SC&A’s Review of Observation 3, 

Potential Radon Calibration Chamber 

Exposure at the Grand Junction Facility

Ron Buchanan, PhD, CHP

Subcommittee for Procedure Reviews

February 16, 2023
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History of Grand Junction Facility TBD that 

resulted in observation 3

 May 18, 2018 – NIOSH issued ORAUT-TKBS-0060 (TBD), 

revision 00 (NIOSH, 2018) for the Grand Junction Facility 

(GJF) in Grand Junction, CO

 August 17, 2021 – SC&A issued its review of the GJF TBD 

(SC&A, 2021)

– SC&A’s review identified 5 observations 

– Observation 3, lack of consideration for potential exposure from the 

radon calibration chamber (RCC), still outstanding
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Addressing observation 3

 February 15, 2022 – the Subcommittee for Procedure Reviews 

(SPR) discussed observation 3 at its meeting

Action item: 

– NIOSH would provide relevant documents for SC&A to review

 May 2022 – SC&A reviewed five GJF RCC documents 

provided by NIOSH

– Documents give several snapshots in time of personnel monitoring and 

resulting intakes and doses
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Site Research Database (SRDB) 160585

 SRDB 160585 (Geotech, 1991a) – addresses radon dose for 

2 years, during which Geotech personnel operated the RCC 

 Used the log entries of stay time and chamber radon concentration 

measurements to determine intakes and resulting doses, assuming:

– 50% equilibrium

– 1 rem per working level month (WLM)

– any individual event dose <1 mrem was entered as zero

– any total dose <10 mrem was entered as zero

 All resulting doses for the 2-year period for all workers were entered 

as zeros
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SRDB 100192

 SRDB 100192 (Geotech, 1991b) – summarizes SRDB 160585 

for 1990 for reporting purposes 

 Document contains no new information
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SRDB 166851

 SRDB 166851 (NIOSH, 2017) – NIOSH interview with a senior 

health physicist in March 2017 about health physics monitoring in 

general

 EE worked at GJF during the period the RCC was operational

 Summary of relevant information about the RCC from the interview:

– RCC is mentioned as an airborne radioactivity area

– One door would be locked at >30 pCi/l, and both doors would be locked at 

>100 pCi/l 

– Radon concentration value multiplied by stay time was used to derive intakes 

and resulting doses, as detailed in Geotech (1995), PDF p. 9

– Several RCC workers made routine entries during a year and were monitored 

per logbook entries (Geotech, 1995)
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SRDB 093732

 SRDB 093732 (DOE, 1985) – RCC operating manual issued 

January 1985 

 A few highlights of the manual:

– Exposure chamber was a steel cylinder 11 feet in diameter by 9 feet in 

height

– Radon generator contained 5 millicuries of radium-226

– Five live-time radon detectors and four live-time radon decay product 

detectors with the results recorded on computer

– No entry into the chamber was allowed at radon concentrations 

>100 pCi/l

– External exposure rate <1.1 mR/h outside the RCC
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SRDB 098093

 SRDB 098093 (Geotech, 1995) – Internal memorandum 

summarizing individual doses and WLM values for EEs who 

entered the RCC periodically during one year of operation

– Appendix A provides the internal dose assessment calculations

– Attachments A.1 through A.6 provide:

• detailed list of the calculated intakes in WLM

• committed effective dose equivalent 

• lung dose for the year for each of the EEs 

– Attachment A.7 contains radon chamber entry log sheets for the year
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SC&A analysis of SRDB 098093

 SC&A analyzed:

– internal dose assessment methodology

– equations used in the calculations

– calculated intakes in WLM, committed effective dose equivalent, and 

lung dose in attachments A.1 through A.6 for a year of RCC operation

 SC&A found methods and calculations to be correct and 

applicable
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Results of SC&A’s analysis of SRDB 098093

 SC&A found:

