Information Notice 1986-23, Excessive Skin Exposures Due to Contamination with Hot Particles
UnS 0 1AL
SSINS No.: 6835 IN 86-23
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C.
20555
April 9, 1986
IE INFORMATION NOTICE 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 facili- ties and consider action, if appropriate, to preclude a similar problem occur- ring 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 radioac- tive 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 contamina- tion 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.
8604040321
IN 86-23 April 9, 1986 2.
It is believed that the insides of protective clothing are being contami- nated 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 trans- ferring hot particles.
3.
In all the reported events, a need for more vigilance in personnel contam- ination 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 NCRP 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 1.0 cm2 and that the radiosensitive basal layer of cells is at a depth of 7mg/cm2 below
the surface.
For purposes of showing compliance with 10 CFR 20.101(a), calculat- ing a skin dose averaged over 1.0 cm2 at a depth of 7 mg/cm2 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.
dward
.ordan, Director
Divisi n/of Emergency Preparedness
and i gineering 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
April 9, 1986 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:
0.5 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 1.2 microcuries (uCi) of Co-60.
Calculation of the absorbed
dose to 1 cm2 of skin resulted in a skin dose of 10.6 rad.
This exceeded the
maximum allowable dose of 7.5 rem in a quarter [10 CFR 20.101(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 protec- tive 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 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 person- nel 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 reconstitu- tion 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 1.3 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
20.101(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 cloth- ing) 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 impor- tance of good frisking practices, use of protective clothing, contamina- tion control, and other H.P. practices.
Attachment 1
IN 86-23 April 9, 1986 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 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> was estimated
resulting in a skin dose of less than 1 rem.
On January 4, 1986, a hot particle (44 nCi CO-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 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br />, 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 radiologi- cal controls.
Attachment 2
April 9, 1986
LIST OF RECENTLY ISSUED
IE INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issue
Issued to
86-22
86-21
86-20
Underresponse Of Radition
Survey Instrument lo High
Radiation Fields
Recognition Of American
Society Of Mechanical
Engineers Accreditation
Program For N Stamp Holders
Low-Level Radioactive Waste
Scaling Factors, 10 CFR
Part 61
Reactor Coolant Pump Shaft
Failure At Crystal River
NRC On-Scene Response During
A Major Emergency
Update Of Failure Of Auto- matic Sprinkler System Valves
To Operate
3/31/86
3/31/86
3/28/86
3/21/86
3/26/86
3/24/86
86-19
86-18
All power reactor
facilities holding
research and test
reactors
All power reactor
facilities holding
recipients of NUREG-
0040 (white book)
All power reactor
facilities holding
All power reactor
facilities holding
All power reactor
facilities holding
All power reactor
facilities holding
All power reactor
facilities holding
All power reactor
facilities holding
All power reactor
facilities holding
86-17
86-16 Failures To Identify Contain- 3/11/86 ment Leakage Due To Inadequate
Local Testing Of BWR Vacuum
Relief System Valves
Loss Of Offsite Power Caused
3/10/86
By Problems In Fiber Optics
Systems
86-15
86-14 PWR Auxiliary Feedwater Pump 3/10/86
Turbine Control Problems
OL = Operating License
CP = Construction Permit