Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 87-39
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
August 21, 1987
Information Notice No. 87-39: CONTROL OF HOT PARTICLE CONTAMINATION
AT NUCLEAR POWER PLANTS
Addressees:
All nuclear power reactor facilities and spent fuel storage facilities holding
an NRC license or a construction permit.
Background and Purpose:
Information Notice No. 86-23 (Reference 1) provided information on events in-
volving excessive skin exposures resulting from skin contamination by small,
highly radioactive particles with high specific activity (hot particles).
Since that information notice was issued, there have been more of these
events, and a recent report by the Institute of Nuclear Power Operations
(INPO) (Reference 2) provides additional information on this subject. This
information notice provides information on some of the subsequent events and
discusses degraded fuel and a lack of proper radiological control during fuel
reconstitution as major sources of hot particles. Generic licensee lessons
learned also are included.
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.
Discussion:
During the first 6 months of 1987, events involving hot particle exposures
were reported at nine different nuclear power stations. Two events in late
1986 (at V.C. Summer and San Onofre) involved exposures apparently exceeding
NRC regulatory limits. Attachment 1 provides summary descriptions of eight of
these events. More detailed descriptions can be obtained from the referenced
inspection reports for each event. (Copies of NRC Inspection Reports are
available from the NRC Public Document Room, 1717 H Street N.W., Washington,
D.C.)
Hot particles come primarily from two major sources: degraded fuel and
neutron-activated corrosion and wear products (e.g., Stellite). While much of
the information in this notice is pertinent to both neutron-activated
corrosion and wear product particles (hereafter referred to as activated
particles) and
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irradiated fuel particles (hereafter referred to as fuel particles), a major
concern of this notice is extended facility operation with degraded fuel and
the resulting problems with fuel particle contamination. On the basis of an
NRC review of licensees' corrective actions, discussions with licensees'
operating staffs, and information obtained by NRC inspectors, the lessons
learned and licensee good practices resulting from the events summarized in
Attachment 1 are as follows:
1. Extended power plant operation with degraded fuel (leaking fuel pins) can
result in widespread dispersal of fuel particles. Some plants continue
to experience fuel particle contamination problems long after leaking
fuel pins have been removed because of the residual contamination of
plant systems. Some plants with these problems have started programs to
account for missing fuel pellets and fragments and to identify measures
to recover this material.
2. Considerations concerning the handling of leaking fuel include the
following:
a. Special techniques and precautions for handling leaking fuel bundles
are necessary to prevent aggravating the spread of fuel particles.
For example, containment devices should be used when reconstituting
fuel. The lack of proper radiological controls and oversight of the
fuel reconstitution process in the San Onofre 3 fuel pool led to
loss of control and dispersal of numerous fuel particles into the
pool. Fuel particles then spread through the plant spent fuel
systems and to the liquid radwaste systems.
b. A damaged, leaking fuel pin that is not properly contained and
segregated from the common fuel pool area could be a significant,
long-term source of fuel particle contamination.
c. Plants should be aware that NSSS vendors' special refueling tools
and equipment could be a source of fuel particle contamination.
These tools and equipment should be carefully surveyed before they
are used and before they are shipped to other facilities.
3. Some plants that have operated for extended periods of time with degraded
fuel and plants with activated particle problems now have instituted
specialized, comprehensive training programs for plant system maintenance
workers and general employees. These programs are designed to better
inform and prepare the plant staff to cope with the continuing fuel
particle problems. Additionally, as part of comprehensive contamination
control programs, special new procedures to improve surveys for detection
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of hot particles have been prepared and health physics technicians have
been trained in their use. Decontamination and dose evaluation methods
and procedures that focus on hot particles have been implemented. (See
summaries of events at Trojan and San Onofre in Attachment 1.)
4. In general, licensees have upgraded their programs for contamination
monitoring of "clean," laundered anti-contamination protective clothing
(PC). However, PC continues to be a means of transferring both fuel
particles and activated particles. Some facilities need to consider
making their PC monitoring programs more sensitive. For example, some
licensees that are using contractor laundry services found the contrac-
tor's alarm on the radiation monitor (used to screen PC) too high to
detect 0.4 microcurie (æCi) particles. Moreover, when commercial laundry
services are used, it is possible that PC from a "particle-free" plant
can be mixed with PC from a plant with hot particle problems. Finally,
at least one licensee was relying solely on monitoring of large bundles
of washed PC (bulk surveys) and was not monitoring samples of individual
PC. For plants with identified particle problems, individual PC items
may have to be checked before they are reused after cleaning.
5. Except for the Trojan event discussed in Attachment 1, to date, no
licensee has reported detecting hot particles during airborne sampling.
