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MEMO 

TO: Mound Work Group 

FROM: Joseph Fitzgerald, SC&A 

DATE: June 1, 2012 

SUBJECT: Reply to NIOSH Comments on SC&A’s Thorium Report of May 2, 2012 

 

On May 2, 2012, SC&A provided the Mound Work Group with a report titled, SC&A’s 

Evaluation of NIOSH’s April 2012 Mound Laboratory Th-232 White Paper. On May 29, 2012, 

NIOSH forwarded the following responses to the comments expressed by SC&A in this white 

paper. NIOSH’s report is provided below, and SC&A replies to the NIOSH responses are 

provided in blue text. 

NIOSH Responses to SCA’s Thorium Report of May 8, 2012 

May 29, 2012 

SC&A comment 1: 

Was access to, and working with, the thorium-containing materials controlled by physical 

barriers and/or procedural requirements? 

NIOSH response 1:

The redrumming effort occurred in a remote part of the site (near the future location of Building 

21 – the thorium sludge storage building), geographically removed from other site activities. 

Former workers have anecdotally told NIOSH that controls (exclusion zones, health physics 

monitoring, respiratory protection, etc.) were established and that the workers involved were on a 

routine urinalysis program (which is supported by the urinalysis records). Therefore, it is highly 

unlikely that a worker would have visited this work location without being on at least gross alpha 

urinalysis. 

SC&A’s reply 1:

This issue comes down to accepting that oversight and control was adequate and in place. 

SC&A comment 2:

Were only persons directly involved with handling the material allowed in the area, or could 

there have been other personnel, such as craft workers, maintenance workers, grounds keeper, 

etc., that may have worked around the material, but were not considered part of the thoriumhandling crew? Exposures could have occurred not only during the periods the material was 

being handled, but also during dormant periods when no specific activity was taking place, and 
Memo: Reply to NIOSH Comments 2 SC&A – June 1, 2012 

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 Worker 

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

no health physics oversight was in place; thorium bioassays would not have been available for 

these types of workers under those circumstances. 

NIOSH response 2:

Craft and maintenance workers were in fact the personnel performing this project. It involved 

Hyster operators and laborers, as well as health physics monitors. It is unlikely that exposures 

occurred during the “dormant” periods. The drums were stored outside in a geographically 

remote part of the site removed from other site activities. Redrumming occurred in the warm 

weather months, and ceased in the winter months. While it would not be physically impossible 

for some worker to visit this remote location in the dead of winter when no activity was being 

performed, reasons for doing so are not obvious. Furthermore, the material was contained in 

drums. While it is true that some drums began rusting, hence the need for redrumming, the 

airborne exposure potential from material so stored would have been minimal unless the material 

was disturbed (e.g. redrumming). 

SC&A’s reply 2:

Again, this issue comes down to accepting that oversight and control was adequate and in place. 

SC&A comment 3:

What situation or procedure triggered the need to obtain urine samples and have them analyzed 

for thorium and the results recorded? 

NIOSH response 3:

As with other radionuclides at Mound, work with 232Th triggered collection of urine samples. 

Workers involved in this activity were on a routine urinalysis program. 

SC&A’s reply 3:

This issue comes down to accepting that administrative requirements were carried out. 

SC&A comment 4:

Was a list of personnel working with or around thorium-containing materials maintained? 

Relying on recorded thorium bioassays and/or applying a coworker model can only be used if it 

can reasonably be assured that the potentially thorium-exposed workers were bioassayed or 

identifiable for coworker dose application, unless the coworker dose is applied to all 

unmonitored workers. 

NIOSH response 4:

NIOSH is aware of no list of workers on the thorium redrumming project beyond what can be 

assembled from the bioassay records. Also see NIOSH response 5. 

SC&A’s reply 4:

Again, this issue comes down to accepting that oversight and control was adequate and in place. 

