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NuclearPlantJournal.com Nuclear Plant Journal, September-October 2015
Severe
Accident
Hydrogen
Monitoring
Systems
By James F. Gleason, GLSEQ, LLC.
James F. Gleason
James F. Gleason, P.E., has a BSME
from Rensselaer Polytechnic Institute
and MSIE from the Ohio State
University. Mr.
Gleason has 38
years’ experience in
nuclear power and is
President of GLSEQ,
LLC, Huntsville,
Alabama .
He has performed
nuclear safety
research for the
NRC, EPRI and
reactor designers. He is a standards
committee member of ANS, IEC, ASME,
and IEEE.
The accident at Tokyo Electric Power
Company’s Fukushima Dai-ichi Nuclear
Power Plant exhibited the difficulty in
measuring important parameters for
monitoring plant conditions in Beyond
Design Basis Accident (BDBA),
Severe Accident (SA) environmental
conditions. Since our team has been
qualifying equipment for over 40 years,
we know the difficulty in meeting Design
Basis Accident (DBA) environments,
which are extreme conditions. The
environmental conditions experienced at
Fukushima were very troubling because
the conditions were considerably higher
than typical instrumentation DBA
qualification levels. The objective was to
develop instrumentation that was needed
for SA and could perform in the worst
case SA.
Thisarticlediscussesthedevelopment
and testing of the GLSEQSevereAccident
(SA) Hydrogen Monitoring System,
which is part of the GLSEQ Intrinsically
Smart- Severe Accident Instrumentation
Line, designed to
make nuclear plants
even safer.
The focus was on
improving the ability
to monitor hydrogen
during SA. Existing
combustible gas sys-
tems rely on sampling
from
containment,
which provides no in-
formation on local ar-
eas of high hydrogen
concentration and dilutes the hydrogen in
the process of sampling gases from con-
tainment. They also require significant
maintenance because of the sampling
systems. Existing systems need sampling
systems, which breach containment at
the time containment is most important,
including isolation valves, flow control-
lers, heat tracing, pumps and motors. In
some of these systems the time to obtain
a measurement of hydrogen could take
an hour. Since the sampling systems may
have been designed for DBA conditions,
the higher pressure of SA conditions may
exceed the design ratings.
The hydrogen explosions outside of
containment at Fukushima were a big
surprise in an accident full of surprises.
After studying the Fukushima SA,
additional SAs, and discussions with
nuclear reactor designers, it was decided
to concentrate on a new advanced type
of hydrogen measurement instrument.
The Fukushima SAs highlighted that
hydrogen measurement and risk of
explosion were important to nuclear
safety and it was decided to develop
advanced hydrogen sensors and hydrogen
monitoring systems with the following
attributes:
• Convert hydrogen to an electrical
signal directly
• Not require a sampling system
• Not require breaching containment
with sampling lines
• Measure hydrogen in less than
1 minute
• Have the capability to operate in
extreme SA environments
• Require no maintenance
• Provide explosive risk information to
the operators
Development was necessary because
of the desire to measure hydrogen quickly
and directly without the need for gas
sampling in the very high environmental
conditions experienced in the Fukushima
SA and environments now predicted
for SA in various Light Water Reactors
(LWR).
The R&D for this project was a part
of the results of the collaborative project
by Japanese electric power companies
and plant manufacturers that was carried
out as the Safety Enhancement for
LWRs program by Agency for Natural
Resources and Energy.
The GLSEQ hydrogen sensor
measures electrical resistance change of
a coating which changes when hydrogen
is present, which is known as a chemi-
resistive method to measure hydrogen.
The unique chemical composition reacts
with hydrogen and lowers the resistance
in proportion to the concentration
of hydrogen. Therefore, the GLSEQ
Hydrogen sensors measure directly and
quickly the hydrogen concentration at
any location in containment or outside of
containment in a nuclear power plant.
The GLS Hydrogen sensors are
designed with high temperature ceramic
materials and high radiation resistant
