neptunium was also recovered from residual 

materials including sand, slag, crucibles, casting 

skulls, and alloys

• The residues were not only from Rocky Flats operations, 

but residues were sent from other sites

 Based on documents and inventories it appears 

most work with Neptunium was completed by the 

end of 1983
Neptunium–cont.

 Annual on site inventories were typically 

maintained around 1 kg

• Does not address throughput

 Batches involving Neptunium typically did not 

exceed 300 grams

 Buildings having Neptunium inventories included 

371, 559, 707, 771, 776, 777, 779, 779A, and 991
Neptunium–cont.

Neptunium Exposure

 Documents indicate some early work was conducted in open 

hoods, but most work was performed in glove boxes

 Based on NIOSH’s review, Neptunium exposure potential 

existed at every processing step, including extraction and 

purification, hydrofluorination, reduction to metal, alloying, 

casting, and rolling
Neptunium–cont.

Personal Monitoring Data

 There are only two bioassay samples for Neptunium 

 They were both taken in 1966

• One “Below Significant Level” and the other 0.9 dpm/24hr

 Gross Alpha bioassay samples existed up until 1970s

Workplace Monitoring Data

 NIOSH has found no workplace monitoring records (e.g., air 

sample, surface contamination samples) specific to 

Neptunium
Neptunium–cont.

Feasibility Determination

 Can we use gross alpha samples as indicator for Neptunium?

• NIOSH interviewed two former Rocky Flats Plant employees involved 

with the Radiological Controls program and the Bioassay lab

• Interviews indicated that it would be questionable based on the 

chemistry whether you would see the Neptunium in the sample

• Interviews indicated that the intent of co-precipitation process used 

after 1961 for “Gross Alpha” analysis was to focus the analysis on 

specific radionuclides typically Uranium and possibly plutonium
Neptunium–cont.

Feasibility Determination-cont.

 Little to no personal or area monitoring data

 Gross Alpha bioassay samples not a viable means for 

estimating Neptunium exposures

 Too many different types of activities including wet and dry 

processes to develop an exposure model

 Additionally, the source term varied in amount and chemical 

form
Neptunium–cont.

Feasibility Determination-cont.

 Quantities and activities associated with Neptunium at 

Rocky Flats are similar to Hanford during the same time 

period

 Based on this, NIOSH has concluded dose reconstruction is 

not feasible for Neptunium exposures for 1962 through 1983
Neptunium–cont.

Why stop at end of 1983?

 Based on NIOSH’s review of documents very little to no work 

occurred with Neptunium after 1983

• Inventories relatively constant

 A 1981 Documents indicates that early work was done in 

open hoods but later “Alpha containment” was used

 In vitro bioassay techniques improved by 1981 and in vivo 

techniques improved by 1976

 NIOSH will continue to evaluate the 1984-1988
Current SEC Classes

Employees of DOE, its predecessor agencies, or DOE 

contractors or subcontractors who were monitored or 

should have been monitored for neutron exposures while 

working at the Rocky Flats Plant in Golden, Colorado, for a 

number of work days aggregating at least 250 work days 

from April 1, 1952, through December 31, 1958, .....

Employees of DOE, its predecessor agencies, or DOE 

contractors or subcontractors who were monitored or 

should have been monitored for neutron exposures while 

working at the Rocky Flats Plant in Golden, Colorado, for a 

number of work days aggregating at least 250 work days 

from January 1, 1959, through December 31, 1966, ....
 NIOSH -

• finds that internal doses cannot be estimated with 

sufficient accuracy from April 1, 1952 through 

December 31, 1983

• intends to use any related internal monitoring data 

that may become available for individual claims; and 

• will continue to evaluate potential Neptunium 

exposures for the 1984-1988 time period.

Feasibility of Dose Reconstruction
Summary

Feasibility Findings for SEC 0192 (Rev. 1) Rocky Flats 

April 1, 1952 – December 31, 1983

Source of Exposure Reconstruction 

Feasible

Reconstruction 

NOT Feasible

Internal

Tritium X

Thorium X (1952-1966)

U – 233 X (1964-1983)

Neptunium X(1962-1983)

External – Not evaluated in this report (See SEC – 0030)
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

Recommended Class
 Data Falsification question

• Classified Interview to be conducted with individual who has 

information concerning data falsification

 Continue to evaluate 1984-1988 period for Neptunium 

exposure potential

 Evaluate the use and exposure potential for Mg-Th alloy 

at Rocky Flats

 Resolve open questions with SC&A and the work group 

concerning tritium

Remaining Issues