Fernald SEC Petition Review

SC&A Status Update since Advisory Board Meeting held 

December 7-8, 2011 in Tampa, Florida

Presented by John Stiver, SC&A

Presented to the Advisory Board on Radiation and 

Worker Health

Full Board Meeting Held in Oakland, California, 

February 28-29, 2012
Work Group Review: Overview

• April 19, 2006: SEC Petition qualified

– “All employees who worked in all facilities at the Feed Materials 

Production Center (FMPC) in Fernald, Ohio, from Jan 1, 1951 through 

Dec 31, 1989”

• Nov 3, 2006: NIOSH Evaluation Report issued

– “NIOSH found no part of the class under evaluation for which it cannot 

estimate radiation doses with sufficient accuracy.”

• Nov 10, 2006: SC&A Site Profile Review 

• July 2, 2007: SC&A SEC PER Review

• August 2007  February 2012: Twelve Work Group meetings

• May 24, 2011, ABRWH Meeting: SC&A presents detailed 

summary of SEC issues (as of April 2011)

2
Work Group SEC Issues

1. Coworker Model for Uranium Internal Exposures – open

2. Validation of the HIS-20 database – closed*

3. Recycled Uranium (RU) – closed*

4. Use of radon breath data for reconstructing doses from 

inhalation of Ra-226 and Th-230 – closed*

5. Review of radon emissions from the K-65 silos and 

associated exposures - moved to site profile discussions

6. Reconstruction of internal exposures from inhalation of Th232

6A: DWE Data (1953 – 1967) – closed*

6B: Chest Counts (1968 – 1989) - open

7. Recycled Thorium (RT) – moved to site profile discussions 

(Feb 9, 2012)

(* recommended by SC&A and/or Work Group concurrence)

3
Description of Issue 6B: Use of chest counts to reconstruct Th-232 

exposures

• No DWE data after MIVRML introduced in 1968 – therefore completely 

dependent on integrity of chest count data thereafter

• 1968-1978 – results reported in mass units (milligrams thorium) with no raw data 

• 1979-1989 – results reported in activity of progeny (nCi Pb-212 and Ac-228)

Status of issue: 

• White papers exchanged; issue first discussed in detail at the April 19, 2011, 

Work Group meeting. Discussed again in detail at August 11, 2011 and February 

9, 2012 WG meetings

• SC&A Position: Two unresolved issues exist related to sufficient accuracy in 

data for 1968-1978 (data reported in milligrams thorium) that may render those 

data inadequate for DR (SEC)

1. Large uncertainties related to how the mg thorium data were derived (potentially 

underestimated by factor of 100)

2. Suitability of the MIVRML as used for accurately determining mg Th-232 lung 

burdens at Fernald (technical shortfall issue)

Open Issue (#6B) Use of Chest Counts to Reconstruct 

Th-232 Intakes (1968-1989) 

4
5

Thorium-232 Decay Chain

Source: Wikipedia

Pb-212 in Sec. Eq. 

with Th-228

MIVRML measured gammas:

Was Ac-228 and/or Pb-212 used

to derive Th-232 burdens in mg?

Ac-228 in Sec Eq. 

With Ra-228
6
7

0 5 1 0 1 5 2 0

0.1

1

Ra224

Ra228

Ra-228 & 224 Present After Separation

Time (years)

Activity (Bq)

Ac-228 (Ra-228) and Pb-212 (Ra-224) Buildup 

Following Single Chemical Purification of Thorium

Source - White Paper: Calculation of Chronic Intake IRFs for Th-232 Assuming Shared Kinetics, T. LaBone
Sub-issue #1: Combination of uncertainties and variability in mg 

thorium data could result in underestimates of intake by up to a factor 

of 100

• Th-232 source terms at Fernald were at varying levels of disequilibrium

• Don’t know the age(s) of the source(s), whether age corrections were made 

based on Ac-228 and Pb-212 or if simplifying assumptions such as presuming 

secular equilibrium were invoked to transform Ac-228/Pb-212 activity into mg Th232 – No raw data, just mg thorium reported

