Revised Memo: Response to NIOSH White Paper 1 SC&A – December 2, 2014 

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. 

M E M O 

DATE: December 2, 2014 

TO: Stu Hinnefeld 

CC: Ted Katz, Fernald WG members, John Stiver, Bob Barton, John Mauro, Joyce 

Lipstein 

FROM: U. Hans Behling 

SUBJECT: Response to NIOSH’s White Paper dated November 26, 2014

1.0 STATEMENT OF PURPOSE 

On November 20, 21, and 28, 2014, SC&A received a series of emails along with two

attachments from NIOSH that informed SC&A that a “White Paper” dated November 26, 2014,

and a “supplement” dated November 28, 2014, had been prepared by NIOSH for the upcoming 

Fernald Work Group meeting on December 4, 2014, regarding radon emissions from the K-65 

silos. One of the emails requested SC&A’s response to the attachment, which in a few sentences

“summarized” 55 pages representing the contents of two separate White Papers submitted by 

SC&A in November 2008 and in April 2010. 

Presented below is SC&A’s response to NIOSH’s White Paper issued November 26, 2014, 

which chronicles previous discussions that date back to 2006 and addresses past and current 

concerns raised by NIOSH regarding SC&A’s estimates of radon release rates from Silos 1 and 2 

at the Fernald facility. 

2.0 ESTIMATES OF RADON RELEASE RATES AND PREVIOUS WORK GROUP 

DISCUSSIONS 

SC&A’s two White Papers critically reviewed modeled radon release estimates cited in a 1995 

report issued by the Radiation Assessment Corporation (RAC Report CDC-5, 1995). Our

assessment of the RAC data/information, however, led to very different values of radon release 

rates that were based on documented empirical measurements and a single assumption: that 

the observed disequilibrium between Ra-226 and Pb-210 measured in 1991 and again in 1993 

likely existed since the time of waste emplacement in the 1950s. 

With regard to NIOSH’s statement that SC&A’s assumed disequilibrium at time of residue 

placement that “. . . neither maximizes nor minimizes the resulting estimates of radon 

emissions,” we would like to respond that SC&A’s assumed disequilibrium value most likely 

underestimates radon release rates derived by SC&A as discussed in Section 3.0 (and in greater 

detail in Attachment 1) of SC&A’s 2008 White Paper. Here, data were presented that support 

much lower disequilibrium fractions (i.e., ~0.8 to 0.9 for Pb-210/Ra-226) than what SC&A 

assumed at time of waste emplacement and project radon releases higher than values derived 

by SC&A. 
Revised Memo: Response to NIOSH White Paper 2 SC&A – December 1, 2014 

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. 

Additionally, there is a second reason that SC&A’s radon release estimates are likely 

low/unconservative. Namely, SC&A’s radon estimates are limited to all years prior to 1980, at 

which time silo repairs and dome covers were added that reduced radon releases, as shown by 

dramatic increases in dose rates on top of the silos. Thus, the disequilibrium measured in 1991 

and again in 1993 would have benefitted from the reduced radon emission and the associated 

buildup of Pb-210 for years 1980 through 1991/1993. 

In brief, SC&A’s model consisted of a straight-forward, easily understood model that was based 

on first principles, which involved the following three sets of measurements and one assumption: 

(1) Two independent sets of empirical measurements from wastes stored in Silos 1 and 2 in 

1991 and 1993 (which were within the range of statistical uncertainty) concluded a 

disequilibrium of ~0.40 for the Pb-210/Ra-226 ratio. 

(2) Multiple empirical dose rate measurements taken in 1964, 1972, and 1973 on top of 

Silos 1 and 2 prior to the sealing of the Silos, which yielded contact dose rate 

measurements that averaged about 70 mrem/hr. 