– The largest recorded acute equilibrium-equivalent radon concentration 

for the one operational year was 22 pCi/l with a stay time of 4 minutes

– The largest dose for the year for any EE who entered the RCC was 

3 mrem 

– The largest derived WLM from the log entry information for that year for 

any EE was 0.0022 WLM

– The maximum recorded number of RCC entries made by an individual 

during the one-year period was recorded in the document
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What this information indicates

 RCC likely operated during the period 1985–1994 but could have been 

operated during other years

 RCC was an established facility with control of who could be present and 

who could operate it 

 Operating and entry information were recorded in logs 

 Exposure was controlled and personnel limited

 There were real-time radon monitors with results recorded on a computer

 Internal radon doses for the 2-year period addressed in SRDB 160585 

were all <10 mrem total for each of the RCC workers

 The largest radon dose in SRDB 098093 for any EE who entered the 

RCC was 3 mrem, and the largest derived WLM from the log entry 

information was 0.0022 WLM
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What is still uncertain

 The following information was not provided in the five 

documents reviewed:

– exact years the RCC was operational (the RCC manual was dated 

1985, and Building 32 was remediated in 1999–2000)

– intakes and doses during operational years other than 1989, 1990, and 

1994

– number of chamber entries that one individual could make per year
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Summary: Use of 5.7 pCi/l intake

 The question raised by observation 3 was: Does the 5.7 pCi/l 

used from Building 30 bound the radon exposure at the RCC? 

 According to table 5-7 in ORAUT-TKBS-0060 for 1975–1998, 

5.7 pCi/l radon at 50 percent equilibrium equals:

– 2.85E-2 working levels

– which equals 0.340 WLM/year 

– at 1 rem per WLM (Geotech, 1991a, pdf p. 3), this would result in a 

dose of 340 mrem/year

 Additionally, thoron dose is assigned per table 5-7 of ORAUTTKBS-0060 at an intake level of 5.7 pCi/l
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Summary: Assigning 0.340 WLM/year

 The assignment of 0.340 WLM/year radon intake (which would 

result in a dose of 340 mrem/year) to all employees during the 

years 1975-1998 would bound:

– individual events of <1 mrem

– a maximum annual total <10 mrem

– a maximum of 3 mrem recorded for one year of operation addressed in 

SRDB 098093

– an intake of 0.0022 WLM for one year of operation addressed in 

SRDB 098093
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Status

 Currently, radon dose information for the period outside the 

3 years of monitoring has not been made available

 Indications are:

– The RCC was a controlled facility with monitoring in place

– 5.7 pCi/l would bound exposures, but those conclusions are somewhat 

subjective outside of the 3 years of monitoring data currently available

– Exceeding 0.340 WLM/year would require substantial deviation from 

standard operations

 Observation 3 remains open until resolved to the satisfaction of 

the SPR
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Questions?
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References

Geotech, Inc. (1991a). Assessment of internal dose for Geotech workers occupationally exposed due 

to radon chamber entries during 1990. SRDB Ref. ID 160585 

Geotech, Inc. (1991b, February 20). Internal dose assessment due to radon chamber entries during 

1990 [Internal memorandum]. SRDB Ref. ID 100192 

Geotech, Inc. (1995, February 28). Internal radiation doses [Internal memorandum]. SRDB Ref. ID 

098093 

National Institute for Occupational Safety and Health. (2017). Documented communication with 

[redacted], March 16 & 29, 2017. SRDB Ref. ID 166851

National Institute for Occupational Safety and Health. (2018). Site profile for Grand Junction Facilities 

(ORAUT-TKBS-0060, rev. 00). https://www.cdc.gov/niosh/ocas/pdfs/tbd/gjf-r0-508.pdf

SC&A, Inc. (2021). SC&A’s review of ORAUT-TKBS-0060, revision 00, “Site profile for Grand Junction 

Facilities” (SCA-TR-2021-PR001, rev. 0). https://www.cdc.gov/niosh/ocas/pdfs/abrwh/scarpts/scagjfsp-r0-508.pdf

U.S. Department of Energy, Technical Measurements Center. (1985). Operating manual for the radondaughter chamber (GJ/TMC-18, UC-70A). SRDB Ref. ID 093732