• Uncertainty in age of source(s) at time(s) of intake (factor of about 5 for a closed 

system using Pb-212; Factor of 100 or more if Ac-228 used)

• Historical reference (Counter Thorium Calibration Runs, March 26, 1976 (Author 

Unknown 1976) recommended using process knowledge obtained from health 

physics staff and process engineers and/or multiple measurements of Ac-228 and Pb212 to determine age of source 

• No evidence has been provided by NIOSH or located by SC&A to suggest that 

these steps were taken and the available data and references suggest that they 

were not 

• SC&A examined claimant files for > MDA (6mg) results (79 results for 59 

workers) – found only 30% had more than 1 measurement within 6 months 

and no correlation between magnitude of 1st result and sampling 

frequency

Issue #6B: Use of Chest Counts to Reconstruct 

Th-232 Intakes, continued 

8
Impacts of uncertainties and variability - 2

• NIOSH methods assume that Pb-212 was used to derive mg Th-232 but has 

presented no hard evidence to support that assertion

• Example from Counter Thorium Calibration Runs, March 26, 1976 indicates Ac-228 

used to derive mg of Th-232, with various equilibrium assumptions – very sensitive to 

age of source 

• Burden of proof is on NIOSH to show that Pb-212 was used pre-1978 (tasking by Work 

Group 2/9/2012) 

• Inconsistencies between mg Th-232 and nCi Pb-212 for period of overlap (1978, 1979) 

suggest that Pb-212 was not used to derive mg Th-232 (next slide) 

• Three highest mg Th-232 correspond to negative Pb-212 results

• 9 values in 1979 reported as 2.9 mg but Pb-212 ranged from 0.19 to 0.40 nCi and Ac-228 from 

0.33 to 0.7 nCi. These data are suspect. Only 1 Pb-212 result was less than the stated MDL of 

0.23 nCi (1987). 

• Expect proportionality between Th-232 and progeny in 1979 data (divided by plant work 

and by dates) because the source was probably the same 

• Results highlighted green: workers co-located and measured in June, yet results of pb-212 

varied from 0.25 to 0.40 nCi with the same result in mg of th-232. 

• Results highlighted pink: workers in plant 4 monitored in October, yet results varied from 

0.19nci of Pb to 0.40nci, with the same result in mg of th-232. Also, no proportionality with ac 

results.

Issue #6B: Use of Chest Counts to Reconstruct 

Th-232 Intakes, continued 

9
Impacts of uncertainties and variability - 3

Issue #6B: Use of Chest Counts to Reconstruct 

Th-232 Intakes, continued 

10

Reported Thorium 

Result (mg)

Reported Pb-212 

Activity (nCi)

Reported Ac-228

Activity (nCi) Monitoring Date Location or Plant #

-5.00 -0.04 -0.02 8/29/1974 7 or Pilot

-0.60 -0.08 0.03 06/08/88 Maintenance

-0.54 -0.18 -0.01 06/12/86 5

-0.16 -0.16 -0.09 06/23/87 5

-0.12 0.06 0.01 07/10/73 6

-0.05 -0.05 0.02 05/02/87 Maintenance

-0.01 -0.01 0.05 12/09/86 No Information

0.01 -0.06 -0.08 05/02/77 Mech

0.30 0.15 0.06 04/06/77 6

1.81 -0.10 0.04 08/09/85 5

2.10 0.25 0.35 06/02/79 7 or Pilot

2.10 0.30 0.5 06/09/79 7 or Pilot

2.10 0.40 0.7 06/12/79 7 or Pilot

2.10 0.40 0.65 06/19/79 7 or Pilot

2.10 0.40 0.5 10/08/79 4

2.10 0.19 0.33 10/22/79 4

2.10 0.27 0.33 10/29/79 4

2.10 0.28 0.41 10/17/79 4

2.10 0.29 0.39 10/15/79 4

2.20 -0.10 -0.1 04/13/77 Mech

4.30 -0.04 0.05 04/26/71 Inspection

5.10 -0.04 0.01 06/04/80 Mech

Source: Table 1. SC&A Final Position on the Th-232 In-vivo Data Quality and Adequacy for FEMP Workers 
Impacts of uncertainties and variability - 4