(3) After sealing Silo openings in June 1979 and the installation of a Radon Treatment 

System (RTS) in 1987, empirical dose rate measurements for Silos 1 and 2 yielded the 

following average contact doses: 

Baseline (No RTS operation) Average Dose Rate (1987) 

 Silo 1: 193 mrem/hr 

 Silo 2: 232 mrem/hr 

After Operation of RTS Average Dose Rate (1987) 

 Silo 1: 55 mrem/hr 

 Silo 2: 68 mrem/hr 

Note: It was stated that the RTS was operated for several hours until there was no further 

reduction in dose rate. It was further concluded that the RTS had removed 97% of radon 

and its short-lived daughters. Thus, it can be concluded that the residual dose rate(s) 

following RTS operation reflects primarily activity levels in the waste package with 

minimal contribution from the 3% residual radon/radon daughters in the Silo headspace. 

(4) SC&A’s Assumption for Deriving Radon Releases: that the empirically defined 

disequilibrium determined in 1991 and 1993 may have existed at time of waste 

emplacement in the 1950s. As explained above, SC&A considers the assumption as 

unconservative with the likelihood of having underestimated actual radon releases. 

On the basis of these empirical measurements and the unconservative assumption of a 

disequilibrium fraction, SC&A derived radon release values of ~88,000 Ci/yr and ~23,000 Ci/yr,

as described in Section 3.2 of the 2008 SC&A White paper enclosed herein as Exhibit #1. 
Revised Memo: Response to NIOSH White Paper 3 SC&A – December 1, 2014 

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 empirically based release model along with a substantial body of supportive data 

contained in SC&A’s two White Papers has been presented/discussed by SC&A during Fernald 

Work Group meetings on several occasions since their issue. To date, however, no significant 

progress has been made that would lead to a final decision/resolution relating to radon releases. 

In earlier discussions, NIOSH never questioned the credibility of the RAC-reported

disequilibrium values of ~0.40 for the Pb-210/Ra-226 ratio, but refuted SC&A’s radon release 

estimates, since it was NIOSH’s opinion that the overwhelming fraction of radon production in 

the waste package was released to the silo headspace, where it decayed with only nominal 

releases to the environment. 

This argument was neutralized by the empirical dose rate measurements taken before 1980 on 

top of the silos, which showed nearly identical values prior to 1980 to measurements taken after 

dome sealing and RTS operations in 1987 that removed 97% of radon in the headspace. 

Thereafter, SC&A’s estimates were dismissed for apparently frivolous/irrelevant reasons that 

included the fact that SC&A’s estimates were neither reviewed by the National Academy of 

Sciences (as was the 1995 RAC Report) nor had the scientific pedigree of the RAC Report, 

which had been adopted/referenced by other “scientists,” including authors of the “Pinney” 

Report. In response to NIOSH’s position, the Fernald Work Group directed SC&A to review the 

National Academy of Sciences review of the 1995 RAC model. SC&A responded to these

concerns in SC&A’s second White Paper issued in April 2010 (see Exhibit #2: Excerpts from 

SC&A’s White Paper Issued in April 2010).

Since 2011, the issue of radon releases at FEMP, along with other site profile issues, has 

remained largely unresolved by the Fernald Work Group in order to address and resolve many 

other issues that were considered relevant to the addition of a Special Exposure Cohort (SEC) 

class. 
Revised Memo: Response to NIOSH White Paper 4 SC&A – December 1, 2014 

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. 

EXHIBIT #1: Radon Release Calculations from SC&A’s 2008 

White Paper

For estimating Rn-222 releases from Silos 1 and 2, the state of disequilibrium empirically 

observed in the 1990s will, therefore, be assumed to have existed at time of the emplacement of 

K-65 material.

RADON RELEASE CALCULATIONS

The following steps may be used to calculate annual Radon-222 releases from Silos 1 and 2:

(1) Determine amount of radon produced per year from 1 curie Ra-226.

(2) Determine specific activity of Ra-226:

SpA N

N

t

  

(ln )( )

/

2

1 2

 where N = Number of radioactive atoms per unit mass

= 6.0225 × 1023 atoms/atomic mass

= 2.6648 × 1021 atoms /g of Ra-226

 t1/2 = physical half-life of Ra-226

= 1602 years

= 8.4201 × 108 min.

