Draft 

ADVISORY BOARD ON 

RADIATION AND WORKER HEALTH 

National Institute for Occupational Safety and Health 

REVIEW OF NIOSH WHITE PAPER, “THE NEUTRON 

EXPOSURE AT THE PIQUA ORGANIC MODERATED 

REACTOR,” DATED MARCH 3, 2011 

Contract No. 200-2009-28555 

Revision 0

Prepared by 

Aris Papadopoulos 

S. Cohen & Associates 

1608 Spring Hill Road, Suite 400 

Vienna, Virginia 22182 

Saliant, Inc. 

5579 Catholic Church Road 

Jefferson, Maryland 21755 

April 2011 

Disclaimer 

This document is made available in accordance with the unanimous desire of the Advisory Board on 

Radiation and Worker Health (ABRWH) to maintain all possible openness in its deliberations. However, 

the ABRWH and its contractor, SC&A, caution the reader that at the time of its release, this report is predecisional and has not been reviewed by the Board for factual accuracy or applicability within the 

requirements of 42 CFR 82. This implies that once reviewed by the ABRWH, the Board’s position may 

differ from the report’s conclusions. Thus, the reader should be cautioned that this report is for 

information only and that premature interpretations regarding its conclusions are unwarranted.
Effective Date: 

April 21, 2011 

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Neutron Exposure Issue 

Page No. 

Page 2 of 9 

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.

Document No. 

Review of NIOSH White Paper – 

Neutron Exposure Issue 

Effective Date: 

Draft – April 21, 2011 

S. COHEN & ASSOCIATES:

Technical Support for the Advisory Board on 

Radiation & Worker Health Review of 

NIOSH Dose Reconstruction Program 

Revision No. 

0 

Review of NIOSH White Paper, “The Neutron 

Exposure at the Piqua Organic Moderated Reactor,” 

dated March 3, 2011

Page 2 of 9 

Task Manager: 

________________________ Date: ___________ 

Aris Papadopoulos 

Supersedes: 

N/A 

Project Manager: 

________________________ Date: ___________ 

John Mauro, PhD, CHP 

Reviewer: 

 John Mauro 

Record of Revisions 

Revision 

Number 

Effective 

Date Description of Revision 

0 (Draft) 04/21/2011 Initial issue 
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April 21, 2011 

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Neutron Exposure Issue 

Page No. 

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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.

TABLE OF CONTENTS 

Abbreviations and Acronyms ..........................................................................................................4 

1.0 Introduction..........................................................................................................................5 

2.0 External Dose from Neutron Exposure Issue.......................................................................5 

2.1 Evaluation Report Methodology..............................................................................5 

2.2 SC&A Concern ........................................................................................................6 

2.3 White Paper Response .............................................................................................6 

2.4 SC&A Conclusion ...................................................................................................8 

3.0 References............................................................................................................................9 
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Page 4 of 9 

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.

ABBREVIATIONS AND ACRONYMS 

AEC Atomic Energy Commission 

CAM Continuous Air Monitor 

cc cubic centimeter 

Ci Curies 

cm

2 square centimeter 

ER Evaluation Report 

INL Idaho National Laboratory 

mR milliRoentgen 

mrem millirem 

MWt megawatt thermal 

NIOSH National Institute for Occupational Safety and Health 

POMR Piqua Organic Moderated Reactor 

rem Roentgen equivalent man 

SC&A S. Cohen and Associates 

SRDB Site Research Database 
Effective Date: 

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Neutron Exposure Issue 

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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.

1.0 INTRODUCTION 

Prior to the July 8, 2010, meeting of the Work Group for the Piqua Organically Moderated 

Reactor (POMR), SC&A was asked to perform a cursory review of the Piqua Evaluation Report 

(ER) (NIOSH 2009). The review consisted only of reading the ER and identifying any areas that 

appeared to be technically weak or “soft.” The review did not include a query of the site 

research database (SRDB), a check of all the numbers, or a site data capture, including 

interviews. “Soft” area issues resulting from this review were raised during the meeting of the 

Work Group on the POMR, held on July 8, 2010. 

At the meeting, NIOSH committed to provide a white paper that would evaluate the so-called 

“soft” areas. These areas included (1) the tritium and carbon-14 assumptions used for the 

occupational inhalation exposures, related lack of tritium concentration measurements, and the 

potential difference in exposure between the general plant environment, as measured by 

Continuous Air Monitors (CAMS) and that experienced by workers who were breaching 

contaminated systems during activities such as filter change outs, and (2) the assumptions for the 

dose calculations due to neutron exposure. 

NIOSH’s white paper, Tritium and Carbon-14 Organic Moderated Reactors at Piqua and INL

(NIOSH 2010), addressed the tritium/carbon-14 issue. SC&A performed a cursory review of the 

white paper (SC&A 2010) and agreed with NIOSH’s position on the volatility issues of tritium 

and C-14 as technically defensible. 