• Uncertainties in resident time in the lung prior to measurement (progeny ingrowth and translocation) Progeny physico-chemical behavior does not follow the 

parent nuclide. Even in its most soluble form, there is generally a long-term retention 

of thorium in the lungs following intake. In contrast, thorium daughter products, such 

as radium and lead, are more readily absorbed from the respiratory tract into 

systemic circulation. This fact was known at the time measurement took place.*

• Data for individual workers inconsistent with accepted biokinetic processes 

(SC&A Memo to NIOSH; April 6, 2011) 

• SC&A final position paper Section 3.1 (p. 9) demonstrate that high values (10 

and 25 mg) followed by low values weeks to months later (0.2 and 0.03, 

respectively) are inconsistent with accepted biokinetic modeling processes. 

• NIOSH suggested that potential clothing contamination could have resulted in 

such large discrepancies. While SC&A acknowledges that possibility, no follow 

up measurements taken on the same day, as expected for clothing 

contamination (Fig 12 from NIOSH Nov 2011 response)

* West; calibration of WB in Mallinckrodt using calibration source of Th-232 in equilibrium daughters 

(1966, ref. number 099712)

Issue #6B: Use of Chest Counts to Reconstruct 

Th-232 Intakes, continued 

11
Sub-issue #2: Suitability of the MIVRML as used for accurately 

determining mg Th-232 lung burdens (technical shortfall issue)

• Historical references (West 1965; 1976 Counter Calibration document, 

SRDB 3292 and 3521) indicate that the MIVRML results could be made 

quantitative only by accurately determining the age of the source (since 

separation) and the time lag between exposure and measurement (related 

to Issue #1)

• mg Th-232 data are consistent with non-quantitative methods (categorical 

data). This is the position still held by FMPC, as seen on the Technical Basis 

for Internal Dosimetry at FEMP (1997 (RSDB 003521) and 2001(RSDB 

003292)

• Currently [1997], in vivo measurements for Th-232 are performed by 

determining the amount of Ac-228 and Pb-212 present in a measurement 

and assuming radioactive equilibrium with the parent. Since the degree of 

equilibrium is rarely known, this technique is only useful for screening 

type measurements and should not be used as the only indication of a Th232 intake”

Issue #6B: Use of Chest Counts to Reconstruct 

Th-232 Intakes, continued 

12
13

• Figures 1-11 of NIOSH November 2011 response: demonstrate 

categorical nature of mg Th-232 data. 97% of results are below the 

stated MDA of 6 mg (next slide)

• Small number of results in upper tail above normal probability line likely 

represent real but highly uncertain (unquantifiable) results while majority 

represent electronic background

• NIOSH position in November 1, 2011 response was that the 

preponderance of results < stated MDA are indicative of background 

level exposure (null distribution) and confirms that only a handful of 

workers were actually exposed. 

• SC&A verified that normal thorium lung content in non-exposed 

populations is around 3 μg, 3 orders of magnitude lower than the mg 

amounts reported.

Issue #6B: Use of Chest Counts to Reconstruct 

Th-232 Intakes, continued 

Sub-issue #2: Suitability of the MIVRML -2
14

Issue #6B: Use of Chest Counts to Reconstruct 

Th-232 Intakes, continued 

Source: Response to SC&A Response to NIOSH White Paper on FMPC MIVRML Calibration, 

Nov 2011 

Red line = 6 mg MDA

Blue line = 95th %
Sub-issue #2: Suitability of the MIVRML - 4

• SC&A final position paper demonstrated that intakes consistent with 6 mg or 

lower chest burdens could result in Sv-level dose commitments to organs of 

concern for thorium exposure (e.g., bone surfaces). 

