Information Notice No. 86-23: Excessive Skin Exposures Due To Contamination With Hot Particles
SSINS No: 6835
IN 86-23
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
April 9, 1986
Information Notice No. NO 86-23: EXCESSIVE SKIN EXPOSURES DUE TO
CONTAMINATION WITH HOT PARTICLES
Addressees:
All nuclear power reactor facilities holding an operating license (OL) or
a construction permit (CP)
Purpose:
This information notice is provided to alert recipients of a potentially
significant problem pertaining to skin contamination incidents It is
expected that recipients will review this information for applicability
to their facilities and consider action, if appropriate, to preclude a
similar problem occurring at their facilities However, suggestions
contained in this notice do not constitute NRC requirements; therefore,
no specific action or written response is required
Description of Circumstances:
Three reactor licensees recently have reported excessive skin exposures to
individuals as a result of contamination from single hot particles of
radioactive material (See Attachment 1 for a more detailed description of
these events) Hot particles are small (in some cases microscopic)
particles of radioactive material with a high specific activity
All three licensees have concluded that the hot particles in those
contamination events most probably were transferred to the individual from
"clean" protective clothing (which are intended to prevent skin
contamination) Review of the events discussed in Attachment 1 indicates
the following additional common considerations:
1 Plants with hot particle problems experience multiple contamination
events Once hot particles are loose in the plant they are difficult to
detect and control Plants with a potential for generating hot particles
(those with stellite components or poor fuel performance) should consider
additional contamination control measures such as providing temporary
containment for "hot" jobs, where feasible The INPO Significant Event
Report (SER) 42-85, "Personnel Skin Contaminations Due to Activated
Stellite Particles," includes a discussion on minimizing the introduction
of stellite to a reactor system
IN 86-23
April 9, 1986
Page 2 of 2
2 It is believed that the insides of protective clothing are being
contaminated in the laundry system Reliance on the laundry process
monitors in the cleaning fluid path and/or bulk gamma surveys of "clean"
protective clothing is ineffective for detecting hot particles Licensees
may want to segregate highly contaminated clothing from potentially
contaminated clothing and launder each group separately to reduce the
chance of transferring hot particles
3 In all the reported events, a need for more vigilance in personnel
contamination control (self-frisking, protective clothing removal
procedures, etc) is evident
A hot particle on the skin produces a very steep dose gradient with the
dose dropping off rapidly as distance from the particle increases The
NCR dose limit recommendations in NBS Handbook 59 (which provide the
basis for the current NRC regulations) assumes that the critical area of
the skin is 10 cm**2 and that the radiosensitive basal layer of cells is
at a depth of 7mg/cm**2 below the surface For purposes of showing
compliance with 10 CFR 20101(a), calculating a skin dose averaged over
10 cm**2 at a depth of 7 mg/cm**2 is appropriate
No specific action or written response is required by this information
notice If you have any questions about this matter, please contact the
Regional Administrator of the appropriate regional office or this office
Edward L Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contacts: Roger L Pedersen, IE
(301) 492-9425
James E Wigginton, IE
(301) 492-4967
Attachments:
1 Description of Events
2 List of Recently Issued IE Information Notices
Attachment 1
IN 86-23
April 9, 1986
Page 1 of 3
DESCRIPTION Of EVENTS
McGuire:
On June 5, 1985, a contractor employee supporting the plugging operation
of a steam generator at Duke Power Company's McGuire Station discovered a
small area of skin contamination under the arm The contamination was
detected by a contamination portal monitor when the individual exited the
controlled area after removal of three sets of protective clothing
Further detailed surveys of the contaminated skin area showed the
following results: 05 mR/hr gamma, 58 mrad/hr beta, and greater than
50,000 cpm with a pancake G-M detector The contamination was
successfully removed using adhesive tape Further evaluation showed that
the contamination was a single particle 40 microns in diameter with an
activity of 12 microcuries (uCi) of Co-60 Calculation of the absorbed
dose to l cm**2 of skin resulted in a skin dose of 106 rad This
exceeded the maximum allowable dose of 75 rem in a quarter [10 CFR
20101(a)]
Prior to the June event, a number of similar contamination incidents with
hot particles of cobalt-60 had occurred but with lesser dose
consequences The licensee's investigation led to the preliminary
conclusion that the cobalt-60 particles were transferred to the
individual from the "clean" protective clothing The licensee has
identified other Co-60 particles in the plant laundry area The licensee
thus far believes the source of contamination to be stellite valve seats
with high cobalt content in the primary coolant system Small particles
of stellite may have been dislodged and transported to the core, where
they would have been activated to Co-60 Subsequently, these particles
became trapped in protective clothing during maintenance activities and
