Draft 

An Alternative Assessment of Radon Releases from K-65 Silos 

An SC&A White Paper 

Contract No. 200-2004-03805 

Prepared by 

U. Hans Behling 

S. Cohen & Associates 

1608 Spring Hill Road, Suite 400 

Vienna, VA 22182 

November 2008 

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.
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TABLE OF CONTENTS 

1.0 Statement of Purpose .......................................................................................................... 1

2.0 Relevant Background Information ...................................................................................... 1

2.1 Raffinates Stored in Silos 1 and 2 ........................................................................... 1

2.2 K-65 Silo Design Flaws and Modifications Aimed to Mitigate Radon 

Releases................................................................................................................... 2

2.3 Radionuclide Concentrations and Distributions in Silos 1, 2, and 3 ...................... 3

2.4 Assumed Radon Releases by NIOSH ..................................................................... 6

2.5 Salient Features of the 1995 RAC Calculational Methods and Conclusions.......... 7

3.0 An Alternate Approach to Estimating Radon-222 Releases from K-65 Silos .................. 12

3.1 States of Equilibrium/Disequilibrium Among RadionuclideS of the U-238 

Decay Chain in Uranium Ores/Raffinates ............................................................ 12

3.2 Radon Release Calculations .................................................................................. 14

4.0 Summary Conclusions ...................................................................................................... 17

References ..................................................................................................................................... 18

Attachment 1: 1977 Study by Claude W. Sill .............................................................................. 20
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1.0 STATEMENT OF PURPOSE 

Under Task Order 5, the Advisory Board on Radiation and Worker Health (the Board) directed 

S. Cohen and Associates (SC&A) to perform a full review of the Feed Materials Production 

Center (FMPC) Special Exposure Cohort (SEC) Petition-00046 and the NIOSH SEC Petition 

Evaluation Report (ER). In compliance with the Board’s directive, SC&A submitted its review 

in a draft report on May 31, 2007. 

Among issues identified by SC&A was Finding 4.2-3, which stated that NIOSH may have 

adopted “. . . incorrect model assumptions pertaining to radon releases from K-65 Silos” 

[Emphasis added]. 

On October 28, 2008, the Board’s Work Group on SEC Petition-00046 (Chaired by Mr. Bradley 

Clawson) conducted a teleconference that focused on several unresolved findings that included 

Finding 4.2.-3. The Work Group issued an action item, which directed SC&A to provide the 

following additional data/information in support of Finding 4.2-3: 

(1) Provide a quantitative calculation that supports SC&A’s claim of potential Rn-222 

releases between 64,500 Ci/yr to 92,000 Ci/yr from Silo 1; and 

(2) Discuss the necessary assumptions and circumstantial evidence, which support these 

release estimates. 

2.0 RELEVANT BACKGROUND INFORMATION 

2.1 RAFFINATES STORED IN SILOS 1 AND 2 

The primary mission at the Feed Materials Production Center was the processing of uranium ores 

(and other feed materials) to high quality, finished uranium metal products. Between 1953 and 

1955, FMPC processed pitchblende ores from the Belgian Congo, which contained unusually 

high activity levels of Ra-226. The liquid extraction of uranium from pitchblende ores in Plant 

2/3 produced waste streams (or raffinates) that must reasonably be assumed to have retained 

nearly all of the Ra-226, as well as other radiocontaminants that had been present in the ore. 

Raffinates generated in Plant 2/3 were disposed directly to the storage Silos 1 and 2. In addition 

to raffinates generated at FMPC, a total of 13,000 55-gallon drums of African pitchblende 

raffinates generated at the Mallinckrodt Chemical Works (MCS) facility were also disposed in 

Silos 1 and 2 between July 1953 and September 1958. In total, the extraction of uranium from 

pitchblende ores at FMPC and MCW produced an estimated 10,000 metric tons of radiumcontaining raffinates that were stored in Silos 1 and 2. 

