pwr_march-2024 - 31

NUCLEAR POWER
yard. In May 2018, the vessel was towed
4,000 kilometers (km), around Finland
and Sweden, to Murmansk, completing
the first leg of its journey to Pevek. Fuel
loading was completed in Murmansk
in October 2018. First criticality was
achieved in November 2018, then in August
2019, the vessel embarked on the
second leg of its journey-a distance of
4,700 km-towed by two tugboats to
the Arctic port town of Pevek, where it
was connected to the grid on Dec. 19,
2019. Akademik Lomonosov was fully
commissioned on May 22, 2020, and it
currently provides heat to the town of
Pevek and supplies electricity to the regional
Chaun-Bilibino power system.
HTR-PM
On Dec. 6, 2023, China National Nuclear
Corp. announced it had commenced
commercial operation of the high-temperature
gas-cooled modular pebble
bed (HTR-PM) reactor demonstrator. The
HTR-PM project was constructed at a
site in Rongcheng, Shandong Province,
roughly midway between Beijing and
Shanghai in eastern China. Touted as the
world's
first
commercially
nuclear
operational
modular nuclear power plant with fourthgeneration
technology,
the
achievement
marked an important milestone,
transitioning the technology from
experiments to the commercial market.
Main Design Features. The HTR-PM
has a capacity of 2 x 250 MWth or 210
MWe. Each reactor is loaded (Figure 2)
with more than 400,000 spherical fuel
elements, or pebbles, each 60 millimeters
in diameter, which is roughly the
size of a tennis ball. Each pebble contains
about seven grams of uranium fuel
enriched to 8.5%.
Each HTR-PM module includes an
RPV, graphite, carbon, and metallic reactor
internals; a steam generator; a main
helium blower; and a hot gas duct. The
primary helium coolant works at a pressure
of 7.0 MPa (1,015 psig) with a rated
mass flowrate of 96 kilograms/second
(761,918 lbm/hr). Helium coolant enters
the reactor in the bottom area inside the
RPV with an inlet temperature of 250C
(482F). Helium coolant flows upward in
the side reflector channels to the top reflector
level where it reverses flow direction
and flows into the pebble bed in a
downward flow pattern.
Bypass flows are introduced into the
fuel discharge tubes to cool the fuel elements
and into the control rod channels
for control rod cooling. Helium is heated
in the active reactor core, then mixed to
March 2024 | POWER
sels installed in March that year. The fuel
plant reached its expected production
capacity in 2017. Startup commissioning
and testing of the primary circuit were
finished by the end of 2020. The HTRPM
achieved first criticality in September
2021, and was ultimately grid connected
on Dec. 20, 2021.
2. Fuel loading at the Shidaowan hightemperature
gas-cooled modular pebble bed
(HTR-PM) in China began in the spring of
2021. It involved putting 870,000 spherical
tri-structural isotropic (TRISO) particle fuel elements
into the two small reactors that will
drive a single 210-MWe turbine. Courtesy:
China National Nuclear Corp.
an average outlet temperature of 750C
(1,382F). It then flows to the steam
generator. The secondary steam normal
operating pressure is 13.25 MPa (1,922
psig) and temperature is 567C (1,053F)
at the steam turbine entrance.
The HTR-PM utilizes a continuous fuel
loading and discharging system. The fuel
elements drop into the reactor core from
the central fuel-loading tube and are discharged
through a fuel extraction pipe
at the core bottom. Subsequently, the
discharged fuel elements pass a burnup
measurement device one by one. If a
fuel sphere reaches the target burnup, it
is discharged to the spent fuel storage
tank, otherwise, it is re-inserted into the
reactor to pass through the core again.
Deployment Details. The HTR-PM
design has a long history, which began in
1992 when the Chinese government approved
the construction of the 10-MWth
pebble-bed high-temperature gas-cooled
test reactor (HTR-10) at Tsinghua University's
Institute of Nuclear and New Energy
Technology (INET). As the HTR-10 unit
neared completion in 2001, the HTR-PM
project was launched. HTR-10 ultimately
achieved full power operation in 2003,
and INET subsequently completed many
experiments on the unit to verify crucial
safety features and validate the design.
Meanwhile, the first concrete for the
HTR-PM demonstration
power
plant
was poured on Dec. 9, 2012. To support
first-of-a-kind (FOAK) equipment
manufacturing and design licensing,
large-scale engineering test facilities
were constructed. Fuel plant construction
started in 2013. The following year,
qualification irradiation tests of fuel elements
were completed.
The civil work for the nuclear island
buildings was completed in 2016 with
the first of two reactor pressure veswww.powermag.com
Spotty
Results at Best
While it is laudable that these SMRs-
the KLT-40S and HTR-PM-have been
placed in commercial operation, their
performance since entering service has
come under fire. In The World Nuclear
Industry Status Report 2023 (WNISR),
a Mycle Schneider Consulting Project,
co-funded by the German Federal Ministry
for the Environment, Nature Conservation,
Nuclear Safety, and Consumer
Protection, it says both designs have operated
at low capacity factors recently.
Concerning the Chinese HTR-PM, the
WNISR says, " Between January and December
2022, the reactors operated for
only 27 hours out of a possible maximum
of 8,760 hours. In the subsequent three
months, they seem to have operated at
a load factor of around 10 percent. " The
Russian units' performance has been
nearly as dismal. " The operating records
of the two KLT-40S reactors have been
quite poor. According to the IAEA's PRIS
[Power Reactor Information System] database,
the two reactors had load factors
of just 26.4 and 30.5 percent respectively
in 2022, and lifetime load factors of
just 34 and 22.4 percent. The reasons for
the mediocre power-generation performance
remain unclear, " the report says.
Meanwhile, the promises of shortened
timelines and lower costs were not
borne out by these projects. " The experience
so far in constructing these two
SMRs as well as estimates for reactor
designs like NuScale's SMR show that
these designs are also subject to the
historical pattern of cost escalations and
time overruns. Those cost escalations
do make it even less likely that SMRs
will become commercialized, as the collapse
of the Carbon Free Power Project
involving NuScale reactors in the United
States illustrated, " the WNISR says.
With that said, it should be noted that
these were FOAK projects, and those
rarely progress without hitches. If the
lessons learned from these two completed
dual-unit SMRs can be parlayed
into future successes, the projects may
yet prove to be incredibly valuable. ■
-Aaron Larson is POWER's
executive editor.
31
http://www.powermag.com
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