Information Notice 1986-43, Problems with Silver Zeolite Sampling of Airborne Radioiodine
SSINS No.: 6835 IN 86-43
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C.
20555
June 10, 1986
IE INFORMATION NOTICE NO. 86-43:
PROBLEMS WITH SILVER ZEOLITE SAMPLING
OF AIRBORNE RADIOIODINE
Addressees
All nuclear power reactor facilities holding an operating license (OL) or a
construction permit (CP).
Purpose
This information notice is provided to alert licensees of the potential hazards
associated with sampling for radioiodines with silver zeolite (AgZ) in the
presence of hydrogen (H2) and oxygen (02). It is expected that recipients will
review the information for applicability to their radiation monitoring and
survey program and consider actions, if appropriate, to preclude similar
problems at their facility.
However, suggestions contained in this notice do
not constitute NRC requirements; therefore, no specific action or written
response is required.
Description of Circumstances
During a recent surveillance test, the LaCrosse Boiling Water Reactor (BWR)
experienced a hydrogen ignition while sampling the plant offgas system. The
high H; concentration in the offgas system was caused by a faulty H2-02 recombiner.
An excerpt from the NRC regional followup inspection report in
Attachment 1 gives a detailed account of the event.
The licensee believes that the ignition source during this event was the AgZ
cartridge used in the .offgas sampling rig.
The cartridge contained dehydrated
(less than 1% water content) AgZ.
The heat of hydration released when the AgZ
absorbed moisture from the sample stream may have added enough heat to allow
catalytic recombination of H2 and 02.
Catalysis also releases heat that would
have rapidly increased the temperature of the AgZ to the H2 ignition point.
Discussion:
Silver zeolite cartridges are used for sampling radioiodines in radioactive gas
mixtures.
The AgZ chemically traps the iodines while letting the noble gasses
(which would interfere with subsequent radioanalysis) pass through.
The
LaCrosse event highlights the following two properties of AgZ that are appar- ently not well understood by the industry.
Copies to: SWithers, YundtF Letitsch, Orser, Steele, E. Burton, E. Jordan, A. Holm, LIS, C. A. Olmstead, S. Hoag, S. Satitter, TNP:GOV REL F:NRC CHRONO,
TNP:GOV REL F:NRC IE Information Notice 86-43 PGE Action -
M. H. Malmros (Due 8/12/86)
NSRD Action -
M. H. Malmros
June 10, 1986 1. Hydration State
The noble gas retention efficiency of AgZ is a function of its water
content (hydration).
Dehydrating AgZ activates its surface, freeing-up
sites for noble gas adsorption.
Data presented in NUREG/CR-3445 (March,
1985), "A Comparison of Iodine, Krypton, and Xenon Retention Efficiencies
for Various Silver Loaded Adsorption Media," show that the retention
efficiency for bound noble gas (gas not residing in the void fraction of
AgZ) of dehydrated AgZ is an order of magnitude higher than AgZ hydrated
to 9% by weight.
Because AgZ is used to minimize noble gas retention and
interference, the use of dehydrated AgZ is self-defeating.
The heat of hydration can also effect AgZ's iodine retention.
Heat
released, if dehydrated AgZ is used to sample humid air, increases its
temperature.
This elevated temperature can reduce the retention effici- ency for iodine.
For the above reasons, when sampling for airborne radioiodine in the
presence of noble gases, use of dehydrated or activated AgZ is not
appropriate.
2. Catalytic Properties
Silver zeolite will act as a catalyst to recombine H2 and 02 into H20
(water).
One manufacturer's study, run with 2% H2 in moderately dry (10%
humidity) air, indicated a threshold temperature at 1500F before the
catalytic reaction becomes significant.
Although the dependence of this
threshold temperature on such parameters as moisture content and H2 concentration are not known, it is assumed that higher H2 concentration
will lower the threshold temperature.
This catalytic property of AgZ
makes its use in sampling from explosive or potentially explosive atmo- spheres (such as BWR offgas or waste gas storage tanks) unadvisable.
Note that for sampling the offsite environment or other onsite areas where
there is no possibility of having a significant H2 concentration, the catalytic
properties of AgZ are of no concern.
In addition to returning the offgas recombiner to an operable state, the
licensee is considering the following actions:
°
using only charcoal cartridges for sampling the offgas radionuclides
o
using a portable H2 analyses and checking for H2 concentration before
sampling the offgas
°
using only partially hydrated (or noncatalyzing cartridges) for
post-accident sampling of stack effluents
o
not using AgZ for post-accident containment sampling unless H2 concentration is less than 4 percent
IN 86-43 June 10, 1986 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.
