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with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

Assessment of Sealed Radioactive 

Sources, and Fission and Activation 

Products as Radiological Exposure 

Sources in the Rocky Flats Plant Critical 

Mass Laboratory (Building 886 Cluster) 

White Paper 

Rev. 0 

National Institute for Occupational 

Safety and Health 

June 9, 2015 

James S. Bogard, Daniel Stempfley, Bob Burns 

Oak Ridge Associated Universities Team

- 

Reviewed by LaVon Rutherford and James W. Neton 

Division of Compensation Analysis and Support 
White Paper: Assessment of Radiological Sources in the RFP CML 

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with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. . NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

PURPOSE 

This white paper describes the Critical Mass Laboratory (CML) at the Rocky Flats Plant and the 

programs and experiments conducted there. It discusses the radioactive materials present and 

their amounts and assesses these materials as radiological sources. 

Radioactive materials at the CML included the nuclear fuels and sealed radioactive sources used 

in criticality experiments. Fission and activation products generated in the fuels, building 

materials, and fixtures as a result of the nuclear criticality experiments conducted there are an 

additional source of radiological exposure. Several liquid fuel spills, especially early in the 

facility’s history, resulted in residual contamination in the rooms where experiments were 

performed and in which the nuclear fuels were stored. The ability to estimate contributions to 

personnel dose from these sources is assessed from detailed accounts of the facility’s history, 

results from surveys and assessments conducted in association with facility decommissioning 

and demolition, and computer-modeled predictions of specific radioisotopes and quantities 

generated as fission and activation products. 

HISTORY OF THE CRITICAL MASS LABORATORY 

Construction of Building 886 (originally called Building 86), the Critical Mass Laboratory 

(CML), was completed in 1963. The Building 886 complex ultimately consisted of Building 886 

(Critical Mass Laboratory), Building 880 (storage facility), Building 875 (filter plenum facility), 

and an underground tunnel containing ventilation ducts that connected Building 886 to Building 

875 (SRDB 104452, PDF p. 3). Highly enriched uranium was introduced into Building 886 in 

the summer of 1965; the first criticality experiments were performed in September 1965. The 

building was used for experiments on enriched-uranium metal and solution, plutonium metal, 

low-enriched uranium oxide, and for several special applications. 

Experiments after 1983 were conducted primarily with uranyl nitrate solutions and did not 

involve solid materials (SRDB 104452, PDF p. 3). The RFP Nuclear Safety Group conducted 

1,600 (SRDB 21358, PDF p. 69) to 1,700 (SRDB 104452, PDF p. 3) critical mass experiments 

using uranium and plutonium in solutions (900 tests), compacted powder (300), and metallic 

forms (500) (SRDB 104452, PDF p. 3). Testing programs at the CML were temporarily 

suspended in 1987 for routine equipment modifications, and for contamination control and 

ventilation repairs; however, the modifications and repairs had not been completed in 1989 when 

all operations at RFP were curtailed as a result of an FBI raid. Criticality research at the CML 

never resumed after the raid (SRDB 21358, PDF p. 69). All the fissile materials were removed 

by 1997 for reprocessing (SRDB 136853, PDF p. 4). Internal fixtures were removed by 2000, 
White Paper: Assessment of Radiological Sources in the RFP CML 

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ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. . NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

with the exception of the Room 101 walk-in hood and the heavily contaminated annular tank on 

its elevated platform in a corner of the Assembly Room (SRDB 21358, PDF p. 411). These were 

eventually also removed, and the CML building was demolished in April 2002 (SRDB 21358, 

PDF p. 411). 

RADIOACTIVE MATERIALS USED IN THE CML 

A variety of sealed radioactive sources and nuclear fuel (uranium and plutonium) was housed at 

the CML. The types and amounts of fuel varied with time, but ranged up to the amounts shown 

in Table 1.

Table 1: Types and Amounts of Fissile Fuels Housed at the Critical Mass Laboratory

Type of Fissile Fuel Amount (kg) SRDB 21358, PDF page(s)

High-enriched uranium hemishells and rods 280 162, 289-295

Low-enriched (4.46% U-235) uranium oxide compacted into 

briquettes and tightly packaged in cubical aluminum cans

2,100 162, 289, 311-314

Plutonium ingots 800 289

Highly-enriched (93% U-235) uranium (as uranyl nitrate 

solution)

570 289, 295-303

Plutonium in the form of metal hemishells Unknown 303-305

Machined plutonium metal cylinders sealed in double containers 375 162, 305-310

Sealed sources of 210Po-Be, Co-60, and Cf-252 were used in the CML for instrument testing and 

for use in experiments (SRDB 21358, PDF p. 162). The 210Po-Be and Cf-252 sources were used 

in criticality experiments involving uranium to provide initiating neutrons that allowed a smooth 

transition toward criticality, giving better experimental results and preventing the inadvertent 

creation of a supercritical geometry. A 210Po-Be source was used before 1970, after which 

Cf-252 was used (SRDB 21358, PDF pp. 315-316). Gamma photons from Co-60 were used in 

testing a gamma-sensitive radiation detector mounted on the north wall of the Assembly Room 

that was used to monitor the gamma-ray field during critical experiments (SRDB 21358, PDF 

p. 316). 
White Paper: Assessment of Radiological Sources in the RFP CML 

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with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. . NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

Sealed sources in use at the facility in 1989 are shown in Table 2 (SRDB 21358, PDF p. 355). 

The relatively short half-lives of Co-60 and Cf-252 made it necessary to replace these sources 

periodically (SRDB 21358, PDF p. 316). The listed sources and their activities are taken as 

typical for the CML. Approximate initial exposure rates1from the Co-60 sources (from lowest 

activity to highest on the specified date) are 13.6 mR m2

h

-1 and 18.5 mR m2

h

-1. Initial dose 

equivalent rates (neutron + photon) from the Cf-252 sources2are 1.0 mrem m2h

-1

, 26.4 mrem m2

h

-1, 31.3 mrem m2

h

-1, and 32.8 mrem m2

h

-1

. 

Table 2: Sealed Radioactive Sources in Use at the Critical Mass Laboratory in July 1989

Registry 

No.