However, as a precaution, some licensees have elected to provide workers
with respiratory protection for performing maintenance on plant systems
known to be a source of hot particles. No plant has reported inhalation
or ingestion of hot particles by any worker.
6. Hot particles in contact with skin produce very high dose rates.
Diligent personnel contamination surveys performed as soon as practical
after completing work involving contamination are needed to minimize
potential exposure times.
7. Approximately 75 percent of the U.S. power reactor facilities are cur-
rently using new high-sensitivity whole-body contamination monitors.
These state-of-the-art contamination monitors increase the probability of
detecting hot particles on plant personnel while reducing the likelihood
of inadvertently releasing particles from the plant site. To date, most
of the particles found on personnel have been detected by these new
monitors. Even with use of the new monitors, a few instances have oc-
curred where hot particles have inadvertently been carried home by
workers and have been detected in the home or on the worker returning to
the site. No significant public exposures have been reported to date.
8. In a recent study for the NRC (Reference 3), it was reported that a plant
operating with 0.125 percent pin-hole fuel cladding defects showed a
general five-fold increase in whole-body radiation exposure rates in some
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areas of the plant when compared to a sister plant with high-integrity
fuel (<0.01 percent leakers). Around certain plant systems the degraded
fuel may elevate radiation exposure rates even more.
9. Maintenance on valves with Stellite components can cause introduction of
cobalt-containing debris with Co-60 as the resultant neutron activation
product. Some plants have instituted work controls (e.g., use of
containment and post-maintenance cleaning) to minimize this input into
reactor systems (Reference 4).
Health Implications and Radiation Protection Criteria for Hot Particle
Exposures of Skin:
A hot particle on the skin gives a high beta dose to a small area. Any radia-
tion dose to the skin is assumed to result in some increased risk of skin
cancer, although this type of cancer is rarely fatal. Experiments with
animals indicate that highly localized irradiation of the skin by hot
particles is less likely to cause skin cancer than more uniform irradiation by
the same quantity of radioactive material.
In addition to any increased risk of cancer, large doses to the skin from hot
particles also may produce observable effects such as reddening, hardening,
peeling, or ulceration of the skin immediately around the particle. These
effects appear only after a threshold dose is exceeded. The doses from hot
particles required to produce these effects in the skin are not known pre-
cisely; however, it appears likely, except for a point reddening, that these
effects will only be seen for doses of hundreds of rems or more. No such
effects have been seen to date on any workers who have been exposed to hot
particles, even though one exposure has been measured or calculated as high as
512 rem.
Recent reviews of radiobiology and radiation protection criteria for skin, in-
cluding considerations of hot particle exposures, have been provided by Wells
(Reference 5) and Charles (References 6 and 7).
The NRC staff recognizes the need for more information on the effects of
radiation on skin and particularly the effects of hot particle irradiation.
The staff has requested the National Council on Radiation Protection and
Measurements (NCRP) to study the health significance of hot particle exposures
and to provide recommendations based on the findings of this study. These
recommendations may result in changes in NRC requirements with respect to hot
particle exposures. However, until these requirements are changed, IE Infor-
mation Notice 86-23 (Reference 1) contains current information for use in
evaluating doses to skin resulting from hot particles.
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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.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: James E. Wigginton, NRR
(301) 492-4663
John D. Buchanan, NRR
(301) 492-7293
References
1. Information Notice No. 86-23, "Excessive Skin Exposures Due to Contamina-
tion With Hot Particles," April 9, 1986.
2. Institute of Nuclear Power Operations, Significant Event Report 18-87
(Rev. 2), "Radiation Exposure From Small Particles," July 16, 1987.
3. Moeller, M. P., G. F. Martin, and D. L. Haggard, "The Impact of Fuel
Cladding Failure Events on Occupational Radiation Exposures at Nuclear
Power Plants. Case Study: PWR During Routine Operations," NUREG/CR-4485
(PNL-5606), January 1986.
4. Heard, D. B., and R. J. Freeman, "Cobalt Contamination Resulting From
Valve Maintenance," Electric Power Research Institute, EPRI NP-3220,
Final Report, August 1983.
5. Wells, J., "Problems Associated With Localized Skin Exposures," in
"Radiation Damage to Skin: Fundamental and Practical Aspects,"
Proceedings of a Workshop held at Saclay, France, on October 9-11, 1985,
Brit. J. Radiology, Supplement No. 19, pp. 146-150 (1986).
6. Charles, M. W., "The Biological Bases of Radiation Protection Criteria
for Superficial, Low Penetrating Radiation Exposure," in "Dosimetry of
Beta Particles and Low Energy X-Rays," Proceedings of a Workshop held at
Saclay, France, October 7-9, 1985," Radiation Protection Dosimetry 14
(No. 2), pp. 79-90 (1986).