SC&A comment 5:

ORAUT-TKBS-0016-5 states: 
Memo: Reply to NIOSH Comments 3 SC&A – June 1, 2012 

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 Worker 

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

Page 30 – Th-230 

Primary 230Th bioassay records consisted of a logbook, and apparently duplicate 

records in a brown notebook. Count data were typically recorded on Form 

O-318 followed by an “I” or “Io.” Secondary 230Th results started as weekly 

reports on March 17, 1958. Weekly reports included Name, Isotope, and Result. 

Prior to 1958, secondary 230Th results were reported on Form O-634 including 

Name, Badge Number, Date, Type of Analysis, Isotope, and Result. However, 

some secondary documents have problems with reporting units. Some results are 

reported to be cph [counts per hour] per 24-hour sample when primary records 

indicate that they are actually cpm [counts per minute] per aliquot. The ORAU 

database should therefore be considered a secondary record extracted from 

primary records. 

Page 32 – Th-232 

Thorium-232 records are diverse due to programs conducted for many years. 

Primary 232Th bioassay data were entered into a small brown spiral notebook 

marked “Radium-Thorium” and “Radium-Thorium Separation from 8/15/1955 to 

2/2/1959 (Meyer 1992). Additional primary 232Th bioassay data were recorded 

in a large hardcover record book. However, the first 38 pages from this record 

book were removed from 7/6/59 to 1/9/61, 7/13/64 to 11/15/64 and 5/30/65 to 

6/6/65. These record books apparently do not contain true primary data, but 

calculated results such as cpm excreted per day. Secondary records in weekly 

reports contained 232Th results as cpm/24-hr samples beginning March 17, 1958. 

In August 1959, secondary results were reported on form O-756. The ORAU 

database is a record of secondary 232Th bioassay data extracted from other 

primary records (ORAU 2003e). [Emphasis added.] 

From this information, it is not apparent that the dose reconstructor has access to copies of all the 

original data sheets, or where they are located. SC&A’s scan of some of the DOE files located 

several of these forms with thorium bioassay data recorded. However, there does not appear to 

be much assurance that all the primary data are available to the dose reconstructor. 

NIOSH response 5:

The quote from ORAUT-TKBS-0016-5 page 30 is not relevant as it deals with ionium (230Th), 

while the subject of NIOSH’s paper was reconstruction of dose from 232Th. The record books in 

question are available in the SRDB. SC&A has seen for themselves that thorium bioassay results 

are included in the DOE files. It is not possible to prove a negative i.e. NIOSH cannot prove that 

there are no records beyond those captured in the SRDB and claimant files. However, it is worth 

considering that the majority (if not the entirety) of the thorium redrumming effort occurred in or 

before 1959. There is already a SEC class at Mound including all workers for this time period. 

The effect of disregarding the thorium bioassay records would be to deny the thorium doses 

calculated from these data from workers who don’t qualify for the existing SEC. This is not 

claimant favorable, and since we demonstrated that thorium doses can be reconstructed in our 

Retrospective Dose Reconstruction for Thorium-232 Activities at the Mound Laboratory, (April, 

2012) in NIOSH’s judgment disregarding this data is not scientifically justified. 
Memo: Reply to NIOSH Comments 4 SC&A – June 1, 2012 

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 Worker 

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

SC&A’s reply 5:

SC&A agrees that the use of the available thorium bioassay records (complete or not) during the 

1949–1959 SEC period is appropriate. However, the 1959–1980 SEC period requires at least 

one tritium bioassay to be considered for the SEC; therefore, adequate thorium bioassay records 

may be important for workers not qualifying under the latter SEC. 

SC&A comment 6:

In addition to the drummed material from United Lead Corporation (ULC), Mound also received 

thorium-containing materials from the St. Louis Airport, according to page 15 of ORAUTTKBS-0016-2 (ORAUT 2004): 

SW building was used in the Cotter Concentrate (St. Louis Airport Cake) starting 

in the early 1970s and terminated late in that decade. Pilot plant operations in 

SW were to recover Th-230 and Pa-231. 