Silo 3, the Metal Oxide Silo, contains the metal oxide waste raffinate from the extraction of 

uranium ores and concentrates. Unlike the K-65 raffinates, the metal oxide was transferred from 

Plant 2/3 by high-pressure air through pipes to Silo 3. All of the metal oxide material stored in 

Silo 3 was derived from onsite processing of ores/concentrates that had Ra-226 levels that were 

about 40-fold lower than the K-65 material. 
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Each of the three silos is 80 feet in diameter with an overall height of 36 feet, of which about 26 

feet 8 inches is the height of the exterior wall with the center of the dome at 36 feet. The vertical 

walls are 8-inch thick concrete and the domes are a nominal 4-inch thickness of concrete. The 

total volume of each silo is about 160,000 feet3. While both K-65 Silos (i.e., Silos 1 and 2) are 

about two-thirds filled, the Metal Oxide Silo (i.e., Silo 3) is filled to near capacity at 150,000 

feet3

of waste. Figure 1 provides a schematic cross-section of the silos and identifies several key 

features that affected the release of radon, as discussed below. 

Figure 1. General Cross Section of the K-65 and Metal Oxide Silos 

2.2 K-65 SILO DESIGN FLAWS AND MODIFICATIONS AIMED TO MITIGATE 

RADON RELEASES 

Over the years, the rate of radon releases from K-65 silos was likely affected by design flaws, as 

well as the many modifications to the silos that attempted to reduce radon emissions. A brief 

review of these flaws/modifications is provided in a 1995 report issued by the Radiological 

Assessment Corporation (RAC Report CDC-5, 1995), which stated the following: 

 From pages 28–29 (of RAC 1995): 

The K-65 Silos have had problems of deterioration, almost since the time of 

construction. Significant cracking in the walls and seepage of the contents was 

noted from the 1950s. Because of these problems, repairs and improvements to 

the Silos occurred from the 1960s through the 1980s. Not all of the changes to 

the Silos would have had a significant effect on the releases of radon. The most 

important change, for radon emissions, was the sealing of penetrations of the Silo 

domes in 1979. This action would have significantly reduced the ventilation of 

the silo air spaces, and thus also reduced the radon releases from the Silos. The 

addition of an exterior foam layer on the silo domes in 1987 may have further 

reduced the emissions of radon. Earthen berms were built around the Silos in 

1964. However, at the time the radon releases occurred primarily through 
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openings in the silo domes, so the addition of the berms would not have altered 

the releases. [Emphasis added.] 

 From page J-22 (of Appendix J, RAC 1995) 

Since the Silos were open to the atmosphere [until 1979] with the gooseneck 

vent, and other unsealed penetrations in the domes, it seems probable that the 

overwhelming majority of Rn releases would have been through the dome 

penetrations . . . 

. . . We also assume that a significant change may have occurred at the end of 

1987, when the foam layer was added to the silo domes. [Emphasis added.] 

Table J-3 in Appendix J of the 1995 RAC Report provides additional summary descriptions, 

dates, and reference documents pertaining to these modifications. For convenience, Table J-3 is 

reproduced herein as Table 1. 

Table 1. Summary of Historical Changes to the K-65 Storage Silos 

(Source: RAC 1995, Appendix J) 

Date Repairs or Improvements

May 1964 Cracks in silo walls were patched, waterproofing sealant applied, and earthen berm 

constructed to counterbalance material inside silos 

End of June 1979 Openings in silo domes, including the gooseneck pipe and other penetrations, were 

sealed, with gaskets installed, to prevent Rn emissions

June 1983 The earthen berms were enlarged to correct erosion problems

Early 1986 Dome covers added to protect the center sections of the silo domes; neoprene 

membrane layer applied to part of Silo 2

November 1987 Radon Treatment System*

installed to treat displaced Rn during work on Silos 

(not continuously operated)

December 1987 Rigid, polyurethane foam layer and urethane coating applied to exterior of silo 

dome surfaces to weatherproof the Silos

November 1991 Addition of layer of bentonite on top of K-65 material in Silos

 

*

 The Radon Treatment System (RTS) is a system that pumps air in the headspace of the silos through a 

series of calcium sulfate and charcoal beds, which adsorb Rn-222.