• Assumed 30-day chronic intake resulting in 6 mg (stated MDA) lung burden

• Tabulated doses are lifetime organ dose commitments that would be 

assigned to the year of intake under 10 CFR 835.202(a)(2)

Issue #6B: Use of Chest Counts to Reconstruct 

Th-232 Intakes, continued 

15

Monitored 

(days post-exposure)

Committed Dose 

Equivalent 

(bone surfaces)

Committed Dose 

Equivalent (lung)

30 130 rem 10 rem

60 170 rem 15 rem

150 320 rem 30 rem

240 560 rem 50 rem

235 970 rem 80 rem

Dose commitments calculated by Dr. Joyce Lipsztein using AIDE 
Suitability of the MIVRML - 5

• SC&A also demonstrated that intakes consistent with lung burdens at 1⁄2 the 

stated MDL (nominally 3 mg) could result in up to Sv-level compensable

doses (e.g., bone surfaces, liver, red marrow, lung).

• Example Scenario (lowest intake considered) 

• Caucasian male born 1948

• Chronic exposure during 5 years to freshly separated Thorium (1968-1972)

• Chest Monitoring taken 1 month after last day of exposure: Result 3mg of Th-232 

(12.24 Bq)

Issue #6B: Use of Chest Counts to Reconstruct 

Th-232 Intakes, continued 

16

Type Bone Liver Leukemia (AL) Lung

CDE IREP CDE IREP CDE IREP CDE IREP

Diagnosed Bone Surf 99% Liver 99% red marrow 99% lung 99%

1978 217.14 94.00% 6.31 62.25% 15.58 85.43% 62.13 88.60%

1982 294.24 95.27% 7.74 67.04% 19.20 86.28% 62.29 88.11%

1987 363.34 95.87% 8.88 68.89% 21.88 87.45% 62.46 86.50%

1992 428.84 95.89% 9.90 68.88% 24.13 87.44% 62.65 86.09%
Suitability of the MIVRML - 6

• System limitations for Th-232 measurement were known at the time and 

methods identified by which quantitative measurements could be made 

yet there is no indication that such methods were implemented at FMPC 

for mg Th data

• Claimant information and historical documentation indicate that the 

MIVRML was used primarily to measure uranium lung burdens and that 

thorium measurements were a secondary concern 

• Only one attempt to measure thorium workers (1968) and roster was 

incomplete 

• Hardcopy NOCTS files of 15 claimants identified from the list of 59 workers 

that had results above 6 mg of thorium. 

• None of the worker files contained any attempt to calculate the % of MPLB for 

thorium. 

• Conversely, almost all the workers had calculations of the % of MPLB for 

uranium. 

• Furthermore, almost all of the in-vivo monitoring results that were repeated 

within a period of 6 months were geared to the calculation of % of the uranium 

MPLB

Issue #6B: Use of Chest Counts to Reconstruct 

Th-232 Intakes, continued 

17
Concluding statements – 1968-1978 mg thorium data

• SC&A interpretation of NIOSH position (February 9, 2012 WG meeting) 

• High intakes based on the MIVRML background distribution are acceptable for a 

coworker model given a stable counting system that yields reproducible results

• Actual burdens were probably in the mg range. Therefore the assignment of high 

doses is plausible and claimant favorable

• Plots show small groups with real lung burdens in the mg range (slide 14)

• Consistent with other bounding “one-size-fits-all” models 

• SC&A Position on mg thorium data

• Limited sensitivity of MIVRML (high MDL) combined with the large uncertainties 

in the mg Th data suggest that from 1968-1978 the counting system was not 

used in a manner that resulted in sufficiently sensitive or accurate results for 

ascertaining Th-232 lung burdens (and intakes) in an SEC context

• Likely that a limited number of workers received Th-232 intakes (categorical)

• Range of dose commitments from an intake consistent with an MDA lung burden can 

be from 01000 rem for bone surfaces. 

Issue #6B: Use of Chest Counts to Reconstruct 

Th-232 Intakes, continued 

18
Concluding statements – 1968-1978 mg thorium data - 2

• SC&A Position - continued

• Upper end of dose range is far in excess of regulatory limits (10 CFR 835 organ 

dose limit of 50 rem CDE/yr) and likely compensable for most specified cancers 

yet is based on a distribution of electronic background noise

• >MDA burdens could have been more than an order of magnitude higher 

than 6 mg

• How can that be bounded? Look for deterministic effects?