NIOSH’s white paper, The Neutron Exposure at the Piqua Organic Moderated Reactor (NIOSH 

2011), addressed the neutron exposure issue. SC&A performed a cursory review of the second 

white paper. The following provides a summary of the issue, the white paper response, and the 

SC&A conclusion. 

2.0 EXTERNAL DOSE FROM NEUTRON EXPOSURE ISSUE 

2.1 Evaluation Report Methodology 

NIOSH has not located any primary external dosimetry records (e.g., original dosimetry records) 

for the Piqua workers during the operational period. External data that have been found are in 

the form of exposure summary reports and monthly and semi-annual operational progress reports 

for the years 1963 through 1966. Based on the available summary data, the individual data 

reports [reported to Atomic Energy Commission (AEC) as whole-body radiation exposures to 

penetrating radiation] would likely have included neutron dose, had any been detected. 

However, in order to interpret the data in a claimant-favorable manner, NIOSH used paired 

measurements of neutron and photon doses to establish a neutron-to-photon ratio, and then added 

the derived neutron dose to the photon dose. In this way, NIOSH ensured that the neutron dose 

was not overlooked. 

Two measured values, each indicated as <0.5 mrem/hr, were taken, one in a location where the 

concurrent gamma reading was 13.5 mR/hr and the other in a location where the concurrent 

gamma reading was 11 mR/hr. The first detectable reading had a resulting neutron-to-photon 
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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.

ratio of 3.7% (0.037 to 1) and the second of 4.5% (0.045 to 1). Based on this information, 

NIOSH used a neutron-to-photon ratio of 10% as a bounding ratio to assess the bounding 

neutron dose, given a bounding photon dose. 

In turn, the bounding photon dose, according to the ER, can be assessed based on bounding 

assumptions from the site summary data for external dose. NIOSH explains that the data are 

sufficient to support bounding whole-body photon estimates for the years 1963 through 1966 

from the upper bound of 1 rem for the years 1963 through 1965, and 2 rem for the year 1966. 

2.2 SC&A Concern 

The SC&A concern lies in the fact that there is no assurance that non-monitored workers could 

have received higher neutron exposures, or that every worker was monitored. There are surveys 

in locations where there are indications of neutron streaming and neutrons escaping. Although 

these locations are outside the containment, SC&A expressed concern that it is uncertain whether 

a worker could be present inside the containment during operation. In response to that concern 

expressed during the work group meeting, NIOSH committed to check and verify that personnel 

had no access to the containment during reactor operation. In general, SC&A indicated that a 

closer look in the neutron survey data is warranted. 

2.3 White Paper Response 

NIOSH’s draft white paper (NIOSH 2011), responds to SC&A concerns by providing 

documented answers to the following questions/issues: (1) Was every worker monitored; (2) 

Did workers have access to containment; (3) What documentation exists on neutron exposure 

levels; and (4) How is worker exposure estimated from survey data? The following summarize 

the white paper positions. 

(1) Was every worker monitored? 

The white paper states that in interviews with former workers, each person interviewed stated 

that film badges were worn at all times by workers and pocket dosimeters were routinely used. 

A former health physics technician at the plant stated that workers in the Auxiliary Building 

wore film badges that were exchanged monthly and later reduced to quarterly. Interviews also 

indicated that workers in the area always wore their film badges. 

(2) Did workers have access to containment? 

The white paper provided a figure showing the physical arrangement of the Reactor Building and 

the Auxiliary Building. The two buildings were adjacent and formed a single structure. The 

access between the buildings was at the 100-foot level, ground level for the Reactor Building. 

Double air-locks were used to maintain reduced air pressure in the Reactor Building. The reactor 

and most of the associated components were below grade to provide additional shielding. 

 The Piqua Operating Limits and Controls (AI 1965) procedures included the following: “No 

person shall enter the reactor containment shell during periods when the procedure is applicable 
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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.

without first obtaining permission from the shift leader.” Activities were controlled under this 

manual by Special Work Permits and Extended Work Permits. 

A column of ordinary concrete surrounded the reactor vessel and extended upward outside of the 

reactor vessel to the floor level. This column served both as a biological shielding and as the 

foundation for the reactor. There was no worker access through this shield. Reactor radial 

shielding was achieved through (1) an inner thermal shield with 1.5-inch steel, (2) an outer 

thermal shield with 4.0-inch steel, (3) a reactor vessel wall with 1.125-in steel, and (4) a 

biological shield with 8 feet and 4 inches of ordinary concrete. Shielding above the reactor was 

achieved through (1) the upper grid plate with 8-inch steel (2) organic coolant, measuring 

17.5 feet, and (3) a reactor vessel head with 8.5-in steel. 

 

(3) What documentation is there on neutron exposure levels? 

The white paper responds to this issue by providing documented information on the existing 

survey data, dosimetry results, interviews with former employees, and a theoretical approach to 

the neutron flux levels that could have existed outside the biological shield. 