Manufacturer’s 

No. Isotope Radiation

Source 

Strength at (Date)

Strength

n/sec

(107)

Half-life

(years)

S-082 --- Co-60 gamma 14.0 mCi (1965) --- 5.27

S-083 NS-28 Cf-252 neutron 5.9 mCi (3/71) 3.3 2.6

S-297 SRCF-134 Cf-252 neutron 7.0 mCi (11/76) 3.9 2.6

S-363 SN-112 Cf-252 neutron 0.225 mCi (~1977) 0.13 2.6

S-475 F-621 Co-60 gamma 10.28 mCi (8/84) --- 5.27

S-507 SRCF-147 Cf-252 neutron 7.32 mCi (7/85) 4.16 2.6

Source: SRDB 21358, PDF p. 355, Table VIII 

NOTE: Encapsulation - All sources used for critical mass measurements are doubly-encapsulated stainless steel 

enclosures except for: (1) source S-082, whose encapsulation is not known; and (2) source S-363, which was used 

for another program and whose encapsulation is not known. 

GENERATION OF FISSION AND ACTIVATION PRODUCTS 

The amounts and types of fission and activation products produced in a criticality (or nearcriticality) vary according to the nuclear fuel and geometry of the event. The products of a 

criticality are radioactive and contribute to radiation dose from the fuel. An assessment of 

experimental parameters used at the CML is necessary to identify the most likely distribution of 

fission and activation products adding to the radiation environment over time. Most of the 

experiments conducted in the CML are described in some detail in the document that presents 

the comprehensive history of the facility (SRDB 21358, PDF pp. 376-394). Table 3 provides 

summary information about the date ranges, materials involved, and number of experiments for 

each program. Table 4 further consolidates the information to show the number of experiments 

using each chemical and physical form of nuclear material. 

 

1

 Exposure rates for Co-60 photons are estimated using Γ =13.2 R cm2 h-1 mCi-1 (SRDB 75017, PDF p. 144). 

2

 The specific activity of Cf-252 is 0.536 mCi/μg, and the dose equivalent rate from 1 μg of Cf -252 at 1 m in 

air is 0.0221 mSv/h (2.21 mremlh) from fast neutrons plus 0.0019 mSv/h (0.19 mrem/h) from gamma rays 

(SRDB 83312, PDF p. 4). 
White Paper: Assessment of Radiological Sources in the RFP CML

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with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. . NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

Table 3: Timeline of Experiments at the Rocky Flats Critical Mass Laboratory

SRDB 21358

PDF Page(s) Dates Material* n** Program Description

380 09/10/1965-04/05/1967 HEU Metal 235 Uranium Spherical Assemblies

380 08/19/1966-03/08/1967 HEU Metal 61 Massive Subcritical Uranium 

Spheres

381 04/20/1966 Weapon 

Component*** 1 Weapons Study

381 ca. 1966 Not Specified 13 Special Materials

381-382 05/09/1967-08/11/1967 U solution 38 Poison Plate I

382 05/31/1967-09/12/1969 Pu metal 167 Oil-Reflected Plutonium

382-383 09/12/1967-01/24/1968 U solution 110 The “Christmas Tree”

383 02/16/1968-10/15/1968 U solution 48 Slab/Cylinder

383 05/24/1968-06/20/1968 U solution 6

Partially-Reflected Solution 

Slab

383-384 02/03/1968-02/07/1968 Pu Oxide 9 Plutonium Calorimeter

384 11/17/1969-04/16/1970, 

10/1970

U metal in U 

solution  206 Coupled Assembly

384-385 late 1960s Pu metal --- Plutonium Ingots

385 02/19/1971-05/11/1971 U metal in U 

solution** ** 52 Uncoupled Coupled Assembly

386 06/01/1972-07/14/1972 U solution***** 20 Poison Plate II

387 late 1973-02/17/1976, with 

11-mo shutdown in 1975 Pu metal 76 Plutonium Cylinders I

388-389 04/21/1976-05/26/1976,

08/1977 U solution 186 Uranium Solution Cylinder Benchmark

389-390 02/1978-09/1981 LEU oxide 116 Uranium Oxide Contract

390-391 Summer 1982-12/20/1982 Pu metal 22 Pu Metal Cylinders II

391-392 05/1983-09/1984 U solution 61 Poisoned Tube Tank

392 07/1985-08/1986 U solution 32 Assorted Fuels Geometry

392-393 Spring 1986-10/1987 U solution 19 Shielded Annular Tank

*HEU (high-enriched uranium) is uranium enriched to 92% U-235 (PDF p. 288); LEU is low-enriched uranium, 

4.5% U-235; U solution is high-enriched uranyl nitrate with a concentration of ~450 gU/L (PDF pp. 289, 381) ; Pu 

refers to ‘weapons grade’ plutonium (PDF p. 288) consisting of 93.56% Pu-239, 5.97% Pu-240, <0.5% Pu-241 

(which decays to Am-241 with a 13.2-y half-life), and 0.01% Pu-242 (PDF p. 307). 

**The symbol n is the number of criticality experiments in this program. The designation ‘---’ indicates that the 

number is unknown.

***The weapon component was returned to production and was not part of the permanent Building 886 inventory. 

 Three different (unspecified) concentrations of uranyl nitrate were used in this study. 

** ***Uranyl nitrate in two concentrations: 450 gU/L and 52 gU/L.
White Paper: Assessment of Radiological Sources in the RFP CML

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ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. . NOTICE: This report has been reviewed to identify and redact any 

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Table 4: Number of Experiments for Each Material Physical and Chemical Form

Material Experiments

HEU Metal 296

HEU Solution 520

HEU Solution + HEU Metal 258

LEU Oxide 116

Pu Metal 274

Unknown >15

Total >1,479

Source: SRDB 21358, PDF pp. 376-394

Fission products in the fuels, and activation products in both the fuel and building materials, are 

sources of external radiation dose to personnel using the fuels and occupying the building; they 

present an internal dose potential for personnel that might ingest or inhale them. Personnel 

dosimeters assigned to RFP radiation workers document the external exposures. Internal 

exposures might result: (1) during operations from re-suspension of contamination on surfaces;

or (2) during facility demolition from airborne dust. CML staff were provided routine bioassay 

(urinalysis and whole-body counts) to detect intakes of radioactive material. No follow-up 

bioassay was performed subsequent to any of several accidental spills of nuclear fuel, however, 

according to a senior staff member involved with the clean-up activities (SRDB 138605, PDF 

pp. 5, 10). NIOSH has found no incident reports or related bioassay results, although many 

documents were lost when RFP was decommissioned (e.g., SRDB 142480, PDF pp. 5, 8).

