Page 4 - AsiaElec Week 38 2022

AsiaElec COMMENTARY AsiaElec

China’s Molten Salt

Reactor finally gets startup

approval - a year late

CHINA THE Shanghai Institute of Applied Physics can withstand the nuclear flux inside the reactor
(SINAP) has been given approval by the Minis- vessel.
try of Environment to start up its experimental Further challenges arise outside the reactor.
thorium-powered molten salt reactor in Wuwei The Thorium fuel cycle generates fission prod-
about 800 km north of Chengdu. Construction ucts that must be removed from the molten
of the 2-MW reactor began in 2018. bne reported salt mix continuously, meaning that a working
in August 2021 that China was one month away reactor must be attached to a chemical separa-
from startup, but it has in fact taken the past year tion plant also capable of handling hot corrosive
to gain ministry approval for the reactor to go molten salt. This plant extracts and holds Pro-
critical. tactinium which, after a short period (about
The new reactor uses molten thorium fluo- a month), fissions into Uranium 233, which is
ride as its fuel source in place of enriched ura- then reinjected into the reactor as its fuel supply.
nium, but will start operations with a mainly
uranium fuel load (20% U235), gradually Molten Salt beats PWR in several ways
replacing it with thorium as operating experi- Thorium molten salt reactors offer very large
ence builds. The initial startup will, however, advantages over the universally accepted pres-
include 50 kgs of thorium fuel. Initially 20% of surised water reactors being built today (some
fission will be sourced from thorium, working 70 reactors are in build or on order around the
up to 80% over the test period. world at present). Principally, the reactor oper-
Initial operation will be on a batch basis but ates at a pressure of only 1.5 atmospheres. This
with some online refuelling and removal of gas- removes the need to build expensive high pres-
eous fission products. The plan is to move slowly sure containment systems and also removes the
to a continuous process whereby reactor fuel and need for expensive multiple-redundant water
waste products are inserted and removed while circulation pumps. Lower pressures mean that
the reactor is online. supporting systems can be down-scaled and
The Wuwei project is not a bolt from the blue. made cheaper, or even removed completely.
China has had some 1,000 people working on On the revenue side, Molten Salt reactors
thorium-based reactors for two decades. The operate at about 500 degrees centigrade hotter
thorium fuel cycle itself is also not new (it’s been than PWRs, which means that thermal conver-
theorised since the beginning of nuclear power sion from reactor power to turbine power rises
in 1945) and works on the principle that (stable) from 35% for PWR to nearly 50% for Molten
thorium can be turned into (fissile) uranium Salt.
233 when it is bombarded with slow neutrons. Production-scale Molten Salt Reactors are
A working molten salt reactor wraps a blanket of expected to have a capital cost of about half that
thorium fluoride salt around the outside of the of a PWR - $5,000 per KW of electrical capacity
reactor core where spare neutrons transform it instead of $10,000, and financial models suggest
into uranium 233 (via protactinium – an inter- that the fuel cost of produced power will start at
mediate element). The U233 is then fed into the $30 per MWh and should fall to about $10 per
core as fuel. MWh as serial production cuts costs.
One source of cost-cutting is the absence
Engineering is the challenge, not physics of high-pressure water and steam. Molten salt
The engineering and chemistry required to run reactors do not need expensive high-pressure
a continuous process are far more challenging containment or multiple large redundant circu-
than the nuclear physics. Thorium and Ura- lating pumps. If a salt reactor overheats it melts
nium Fluoride salts flow through the reactor at a “freeze plug” below the reactor core, allowing
800 degrees Centigrade and are highly corrosive, the molten salt to flow into a cooling pan where
requiring the development of steels, pumps, it cools, freezes and stops fissioning. There are no
valves and pipes that can withstand the molten pumps to fail, and no reactions between water
salt environment. It has also been necessary to coolant and zirconium fuel rods to generate
develop control and monitoring systems that explosive hydrogen to breach containment (at

P4 www. NEWSBASE .com Week 38 21•September•2022