• Coworker model will compensate a large number of Fernald workers (no 

constraint based on building/year as with DWE) yet lacks a defensible technical 

basis. 

• Fairness considerations for workers outside timeframe or at other sites?

• SC&A and NIOSH have reached divergent conclusions based on their 

respective interpretations of the facts regarding mg Th-232 

• We both acknowledge large uncertainties and very high doses that result from 

using the mg thorium data. Disagreement is in regard to whether the data meet 

the intent of sufficient accuracy as applied to SEC determinations under 

EEOICPA 

• SC&A believes that the technical issues regarding the use of the 1968-1978 

have been fully explored and debated and that this is now a policy decision to 

be taken up by the Board

Issue #6B: Use of Chest Counts to Reconstruct 

Th-232 Intakes, continued 

19
1979–1988: Data reported in nCi thorium (based on Pb-212 and Ac228) (period of stewardship)

• Uncertainty and variability

• “Raw data” (nCi Pb-212 and Ac-228) are available – allows quantification of 

source age since separation within reasonable limits

• Other sources as stated for mg thorium (1968-1978)

• New NIOSH paper (White Paper: Calculation of Chronic Intake IRFs for Th232 Assuming Shared Kinetics, T. LaBone) reviewed by SC&A

• A good theoretical paper that shows a method to calculate IRF for 

chronic intakes (not available in IMBA)

• Appendix A is very useful for bounding doses for the period after 1979 

when results of Pb-212 are explicitly given

• Worst case adjustment factor of about 5.3 based on 3 sequential 

chemical separations

• Formal white paper response to be delivered to WG

• Conclusion: Can probably assign plausible upper bound intakes based on 

these data

Issue #6B: Use of Chest Counts to Reconstruct 

Th-232 Intakes, continued 

20
1979–1988: nCi thorium - 2

• Suitability of the MIVRML methodology 

• About 96 percent of the data are less than the Pb-212 MDA of 0.23 

nCi

• May still have issues regarding sufficient accuracy for results 

based on sub-MDL data when combined with high 

(compensable) organ doses

• Not until 1990s when better urine bioassay techniques using ICP 

mass spectroscopy were employed to yield results in ug Thorium 

(actual background levels)

• The issue of technical shortfalls in historic measurement techniques 

as applied in dose reconstruction and SEC determinations may be 

an overarching issue to be considered by the Board

Issue #6B: Use of Chest Counts to Reconstruct 

Th-232 Intakes, continued 

21
Description of Issue –

Concerns regarding the completeness and adequacy of the uranium 

bioassay data available for dose reconstruction and supporting the 

Fernald internal dosimetry co-worker model (OTIB -0078, dated 

November 6, 2007)

Status of Issue –

Resolved except for matters related to the applicability of the co-worker 

model to Fernald construction/subcontract workers

Open action Items – 

NIOSH to perform an analysis of construction worker (CW) vs. non-CW 

uranium bioassay data for TIB-0078 and deliver a report 

• Report delivered November 4, 2011

• SC&A response delivered January 23, 2012

Open Issue (#1): Co-worker Model for Uranium 

Internal Exposures

22
Issue #1: Co-worker Model for Uranium Internal 

Exposures-2

23

SC&A Observations – January 23, 2012 response

• NIOSH concluded that most construction worker bioassay records in the 

database are coded with sample “Type 50” (meaning “special sample”)

• These "special" records were not included in the original coworker model 

because they were presumed to not reflect normal worker intakes

• New analysis: when these records are considered, the coworker model 

estimates go up by a factor around 1.25 or 1.6, depending whether it's annual 

or quarterly data

• If directly compared, data for subcontractors would be much higher than the factors 

they found (58). How much higher depends on the relative sample sizes

• Basis for rejecting direct comparison in lieu of a “pooled” approach is not 

substantiated

• The paper contains minimal details of the analysis, only a graph with the final 

results

• SC&A believes that NIOSH should provide a new revision with details (e.g., 

sample sizes, fitted distributions by time periods) to substantiate their position
Issue #1: Co-worker Model for Uranium Internal 