All the nuclear materials at the CML, except for HEU solution, were treated in some way to 

reduce contamination. Plutonium metal cylinders (SRDB 21358, PDF pp. 288, 305) and 

hemishells (SRDB21358, PDF p. 305) were coated with a light film of grease or oil, as were the 

HEU hemishells (SRDB 21358, PDF pp. 268, 295). LEU oxide was compacted into briquettes 

on receipt, sealed in plastic, and then sealed in an aluminum can with small holes drilled for 

injection of water (SRDB 21358, PDF p. 312). Plutonium ingots, borrowed from RFP

production and returned immediately after conclusion of the experiments, were contained in 

thin-walled film cans (SRDB 21358, PDF p. 385). The HEU solution represents the most likely 

source of internal contamination by fuel and associated fission and activation products because it 

was handled in open tanks, and because several spills occurred requiring clean-up and recovery 

of the spilled fuel, leaving residual contamination that could dry and be re-suspended from 

surfaces (SRDB 21358, PDF pp. 447, 449, 452, 454-458, 464, 467-468, 486, 498, 500). 

Four incidents involving facility contamination by solid material (powder) are reported; two of 

these incidents involved dried uranyl nitrate salt (from HEU solution) on reactor components:
White Paper: Assessment of Radiological Sources in the RFP CML

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 Plutonium metal sealed in a can reacted with water in the can, oxidizing the plutonium to 

powder and pushing off the can lid (SRDB 21358, PDF pp. 488-471).

 A can containing compressed low-enriched uranium powder dropped from a table to the 

floor, rupturing the can and spilling the powder (SRDB 21358, PDF p. 479).

 Two almost identical incidents involved dried uranyl nitrate salt (from an HEU solution 

experiment) on the surface of a suspended metal “reactivity shim” being knocked to the 

floor, contaminating the facility and workers (SRDB 21358, PDF pp. 500-502).

The fission and activation products most important from either an acute or chronic personnel 

exposure perspective are clearly those generated in criticality experiments involving HEU 

solution because of the predominance of solution spills over the course of CML’s history (11 

spills involving solutions or dried salts from solution experiments, compared with two 

contamination events involving solid fuels).

The experiments conducted in Building 886 generally involved power levels of no more than 

10 milliwatts for no more than one hour (SRDB-20170, PDF p. 16). Approximately half of the 

experiments conducted in Building 886 actually achieved criticality. Only rarely were the 

radiation levels such that it was not possible to directly touch the fissile material and testing 

apparatus immediately after the experiments (SRDB 104452, PDF p. 3). RFP never had a 

criticality accident, or even a close call, according to a Senior Research Scientist and author of a 

history of the Critical Mass Laboratory (SRDB 21358, PDF p. 79); CML operating specifications 

were designed to prevent such an accident from criticality experiments intended to approach (but 

never achieve) prompt criticality or nuclear excursion. A discussion of the adopted safety 

parameters is found in the Technical Specifications for the Rocky Flats Critical Mass Laboratory

is provided in Attachment 2. The Site Description portion of the RFP Technical Basis Document

includes this summary of criticality experiments at Building 886:

Approximately half of the 1,600 criticality experiments in Building 886 achieved criticality. 

Experiments in the RFP laboratory generally involved power levels of no more than 

10 milliwatts, for no more than an hour. Approximately six high-power experiments were 

taken to between 10 and 100 times the power of typical tests. Using a conversion factor of 

3x1016 fissions per megawatt-second, this power level and duration corresponds to a 

maximum of 1.01x1012 fissions from a typical RFP criticality experiment and a maximum of 

1x1014 fissions from a high-power experiment. Records indicate that there were no incidents 

at Rocky Flats in which the power level of fissionable material became uncontrollable. The 

experiments were controlled by bringing the materials slowly to near criticality, observing 

the neutron flux to observe the reaction state. There is no indication in the available records 
White Paper: Assessment of Radiological Sources in the RFP CML

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information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

that gamma exposure or exposure to created fission products was a worker exposure 

problem during these experiments. (SRDB 20170, PDF p. 16)

The same document cites the ChemRisk study in concluding that some short-lived fission 

products were generated, but resulted in no personnel exposures (SRDB 20170, PDF p. 42):

Materials used in the experiments (uranyl nitrate metal powder) [sic] were re-used. Shortlived fission products were produced and none were indicated as having been released to the 

work or outdoor environment. The isotopes decayed rapidly and were contained until stable. 

(ChemRisk, 1991).”

NIOSH simulated fission and activation product build-up in uranium solution experiments at the 

CML using ORIGEN-S, a computer code system for calculating time-dependent concentrations 

of radionuclides that are simultaneously generated or depleted by processes such as fission, 

neutron absorption and transmutation, and radioactive decay. The code was used to estimate the 

production of fission and activation products in an unreflected stainless steel tank containing a 

solution of high-enriched uranyl nitrate. The composition used for the ORIGEN-S calculations 

was a homogenized mixture of the uranyl nitrate solution, the 304 stainless steel tank, and the 

associated impurities. All input data were derived from the published criticality benchmark case 

for this series of experiments (SRDB 142464, PDF pp. 3-10). The calculations used a 

case-specific cross section library created using the TRITON analysis sequence of the SCALE 

code system. The TRITON case used the heterogeneous geometry with the height of the tank 

truncated to the solution height of 31.2 cm (the solution height of the benchmark case). 

KENO-VI was used to model neutron transport. 

Analysis of the number and duration of experiments at CML involving uranium solution (from 

Table 4) yields the results shown graphically in Figure 1, which is a time distribution of HEU 

solution critical experiments over the history of CML. Dates correspond to Program dates in 

Table 3. Heights of the bars represent the average number of experiments per day during the 

Program period, and numbers above the bars are the total number of experiments. The dotted line 

shows the overall average number of HEU solution critical experiments over the history of 

operations at CML.
White Paper: Assessment of Radiological Sources in the RFP CML

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ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. . NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

Figure 1: Time Distribution of HEU Solution Critical Experiments Over the History of CML

Most of the solution experiments (480 of 778 total) were conducted in the first six years of the 

facility’s history, from 1967 through 1972. Another 186 experiments were conducted in 1976 

and 1977, and the remainder (112) from 1983 to October 1987. The rate of experimentation 

ranged from just over 0.8 per day (1967-1968) to less than 0.04 per day (1986-1987), with an

overall rate of 0.104 per day. 