Survey Data 

According to NIOSH, a series of Post-Critical Operational Tests were performed at several 

power levels, increasing eventually to full power (45.5 MWt). Twenty-nine (29) points were 

selected in the Reactor Building prior to power operation and surveyed during each step increase. 

Measurements taken at the 55% power level showed gamma radiation to be at background levels 

within the Reactor Building on the main floor, the 100-foot level above the reactor. No neutrons 

were detected at any location surveyed when testing. During a neutron survey with the reactor at 

full power, the only detectable neutron levels that were found were within the pump rooms at the 

two coolant lines where they emerged from the biological shield. The radiation survey data for 

the full power test, including the neutron results, were presented in the white paper. The only 

detectable neutron levels were reported as “less than 0.5 mrem/hr.” 

Dosimetry 

A report to the AEC summarized personnel exposures for Atomic International workers who 

worked at the Piqua Plant. It indicated zero collective neutron exposure for the period April 

1963 through August 1965 for those workers. 

Interview 

During the interviews, a health physics technician stated that neutron surveys were performed 

routinely, at least monthly, and that extensive surveys were performed whenever the reactor 

increased power levels. The interview reinforced the assumption that 0.5 mrem/hr was the 

highest neutron level encountered during the surveys. 
Effective Date: 

April 21, 2011 

Revision No. 

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Document No. Review of NIOSH White Paper – 

Neutron Exposure Issue 

Page No. 

Page 8 of 9 

 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:

Activation in Concrete Shield 

According to NIOSH, a 1969 report from Atomics International (Hewson 1969) included 

estimates of the average lifetime neutron flux within the reactor components and within the inner 

concrete of the biological shield. A graph of the calculated flux levels, presented in the white 

paper, showed approximately 107 neutrons/cm2

/second at about 60 centimeters into the concrete 

shield. Extending the plotted line to the outer edge of the shield at 390 centimeters from the core 

centerline provides an estimate of 10-2 neutrons/cm2

/second at the outer surface. Using the 

Nuclear Regulatory Commission generic conversion factor for typical nuclear plant neutron 

spectra (9.0E-6 mrem cm2), the resulting average exposure due to neutrons would have been 

about 3 microrem/hr, or approximately 6 mrem/yr for 2,000 working hours per year. 

(4) How is worker exposure estimated from survey data? 

As discussed in NIOSH’s ER methodology above, annual reports were made to the AEC and the 

data were subsequently published in AEC reports that summarized annual, whole-body 

exposures. For the years 1963 through 1965, 8 persons were reported to be in the 1 to 2 rem 

range. This was the maximum range reported. Although it is expected that any neutron 

exposures would have been included in the values reported to the AEC, the 1 and 2 rem values 

were assumed to be solely gamma exposure. NIOSH used a neutron-to-photon ratio of 10% as 

the ratio to assess the bounding neutron dose, given a bounding photon dose. This was based on 

the assumption that there was no place within the plant during its operation where a worker could 

receive a neutron dose without also receiving an associated gamma dose. 

2.4 SC&A Conclusion 

Based on the cursory review of the white paper, SC&A concludes that the position taken by the 

white paper on the External Dose from Neutron Exposure issue is technically defensible. 

Moreover, the paper’s extensive close look at the data available alleviates SC&A concerns on the 

uncertainty issues related with neutron exposures at the POMR. SC&A concurs that the 

approach used in the ER for calculating doses from neutron exposure is bounding and claimant 

favorable.
Effective Date: 

April 21, 2011 

Revision No. 

0 – Draft 

Document No. Review of NIOSH White Paper – 

Neutron Exposure Issue 

Page No. 

Page 9 of 9 

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.

3.0 REFERENCES 

AI 1969. Compilation of Piqua Nuclear Power Facility Operating Limits and Controls and 

Post-Critical Operational Tests. Atomics International, February 5, 1965. SRDB Ref ID: 

55946. 

Hewson, R.A. 1969. PNPF Retirement Safety Analysis Reevaluation of Residual Nuclides. AlAEC-MEMO-12708 Supplement A. January 15, 1969. SRDB Ref ID: 58051. 

NIOSH 2009. SEC Petition Evaluation Report, Petition SEC-00126, Report Rev. 1, National 

Institute for Occupational Safety and Health, Cincinnati, Ohio. September 14, 2009. 

NIOSH 2010. White paper: “Tritium and Carbon-14 Organic Moderated Reactors at Piqua and 

INL.” National Institute for Occupational Safety and Health, Cincinnati, Ohio. August 26, 

2010. 

NIOSH 2011. White paper: “The Neutron Exposure at the Piqua Organic Moderated Reactor.” 

National Institute for Occupational Safety and Health, Cincinnati, Ohio. March 3, 2011. 

SC&A 2010. Review of NIOSH White Paper, “Tritium and Carbon-14 Organic Moderated 

Reactors at Piqua and INL.” S. Cohen and Associates, Vienna, Virginia, and Saliant, Inc., 

Jefferson, Maryland. December 20, 2010.