Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
June 20, 1997
NRC INFORMATION NOTICE 97-36: UNPLANNED INTAKES BY WORKER OF TRANSURANIC
AIRBORNE RADIOACTIVE MATERIALS AND EXTERNAL
EXPOSURE DUE TO INADEQUATE CONTROL OF WORK
Addressees
All holders of operating licenses and construction permits. All licensees of
nuclear power reactors in the decommissioning stage and fuel cycle licensees.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert licensees to inadequate radiological work controls in highly
contaminated areas. These inadequate controls created a substantial potential
for personnel radiation exposures in excess of NRC limits and resulted in
unplanned intakes by workers of airborne radioactive materials, including
transuranics (alpha emitters). It is expected that recipients will review the
information in this notice for applicability to their facilities and consider
actions, as appropriate, to avoid similar problems. However, suggestions
contained in this information notice are not NRC requirements; therefore, no
specific action or written response is required.
Description of Circumstances
On November 2, 1996, the Haddam Neck plant was in a refueling and maintenance
outage. Before flooding the reactor cavity, the fuel transfer canal (FTC), the
fuel transfer cart and tracks, and the upender needed to be inspected and
debris removed to ensure cleanliness.
In preparation for the inspection and entry to the FTC, two workers (a
maintenance supervisor and a reactor vendor representative) met with health
physics (HP) supervisors and HP technicians (HPTs) to discuss the entry. As
this work was not on the master outage schedule, this was the first notice to
HPTs of the work. The governing work procedure provided no work scope detail.
The meeting was not effective; there was no common understanding between the
workers and the HPTs as to what work was to be done and the radiological
conditions in the work area. The HPTs mistakenly believed that the workers
would principally walk along the FTC tracks but could periodically leave the
tracks to pick up debris (e.g., tie wraps) that had fallen down from the
charging floor. The HPTs did not know that the workers would collect, by
hand, paint chips, metal rust, and dried, dirtlike materials from the floors
and walls.
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Just before the entry, the HPTs briefed the workers on the radiological
conditions. Since the FTC was decontaminated in August 1996, the workers were
led to believe that the canal was generally "clean." The licensee had not
performed any prework contamination or radiation surveys to support the job.
Surveys later found that the FTC contained removable contamination of up to
800 microgrey/h [80 millirad/hr] (beta/gamma) and 500 Bq [30,000
disintegrations per minute] per 100 square centimeters (dpm/100 cm2) alpha
contamination. In addition, a local hot spot on the canal floor, readily
accessible to the workers, exhibited external radiation levels of 250 mSv/h
[about 25 R/h] on contact and 80 mSv/h [about 8 R/h] at waist level. The
prework briefing of the workers was inadequate, and the workers were not
informed of the actual radiological conditions. Additionally, the work was
allowed to commence under an invalid (because it did not allow FTC entry)
radiation work permit (RWP), rather than a specific RWP for the FTC. As a
result, no comprehensive, prework radiation or contamination surveys were
performed. The decision not to issue respiratory protection was based on
previous air sample results (after the August 1996 reactor cavity
decontamination to support worker tours of the area). However, this dated
sampling was not representative of the extensive debris cleanup activity on
November 2, 1996.
While in the FTC, the workers scraped up debris from the FTC and placed it in
a plastic bag. Unknown to the workers, this activity generated significant
airborne radioactive materials and created a high-intensity external radiation
source.
After completion of the work, one worker's dosimeter alarmed upon exiting the
reactor cavity. The plastic bag of debris was surveyed for the first time and
read 200 mSv/h [about 20 R/h] on contact (it was placed in shielded storage).
A later survey of the bag indicated 600 mSv/h [about 60 R/h] on contact and
about 40 mSv/h [about 4 R/h] about 30 centimeters away. The workers wore no
additional dosimetry other than their electronic alarming and standard chest
thermoluminescence dosimeters (TLDs). The workers found significant
contamination, while whole-body frisking. Nasal smears of the workers
indicated 3333 Bq [200,000 dpm] (beta/gamma) shortly after exiting the cavity.
Subsequent to the event, the licensee determined (by analysis and
reconstruction) the workers' deep-dose equivalent (DDE), the shallow-dose
equivalent (SDE, whole body), the maximum doses to the extremities, and the
lens dose equivalent (LDE) from the collection and handling of the debris.
None of the worker's external doses were in excess of the limits, with the
maximum assigned doses (mSv) of 4.73 [473 mrem], DDE; 4.73 [473 millirem],
SDE; 11.6 [1164 mrem], extremity; and 3.97 [397 mrem], LDE.
With the workers out of the cavity, an HPT checked the FTC air sample using a
hand-held frisker and found that the sample exhibited an elevated count rate,
indicating the presence of potential airborne radioactive material. This air
sample later indicated about 0.8 derived air concentration (DAC) beta and 24
DAC alpha. The general area air sample was not representative (not in the
breathing zone of the workers) of the concentrations encountered by the
workers during the debris cleanup.
A backup air sample of the reactor cavity was started, well away (non-
representative) from the FTC. The sample was also checked in the field with a
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Page 3 of 5
frisker, which erroneously indicated no airborne radioactive materials were
present. Other HPTs in the area were then notified (misinformed) that the air
within the reactor cavity was clean. The inspector later found that the
licensee had failed to establish and implement an effective program to
adequately check for proper operability of the frisker in containment.