The ORIGEN-S calculations assumed that each experiment took one hour and was conducted at 

a power level of 10 mW. All experiments during a Program period were assumed to have been 

performed serially and continuously at the end of the period, and then the resulting reaction 

products were allowed to decay until the start of the next Program period.3 The fuel was 

 

3 For example, there were three Program periods involving HEU solution from 05/09/1967 to 06/20/1968, consisting 

of 38, 110, and 54 experiments. The analysis considers continuous runs (at a power level of 10 mW) of 38 h and 

110 h, followed respectively by decay over 32 d and 23 d between periods, and then a 54-h run followed by decay 

over the idle time between this Program and the next in 1976.

Date

1/1/19681/1/19701/1/19721/1/19741/1/19761/1/19781/1/19801/1/19821/1/19841/1/1986

Experim ent Rate (d- 1

)

0.0

0.2

0.4

0.6

0.8

1.0

3 8

110

5 4

206 5 2

2 0

186

6 1

3 2

1 9

Average H EU Solution

Experim ental R ate

(0.104 d- 1)
White Paper: Assessment of Radiological Sources in the RFP CML

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assumed to have an HEU concentration of 145.68 g U/L in each experiment. Total activities of 

the dosimetrically important fission and activation products4in the fuel at the end of CML 

operations, plus 10 days’ decay time (the shortest decay time allowed by ORAUT-OTIB-0054

[SRDB 140847] in assessing worker exposures) are provided in Table 5.

Table 5: Activity of Dosimetrically Important Fission and Activation 

Products 10 Days After the End of CML Operations

Radioisotope (Ci) (Bq)

Mn-54 7.825E-09 2.895E+02

Fe-55 6.860E-08 2.538E+03

Co-58 2.131E-08 7.885E+02

Co-60 9.777E-11 3.617E+00

Sr-89 4.585E-06 1.696E+05

Sr-90 8.719E-07 3.226E+04

Y-90 8.703E-07 3.220E+04

Y-91 5.120E-06 1.894E+05

Zr-95 6.017E-06 2.226E+05

Nb-95 3.110E-06 1.151E+05

Mo-99 7.765E-06 2.873E+05

Ru-103 3.277E-06 1.212E+05

Ru-106 1.835E-07 6.790E+03

Cd-113m 5.792E-11 2.143E+00

Cd-115m 4.752E-10 1.758E+01

Sb-125 1.236E-08 4.573E+02

Te-129m 1.212E-07 4.484E+03

Te-132 7.020E-06 2.597E+05

I-131 7.149E-06 2.645E+05

I-132 7.231E-06 2.675E+05

Cs-134 2.810E-12 1.040E-01

Cs-136 1.152E-08 4.262E+02

Cs-137 8.927E-07 3.303E+04

Ba-140 1.325E-05 4.903E+05

La-140 1.490E-05 5.513E+05

Ce-141 7.126E-06 2.637E+05

Ce-144 2.816E-06 1.042E+05

Pr-143 1.349E-05 4.991E+05

Pr-144 2.817E-06 1.042E+05

Nd-147 5.067E-06 1.875E+05

Pm-147 7.897E-07 2.922E+04

Pm-148m 8.407E-15 3.111E-04

Sm-151 2.361E-08 8.736E+02

Eu-154 6.034E-14 2.233E-03

 

4 Radionuclides contributing ≥ 1% of the committed organ dose are considered to be dosimetrically important, as 

specified in ORAUT-OTIB-0054 (SRDB 140847).
White Paper: Assessment of Radiological Sources in the RFP CML 

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information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

Table 5: Activity 

Products 

of Dosimetrically Important Fission and Activation 

10 Days After the End of CML Operations

Radioisotope (Ci) (Bq)

Eu-155 1.175E-08 4.348E+02

Ta-182 0.000E+00 0.000E+00

These inventories would have been fairly uniformly distributed within the total volume of 

uranium solution at the CML because the solution used in experiments was eventually 

transferred back to the tank farm for storage. These back-and-forth transfers would tend to result 

in fairly uniform mixing; in addition, transfers between storage tanks were sometimes performed 

intentionally for homogenizing the solutions (SRDB 21358, PDF p. 449). 

Organ doses for CML staff from intakes of these radionuclides are discussed in the later section, 

Assessment of Unmonitored Radiation Dose at the CML.

DECOMMISSIONING AND DEMOLITION 

The potential for fission and activation product contamination in the nuclear materials used as 

fuel, in building fixtures, and in facility construction materials was recognized and considered in 

planning the Building 886 Cluster decommissioning and demolition. However, based on survey 

results, personnel interviews, and the historical record, the isotopes of concern were instead 

determined to be components of the fuels themselves used in the experiments (U-235, U-234, 

U-238, Pu-239 and Am-241). High Contamination Areas were posted in Buildings 886, 875 

(filter plenum), and 880 (storage shed)5and controlled to the transuranic limits of 10 CFR 835 

(SRDB 104734, PDF pp. 22-23).

DCAS has captured copies of original neutron, gamma, removable alpha, and removable 

beta/gamma survey results forming the basis of this radiological characterization (SRDB 104734, 

PDF pp. 32-265). A summary of the dose rate survey results is shown in Table 6. Penetrating 

dose rates from gamma-emitting radionuclides ranged from 0.03 mrem/h to 3.4 mrem/h in 

Building 886, Rm 103 on 07/18/1994 (SRDB 104734, PDF pp. 83-85). Dose rates associated 

with the tank farm, which housed both the enriched uranium solution inventory and a set of 

metal plutonium hemishells in Room 103, ranged from 0.25 mrem/h – 3.4 mrem/h, whereas dose 

rates around the glove box, cabinets, and hood varied from 0.03 mrem/h – 0.5 mrem/h. Surveys 

 

5

 Parts and equipment used in experiments were stored in Building 880. Contaminated items were sealed in plastic 

bags, but these tended to degrade with time (SRDB 21358, PDF p. 263). 
White Paper: Assessment of Radiological Sources in the RFP CML 

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information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

of Building 886, Rooms 101, 102, and 103 in November and December 1997 document greatlyreduced gamma exposure rates of <0.5 mrem/h (SRDB 104734, PDF pp. 33-35 and 48-51).