Exposures-3

24

February 9, 2012 WG meeting

• NIOSH concluded that many of the “Type 50” bioassay records in the 

database are for construction workers. It has not been established how many 

“Type 50” records actually represent subcontractors vs. site employees

• NIOSH analysis adds these “Type 50” samples to the coworker dataset to 

determine a ratio between the new and old coworker doses but does not 

perform a direct comparison (subcontractors versus rest of workers)

• NIOSH rationale for “pooling” the data:

• Observation 1: many samples appear to be contaminated with large differences in 

“end of shift” samples and samples taken following morning

• Observation 2: given the smaller sample size for ‘Type 50’, direct comparisons can 

be greatly influenced by outlier values

• Observation 3: ‘Type 50” records represent acute intakes over short duration. 

Without knowing employment start dates, intakes based on such measurements 

could be implausibly high

• Therefore “pooling” the data with the original coworker model and assigning 

chronic intakes would be plausible yet bounding for subcontractors
Issue #1: Co-worker Model for Uranium Internal 

Exposures-4

25

February 9, 2012 WG meeting

• Observations and rationale have not yet been quantified (number of 

suspected contaminated samples, actual employment periods, effect of 

outliers, etc.)

SC&A Action Items:

• Obtain from NIOSH the complete urine bioassay spreadsheet (not 

previously provided) and hardcopy subcontractor bioassay records (from 

Table 1 references in NIOSH white paper) and identify records that 

pertain to these subcontractors only. Revise January 2012 white paper 

comparison accordingly.

• If NIOSH determines that intake determinations are feasible for individual 

subcontractors, they will prepare a white paper comparison of 

subcontractor and site employee intake distributions over specified 

employment periods. SC&A will review that document when it becomes 

available. 
Issue (#3): Recycled Uranium (RU)

Description of Issue: Concern that default concentrations of Pu-239, Np-237, and 

other isotopes associated with RU at Fernald may not be bounding for some classes 

of worker activities, buildings, and time periods.

Status of issue: Numerous white papers have been exchanged where NIOSH 

provides its technical basis in support of its default values and SC&A provides the 

reasons it believes that the default values may not be bounding for all workers and 

time periods. Moved to site profile discussions at February 9 WG meeting

26

Recap: August 11, 2011, Work Group Meeting New NIOSH Position on Default Values

1953-1960: Proposes no RU constituent intakes

1961-1972: Proposes “original” defaults

Pu-239 (100 ppb U) Np-237 (3500 ppb U) Tc-99 (9000 ppb U)

1973-1989: Proposes increased default values (value, basis)

Factor of 4 for Pu-239 (100 ppb U  400 ppb U) (Subgroup 8; MgF2)

Factor of 3 for Np-237 (3500 ppb U  11,000 ppb U) (Subgroup 11; Waste Residues)

Factor of 2 for Tc-99 (9000 ppb U  20,000 ppb U) (Subgroup 6B; LEU products)

Based principally on MgF2 concentration in metal reduction (Plant 5)  highest continuous 

worker exposures
Issue #3: Recycled Uranium - continued 

SC&A position on new proposed NIOSH default values (August 2011)

1953-1960: 

• This period can be bounded (site profile); however, SC&A believes that a default 

of zero may not be adequate in an SEC context 

1961-1972: 

• This period can be bounded (site profile); questions remain as to what the default 

should be (original vs. some higher value)

• Impact of MgF2 concentration with low feed levels – factor of 10 increase from < 10 ppb 

appears to support 100 ppb chronic intake as bounding

1973-1989: 

• Proposed higher defaults; probably bounding for the highest continuously exposed

subgroup of workers (Plant 5 metal workers and associated millwrights)

• Subgroup 10A feed concentrations could have impacted handlers and downblenders; also indirect exposures (bystander effect) (SEC issue 1973-1985 (1980-

85); 1986-1989 – good HP/IH program)

• Small subset of workers but cannot identify based on work records

• Intermittent exposures - covered by 400 ppb chronic intake? Intervals not quantified