2.3 RADIONUCLIDE CONCENTRATIONS AND DISTRIBUTIONS IN SILOS 1, 2, 

AND 3 

While a very limited amount of K-65 waste sampling data was collected prior to 1989, only 

sampling data first obtained in 1991 provide a reasonable assessment of the distribution of 

nuclide-specific activities in Silos 1, 2, and 3 (ASI/IT 1992). Sample locations from this 

program are defined by the zone and the four silo manholes from which the sample was 

obtained. Each zone refers to roughly one-third of the K-65 material in the Silo with Zone A the 

top third, Zone B the middle third, and Zone C the bottom third. 
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A similar set of waste samples were obtained through 3 out of 4 influent manholes of Silo 3 in a 

1989 survey that was part of a Remedial Investigation (RI) Report (DOE 1990). However, the 

RI does not identify the locations in behalf of the individual samples. For convenience, 

summary results of sampling data for Silos 1 and 2, and Silo 3 are presented herein in Tables 2 

and 3. Most relevant to this report are sampling data that identify the absolute, as well as 

relative, activity concentrations for Ra-226 and its long-lived radioactive daughter Pb-210 (t1/2 of 

22 years) for a given silo, as well as differences between the K-65 Silos and the Metal Oxide Silo 

3, as summarized in Table 4 below. An important distinction between the K-65 Silos and the 

Metal Oxide Silo is the extent to which Pb-210 is in disequilibrium with its parent Ra-226. 

It must also be noted that NIOSH elected to cite core sampling data in Table 5-16 of ORAUTTKBS-0017-5 that were taken in 1993 and reported by Tomes 2001. In behalf of the 1993 

sample set, the mean activity values cited in Table 5 below were reported. 
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Table 2. Results of Radionuclide Analyses on K-65 Material Obtained by ASI/IT 

from 1991 Sampling 
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Table 3. Radionuclide Analyses on Metal Oxide Material from 1989 Sampling of Silo 3 

Table 4. Average Activity Levels for 1991 Data Set as Given in Tables 2 and 3 Above 

Mean Activity (pCi/g)

K-65 Silos Ra-226 Pb-210 Ratio Pb-210/Ra-226

Silo 1 525,000 194,000 0.37

Silo 2 417,000 160,000 0.38

Metal Oxide (Silo 3) 2970 2620 0.88

Table 5. Average Activity Levels fro 1993 Data Set as Cited in ORAUT-TKBS-0017-5

Mean Activity (pCi/g)

K-65 Silos Ra-226 Pb-210 Ratio Pb-210/Ra-226

Silo 1 477 202 0.42

Silo 2 263 190 0.72

Metal Oxide (Silo 3) 3.87 3.48 0.90

2.4 ASSUMED RADON RELEASES BY NIOSH 

Section 5.2.4 of ORAUT-TKBS-0017-5 provides the following: 

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). Considering the expected large differences in release rates due to 
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barometric pressure changes, the release rates would average up to 15 to 20 

Ci/day after addition to the Silos were complete. [Emphasis added.] 

2.5 SALIENT FEATURES OF THE 1995 RAC CALCULATIONAL METHODS AND 

CONCLUSIONS 

The credibility of the release quantities cited in the 1995 RAC Report must be viewed with 

considerable caution for the following reasons: 

(1) Release values of 5,000 to 6,000 Ci/yr from Silos 1 and 2 represent median values; and 

(2) Release estimates were based purely on complex models that are largely defined by 

diffusion kinetics of radon through the waste package and head-space ventilation rates. 