SpA

x

x

Ra  226

21

8

0 693 2 6648 10

8 4291 10

. ( . )

. min

 = 2.1932 × 1012 dpm/g of Ra-226

 = 0.99669 Ci/gram of Ra-226

(3) Determine the number of Ra-226 atoms that decay in 1 curie per year that are 

transformed into Rn-222:

 1 Ci Ra-226 = 1.012 g of Ra-226

 = (6.0225 × 1023 atoms/226 g)(1.012 g)

 = 2.6928 × 1021 atoms of Ra-226
Revised Memo: Response to NIOSH White Paper 5 SC&A – December 1, 2014 

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. 

EXHIBIT #1 (Continued)

No. of Rn-222 atoms formed/yr from the decay of 1 Ci of Ra-226:

 Rn-222 atoms/yr = Ao – A 1 yr

= 1.16600 × 1018 atoms of Rn-222

= 4.298 × 10-4g of Rn-222

(4) Calculate the specific activity of Rn-222:

SpA Rn-222 = 153,881 Ci/g

Thus, the 4.298 × 10-4g of Rn-222 generated per year from 1 Ci of Ra-226 correspond to 

the production of 66.15 Ci of Rn-222 per year.

(5) Calculate annual Rn-222 production in Silo 1 and Silo 2 based on data presented in 

Table 5-16 of ORAUT-TKBS-0017-5:

 Silo 1:

Total Ra-226 Activity = (477 nCi/g)(5000 MT)

= (477 nCi/g)(5 × 109g)

= 2385 Ci

 Rn-222 per year = 2385 Ci Ra-226 × 66.15 Ci/yr/Ci Ra-226

Rn-222Silo 1 = 157,767 Ci/yr

 Silo 2:

Total Ra-226 Activity = (263 nCi/g)(5 × 109g)

= 1315 Ci

 Rn-222 per year = 1315 Ci Ra-226 × 66.15 Ci/yr/Ci Ra-226

Rn-222 Silo 2 = 86,987 Ci/yr

(6) Estimate annual release of Rn-222 into headspace of Silos 1 and 2

As stated in Section 3.1 above, the state of disequilibrium observed in 1993 between Ra226 and Pb-210 is assumed to have existed unchanged from the beginning of K-65 

material emplacement in silos. Under a steady-state of disequilibrium, it is assumed that 

the fraction of radon released from the waste package is proportional to the degree of 

disequilibrium.
Revised Memo: Response to NIOSH White Paper 6 SC&A – December 1, 2014 

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. 

EXHIBIT #1 (Continued)

 Rn Ci yr  Ci yr

nCi g Pb

nCi g Ra Silo   















222 157 767 1 

202 210

477 226 1

( / ) , /

/

/

 = 157,767 Ci/yr (1 – 0.4235)

 = 90,955 Ci/yr

Rn Ci yr  Ci yr

nCi g Pb

nCi g Ra Silo   















222 86 987 1 

190 210

263 226 2

( / ) , /

/

/

= 24,144 Ci/yr

(7) Estimate Rn annual release rates into environment for all years prior to 1980:

In Section 2.0 of this report, the transient use of the RTS was estimated to reduce the 

Rn-222 (and daughter products) to 3% of its equilibrium value in the silo headspace. 

Under RTS operation, the contact dose rate on top of the dome was essentially identical 

to the dose rate prior to the sealants applied to dome in 1979.

On the basis of this relationship, it may be concluded that prior to 1980, approximately 

97% of radon entering the headspace was released to the environment:

Annual Environmental Releases prior to 1980:

 Rn-222 (Silo 1) = (0.97)(90,955 Ci/yr)

= 88,226 Ci/yr

 Rn-222 (Silo 2) = (0.97)(24,144 Ci/yr)

 = 23,419 Ci/yr
Revised Memo: Response to NIOSH White Paper 7 SC&A – December 1, 2014 

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. 

EXHIBIT #2: Excerpts From SC&A’s 2010 White Paper

1.0 RELEVANT BACKGROUND INFORMATION 

On January 29, 2010, the Fernald Work Group met in Cincinnati, Ohio, to discuss/resolve six 

outstanding issues pertaining to the Fernald site. Among the unresolved issues was SC&A’s 

contention that radon releases from the K-65 Silos may have been significantly underestimated 

by NIOSH, as stated in ORAUT-TKBS-0017-5 (ORAUT 2004):

As previously stated, the contents of the silos have not been disturbed during 

storage to any large degree. However, it has been calculated that during the 

1953 to 1978 period 5,000 to 6,000 Ci/year of 222Rn were released from the silos 

(RAC 1995). [Emphasis added.]