NIOSH Action Item: quantify down-blending intervals; assess impact

SC&A action item: review NIOSH assessment

27
Issue #3: Recycled Uranium - continued 

NIOSH “Downblender” assessment delivered November 2011

“Rationale for 400 ppb U Pu for 10A Process Stream at Fernald,” November 1, 

2011 (Rich)

SC&A response provided February 6, 2012

SC&A Observations on NIOSH report:

• Estimates that any single worker would have spent at most 8 percent of their 

annual work hours handling unblended POOS* (Group 10A) materials

• Relies on documented time to repackage 5 hoppers into drums in April-May 1982 

(SRDB 33730) and assumes sufficiently bounding for subsequent steps

• SC&A concurs that this is an acceptable approach given weight of evidence

• Relies on unsubstantiated assumptions regarding shift time and number of 

hoppers handled ( 8 hoppers > 400 ppb measured Pu) to reach 8% estimate

• Does not consider variability in measured Pu content/hopper (up to a factor of 3 based 

on DOE mass balance reports)

• Time fraction could be higher based on reasonable alternative assumptions (e.g., all 

hoppers considered, 8-hour shifts)

*Plutonium Out Of Specification

28
Issue #3: Recycled Uranium - concluded 

29

SC&A Observations on NIOSH report, continued:

• SC&A estimates that any single worker could have spent up to 14 percent of their 

annual work hours handling unblended Group 10A materials based on:

• Average plutonium concentration in the 16 hoppers on a U mass basis 

was about 1,122 ppb

• Assumed baseline concentration for less exposed workers (other than 

Plant 5 metal workers and Plant 1 millwrights) = 100 ppb

• Shift time = 8 hours (no reduction for protective measures and 

respirators)

• Average mass processed per shift = 11,875 kg/19 shifts = 675 kg/shift 

• Given 8 hours per shift, it would take about 288 hours in 36 shifts to 

process all 16 hoppers

• Maximum percentage of annual time allotted to POOS handling = 

288/2,080 = 13.86%

Weighted average Pu concentration over a year:

Puavg = ((1,792 hr × 100ppb) + (288 hr × 1,122 ppb))/2,080 hr = 242 ppb

Conclusion: 400 ppb is probably bounding for workers handling Group 

10A materials – Move to SP discussions
• SC&A first became aware of receipts of recycled thorium at Fernald at the SRS 

teleconference on August 12, 2011

• SRDB review - hundreds of metric tons of recycled thorium were received at Fernald from 

mid-1960s to late 1970s (most from SRS)

• Principal concern is exposures to U-233, U-232, Th-234, Pa-233, and fission products 

during processing, handling, and storage of RT (similar to RU)

• Previous investigations of thorium intakes have focused on proposed NIOSH coworker 

models based on air sampling and chest count data (SEC issue #6) and intakes of Th-230 

from raffinates (SEC issue #4)

• Ability to reconstruct intakes of RT constituents is predicated on the veracity of the thorium 

coworker models (SEC issue)

• SC&A delivered a paper for discussion at the February 9, 2012 WG meeting

• Determined that presence of RT at Fernald does not significantly contribute to 

unmonitored external exposures

• Internal exposures from RT are predominantly from thorium. However, determined 

that U-232 and U-233 intakes at bounding levels can result in rem level organ doses

• NIOSH may wish to further investigate the impact of uranium contaminants in RT 

when assigning internal dose commitments from intakes of thorium at Fernald (SP 

issue) 

Recycled Thorium (new issue)

30
Summary

Issues remain to be dispositioned with NIOSH and 

SC&A

• Work Group deferring action on thorium chest count data (1978-1988) 

pending further assessment

– SC&A to provide formal responses to NIOSH white paper Calculation of 

Chronic Intake IRFs for Th-232Assuming Shared Kinetics

• Work Group deferring action on adequacy of uranium urine bioassay 

coworker model as applied to subcontractors pending further assessment

• SC&A to revise January 2012 white paper comparison based on identification 

and analysis of records that pertain to these subcontractors only.

• If NIOSH determines that intake determinations are feasible for individual 

subcontractors, they will prepare a white paper comparison of subcontractor 

and site employee intake distributions over specified employment periods. 

SC&A will review that document when it becomes available.

31
Questions?