The authors of the 1995 RAC Report acknowledge the following limitations and uncertainties 

regarding these estimates: 

 From Page 29: 

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: 

. . . releases from the K-65 Silos through the diffusion pathway are relatively 

small, but not insignificant, compared to releases through air exchange . . . 

[Emphasis added.] 

. . . 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 . . . 
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 From Page J-27 of Appendix J: 

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.] 

 From Page J-28 of Appendix J: 

. . . The silo interior air was sampled on November 4, 1987, prior to the operation 

of the Radon Treatment System (RTS) and prior to the application of the exterior 

foam layer to the silo domes . . . The RTS is a system that pumps air from the silos 

through a series of calcium, sulfate and charcoal beds, which . . . removes Rn222, and thus potential daughter products of Rn-222, from the air space of the 

silos, and reduces the direct radiation exposure rates on the silo domes. The 

system is used to reduce radiation exposures to personnel involved in work on the 

silos. [Emphasis added.] 

 From Pages J-41 through J-44: 

If measurements of the exposure [dose] rate are obtained for a consistent 

geometry, for a time period when the 222Rn concentration is also known, an 

exposure rate factor (mR h-1 per pCi L-1, or similar) can be developed. Then, the 

222Rn concentration can be estimated for other time periods when only exposure 

rate data exist . . . 

Searches through historical records of the FMPC have located some results of 

radiation exposure rate measurements on [top of] the K-65 silo domes which are 

summarized in Table J-19 . . . [Note: Table J-19 is reproduced herein as Exhibit 1 

and Exhibit 2]. 

The data for the period prior to the sealing the openings, 1959 to 1979, do not 

indicate a significant variation in exposure rate. These measurements ranged 

from 65 to 90 mR h-1

. . . 

For the period after sealing openings, 1980 to 1987, the data show considerable 

variations (Figure J-4), but no clear trend is evident. . . [Note: Figure J-4 is 

reproduced herein as Exhibit 2]. 

The RTS was operated . . . on one silo at a time, with a flow rate of about 1000 ft3

min-1, and was operated until radiation levels on [top of] the silo dome surface

[i.e., contact] stopped decreasing . . . With these flow rate and operating times, 
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and an assumed removal efficiency close to 100%, the 222Rn concentrations in the 

silo air space should have been reduced to less than 3% of the initial 

concentrations. . . 

Thus, for this analysis, the exposure rate measurements made after operaton of 

the RTS are considered to represent the “background” exposure rate, in the 

absence of 222Rn daughters in the silo air. [Emphasis added.] 

From these statements contained in RAC 1995, the following conclusions may be drawn: 

(1) The release rates of Rn-222 (and its short-lived daughters) varied greatly over time and 

reflect incremental modifications to the K-65 silos aimed to mitigate the releases of 

Rn-222.

(2) Undoubtedly the single most important modification for reducing radon releases was the 

sealing of multiple penetrations that included manhole covers, a six-inch diameter 

gooseneck pipe, and large numbers of cracks in June of 1979. 

(3) Contact dose rate readings on top of the silos prior to 1979 are essentially identical to the 

1987 contact dose rate readings taken after the operation of the RTS (see Exhibit 1). 

(4) Based on the relationship of the 1987 contact dose rate readings on top of the silo domes 

and reduced activity levels in silo headspace, the derived headspace ventilation rate prior 

to 1980 can be assumed at 1.2/hour. Implicit in this assumption is that for years prior to 

1980, there was little or no buildup of radon/radon daughters in the headspace of the K65 silos as a result of unfettered releases to the environment. 