In a previous White Paper issued in November 2008 (SC&A 2008), SC&A conducted a critical 

review of the Radiological Assessment Corporation 1995 model (RAC 1995). Based largely on 

empirical measurements taken on top of the silos that ironically were included in Appendix J of 

the 1995 RAC Study, SC&A concluded that the modeled release estimates cited in the 1995 

RAC Study were likely a factor of 10 to 20 too low.

In a memorandum to the Work Group Chairperson, dated October 6, 2009, NIOSH rejected 

SC&A’s analysis and conclusions with the following statements:

NIOSH disagrees with the draft findings reported by SC&A. The RAC model was 

supported by a National Academy of Sciences review; SC&A’s was not. NIOSH 

will rely upon the individual exposure estimates produced using the Pinney/ 

Hornung model which utilized radon exposure levels from the RAC study, plus an 

additional radon source term at Fernald. . . . [Emphasis added.]

In response to NIOSH’s position, the Work Group directed SC&A to review the National 

Academy of Sciences’ (NAS) review of the 1995 RAC model (NAS 1994).1 On January 26, 

2010 (or three days before the Work Group meeting held on January 29, 2010 [SC&A 2010]), 

SC&A submitted its findings regarding the NAS review to the Work Group/NIOSH in the form 

of a memorandum. Our review of the NAS Report showed that there was little support for the 

RAC model.

 

1

 Note that the National Academy of Sciences performed their review on a 1993 draft of the 1995 RAC 

report. 
Revised Memo: Response to NIOSH White Paper 8 SC&A – December 1, 2014 

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. 

EXHIBIT #2 (Continued)

2.0 DISCUSSION POINTS RAISED DURING THE FERNALD WORK 

GROUP MEETING HELD ON JANUARY 29, 2010

A review of the Work Group’s transcript shows that the issue of radon emissions from the K-65 

Silos was discussed on pages 266 through 294 (NIOSH 2010). For convenience, select 

statements contained in the transcript will be cited below for further discussion.

 Regarding the “NAS Endorsement” of RAC (1995) Model: (pp. 278–279 of transcript)

MR. ROLFES: Okay. Looking at the National Academy of Sciences' 

review, it's got a -- I'm reading from the National Academy of Sciences' review of 

the RAC dose reconstruction for Fernald, and on page 17 of the PDF, it has a 

radon section, and I can read that if you'd like.

DR. MAURO: Is that what you're reading now? 

MEMBER ZIEMER: I'm reading it right now, yes. It certainly leaves 

the question open. 

MR. ROLFES: I'll go ahead and read that into the record. "The 

importance of the radon source term associated with the K-65 silos is difficult to 

establish primarily because the silos have been modified several times over the 

years. If the head space has been adequately sampled, the silos inventory could 

be modeled for release, assuming no retardation by the cap which has been 

sealed to various degrees over the years as a worst case endpoint.

"It is reasonable to separate the calculations into daytime and nighttime 

dispersion because the dispersion figures would certainly differ. However, there 

is no justification given for the release terms of 140 curies per year continuous or 

810 curies per year during the daytime only. It also might be a reasonable 

refinement to have transition periods in between." 

So I think that's really the part that is relevant, and it basically calls into 

question what the release is, and so the RAC report doesn't really get us any 

further down the road on, you know, validating the radon releases. . . . 

[Emphasis added.]

From these statements, SC&A concludes that neither the Work Group nor NIOSH is of the 

opinion that the NAS concurred with the RAC (1995) model.
Revised Memo: Response to NIOSH White Paper 9 SC&A – December 1, 2014 

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. 

EXHIBIT #2 (Continued)

2.1 REGARDING THE USE OF THE “PINNEY STUDY” AS A MEANS FOR THE 

VALIDATION OF RADON RELEASES

The “Pinney Study” was referenced multiple times in the Fernald Work Group transcript and is a 

reference to a study that was published in 2008 entitled, Estimation of Radon Exposure to 

Workers at the Fernald Feed Materials Production Center 1952–1988, by R.W. Hornung, S.M. 