7. Charles, M. W., "Skin, Eye, and Testis: Current Exposure Problems and
Recent Advances in Radiobiology," J. Soc. Radiol. Prot. 6 (No. 2), pp.
69-81 (1986).
Attachments:
1. Event Summaries
2. List of Recently Issued NRC Information Notices
. Attachment 1
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EVENT SUMMARIES
San Onofre 3, Events During November 1986 - March 1987, Inspection Report
No. 50-362/86-37
Background:
At the onset of the first fuel cycle, significant fuel degradation was
evident. The plant continued to operate with approximately 105 defective fuel
pins. In late 1985 during the first refueling outage, a fuel pin was
inadvertently pulled apart during the fuel reconstitution process. Several
fuel pellets fell and dispersed throughout the fuel pool. Fuel particles had
previously been detected early on during reconstitution on fuel handling tools
and on the refueling floors. All the severely damaged fuel pins were then
grouped into one fuel bundle and stored in the pool without any containment.
Event Specifics:
From January 2 through February 20, 1987, the licensee's aggressive hot parti-
cle inventory and tracking system indicated that 92 "new" fuel particles
(recently neutron irradiated), 155 "old" fuel particles, 51 ruthenium, 84
crud, and 42 cobalt particles had been found and analyzed. Before 1987, no
formal tracking program existed.
Several incidents involving hot particles have occurred, including an apparent
worker extremity exposure (hand) of 512 rem during November 1986. As a
result, appropriate NRC enforcement actions are currently underway. Three
events involving the inadvertent release of hot particles from the plant site
occurred in February 1987. In two of these events, the radiation dose to the
public was determined to be negligible. However, the third event involved a
0.2 æCi particle found by a worker at his home during a self-initiated
radiological survey. The licensee has not yet estimated the potential dose to
the worker's family as a result of this occurrence.
In the licensee's licensee event report (LER No. 86-015, Revision 1) of Febru-
ary 22, 1987, the following program improvements for detecting hot particles
and controlling personnel exposures from hot particles were described:
Extensive, mandatory use of exceedingly sensitive fixed instrumentation
(frisking booths) for the detection of personnel contamination;
Special training (including hands-on laboratory exercises) in radioactive
particle characteristics and survey techniques for all Health Physics
Technicians;
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Oral and written indoctrination of all managers, first line super-
visors and workers in the special problems associated with radio-
active particles, including the methods each person must employ to
protect himself;
Special procedures to assure detection and control of radioactive
particles which feature the establishment of a clearly identifiable
zone, to demark and contain such particles, surrounded by clearly
identified buffer zones (or solid physical barriers) which are
surveyed frequently to verify that control is being maintained;
Maintenance and wide publication of a radioactive particle census
during outages to maintain station awareness;
The establishment of a Task Force to recommend and implement action to
minimize the future production and movement of radioactive particles.
Trojan, April, 1987, Inspection Report No. 50-344/87-15
Background:
The facility has operated since July 1982 with an estimated 112 fuel pellets
unaccounted for throughout the reactor and support plant systems. The
licensee recovered or located about 264 pellets of the estimated 376 missing
after the 1982 refueling outage, which occurred because of the baffle jetting
problems of the 1981 fuel cycle. (See Information Notice No. 82-27, "Fuel Rod
Degradation Resulting From Baffle Water-Jet Impingement," August 5, 1982.)
Event Specifics:
Shortly after the start of the 1987 refueling outage in April, a significant
increase in personnel skin contaminations occurred. On April 9, high surface
contamination (up to 300,000 dpm/100 cm 2) and high airborne activity levels
(2E-7 æCi/cc, mixed fission products) in containment resulted from the dis-
persal of fuel fragments during reactor vessel stud removal and stud-hole
plugging operations. The workers in the reactor cavity were wearing respira-
tors and no excessive uptakes of radioactive materials were detected during
followup whole-body counting. Because of the spread of contamination to the
spent fuel building, the licensee stopped all reactor building cavity work and
all personnel evacuated the area that afternoon.
On April 10, a licensee radiation survey located a hot spot on the cavity
floor near a reactor vessel stud hole (>100 rad/hr beta and 30 R/hr gamma
contact reading using a portable ion-chamber survey instrument). On April 11,
another worker located what appeared to be about one-half of a fuel pellet in
the flange area at the stud hole. This partial fuel pellet was removed on
April 12.
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On April 17, a radiation protection technician, after performing a survey of
the lower refueling cavity, discovered a fuel particle lodged in his
protective rubber shoe cover. This particle was later determined to be
composed of approximately 50 mCi of mixed fission product activity; showed
readings of 1200 mR/hr with the window open and 250 mR/hr with the window
closed. After a careful time-and-motion study of the technician's activities,
the licensee determined that no NRC regulatory dose limits were exceeded.