(5) The release rate of Rn-222 from the contained waste into the silo headspace, however, is 

key to an understanding of the radon release rate to the environment. The release of Rn222 from the waste into the silo headspace and/or the environment precludes further 

decay and the formation of Pb-210 within the waste. The resultant disequilibrium 

between Ra-226 and Pb-210 in the raffinate may serve as the basis for estimating the 

environmental releases of radon, as discussed in Section 3.0 below. 
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EXHIBIT #1 
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EXHIBIT 2 
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3.0 AN ALTERNATE APPROACH TO ESTIMATING RADON-222 

RELEASES FROM K-65 SILOS 

3.1 STATES OF EQUILIBRIUM/DISEQUILIBRIUM AMONG RADIONUCLIDES 

OF THE U-238 DECAY CHAIN IN URANIUM ORES/RAFFINATES 

In general, uranium ores are mined from deep-lying strata. The extracted ore exists in relatively 

large pieces that may be stockpiled for variable time periods before being transported to a 

uranium processing facility. The initial steps in processing raw ores involve mechanical 

crushing and grinding in order to produce uniformly sized smaller particles. The ground ore is 

subsequently placed in a slurry, which is subject to either an acid- or alkaline-based leaching 

process that separates the solubilized uranium from the residual and insoluble solids that become 

waste streams. 

A condition placed on the ores from the Belgian Congo by African Metals was that the Ra-226, 

Ra-226 daughters, and the lead and precious metals be further extracted, stored, and returned to 

African Metals. Steps to extract these materials as a separate residue from the bulk ore residue 

resulted in the radium- and lead-bearing K-65 wastes that were subsequently stored in Silos 1 

and 2. 

In behalf of this assessment, SC&A attempted to identify documents from FMPC and MCW that 

might provide quantitative data regarding the activity levels of select radionuclides in 

pitchblende ores at time of receipt and in K-65 raffinates at time of emplacement in the K-65 

silos. Specifically, our focus was to identify absolute and/or relative activity levels of Ra-226 

and Pb-210 in pitchblende and raffinates. At this time, however, our effort has not yielded any 

useful information. 

Data in the Scientific Literature 

In a 1977 study (Sill 1977), uranium ores, uranium dust, and uranium mill tailings were analyzed 

for U-238, U-234, Th-230, Ra-226, and Pb-210 activity levels. For convenience, this study is 

enclosed herein as Attachment #1. 

Table 2 of Attachment #1 identifies the results of several uranium ores from three different mills 

(i.e., Uravan Co., Mill A, Mill B, and Mill C) and three special samples from USGS. The second 

column of Table 2 gives the activity of the U-238 parent. Please note, the remaining columns 

give the ratios of each daughter to that of U-238 parent. 

Inspection of Table 2 shows that, with the exception of USGS ores, values for Pb-210 are 

generally only a few percentage points lower than those of Ra-226, which suggests that Pb-210 

exists in near equilibrium with Ra-226.

In addition to ore samples, this study analyzed mill tailings from two different sources: A large 

sample was obtained from a single mill representative of those on the Colorado plateau; and the 

other sample was a composite, prepared from 16 different mills (see page 403 of Attachment #1). 
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The tailings used in the composite were about 13 years old and the sample from the single mill 

was a few years younger. The analysis yielded the following results: 

Source Ra-226 (dpm/g) Pb-210 (dpm/g) Pb-210/Ra-223

Single mill 743 665 90%

Composite (16 mills) 1100 962 87%

The author, Claude W. Sill, concluded that: 

Lead-210 is slightly lower than its Ra-226 precursor in both samples, similar to the 

results obtained with the ores studied . . . analyses on the individual tailings when they 

were collected initially from active piles showed that the Pb-210 activity was nearly 

equal to or only slightly less than that of Ra-226 . . . 

. . . Because of the 1602-yr half-live of its Ra-226 parent, the Pb-210 will 

obviously not decay significantly with age, except for that resulting from loss of 

Rn-222. [Emphasis added.] 

From information presented above, it can be concluded that the degree of disequilibrium between 

Ra-226 and Pb-210 is quantitatively linked to the loss of Rn-222 from ores/tailings. The 

observed disequilibrium values among core samples taken from Silos 1 and 2 in the early 1990s 

(see Tables 2 and 3) in themselves, however, are incomplete for estimating radon releases from 

Silos 1 and 2. Essential to estimating radon releases is an understanding of the state of 

disequilibrium that existed at the time(s) of raffinate disposal. 