These surveys bracket the beginning and end of the project to remove enriched-uranium solution 

(the most difficult and time-consuming part of decommissioning prior to demolition), that 

spanned the 2-year period from June 1995 to June 1997 (SRDB 136853, PDF p. 4). Removal of 

the uranyl nitrate solution concluded by the end of 1996 (SRDB 21358, PDF p. 407; 22018, PDF 

p. 5. The results suggest that the source for personnel dose from penetrating radiations was 

predominantly the radioactive fuel used in experiments. Any dose contributions from activation 

products in the building materials and fixtures after removal of the fuel in late 1996 were too 

small to be detected by instruments used for the 1997 radiological surveys. 

Table 6: Dose Rate Survey Results for Building 886, Rocky Flats Plant Critical Mass Lab

Dose Rate Range of Values (mrem/h)

Survey Date Area n* Gamma Neutron (Gamma + 

Neutron) Beta/Gamma

07/18/1994** B886, Rm 103 – Glovebox, 15 0.03-0.5 0.0-0.1 0.03-0.5 0.05-0.3

Cabinets, Hood

07/18/1994** B886, Rm 103 – Tank Farm 18 0.25-3.4 0.0-0.2 0.25-3.5 0.18-2.40

11/04/1997*** B886, Rms 101, 102 & 103 15 <0.5 <1.0 <1.5 ---

12/02/1997*** B886, Rms 101, 102 & 103 15 <0.5 <1.0 <1.5 ---

Source: SRDB 104734, Appendix A, PDF pp. 33-35, 48-51 and 83-85

* n = number of measurements 

**Survey instruments used on 07/18/1994 were the Victoreen 450B for γ and β-γ measurements and the Ludlum 12 

4 for neutrons, with reported backgrounds of 0.01 mrem/h and 0.0 mrem/h, respectively (SRDB 104734, PDF p. 83). 

***Survey instruments used on 11/04/1997 and 12/02/1997 were the Eberline RO-20 for γ and β-γ, and the Ludlum 

12-4 for neutrons, with reported backgrounds of <0.05 mrem/h and <1.0 mrem/h, respectively (SRDB 104734, PDF 

pp. 33, 48). 

Contamination levels determined for specific areas in the Building 886 Cluster are described in a 

pre-demolition characterization study (SRDB 22002, PDF pp. 22-25). 10 CFR 835 unrestricted 

release criteria for surface radiological contamination on equipment and building materials were 

specified for post-deactivation decontamination and decommissioning activities (SRDB 22002, 

PDF p. 38). Neutron activation of U-238, with subsequent beta decay of the short-lived Np-239

product to Pu-239, was considered as a source of plutonium contamination in the Building 886 

Cluster; however, it was not believed to be a source of significant plutonium production because 

of the low power and short criticality times historically attained during experiments at CML. An 

RFP technical basis document (TBD) on building release criteria contains an analysis of the 
White Paper: Assessment of Radiological Sources in the RFP CML

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neutron activation scenario and notes that, due to the low power levels and short criticality times 

involved:

Analysis for low levels of plutonium within the solutions (or hold-up) has never been deemed 

necessary. (SRDB 103869, PDF pp. 3-4)

The TBD containing this analysis also states:

In spite of the fact that low-level criticality experiments were performed in Room 101 of 

Building 886, residual radioactivity resulting from the production of fission products is not 

expected to exist within the facility, refer to Process Knowledge Characterization Building 

886 Highly Enriched Uranyl Nitrate Solutions, TD 95-012, June 28, 1995.6 (SRDB 103869, 

PDF p. 5)

A Los Alamos Technical Associates Project Manager responsible for removing the weaponsgrade enriched uranium from the CML from 1995 to 1997 indicated in a NIOSH interview that 

baseline contamination surveys were performed in support of the facility deactivation project; he

does not recall any measurements that were out of the ordinary (SRDB 136853, PDF pp. 4-5).

The Final Project Closeout Report for the Building 886 Cluster demolition and closure 

summarizes actions taken and the final condition of the site. Uranium was the predominant 

contaminant addressed in the Building 886 Cluster closure project because of multiple enriched 

uranium solution spills over the facility’s history. Uranium release limits based on DOE Order 

5400.5 were adopted7for property and waste release, and for final building disposition (SRDB 

103869, PDF pp. 4-5). The Final Project Closeout Report includes a breakdown of waste types 

generated by the closure project, which is reproduced in Table 7 (SRDB 22018, PDF p. 14). 

Over 90% of the waste (by volume) from the closure project was disposed of as follows: in a 

sanitary landfill (52%), or recycled and used as onsite backfill (39%). Less than 3.5% of the 

waste and debris from closure of the Building 886 Cluster included a radiological component

broken down as follows: low-level radiological waste (3.3%), low-level mixed waste (0.02%) 

and transuranic waste (0.04%).

 

6 TD 95-012 was prepared by Environmental Technologies Technology Development, E&WM EG&G Rocky Flats, 

Inc. (Kathy Swan-Bogard and Angelo E. Hodges, III). NIOSH has been unable to capture this document.

7 Release limits are the same in DOE Order 5400.5 and 10 CFR 835 (specified in the earlier Interim 

Measure/Interim Remedial Action Plan for the 886 Cluster (SRDB 22002, PDF p. 38), except that the guideline 

values of DOE Order 5400.5 specify limits on alpha activity “for uranium, associated decay products and alphaemitters, and beta/gamma activity for these emitters.”
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information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

Table 7: Disposition of B886 Demolition Wastes

Waste Type Volume Description

Sanitary 3,835 yd

3

(2,420 tons)* Above-grade building debris

Hazardous Minor amounts

Electronic circuit boards, thermostats, exit signs, 

batteries, fluorescent light bulbs, and any other RCRA 

hazardous components were removed and taken for 

combination with like waste streams for disposal.

TSCA Waste 0.132 m3 PCB ballasts were removed and packaged for disposal.

Asbestos 265 m3 Friable asbestos, including the hydrolasing waste from 

removal of the skimcoat.

Low-Level Radiological 187 m3 Miscellaneous decommissioning and demolition debris

Low-Level Mixed 0.865 m3 Miscellaneous decommissioning and demolition waste

Low-Level TSCA 71 m3 Low-Level PCB Bulk Product waste

TRU 2.32 m3 Glove box and associated waste

Recycled Material 2,171 m3 Concrete for onsite backfilling

Source: SRDB 22018, PDF p. 14

* 3,835 yd

3 = 2,932 m3

The Final Project Closeout Report also provides results of air monitoring for alpha-emitting 

radionuclides during the Building 886 Cluster demolition activities, as performed by a 

10-sampler network within and around the RFP perimeter, and outside the perimeter toward the 

Denver metropolitan area (SRDB 22018, PDF pp. 13, 40-41). Filters were analyzed weekly. 