On the basis of the erroneous negative air sample result, HPTs authorized two
other workers to enter the reactor cavity and clean the reactor vessel stud
holes. These workers unknowingly spent about 15 minutes in an area with
elevated airborne radioactive material levels and subsequently exited the
reactor cavity. Their subsequent whole-body counts showed no significant
intakes.
The licensee's subsequent counting of the backup air sample prompted
identification of the inoperable frisker and subsequent evacuation of the
reactor cavity and initiation of an investigation. The backup air sample was
found to indicate airborne radioactivity concentrations of 3.5 DAC beta and
108 DAC alpha. The air sample collected near where the two workers were
working on the reactor vessel studs was later found to indicate 1.5 DAC beta
and 53 DAC alpha. In spite of these air sample results (high alpha DACs),
their non-representative nature (not near the FTC), and the stay-times of the
workers and their work practices in the FTC (handling contaminated debris),
the licensee did not recognize the potential for excessive personnel exposure
until about a week after the event.
Discussion
In the Haddam Neck event, inadequate radiological evaluations and controls led
to unplanned internal exposures with a substantial potential for worker
overexposures. Of more concern was that until identified by an NRC inspector
five days after the event, the licensee failed to recognize the potential for
significant internal doses from transuranic radionuclides known to be present
in the FTC. The presence of these alpha-emitting nuclides was evident from
loose surface contamination sampling (smears) and air samples. This failure
led to untimely initiation of in-vitro bioassays (fecal sampling) for the
transuranic material intake to assess personnel exposures. While the
whole-body counting (WBC) indicated a relatively low intake/dose from cobalt-
60, the licensee failed to use the high alpha-to-beta gamma ratios (from the
air and smear samples) to identify the potential for significant internal
doses to workers from the transuranic component. When the NRC inspector noted
the WBC result for the gamma emitters (power plant WBC's do not detect alpha
radiation) and took into account the relative workplace abundance and typical
DAC alpha-to-beta gamma nuclide ratios, he informed the licensee of the
transuranic concern.
The licensee then initiated fecal sampling to account for doses from all
nuclides (including alpha emitters). The licensee contracted outside
consultants to perform a detailed analysis of the event and calculate the
workers' internal dose. On the basis of this effort, the licensee reported a
maximum 9.13 mSv [913 mrem] committed effective dose equivalent (CEDE) and
58.7 mSv [5873 mrem] total organ dose equivalent (TODE) to the bone surface.
None of the reported doses are in excess of regulatory limits. However, the
NRC staff is still reviewing the licensee's methods, assumptions and models
for the internal dose assessment.
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For reactor facilities that have experienced fuel defects, experience has
shown that long after the defective fuel has been removed, significant alpha
contamination may remain in generally inaccessible locations, such as the FTC
equipment drains and sumps, and other refueling areas. Even minor disturbance
of the contaminated surfaces can result in the release of alpha-emitting
radionuclides, whose DACs are orders of magnitude more restrictive and
limiting (at much lower concentrations) compared with the normal beta-emitting
and gamma-emitting isotopes usually encountered in reactor plant environments
(fission, corrosion, and wear products). Additionally, alpha contamination
may be incorporated into a contamination/corrosion layer on the interior
surfaces of system components that carry primary fluids or steam. Surveys for
loose surface contamination may not identify the fixed alpha contamination,
but abrasive work (e.g., grinding or welding) may result in alpha-emitting
airborne radioactive materials. This latter characteristic may be
particularly important at reactor facilities undergoing decommissioning.
As a result of this event, the licensee performed root cause analyses. On the
basis of these analyses and the findings of an independent review team, the
licensee has initiated certain corrective actions, which include the
following:
1. All work presenting a significant radiological challenge (within
designated high-risk areas) was suspended until a work approval program
was instituted. This program now requires review of all RWPs by the
plant Radiation Protection Manager (RPM) and the Work Services Director,
and RWP approval by the RPM or the Radiological Protection Supervisor.
2. The work control program now includes an RWP procedure requiring clear
descriptions of authorized work and controls, improved procedures for
high-risk evolutions, and representative prework surveys.
3. The license stopped the use of in-field counting and checks for air
samples as a basis for reducing or relaxing radiological work controls.
4. All work in high alpha-intake risk areas requires the use of respirators
until representative air sampling justifies work without respiratory
protection.
Events involving unplanned intakes of airborne radioactivity at nuclear power
plants occur generally during maintenance and refueling outages, are
infrequent, and typically result in intakes by workers of radioactive material
that are well within the limits of 10 CFR Part 20. However, as indicated in
the event describe in this notice, the potential for significant unplanned
personnel exposures does exist at nuclear power plants (see related
correspondence).
Related Communications and Correspondence
The following related communications and correspondence are noted:
. NRC Inspection Report No. 50-219/96-12, dated December 19, 1996.
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June 20, 1997
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. NRC Information Notice 90-47, "Unplanned Radiation Exposures to
Personnel Extremities Due to Improper Handling of Potential Highly
Radioactive Sources," dated July 27, 1990.
. NRC Information Notice 92-75, "Unplanned Intakes of Airborne
Radioactive Material by Individuals at Nuclear Power Plants," dated
November 12, 1992.
This information notice does not require any specific action or written
response. If you have any questions about the information in this notice,
please contact one of the technical contacts listed below.
signed by S.H. Weiss for
Marylee M. Slosson, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: Ronald L. Nimitz, RI
(610) 337-5267
E-mail: [email protected]
William J. Raymond, RI
(860) 267-2571
E-mail: [email protected]
James E. Wigginton, NRR
301-415-1059
E-mail: [email protected]