(Licensee estimates were 1.2 rem to whole body; 4.6 rem to skin; 9.6 rem to
extremities.)
In general, it appears that the licensee experienced a programmatic breakdown
that resulted in several workers receiving significant, unnecessary radiation
exposures from fuel particle contamination. In LER No. 87-08 dated May 8,
1987, the licensee identified the following additional concerns and corrective
actions. The LER stated in part:
Workers entering containment on April 9 were not aware of the fuel
particle hazards. As a corrective measure, all personnel with
access to radiological control areas were retrained to be informed of
the fuel particle problem and perform hands-on training to demonstrate
competence in anti-contamination clothing use. Daily reports
are being provided to workers on the status of containment activities.
Radiation surveys and record keeping were inadequate. As a corrective
measure, new procedures were developed to specifically address
discrete radioactive particles. All radiation protection technicians
have been trained on these new procedures.
There was insufficient extremity monitoring and no procedures for
particle control. As a corrective measure, procedures have been
prepared to address particle control. Additional extremity moni-
toring is being utilized.
Evaluation of radiological events needs to be improved. A new pro-
cedure will be prepared for documenting and evaluating radiological
events.
Review of radiation protection activities is insufficient. A new
separate onsite review committee will be established to evaluate
radiological events and to routinely review the performance of the
Radiation Protection Department.
Insufficient staffing existed. Increasing the manpower in both the
onsite Radiation Protection Department and the corporate Radiological
Safety Branch of the Nuclear Safety and Regulation Department is being
pursued.
. Attachment 1
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Problems existed due to insufficient radiation monitoring and surveying
equipment. Additional equipment including new portal monitors and
radiation monitoring equipment has been procured.
There was the potential for radiation exposure to individuals from fuel
particles on anti-contamination clothing. An evaluation for potential
exposure is in progress.
V. C. Summer, November 1986, Inspection Report No. 50-395/86-22
After working in a "clean" area where no protective clothing was required,
contamination was detected on the hand of an electrician who had worked on a
control panel for the overhead crane in the fuel handling building. After
measuring the dose rates (window open and window closed) with a portable
survey instrument the worker's hand was decontaminated. The contaminant was
not retained for further analysis. Based on the survey instrument readings,
the dose to the workers hand was calculated to be about 420 rems (at a depth
of 7 mg/cm 2 averaged over an area of 1 cm 2).
Salem Unit 2, April 1987, Inspection Report No. 50-311/87-11
A fuel particle was detected by a whole-body contamination monitor on a work-
er's arm. The particle was identified as a fuel particle (about 225 days
since in core) by using a gamma-ray spectrometer [Ge(Li) detector]. The
licensee believes that the source of the particle was from the last refueling
outage about 8 months earlier.
Yankee Nuclear Power Station, May 1987, Inspection Report No. 50-29/87-10
A potential skin exposure of 7.6 rem to a worker's scalp occurred from an
activated particle. The apparent source of the particle was the worker's PC
hood. After its discovery, the particle remained on the worker's scalp for
about 78 hours, awaiting medical assistance to remove the particle. Prior to
medical assistance arriving on site, the particle was removed by shaving the
hair. Earlier in May, the licensee reported that, during fuel assembly move-
ment, pieces of fuel rods were seen to have fallen away from the assembly and
land on top of the reactor core and in the refueling cavity area. Fuel recon-
stitution was in progress.
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Indian Point Unit 3, May 1987, Inspection Report No. 50-286/87-18
A maintenance foreman exiting the containment after helping to replace steam
generator manway covers received an estimated 4 rem dose to the skin (in back
of neck) from an activated zirconium particle. It appears the particle dis-
lodged from his PC hood and fell on his neck during temporary removal of the
hood during a work rest-break.
Quad Cities/Dresden/Zion, 1986 and 1987
A special program to investigate hot particle incidents has been in place at
these Commonwealth Edison Company facilities for the last 1-2 years. A total
of approximately 100 individual hot particles were found on workers' skin or
clothing in 1986. Approximately 130 particles were found in the first six
months of 1987. The particles have been predominantly Co-60 with activities
ranging from about 0.01 to 1 æCi. Those particles were analyzed for physical
size; the smallest was 20 microns. The licensee investigated each event and
calculated skin doses. No overexposures have been reported. The transfer
mechanism of the particles to the workers has not been positively identified.
Callaway Station, 1986 Period, Report No. 50-483/8700 (DRSS)
The licensee experienced ten hot particle skin contamination incidents
primarily during the refueling outage early during the year. No NRC dose
limits were exceeded. Ineffective frisking (hand-held pancake GM-tube) of
laundered PC and potentially degraded dry-cleaning fluid quality (leading to
cross-contamination of PC during cleaning) were identified by the licensee as
possible contributors to this contamination problem.
