Saturday, December 19, 2020

NuScale: The Future of Carbon Free Energy??

Let's be clear, the future of US energy must include more nuclear energy as a carbon-free, base-load power source along with other energy supplies and fuels. It's because the quantity of energy used in this country is so enormous that solar and wind can never economically provide anywhere near all of it.

There is a role for the low-quality, expensive intermittent energy supplies from solar and wind power up to about 10 to 15% of the total, but they are very costly in part because they are low-intensity supplies and require virtually 100% backup. Also once solar and wind reach 10 to 15% of total supply, the cost of grid re-design and re-build renders these already-expensive alternatives uneconomic.  See my posts for an explanation: 

Large Scale Solar & Wind Power Not The Solution: Too Many Problems and Costs

More Analyses Confirm Solar & Wind Power Is More Of a Problem Than Solution

The problems with older style nuclear reactor projects have turned out to be numerous enough to limit their further adoption. They were conceived as massive and complex site-built projects where the cost to build became prohibitive (and that does NOT include decommissioning costs; read below). And there have been failures and severe nuclear material release accidents. One was Fukishima and another was Chernobyl. There have been several other nuclear plant accidents in Russia: Nyonoska (2019) and Kyshtym (1957). 

So, the cost overruns and the safety record of the old types of reactors has halted most new projects, and the complexity of these giant-sized plants has become impractical and unaffordable.  A list of other problems with "conventional" nuclear energy includes:
  1. The cost and construction duration of giant-scale plants built on-site has become unmanageable and cost prohibitive.
  2. Each facility design was unique and required enormous costs of engineering and an extremely long time for local, state and national government approvals. And time is money.
  3. The logistics and costs of weld inspection, quality control and record-keeping of super-large plant construction is impractical and even disruptive to site locales.
  4. The requirement of mechanical cooling systems in old plants is a major safety concern if power is lost. This leads to the requirement of emergency cooling pumps as backup. In other words, these reactors are not inherently safe. Emergency pumps failed to start in Fukishima.
  5. Due to the concern for safety and large quantities of nuclear fuel in the giant plants requires a 10 mile radius for emergency planning. So, we're talking a surrounding zone with a 20 mile diameter emergency preparedness zone!
  6. The logistics cost of abandonment, decommissioning and disposal of the old, very large plants, is massive and, once included, renders the economic case for the very large plants as infeasible and impractical.
But most of these problems have been addressed in new reactor designs. Back in 2013, I presented several posts calling out the advantages of the Thorium molten salt reactors as a possible avenue for abundant and carbon free nuclear energy. These reactors are designed to be inherently safe and the availability of Thorium is some 5 times that of Uranium. Because Thorium MSR units operate at very high temperature and the heat transfer medium is liquefied inorganic salts, this allows the unit to operate at atmospheric pressure (no pressurized containment). The thermal efficiency of very high temperature steam for turbine power generation is also very high.  Have a look at these posts for more information:

Thorium Reactors May Solve World's Energy Crisis

How Thorium Reactors Work

The disadvantage of the Thorium molten salt reactors is the need to concentrate fissile uranium in an adjacent unit operation. Once separated, uranium is fed back into the reactor via pumps. This is complicated and has some risks due to the use of fluorine gas for the uranium concentrator. The extremely high operating temperatures of the reactors also create challenges for material selection for this application, although no requirement for pressure containment helps. Thorium technology was developed by the US and is more than 50 years old

Introducing Small Modular Standard Designs from NuScale

A small company in Portland Oregon, NuScale, has come up with new concept in safe nuclear power. Their concept is to build small modular reactor units that are "mass produced" in a factory using an already-approved standard design. Quality control and inspection is much more manageable and construction costs are much more manageable at a factory that specializes in a standard module design. 

These modules are small enough to be shipped to site via truck, train or barge and installed below grade in large pools of water. The other advantages to this concept is listed on NuScale's website is: 
  1. Each reactor uses natural convection for the cooling loops to eliminate the need for circulating pumps. The reactor fails-safe with no requirement for AC or DC power or emergency pumps.
  2. Each module is immersed in a large pool of water that acts as a passive heat sink in a shutdown.
  3. The standard design is now approved by the US Nuclear Regulatory Commission
  4. Each reactor is about 9 feet in diameter and 65 feet long (tall) and arrives tested, inspected and ready to install.
  5. Each module only contains 5% of the nuclear fuel compared to conventional plants.
  6. Each module can generate 77 Megawatts. The standard plant designs include a facility with 4, 6 or 12 modules of standard design. All of these modules are installed in a below-grade single pool of water.
  7. The water pool is large and can absorb all the heat from the reactors for cool-down.
  8. Modular delivery can be by truck or barge.
  9. No requirement to be connected to a power grid for start-up or shut down. It is impervious to EMP attack due to this isolation. (Obviously the produced power is fed to the local electrical grid.)
  10. Each module contains a small fraction (5%) of the uranium found in a conventional plant.
  11. The required emergency safety zone around the plant is only a 40 acre site, not the 10 mile radius required in existing nuclear plants
  12. Site construction is substantial: a large below-grade pool to provide a heat sink for the reactor modules, piping to the steam generators, steam condensers, generators and a control room and workshops.
  13. Eventual decommissioning is manageable since each module can be removed and shipped to a disposal site via rail, truck or barge.
  14. Although the NuScale plant can be built with air coolers, it's more practical to use river or ocean water for cooling like the conventional nuclear (condensing the turbine exhaust steam and cool the reactor pool water).
Suggested methods for shipping components to site (and decommissioning):

Truck Delivery


Barge Delivery

Here's an image showing a cross-section of 12 module facility:

Cross Section Profile of the Containment Pool and installed Reactor Modules

Here's a short video (1:44 minutes) to show how these reactors work. Here's the link

Here's a 4:24 minute video animation (link found here) showing how the small module's are installed and fueled:

Here's another image showing a cross sectional view of the reactor and it's design features:

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