L. Jordan, Director
"
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contacts:
Roger L. Pedersen, IE
(301) 492-9524
Edward F. Williams, IE
(301) 492-7611 Attachments:
1. Hydrogen Ignition in an Offgas Sampling Rig
2. List of Recently Issued IE Information Notices
Attachment 1
IN 86-43 June 10, 1986 HYDROGEN IGNITION IN AN OFFGAS SAMPLING RIG
(Excerpted from Referenced Inspection Report, Edited Version)
On March 6, 1986, a senior health physics technician at the LaCrosse Boiling
Water Reactor set up a portable sampling system to sample particulate and
radioiodine activity in the operational offgas line both upstream and down- stream of the on-line offgas system final high-efficiency particulate air
(HEPA) filter and charcoal adsorber bank.
The sampling was being conducted to
test the collection efficiency of the HEPA filter and charcoal adsorber using a
differential radionuclide concentration method.
The sampling equipment consisted of new tygon tubing, a flow meter, an aluminum
filter paper holder containing an acetate filter paper, and a dual cartridge
holder containing two plastic cartridges containing silver zeolite (AgZ).
The
AgZ had been dehydrated by the manufacturer to less than 5 percent moisture.
Past sampling of the offgas line was performed using two standard 2-inch
charcoal cartridges instead of AgZ cartridges.
AgZ cartridges were substituted
because they adsorb less noble gaseous activity than charcoal cartridges and, therefore, reduce sample analysis interferences.
Two minutes after starting the sampling equipment (flow rate of 0.6 cfm), the
technician noted that water droplets had formed on the inside of the tygon
tubing downstream of the filter holders.
One minute later, the technician
heard a loud bang and saw a bluish flash inside the sample tubing.
The techni- cian then turned off the sampling pump, isolated the sampling lines, and
inspected the sampling equipment.
The tygon tubing was a burnt brown color;
the inside of the flow meter was covered with a brown-colored oil film; the
cartridge holder was hot, difficult to open, and had a burned odor when opened;
plastic parts of the zeolite filters and holder displayed some melting and were
fused; the plastic retaining screens in the zeolite holders were no longer
intact; and the HEPA filter had disintegrated.
The licensee believes that an ignition began in the sample holder and that
sufficient H2 must have been present in the sample lines to sustain an
ignition.
Sufficient H2 could be present if the offgas system catalytic
recombiner, located upstream of the filters being tested, were not operating
optimally.
There is no H2 monitor downstream of the catalytic recombiner.
The
licensee's Radiation Protection Engineer discussed the potential of H2 and 02 recombination catalysis by AgZ at ambient temperatures with two outside sup- pliers.
It was determined that dehydrated AgZ will absorb moisture from the
sample stream until it reaches hydration.
During this hydration, which creates
a slightly exothermic reaction, the AgZ granules will heat up.
During this
heating, additional H2 and 02 alignment with the AgZ molecules may occur, and
some controlled catalytic recombination also may occur, which may further
increase the AgZ granules' temperature.
At about 1500F, the AgZ will reach its
threshold temperature for H2 and 02 catalytic recombination.
At this threshold
temperature, the AgZ may cause a rapid recombination (ignition) of H2 and 02 if
the H2 concentration is above 4 percent.
This may rapidly generate temper- atures inside the AgZ in excess of 10650F.
Attachment 1
IN 86-43 June 10, 1986 The offgas system continued to operate after the ignition. There were fluctua- tions in effluent noble gas, particulate, and halogens for several hours after
the ignition; however, no alert setpoint was reached.
The licensee noted an
increase in the temperature of the offgas storage tanks and the catalytic
recombiner (monitored parameters). The system slowly returned to near normal
except that an identifiable increase in halogen and particulate effluent
remained. These remaining increases indicate a possible degradation of the
final HEPA filter and charcoal adsorber.
The licensee plans to inspect the
filter bank for damage and replace the HEPA and charcoal as necessary during
this outage.
Reference:
LaCrosse Boiling Water Reactor Inspection Report No. 50-409/86003 (DRSS), March
28, 1986.
Attachment 2
June 10, 1986
LIST OF RECENTLY ISSUED
IE INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issue
Issued to
86-42
86-41
Improper Maintenance Of
Radiation Monitoring Systems
6/9/86 Evaluation Of Questionable
6/9/86
Exposure Readings Of Licensee
Personnel Dosimeters
86-32 Sup. 1
86-40
86-39
86-38
86-37
Request For Collection Of
Licensee Radioactivity
Measurements Attributed To
The Chernobyl Nuclear Plant
Accident
Degraded Ability To Isolate
From Low-Pressure Coolant
Systems in BWRS
Failures Of RHR Pump Motors
And Pump Internals
Deficient Operator Actions
Following Dual Function Valve
Failures
Degradation Of Station
Batteries
Change In NRC Practice
Regarding Issuance Of
Confirming Letters To
Principal Contractors
6/6/86
6/5/86
5/20/86
5/20/86
5/16/86
5/16/86
All power rector
facilities holding
All byproduct
material licensees
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
86-36
86-35 Fire In Compressible Material 5/15/86
At Dresden Unit 3
OL = Operating License
CP = Construction Permit