In the absence of empirical measurements involving pitchblende ores, the degree of 

disequilibrium between Ra-226 and Pb-210 at time of raffinate disposal in Silos 1 and 2 is 

unknown. That a significant disequilibrium from the loss of Rn-222 existed, however, must be 

assumed due to substantial time periods and processes that separated the initial mining of the 

ores and the emplacement of K-65 material in Silos 1 and 2. The following excerpt from 

Section 4.6 of ORAUT-TKBS-0005 identifies approximate time periods, processes, and 

conditions that may have led to radon releases and disequilibrium between Ra-226 and Pb-210 

before emplacement: 

Most of the high-grade pitchblende ore processed by Mallinckrodt was obtained 

by AEC as a concentrate from the Belgian Congo in 1944 (AEC 1967) the socalled African ore. There is some disagreement as to how it came to St. Louis. 

DOE (1997) states that from 1943 on, the receiving and storage facility operated 

at Middlesex, New Jersey (DOE 1997) assayed, crushed, riffled, and redrummed 

the ore as it came into the United States, then sent it to the various refineries, 

including Mallinckrodt (AEC 1949b, Eisenbud 1975). MED (1945n) states that 

the African ore came through the Eldorado (Port Huron, Canada) area for 

processing before being sent on to the US refineries. AEC (1967) states that the 

concentrate was shipped from the Belgian Congo to St. Louis in 55-gallon drums 

(but this could mean that it came by way of Middlesex). Whatever the case, it was 
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not likely that significant milling of this ore (as opposed to simply grinding to 

somewhat smaller size) was done at Mallinckrodt. . . .

. . . The radon in the Belgian Congo ore was also significant because it built up 

over time in containers and enclosed spaces. When drums, enclosed storage 

areas, the thaw house, etc., were opened, a worker could be enveloped in the 

escaping radon. [Emphasis added.] 

A lower-bound (and, therefore, claimant unfavorable) value of a disequilibrium activity ratio 

between Pb-210 and Ra-226 of 0.5 at time of emplacement may be estimated based on the 

following assumptions related to radon releases: 

(1) At time of mining, Ra-226 and Pb-210 is assumed to have existed in secular equilibrium

(i.e., there had been no in situ loss of Rn-222) 

(2) A maximum time interval of about 22 years elapsed between mining of pitchblende and 

disposal of K-65 material (Note: This 22-year time interval is equal to the half-life of 

Pb-210.) 

(3) A 100 percent loss of Rn-222 gas from ore/raffinates throughout the 22-year time period 

is assumed.

In addition to the release of Rn-222, the above-cited disequilibrium ratio value of 0.5 could 

potentially be further reduced (or increased) due to chemical processes. For example, the 

extraction of uranium from pitchblende and/or the extraction of raffinates from bulk tailings may 

have differentially impacted the distribution of Ra-226 and Pb-210 on the basis of their 

solubility. 

In the absence of empirical data, a further reduction of disequilibrium will be assumed (that 

again will lead to reduced estimates of Rn-222 releases) at time of emplacement.

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. 

3.2 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 
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 = 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 

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 × 10-4 g of Rn-222 

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

SpA Rn-222 = 153,881 Ci/g 

 Thus, the 4.298 × 10-4 g 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 
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 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 Ra-226 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. 

 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, 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 
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4.0 SUMMARY CONCLUSIONS 

NIOSH’s adopted model for radon releases, as given in Section 5.2.4 of ORAUT-TKBS0017-5, assumes “. . . that during the 1953–1978 period 5,000 to 6,000 Ci/year of Rn-222 

were released from the silos (RAC 1995).”