were not removed during normal laundering
The licensee subsequently initiated the following protective measures:
1 Disposal of all cotton protective clothing in use at the time of the
event;
2 Increased surveillance of protective clothing after laundering
(including comprehensive surveys of both the inside and outside of
laundered protective clothing using pancake probe G-M meters);
3 Increased vigilance in self-frisking procedures when exiting
contaminated area and when traversing between frisking locations within
contamination control zones; and
4 Further evaluations to determine where stellite valve seats are used
and where they could possibly be eliminated
San Onofre:
On October 30, 1985, a firewatch employee found contamination while
"frisking out" of the radwaste building (RWB) Investigation showed the
contaminant to be a small speck of material attached to the outside back
of the individual's
Attachment 1
IN 86-23
April 9, 1986
Page 2 of 3
modesty garment worn under protective clothing Frisker readings near the
particle were in excess of 50,000 cpm beta-gamma An alpha count with a
SAC-4 survey instrument yielded 2,000 cpm Gamma spectrometric analysis
showed about 4 uci of material made up of Nb-95, Zr-95, Ru-103, Ru-106,
Ba-140, La-140, Ce-141 and Ce-144 This composition suggests that the hot
particle is a tiny fragment of fuel rather than the normal mix of
activation and fission products which originate within the reactor
coolant system Careful frisking by personnel at the RWB exit point
turned up a few more hot particles on modesty garments and shoes
Extensive surveys pointed to the fuel reconstitution equipment and work
area in the Unit 3 FHB as the most significant sources of hot particles
Unit 3 has experienced significant fuel integrity problems Recently San
Onofre performed fuel reconstitution in the spent fuel pool by replacing
defective fuel pins in the affected fuel assemblies
On November 19, two additional instances of personnel contamination with
hot particles were detected On November 21, a similar personnel
contamination was detected Additionally, two more hot particles were
found in the FHB Work was halted and the FHB was isolated Access to the
FHB is presently limited to required operator surveillances with constant
HP coverage The licensee determined that these skin contaminations
resulted from hot particles transferred from "clean" protective clothing
Checks of protective clothing on the ready-to-issue shelves revealed two
cases where protective clothing (which met the "return to normal service"
criteria of less than 5,000 cpm/probe area) were found, upon very slow
and careful frisking (15 minutes), to have hot particles with activities
that exceeded this value Accordingly, a program is being implemented to
withdraw all protective clothing presently in use for thorough survey
under more restrictive criteria The clothing will be replaced with
protective clothing that has been out of service since Unit 3 fuel
reconstitution was initiated or with one-time-use disposal garments
A preliminary assessment of the dose received by the two individuals
involved in the November 19 events indicates 13 rem to the skin of the
whole body and 7 rem to the skin of an extremity These are below the
dose limits set in 10 CFR 20101(a) However, these dose calculations are
currently under review by the NRC
Other actions taken by the licensee include:
1 An extensive, special survey program (of workplace and protective
clothing) is being maintained to assure the prompt detection and removal
of additional hot particles
2 Full face respirators are required in FHB during work involving the
removal of reconstitution tools
3 A special instruction was given to station personnel stressing the
importance of good frisking practices, use of protective clothing,
contamination control, and other H P practices
Attachment 1
IN 86-23
April 9, 1986
Page 3 of 3
Dresden:
On December 11, 1985, a hot particle was found near the abdomen area on
the outside of an individual's undershirt The contamination was
initially found by a portal monitor On analysis, the hot particle was
determined to contain 110 nanocuries (nCi) of Co-60 The licensee
concluded that the particle was most likely transferred from protective
clothing to this undershirt Based on the individual's work activities an
exposure time of 7 hours was estimated resulting in a skin dose of less
than 1 rem
On January 4, 1986, a hot particle (44 nCi C0-60 and 1 nCi Cs-137) was
found on a contract worker's abdomen while passing through a whole body
frisker The licensee performed instrument response checks on the whole
body friskers, postal monitors, and laundry monitors using the collected
hot particle The licensee concluded that the particle was transferred
from protective clothing to the worker's skin During interviews the
worker admitted that he routinely omitted frisking after removing his
protective clothing at step-off pads With the particle replaced near its
original position the licensee had the worker pass through whole body
friskers several times; an alarm was received about 50 percent of the
time The licensee estimated the maximum probable time of exposure to be
16 hours, resulting in a calculated skin dose of less than 5 rems
Actions taken by the licensee to prevent reoccurrence include:
1 Initiating a more aggressive laundry monitoring program; and
2 Emphasizing to contractors the need for worker compliance with
radiological controls
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