Figure 2 shows these results graphically. Results are compared with the mean plus two standard 

deviations value from demolition of an uncontaminated structure (B111). The Building 886 

Cluster results were consistently below the 0.002 pCi/m3 Action Level 1 (corresponding to a

1 mrem annual dose to a public receptor). 
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Sam ple Period Start Date (sam ples run for 1 week)

3/13 3/20 3/27 4/3 4/10 4/17 4/24 5/1 5/8 5/15 5/22 

Alpha Concentration (pCi/m

3

)

-0.0010

-0.0005

0.0000

0.0005

0.0010

0.0015

0.0020

B111 Baseline

C oncentration

(M ean + 2 SD )

Action Level 1 =

0.002 pC i/m 3

D elam ination

4/12

B886 D em olition &

Slab R em oval

Active D em olition

4/12-4/20

Source: SRDB 22018, PDF pp. 13,40 

Figure 2: Results of Continuous Alpha Air Monitoring During Demolition of the CML Building 886 Cluster 

ASSESSMENT OF UNMONITORED RADIATION DOSE AT THE CML 

From 1964 until the early 1990s, all Rocky Flats workers (including those at CML) were 

assigned dosimeters that monitored external radiation dose; this time span includes the entire 

period of CML operations (SRDB 20175, PDF pp. 19-20). The available RFP internal 

monitoring information indicates that RFP workers with the potential to receive intakes primarily 

of plutonium, americium, enriched uranium, or depleted uranium were monitored accordingly 

(SRDB 132776, PDF p. 30). A principal CML scientist indicated in a NIOSH interview that he 

participated in urinalysis and body count bioassays on an approximately annual basis, and that he 

believed everyone working with uranium or plutonium was similarly monitored (SRDB 138605, 

PDF pp. 5, 10). These personnel dosimetry and bioassay records are available to NIOSH. Doses 

from external penetrating radiation sources (nuclear fuel, sealed radioactive sources, fission and 

activation products) and intakes of uranium or plutonium are accounted for by the RFP radiation 

dosimetry monitoring programs. Sufficient detail exists about both routine operations and 
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positions taken on technical issues prepared by NIOSH or its contractor. . NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

incidents, as well as about the ambient radiation dose environment prior to decommissioning, 

that external doses to, and intakes of radioactive materials by, individual claimants could be 

reconstructed with sufficient accuracy if dosimetry records are unavailable.

Possible exceptions to the ability to reconstruct dose with sufficient accuracy lie in the reported 

absence of confirmatory bioassays after any of the contamination incidents or spills, and in the 

likelihood that routine bioassays (designed to detect primarily plutonium and uranium) could fail 

to recognize the presence of fission or activation products. In-vivo gamma spectrometry would 

likely detect gamma-emitting nuclides, but would be insensitive to pure beta emitters, like Sr-90. 

Urinalysis by alpha-counting or spectrometry is unlikely to detect any of the fission products, 

which tend to be beta-gamma emitters and require different chemical separation techniques. 

However, sufficient detail about contamination incidents exists to provide a basis for deriving 

bounding estimates of resulting acute intakes. The possibility that fission and activation products 

might have been missed in routine radio-bioassays is addressed below by evaluating the 

bounding chronic intake of these radionuclides and their contribution to internal dose.

Radiation dose from intake of fission and activation products could have occurred during the 22 

years of CML operation or from the generation of dust during facility demolition. The vast 

majority of CML building debris was buried in sanitary landfills or used as backfill for onsite 

projects. These means of disposal, coupled with the low alpha concentrations in air around the 

facility, indicate that personnel dose from uranium, transuranic, or fission and activation product 

contamination in the CML during demolition was unlikely. Dose to personnel during operations 

might have resulted from intakes occurring during clean-up of fuel spills (mostly from spills of 

uranyl nitrate solution) or from re-suspension of contamination deposited on surfaces as a result 

of these spills.

Information about reported HEU solution spills is provided in Table 8. Most of the large 

solution spills occurred in the first four years of facility operation and involved up to 16.1 kg of 

uranium. One spill in 1980 involved 2.66 kg of solution. Other spills were small enough that the 

volume of solution or mass of uranium involved were not mentioned. Considerable effort was 

spent to recover as much uranium as possible from the larger spills because of monetary, 

radiological health, and accidental criticality considerations. All the spills were confined within 

either the Assembly/Experiment Room (Room 101) or the Mixing Room (Room 103), except for

the November 30, 1967 event, which involved an exhaust duct and filter plenum. These rooms 

were located in the “Hot Area,” to which access was controlled (in contrast to the “Cold Area”

where offices were located) (SRDB 21358, PDF p. 110).
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Table 8: High-enriched Uranium Solution Spills Over the History of the CML

Date Volume 

(L)

Uranium

Mass (kg) Contaminated Area PDF Page(s)

7/2/1965 0.5 0.225 22 m2(Floor) 447

7/14/1965 --- --- 10 m2(Floor) 448-449

7/22/1965 --- --- Small amount (Floor) 449

11/30/1967 --- 9 (Inside large duct, filter housing, vent line)* 452-462

2/16/1968 --- 1.14** (Floor and cable trenches) 464-467

5/11/1968 0.06 --- (Workman’s knee) 467

5/9/1969 150. 1 16.1 20 m2(Mixing Room floor)*** 467-473

11/25/1980 7 2.66 (Assembly Room hood) 486-487

7/7-20/1984 --- --- (Walk-in hood)  498

2/14/1987 --- --- (Personnel, facility and fixtures)** *** 500-501

3/13/1987 --- --- (Personnel, facility and fixtures)***** 501

Source: SRDB 21358

*Although contamination was confined to ducts and a filter housing, clean-up of this incident resulted in a blowback 

of dried salts, resulting in facial contamination of a staff member. 

**Two conflicting accounts refer to this value as either the solution mass or uranium mass. 

***Standing HEU solution covering the floor was cleaned up by a staff member using a critically safe vacuum and 

wearing plastic booties and a half-face respirator. 