Pinney, J. Lodwick, G. Killough, D.E. Brewer, and J. Nasuta in the Journal of Exposure Science 

and Environmental Epidmiology, pages 1–12 (Hornung et al. 2008).

From page 291 of the transcript:

MR. MORRIS: Okay. I'd like to also point you to a memo that Dr. Pinney 

wrote to [redacted] on September 13th, 2006, while [redacted] was preparing 

information for the SEC petition apparently, and she writes to [redacted] about 

using the data from the RAC report which was an off-site dosimetry model and 

extending it, extrapolating it back toward the source term to reconstruct the doses 

on the site. She got assurance from the model developer, Dr. Killough or Mr. 

Killough, that it could be extrapolated back on-site, and then took the initial 

action that she describes of validating that model based on some on-site 

information that was available. . . . [Emphasis added.]

From page 293 of the transcript:

MR. ROLFES: Right. That seems that the Pinney model has the 

validation of the RAC model essentially in it, and what we had previously said had 

been reviewed by the National Academy of Sciences, when the RAC model was 

reviewed by the NAS, we thought that it had spoken to the radon effluent, but it 

didn't very much, and now what we have here when we look back at the 

documentation we have, we found that the Pinney model actually relies upon the 

RAC model, which has been validated by Susan Pinney's model as well. 

[Emphasis added.]

These statements lack clarity and appear contradictory, inasmuch as they suggest that Pinney 

“relied” upon the RAC model, but then states that it was “validated” by the “Susan Pinney 

Model.”

 
Revised Memo: Response to NIOSH White Paper 10 SC&A – December 1, 2014 

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. 

EXHIBIT #2 (Continued)

From page 300 of the transcript:

CHAIRMAN CLAWSON: Well, you know, the bottom line comes down to 

SC&A has not been able to see this, and we've got to go back a little ways 

because this was held up to us as the holy grail for the radon and that everything 

was good with it, and now we've changed our whole course to that. So we're 

going to have to have SC&A review what NIOSH has put out there, the Pinney 

report, and so forth because, you know, we're changing whole directions. 

MR. ROLFES: That's a slightly different -- we've always said since our 

Evaluation Report that we were relying upon the Pinney data. So I did want to 

point that out. [Emphasis added.]

2.2 REVIEW COMMENTS AND RELEVANT CONCLUSIONS REGARDING THE 

“PINNEY REPORT”

At the request of the Fernald Work Group, SC&A reviewed the 2008 “Pinney Report” (Hornung 

et al. 2008) with regard to its use/validation of radon releases that were modeled by RAC. Based 

on our review, SC&A concludes the following:

(1) The Pinney Report simply accepted the source term releases of radon from the 

K-65 Silos, as described by the following two RAC reports issued in 1995 and 1998:

 RAC (1995): The Fernald Dosimetry Reconstruction Project, Tasks 2 and 2 

Radiologic Source Terms and Uncertainties.

 RAC (1998): The Fernald Dosimetry Reconstruction Project, Task 6 Radiation Doses 

and Risks to Residence from FMPC Operations from 1951–1988.

(2) Using the modeled RAC (1995)/RAC (1998) radon release source terms, the “Pinney 

Report” investigators applied a modified Gaussian dispersion model originally intended 

for estimating exposure to residents living within a 10-km radius to estimate onsite radon 

exposures to Fernald workers, as explained in their report:

 From page 2 of the 2008 “Pinney Report”:

The radon dispersion model was developed by Radiological Assessments Corporation 

(RAC) under contract to the CDC as part of the overall dose reconstruction that also 

included uranium and thorium doses from air and water transport. The model had been 

applied to the estimation of radon exposures to residents living near the facility. Details 

of the development of this model are given by Voilleque et al . (1995) [RAC 1995] and 

Killough et al. (1998) [RAC 1998] and are beyond the scope of this paper. We have, 

however, included an abbreviated description of the atmospheric dispersion model in 
Revised Memo: Response to NIOSH White Paper 11 SC&A – December 1, 2014 

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. 