The Cotter concentrate contained 99.9 g/drum of Th-232 and 11.1 g/drum of Th-230, according 

to page 16. 

NIOSH response 6:

The Cotter concentrate material actually came from the Cotter Corporation in Canon City, 

Colorado. The Cotter Concentrate program has been extensively discussed in NIOSH Evaluation 

of Data Adequacy and Completeness Issues at the Mound Laboratory (August 2011) [see 

NIOSH Responses 6, 9, 52, and 56 in that document]. 

SC&A’s reply 6:

This item was listed because it illustrates that Th-232 was present in sources other than the 

redrumming operations of the 1950s. Regardless of where the thorium-containing materials 

came from (or when workers were exposed), the issue of the workers being adequately 

bioassayed and the results available is still of concern, as has been discussed in the previous 

issues. 

SC&A comment 7:

Additionally, thorium was used in other areas at Mound as stated on page 12 of ORAUT-TKBS0016: 

Thorium-232 was often substituted for 238Pu compounds for modeling purposes in 

research and development, because this isotope was less expensive and less 

hazardous, and had physical characteristics similar to 238Pu. It is possible, 

therefore, to find 232Th compounds identical to the 238Pu compounds. 

These were not included in the paper that SC&A could find, and most likely not in the cleanup 

date of September 1975 as stated on page 20 of the paper. Although the drummed material from 

ULC most likely presented the greatest exposure potential, the issue of thorium 

exposure/monitoring did not go completely away in mid-1975. These other sources of thorium, 

and thorium contamination present during decontamination and decommissioning (D&D), are 

sources that could also result in personnel exposures and require bioassay data for DR. 
Memo: Reply to NIOSH Comments 5 SC&A – June 1, 2012 

 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 Worker 

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

NOTICE:

NIOSH response 7:

Just as was the case for thorium at Rocky Flats, where thorium was used as a stand-in for 

plutonium, the exposure potential from these applications would be minimal. While NIOSH 

never asserted, “the issue of thorium exposure/monitoring did not go completely away in mid1975”, we agree with SC&A’s assessment that the monazite sludge redrumming program would 

have been the activity performed at Mound with the highest thorium-232 internal dose potential. 

However, as extensively discussed in NIOSH Evaluation of Data Adequacy and Completeness 

Issues at the Mound Laboratory (August, 2011) [see especially NIOSH Response 63], the gross 

alpha procedure used at Mound was capable of isolating actinium, neptunium, americium, 

curium, and thorium. As described in NIOSH’s Retrospective Dose Reconstruction for Thorium232 Activities at the Mound Laboratory, (April, 2012), nuclide specific procedures could be (and 

were) performed to determine which of these nuclides were present. But in the absence of 

nuclide-specific results, the results of gross alpha urinalyses can be conservatively attributed to 

whichever of these nuclides is plausibly present, and gives the highest organ-specific dose for the 

dose reconstruction being performed. This is the way NIOSH handles gross alpha urinalysis 

results at every other facility, and the procedures used at Mound will be no different. In any 

case, the twenty dose-reconstructions performed in NIOSH’s Retrospective Dose Reconstruction 

for Thorium-232 Activities at the Mound Laboratory, (April, 2012) indicate that doses calculated 

by assuming the activity in the sample came from thorium-232 would be comparable to those 

calculated by assuming plutonium-238. 

SC&A’s reply 7:

SC&A agrees that the use of the current dose reconstruction (DR) protocol when only gross 

alpha data is available is claimant favorable. As previously discussed, the issue comes down to 

determining if all workers potentially exposed to thorium were adequately bioassayed. 

SC&A’s Summary:

SC&A finds that if the workers exposed to Th-232 were adequately bioassayed (during all 

periods Th-232 exposure was present at Mound), then DR methods are available to perform 

claimant-favorable intakes and assign resulting doses. However, this requires that it be assumed 

that procedures and controls were in place, implemented, and enforced, for adequate bioassays 

records to be available for DR; to date, SC&A has found no solid indications this was, or was 

not, the case for Mound.