This estimate (as openly admitted by the authors of RAC 1995) was based purely on a 

model for which the most basic model parameters (e.g., diffusion coefficient and radon 

emanation fraction) were unknown. Central to the RAC 1995 release rate(s) were 

estimates of air exchanges between the silo headspace and outside air that were driven by 

diurnal changes in temperature and barometric pressure. 

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 of an airplane wing that creates the necessary lift). 

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 before 1979 and after 

1989 with the operation of the Radon Treatment System. Based on these data and the 

persistent disequilibrium between Pb-210 and Ra-226, SC&A estimates combined 

Rn-222 releases prior to 1980 in excess of 100,000 Ci/yr from Silos 1 and 2. 
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REFERENCES 

ASI/IT (ASI and IT Corporation). 1992. Radiological Validation Qualifiers for OU4. 

Tables of Results of Radiological Analyses on Samples, from the ASI/IT Database. 

Fernald, Ohio. 

Atomic Energy Commission (AEC). 1967. Historical Review of the Mallinckrodt 

Airport Cake. Report transmitted with cover letter from J. R. Katz, legislative assistant to 

Missouri Congressman Robert A. Young, to Dr. W. E. Mott, Director, Division of 

Environmental Control Technology, Department of Energy, July 26, 1978). 

Atomic Energy Commission (AEC). 1949b. Health Hazards in NYOO Facilities 

Producing and Processing Uranium. Report by the New York Operations Office 

Medical Division. April 18, 1949.

Department of Energy (DOE). 1990. Remedial Investigation Report for Operable Unit 

4, Task 6 Report, Feed Materials Production Center, Fernald, Ohio, Remedial 

Investigation and Feasibility Study. Draft Final. Oak Ridge, Tennessee. 

Department of Energy (DOE). 1997. Office of Environmental Management. Linking 

Legacies: Connecting the Cold War Nuclear Weapons Production Processes to Their 

Environmental Consequences. DOE/EM-3019; Appendix B; January 1997. 

Eisenbud M. 1975. Early Occupational Exposure Experience with Uranium Processing. 

In: Occupational Health Experience with Uranium. Proceedings of a United States 

Atomic Energy Commission Conference. Arlington, Virginia: ERDA-93; 1975: 9-24.

Manhattan Engineer District (MED). 1945n. Shipment Security Survey at Mallinckrodt 

Chemical Works. Memorandum to the Officer in Charge from Lt. F. W. Simmons, 

Shipment Security Control Officer of the Intelligence and Security Division; 15 February 

1945. 

ORAUT-TKBS-0005. 2007. Basis for Development of an Exposure Matrix for the 

Mallinckrodt Chemical Company St. Louis Downtown Site and the St. Louis Airport Site, 

St. Louis, Missouri, Rev. 02. Oak Ridge Associated Universities Team: Cincinnati, 

Ohio. 

ORAUT-TKBS-0017-5. 2004. Technical Basis Document for the Fernald 

Environmental Management Project – Occupational Internal Dose, Vol. 5, Rev. 00, 

National Institute for Occupational Safety and Health (Kuykendall), May 28, 2004. 

RAC 1995, The Fernald Dosimetry Reconstruction Project, Tasks 2 and 3 Radionuclide 

Source Terms and Uncertainties, RAC Report No. CDC-5. Radiological Assessments 

Corporation, Neeses, South Carolina, 1995. 
Draft White Paper – K-25 Silos 19 SC&A – November 21, 2008 

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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. 

Sill, C.W. 1977. Simultaneous Determination of 238U, 234U, 230Th, 

226Ra, and 210Pb in 

Uranium Ores, Dusts, and Mill Tailings, Health Physics 33:393–404. Pergamon Press. 

Tomes, T. 2001. Technical Basis for Internal Dosimetry at the Fernald Closure Project, 

SD-2006. Fernald Closure Project, Fernald, Ohio.
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ATTACHMENT 1: 1977 STUDY BY CLAUDE W. SILL 
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