Page 36 - Nuclear Plant Journal - March April 2013
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36
Nuclear Plant Journal, March-April 2013
Spent Fuel...
sensors. This approach is problematic for
plants because the addition of multiple
long cable runs adds combustible
material to the containment environment,
which plants are required to minimize.
Furthermore, some plant budgets are
unlikely to support the high labor
and material costs associated with
installing and maintaining the additional
cable infrastructure which, as seen at
Fukushima, can be easily compromised
during an accident. As such, a different
approach is needed as described in this
paper.
System Description
The solution is a robust, cost-effective
system for enhanced spent fuel pool
monitoring, integrating commercially
available wide-range instrumentation
(e.g., level sensors, temperature sensors,
radiation-hardened video equipment)
with existing wireless data transmission
devices. Though the NRC only requires
monitoring the water level, this design
can accommodate other parameters, such
as water temperature and recirculation
flow, which can contribute to producing
a more complete picture of the fuel
pool condition both during and after
an accident. Additionally, radiation-
hardened video equipment would provide
continuous surveillance of critical
components and conditions in and around
the spent fuel pool.
There are a number of important
benefits to wireless data transmission.
Wireless systems eliminate costs
associated with installing and maintaining
long cable runs, minimize the addition
of combustible material, and help
overcome issues associated with aging or
compromised cables.
Figure 2 is a graphical representation
of the wireless system design. The design
uses conventional instrumentation wired
directly to a remote unit that provides
both instrument power and wireless data
communication to a hub. The hub receives
wireless data from one or more remotes
and transmits the data over a wired link
through a penetration and then onto the
plant network.
While the design would most likely
be powered with 120Vac, it is anticipated
that a rechargeable battery backup system
is also needed for both the remote and the
hub. The battery backup would engage in
the event of a loss of power to the unit and
enable the sensors to maintain function
and transmission for a limited period of
time under post-accident conditions.
Challenges with
Wireless Implementation
Nuclear power plants have been slow
to incorporate newer technologies, such
as wireless data transmission, often due
to concerns regarding electromagnetic
compatibility (EMC) and cyber security.
A legitimate concern is that wireless
transmissions may adversely impact the
electrical equipment and systems within
the vicinity of the wireless device. To
addressthisconcern,anumberofstepsmay
be taken. This includes characterizing the
electromagnetic environment (EME) of
the intended installation area, identifying
systems vulnerable to electromagnetic
interference (EMI) through walkdowns
and targeted immunity testing, and
establishing exclusion zones where
wireless transmissions are not permitted
based upon the power level of the
transmitter.
Recent
high-profile
computer
virus attacks have heightened concerns
regarding the security of nuclear power
plant computer networks (cyber security).
An effective cyber security program
prevents malicious intrusion into plant
systems by ensuring that network devices
are only accessed by employees and other
devices with proper credentials. Wireless
devices incorporate security protocols,
such as Wi-Fi Protected Access II
(WPA2) available in Wi-Fi networks
IEEE 802.11b, 802.11g, and 802.11n, to
maintain access integrity; these protocols
meet or exceed the guidelines established
in IEEE 802.11i and NIST FIPS 140-2.