EXHIBIT #2 (Continued)

Appendix A. The model was studied to determine what revisions would be required to 

make it applicable to the estimation of radon exposures to Fernald workers who were 

considerably nearer to the K-65 silos. The radon transport model involved emission 

rates from the silos, meteorological data, distance from the source, and decay rates of 

radon decay products. The output of the model was annual average exposure in either 

pCi/l or Bq/m3at any location specified by longitude and latitude coordinates. . . .

[Emphasis added.]

 From Appendix A of the 2008 Pinney Report:

The K-65 source term model is an empirical representation of the annual release 

of radon from the K-65 silos from 1952 through 1988. It was calibrated to a 

variety of data, primarily (1) the concentration of radon in the silo headspace gas, 

measured in 1987, (2) measurements of g-ray exposure on the external silo dome 

surfaces before and after they were sealed, and (3) a series of temperature and 

pressure readings in the silo headspace gas, taken in 1987. It is a stochastic 

model, with some parameters derived as probability distributions, which 

propagate into the annual release estimates. Detailed information about the 

K-65 source term model and the ratio of decay products at the point of release is 

given in Appendix Q of Killough et al. (1998) [RAC 1998], with references to 

the earlier report of Voilleque et al. (1995) [RAC 1995] for some details.

. . . The transport model used for the study described in this paper is adapted from 

the transport model of Killough and Schmidt (2000), but it is coupled with the 

original K-65 source term developed for the CDC dose reconstruction study, as 

described in Appendix Q of Killough et al. (1998) [RAC 1998] and in Voilleque 

et al. (1995) [RAC 1995]. [Emphasis added.]

This last statement clearly states that the “Pinney Model” simply “ . . . coupled the 

original K-65 source term . . .,” as defined in RAC 1995 and RAC 1998, to the radon 

transport model employed by the “Pinney Model.” Thus, contrary to NIOSH’s opinion, 

the “Pinney Report” made no effort to validate the radon source terms defined in RAC 

1995 and RAC 1998.
Revised Memo: Response to NIOSH White Paper 12 SC&A – December 1, 2014

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 SC&A’S COMMENTS PERTAINING TO NIOSH’S WHITE PAPER DATED 

NOVEMBER 26, 2014

NIOSH’s White Paper of November 26, 2014, states that “. . . NIOSH has not found a 

technical error in either SC&A’s or RAC’s approach, and cannot reconcile the widely 

disparate release values.” [Emphasis added.] Presented below is a comparison between the two 

models that may explain why corresponding release estimates differ.

SC&A selected a simplistic approach that employed the credible measurements involving the 

radioactive disequilibrium between Pb-210 and Ra-226, and measured dose rates on the top of 

the silos prior to 1980 and after sealing of silos and operation of the RTS. In summary, SC&A’s 

simplistic method is based on measured data with only one assumption for the initial state of 

disequilibrium that is likely to have underestimated radon release rates for years prior to 1980. 

(Note: SC&A did not attempt to estimate radon release rates for years post-1980.)

In contrast to SC&A’s simplistic and empirically based method, the RAC model is a complex

model that is based solely on (1) passive diffusion kinetics for the release of radon in the 

headspace, (2) their subsequent environmental release rates that are based on ambient 

temperature-driven diurnal expansions and increased pressures within the silos headspace, and 

(3) the resultant release of the “excess” volume (i.e., air containing radon) to the environment.

In addition to the RAC model’s complexity and associated uncertainties that reflect the need to 

account for diurnal temperatures on a daily basis, the model also suffers from two serious 

deficiencies identified below.

3.1 RAC’s Failure to Include the Impact of Wind and the Venturi Effect

In Section 4.0 of SC&A’s White Paper dated November 2008, SC&A had concluded the 

following (SC&A 2008): 

A serious deficiency of the RAC model is its failure to properly account for the 

Venturi effect that is likely to have dominated the release of Rn-222 from the silo 

headspace prior to June of 1979, when the silos were subjected to major sealing 

modifications. The Venturi effect would have the following impact: during 

periods of low to moderate winds, a steady flow of air over the curved smooth 

surface of the silo dome creates a partial vacuum (much like that over the leading 

edge of a forward-moving airplane wing that creates the necessary lift for flight). 