 Potentially-contaminated workmen repairing a leaking flange were required to evacuate when a criticality 

alarm was triggered by an electrician.

** ***Two essentially identical events resulted in personnel, fixture, and facility contamination by re-suspended 

high-enriched uranyl nitrate salts accidentally knocked from the surface of a large reactivity shim.

As shown in Table 8, the recorded amount of high-enriched uranyl nitrate solution spilled is just 

under 30 kg. Almost all of this spilled fuel was recovered and the surfaces decontaminated. 

Radiological characterization of the CML prior to demolition (SRDB 22002, PDF p. 25) noted 

that Rooms 101 (Experiment/Assembly Room), 102 (dry HEU storage), 103 (HEU solution tank 

farm and Pu hemishell storage), and 108 (hallway) were all Contamination Areas (<2,000 

dpm/100 cm2alpha).

The only High Contamination Areas found prior to demolition were in the Assembly hood 

(Room 101) and the downdraft table with attached glove box (Room 103). The exhaust air duct 

from Building 886 to the exhaust plenum in Building 875 was listed as an area of radiological 

concern. The Assembly hood, downdraft table with attached glove box, and exhaust air duct and 
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plenum are locations designed to prevent exposure and move air out of the building; therefore, 

they would not contribute to re-suspended radiological activity in the CML. 

The Contamination Area limit of 2,000 dpm/100 cm2alpha corresponds8to 9×10-4 μCi/100 cm2

or 9 μCi/m2 HEU. The total floor area of these rooms9

is approximately 220 m2, giving the total 

amount of contamination to be 1,980 μCi HEU. 

Bounding estimates for intake of the fission and activation products from re-suspended 

contamination during routine operations at CML are derived using Equation 1 below: 

(Equation 1) 

Where: 

 I = Intake for each of the dosimetrically-important radionuclides 

 C = Radionuclide concentration 

 S = Spill fraction evaluated for this assessment to be 0.002917 (1,980 μCi divided by 70 

μCi/g for HEU, divided by total HEU mass in the ORIGEN-S model) (SRDB 144472) 

 fR = Re-suspension factor of 1.5×10-4 m-1, corresponding to the 95th percentile value in the 

distribution of re-suspension factors reported in Figure 3-2 of ORAUT-OTIB-0070

(SRDB 108851, PDF p. 9). 

 R = Breathing rate of 1.2 m3

h

-1 from ORAUT-OTIB-0054 (SRDB 140847) 

 t = Intake period of 2 y = 4,000 h from ORAUT-OTIB-0054 (SRDB 140847) 

 A = Combined surface area of 220 m2of Building 886 Rooms 101, 102, 103, and 108 

 

8

 The specific activity of HEU, given by the empirical formula S = 0.4 + 0.38 E + 0.0034 E

2

, is approximately 

70 μCi/g for E = 93% enrichment in 235U (SRDB 1781, PDF p. 25). 

9

 Estimated floor areas for the individual rooms (SRDB 21358) are 120 m2 for Room 101 (PDF p. 120); 40 m2 for 

Room 103 (PDF p. 167); and 60 m2 for Rooms 102 and 108 combined, assuming this area to be about half that of 

Room 101 (PDF p. 110). 
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The total activity of each radionuclide in the 1,980 μCi of HEU contamination is given as the 

product of the total radionuclide inventory and spill fraction minus the ratio of HEU in 

contamination to HEU in the total fuel inventory used in the ORIGEN-S calculations. The intake 

I for each of the dosimetrically important radionuclides in Table 5 was estimated and the 

resulting values are shown in Table 6.

Table 6: Intakes of Dosimetrically Important Fission and Activation 

Products from Re-suspension of Contaminants in CML

Radioisotope Total Inventory (Bq) Intake (Bq)

Mn-54 2.895E+02 2.764E-03

Fe-55 2.538E+03 2.423E-02

Co-58 7.885E+02 7.528E-03

Co-60 3.617E+00 3.454E-05

Sr-89 1.696E+05 1.620E+00

Sr-90 3.226E+04 3.080E-01

Y-90 3.220E+04 3.074E-01

Y-91 1.894E+05 1.809E+00

Zr-95 2.226E+05 2.125E+00

Nb-95 1.151E+05 1.099E+00

Mo-99 2.873E+05 2.743E+00

Ru-103 1.212E+05 1.158E+00

Ru-106 6.790E+03 6.482E-02

Cd-113m 2.143E+00 2.046E-05

Cd-115m 1.758E+01 1.679E-04

Sb-125 4.573E+02 4.366E-03

Te-129m 4.484E+03 4.281E-02

Te-132 2.597E+05 2.480E+00

I-131 2.645E+05 2.525E+00

I-132 2.675E+05 2.554E+00

Cs-134 1.040E-01 9.926E-07

Cs-136 4.262E+02 4.069E-03

Cs-137 3.303E+04 3.153E-01

Ba-140 4.903E+05 4.681E+00

La-140 5.513E+05 5.263E+00

Ce-141 2.637E+05 2.517E+00

Ce-144 1.042E+05 9.947E-01

Pr-143 4.991E+05 4.765E+00

Pr-144 1.042E+05 9.951E-01

Nd-147 1.875E+05 1.790E+00
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Table 6: Intakes of Dosimetrically Important Fission and Activation 

Products from Re-suspension of Contaminants in CML

Radioisotope Total Inventory (Bq) Intake (Bq)

Pm-147 2.922E+04 2.790E-01

Pm-148m 3.111E-04 2.970E-09

Sm-151 8.736E+02 8.340E-03

Eu-154 2.233E-03 2.131E-08

Eu-155 4.348E+02 4.151E-03

Ta-182 0.000E+00 0.000E+00

Maximum organ doses from these intakes are shown in Table 7. The largest total organ dose, if 

radioiodines are included10, is 1.1×10-6 Sv to the thyroid, primarily from soluble I-131. The 

largest total organ dose if radioiodines are excluded is 6.1×10-7 Sv to lungs. Dose conversion 

factors and individual organ doses are provided in an Excel spreadsheet (SRDB 144472). All 

individual organ doses are less than 1×10-6 Sv. Therefore, NIOSH concludes that doses to CML 

staff from re-suspension of contamination containing fission and activation products are 

negligible. 