In essence, the wind-induced Venturi effect results in the reduction of atmospheric pressure over 

the external surface of the dome cap relative to the atmospheric pressure within the silo’s

headspace. Under sustained steady wind conditions, this pressure differential not only induces a 

pressure-driven release of air from the silo’s headspace into the environment, but in time also 

results in a reduction of pressure within the headspace relative to the pressure within the waste 

material that is the radon source term. This secondary pressure differential between the 
Revised Memo: Response to NIOSH White Paper 13 SC&A – December 1, 2014

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

headspace and silo waste material will also result in a pressure-driven migration of radon gas 

from the waste material into the dome’s headspace.

Based on the fact that the cylindrical dome-capped silos represent a configuration that is 

optimally affected by wind-induced pressure differentials, it is puzzling why the RAC model 

excluded this important radon release mechanism, even though its authors were fully aware of 

its potential role and stated the following in their 1995 report:

 From pages J-31 and J-32 of Appendix J of RAC 1995: 

Since the silo can not hold any significant pressure, it is certainly plausible that 

the cracks and other remaining penetrations in the silo domes are large enough 

and numerous enough that additional ventilation of the silos occurs, due to winds 

across the domes. For the present work, it is assumed that the silo ventilation is 

the sum of the ventilation rate due to the temperature effects and a ventilation 

rate due to wind effects. That is, 

λV, post = λV, ΔT + λV, wind

However, the authors subsequently elected to ignore the potential contribution of wind-induced 

ventilation, as given on page J-34 of Appendix J:

As discussed earlier, it is plausible that the cracks in the silo domes are numerous 

enough and large enough that the action of winds on the domes could create 

additional ventilation in the silos, represented by λV, wind. However, no data 

have been found to substantiate an estimate of λV, wind. . . . Since additional 

information has not been located to substantiate a value for λV, wind, we now 

assume a value of zero. [Emphasis added.] 

In summary, it is SC&A’s firm belief that prior to 1979, the wind/Venturi effect was likely the 

dominant mechanism for the migration of radon into the headspace, ventilation of the headspace, 

and the release of radon to the environment. Support for high ventilation rates prior to June of 

1979 and the role of the Venturi effect comes from the near-equal contact dose rate 

measurements taken on top of the dome before 1979 and after 1987 with the operation of the 

Radon Treatment System.

3.2 The Absence of Direct Radon Release Measurements as Well as Measurement of 

Parameters Used by RAC to Indirectly Estimate Radon Releases for Years Prior to 

1980

In describing data limitations for estimates of radon releases for years prior to 1980, the authors 

of the 1995 RAC Report further acknowledged the following deficiencies and uncertainties 

regarding their estimates: 
Revised Memo: Response to NIOSH White Paper 14 SC&A – December 1, 2014

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.

 From Page 29 of the 1995 RAC Report: 

For some other releases at the FMPC, extensive data sets of direct measurements 

of release quantities are available. However, for radon and radon decay product 

releases there are no direct measurements of release quantities. In addition, 

until the 1980s there were few measurements of parameters that can be used 

indirectly to calculate radon releases . . . 

The traditional model used to estimate radon releases from radium-226-bearing 

materials, such as uranium mill tailings, involves calculations of the quantity of 

radon formed in the material, and the subsequent diffusion of the radon through 

the material to the outside air. For the K-65 materials, measurements have not 

been made of the diffusion coefficient and radon emanation fraction, which are 

two key parameters in this traditional calculation. Literature values can be 

obtained for these parameters, but without site-specific values, the uncertainty 

ranges are extremely large. [Emphasis added.] 

 From Pages J-71 and J-72 of Appendix J (RAC 1995): 

. . . even with the large associated uncertainties, it is clear that the release rate of 

Rn-222 from the K-65 Silos was much greater in 1959–1979 period than in the 

1980–1987 period . . . [Emphasis added.]