Table 7: Maximum Committed Organ Doses from Inhalation

of Fission and Activation Products in Re-suspended Contamination

Category Organ Committed Dose (Sv)

Excluding Radioiodines

Organ Committed Dose (Sv)

Soluble Thyroid 1.1×10-6 Bone Surface 3.7×10-7

Moderately Soluble Thyroid 1.0×10-6 Lungs 4.0×10-7

Insoluble Thyroid 1.0×10-6 Lungs 6.1×10-7

 

10 Iodines are volatile and vaporize from the matrix quickly; therefore, including them in the analysis is very 

claimant-favorable. 
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SUMMARY AND CONCLUSIONS 

NIOSH concludes that external radiation exposure to CML workers and staff is accounted for by 

Rocky Flats’ personnel dosimetry program, which assigned radiation dosimeters to all workers. 

The personnel dosimetry program also included periodic bioassay (urinalysis and body counts) 

that focused primarily on identifying uranium and plutonium intakes. The in-vivo bioassay, 

using gamma spectrometry, would be expected to easily detect most fission and activation 

products present in any significant amount, except for radioisotopes like Sr-90, which emit beta 

radiation not detectable in a routine body count or in a urinalysis evaluated for alpha-emitters. 

No monitoring results or theoretical assessments suggest that fission products from the criticality 

experiments in the Critical Mass Laboratory, or activation products from neutrons produced in 

the controlled low-level criticalities, resulted in the production of other than low levels of 

radioactive materials in the fuels. The fuel itself was removed by the end of 1996 (SRDB 21358, 

PDF p. 407; 22018, PDF p. 5) for reprocessing (SRDB 136853, PDF p. 4) prior to facility 

demolition. The possibility of activation products in Building 886 construction materials and 

fixtures was considered in pre-demolition characterization studies, but monitoring results failed 

to detect beta or gamma emissions characteristic of these radionuclides (SRDB 104734, 

Appendix A, PDF pp. 33-35, 48-51, and 83-85). Release criteria based on requirements of DOE 

Order 5480.5 were adopted for property, waste release, and final building disposition (SRDB 

103869, PDF pp. 4-5). Over 90% of waste (by volume) from the closure project was disposed of 

in a sanitary landfill or recycled. Less than 3.5% of the waste and debris from closure of the 

Building 886 Cluster included a radiological component sufficient to require disposal in a 

low-level radiological, low-level mixed waste, or TRU waste site (SRDB 22018, PDF p. 14). 

Estimates of the total activity in fission and activation products from irradiation of high-enriched 

uranyl nitrate solution fuel (the fuel contributing most to contamination within the facility) 

indicate that only inconsequential amounts of these products were available to contribute to 

radiation doses from re-suspension of residual contamination. Organ doses to individual 

radionuclides from inhalation of re-suspended contamination at CML are less than 10-6 Sv, with 

the largest total organ dose being 1.1×10-6 Sv to the thyroid, if radioiodines are included (a very 

claimant-favorable assumption). 
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with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. . NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

It is possible that some personnel could have inhaled or ingested dosimetrically-significant 

amounts of fuel (particularly high-enriched uranyl nitrate) during clean-up of several accidental 

spills. NIOSH has found no record of follow-up bioassay related to these accidents; and one 

interviewee closely associated with the facility and involved in the clean-up activities stated that 

no follow-up bioassay was performed. However, the number of individuals who might have 

been so exposed is limited to a single senior staff member and a few workers and radiation 

monitors. Considerable information about the spills and clean-up activities is provided in the 

published facility history; therefore, individual assessment of their exposure potential is possible. 

The resulting dose, in any case, would be dominated by uranium (or, in one case, plutonium) 

because of the very low ratio of fission and activation products to fuel. All the CML staff 

members are believed to have been included in routine bioassay programs for uranium and 

plutonium.

NIOSH concludes, based on the weight of evidence from the detailed history of the CML, 

computer modeling of criticality experiments, and radiological measurements after operations 

ceased, that no significant personnel dose to Rocky Flats workers or contractors resulted from 

the generation of fission or activation products in the building materials and fixtures of the 

Building 886 Cluster as a result of the criticality experiments conducted there over its lifetime.
White Paper: Assessment of Radiological Sources in the RFP CML 

Page 23 of 24

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. . NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

REFERENCES 

SRDB 20170: Technical Basis Document for the Rocky Flats Plant – Site Description (ORAUTTKBS-0011-2)

SRDB 20175: Technical Basis Document for the Rocky Flats Plant – Occupational External 

Dosimetry (ORAUT-TKBS-0011-6) 

SRDB 21358: A Technically Useful History of the Critical Mass Laboratory at Rocky Flats 

SRDB 22002: Interim Measure/Interim Remedial Action Plan for the 886 Cluster

SRDB 22018: Final Project Closeout Report for the 886 Cluster Closure Project 

SRDB 22731: Annals of the ICRP – Dose Coefficients for Intakes of Radionuclides by Workers

SRDB 103869: Methodology for Establishing Property, Waste, and Building Release Criteria 

for the 886 Cluster

SRDB 104452: Historic American Engineering Record – Rocky Flats Site Building 886

SRDB 104734: Reconnaissance Level Characterization Report for the 886 Cluster 

Decommissioning Project with Appendices

SRDB 132776: SEC Petition Evaluation Report, Petition SEC-00030

SRDB 136853: Rocky Flats Interview – Radiological Exposure Sources at the Critical Mass 

Laboratory 

SRDB 138605: Rocky Flats Interview – Anomalous Events at the Critical Mass Laboratory 

SRDB 140847: Fission and Activation Product Assignment for Internal Dose-Related Gross 

Beta and Gross Gamma Analyses (ORAUT-OTIB-0054)

SRDB 142464: Minimally Reflected Cylinders of Highly Enriched Solutions of Uranyl Nitrate

SRDB 142480: Preservation and Dissemination of the Hardcopy Documentation Portion of the 

NCSP Nuclear Criticality Bibliographic Database 
White Paper: Assessment of Radiological Sources in the RFP CML

Page 24 of 24

This working document prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in discussions 

with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or 

ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents preliminary 

positions taken on technical issues prepared by NIOSH or its contractor. . NOTICE: This report has been reviewed to identify and redact any 

information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

SRDB 108851: Dose Reconstruction During Residual Radioactivity Periods at Atomic Weapons 

Employer Facilities (ORAUT-OTIB-0070)

SRDB 144472: Rocky Flats CML – DCFs and Organ Doses from Resuspension of CML F&AP