For the post-1980 years, radon release estimates were still based on a ventilation rate that was 

modeled around daily temperature fluctuations (as previously described), but now at least 

included measured concentrations of radon in the headspace as a starting point, as described by 

RAC:

 From Page J-27 of Appendix J (RAC 1995):

During the period from 1980 through 1987 the major penetrations through the 

silo domes, like the six-inch gooseneck pipe, had already been sealed. However, 

exchange of air between the silos and the atmosphere continued, through 

numerous cracks in the concrete of the domes. Radon releases for this time 

period are based on measured concentrations of Rn-222 in silo air and on a silo 

ventilation rate calculated from the daily temperature changes in air. 

[Emphasis added.]

For years post-1980, however, RAC estimates are still likely too low, since these do not take into 

account enhanced ventilation rates that reflect the Venturi effect.

In an email that supplements NIOSH’s 2014 White Paper, NIOSH addressed this RAC 

deficiency and calculated a 13.8% increase in the release rate for time periods after June 1979 to 

1987 to account for the wind/Venturi effect.
Revised Memo: Response to NIOSH White Paper 15 SC&A – December 1, 2014

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.

As previously noted, radon release estimates by SC&A were derived from data that restricts 

radon release estimates to all years prior to 1980 only. In the absence of SC&A’s attempt to 

estimate releases post-1980, SC&A concurs with the radon release estimate revised by NIOSH 

for time periods from June 1979 to 1987. For years prior to June 1979, however, SC&A remains 

committed to radon release estimates described in our original White Paper issued in 2008.

4.0 REFERENCES

42 CFR 82. Methods for Radiation Dose Reconstruction Under the Energy Employees

Occupational Illness Compensation Program Act of 2000; Final Rule, Federal

Register/Vol.67, No. 85/Thursday, May 2, 2002, p. 22314.

Hornung, R.W., Pinney, S.M., J. Lodwick, G. Killough, D.E. Brewer, and J. Nasuta, 2008. 

Estimation of Radon Exposure to Workers at the Fernald Feed Materials Production Center 

1952–1988, Journal of Exposure Science and Environmental Epidemiology, 1–12.

NAS (National Academy of Sciences) 1994. Dose Reconstruction for Fernald Nuclear Facility: 

A Review of Task 4, National Research Council, National Academy Press, Washington, DC.

NIOSH (National Institute for Occupational Safety and Health), 2010. Transcript of Work 

Group on Fernald Site Profile and SEC. Cincinnati, Ohio. January 29, 2010.

ORAUT 2004. Technical Basis Document for the Fernald Environmental Management Project 

(FEMP) – Occupational Internal Dose, ORAUT-TKBS-0017-5, Rev. 00, ORAUT, Cincinnati, 

Ohio.

RAC (Radiological Assessment Corporation) 1995. The Fernald Dosimetry Reconstruction 

Project, Tasks 2 and 2 Radiologic Source Terms and Uncertainties, prepared by Voilleque, P.G., 

K.R. Meyer, D.W. Schmidt, S.K. Rope, G.G. Killough, M. Case, et al., RAC Report No. CDC-5, 

Neeses, South Carolina.

RAC (Radiological Assessment Corporation). 1998. The Fernald Dosimetry Reconstruction 

Project, Task 6 Radiation Doses and Risks to Residence from FMPC Operations from 1951–

1988, prepared by Killough G.G., M.J. Case, K.R. Meyer, R.E. Moore, S.K. Rope, D.W. 

Schmidt, et al. (RAC) Report No. CDC-1. Volumes I and II (final report). Neeses, South 

Carolina.

SC&A (S. Cohen and Associated) 2008. An Alternative Assessment of Radon Releases from 

K-65 Silos. Draft SC&A White Paper. SC&A, Inc., Vienna, Virginia. November 21, 2008.

SC&A 2010. Memo from Hans Behling to the Fernald Work Group, Subj: Response to 

NIOSH’s Statements Regarding the RAC Model for Estimating Radon Releases from K-65 

Silos. SC&A, Inc., Vienna, Virginia. January 26, 2010.

SC&A (S. Cohen and Associated) 2010. A Second White Paper Addressing Enhanced Radon

Releases from the K-65 Silos at the Fernald. Draft SC&A White Paper. SC&A, Inc., Vienna, 

Virginia. April 6, 2010.