Fission Island
Fission Island is the only area of the power plant that (contain) nuclear. The fission island consist of FWD Hall and Power Module (PMOD).
Table of Contents
FWD Hall
The FWD Hall provides full passive air cooling utilizing chimneys instead of Ponds for heat decaFy and fans to assist in lowering operating temperatures. The design is made to avoid boiling off of basement water even at full decay heat with no fans operating.
The four (4) main components of FWD Hall are:
1.Dry Radiators
2.Draft Towers
3.Fans
4.Expansion Tank
Radiator Design
1.Econocoil hydro expanded plates with standard light duty plate radiators (subclass of platecoils).
2.Easily customizable with number of passes, number of headers to optimize performance.
3.Structure with Titanium for good corrosion resistance and long life in marine atmosphere.
Fans
1.There are four fans per Power Module to improve long term operations at normal conditions.
2.With 3.8 m diameter, it can flow up to 100 kg/s air at 1.1 kWe each.
3.In 40oC dry air with no wind, the fans reduce the basement water from 83oC to 58oC.
Chimney and Expansion Tank
There are two chimneys with expansion vessel in between (T-style).
Mechanism:
Hot intake from top of basement and cold return to top of basement.
Expansion Tank
Details:
1.Basement water expands by 371 m3 when heated from 30oC to 120oC.
2.Expansion tank volume is 428 m3. Therefore, it leaves 57 m3 for non-condensibles.
3.Pressure relief at 2 bar (120oC) via a standpipe to the steam generator cell.
PMOD
ThorCon Fission Island consist of two 250MWe PMODs. Each PMOD is divided into three sections:
- Section 1 – the Silo Hall
- Section 2 – the Secondary Heat Exchanger Hall (SHX Hall)
- Section 3 – the Steam Generating Cell Hall (SGC Hall)
The PMOD roof is a 3 m deep, double sided structure similar to a tanker double bottom. It is fitted with hatches that allow all the major components to be extracted and replaced. The basements in all three sections are flooded. The basements play an important role in decay heat removal and responding to casualties.
SILO Hall
The SILO HALL contains Cans, Fuel Drain Tank, and the primary as well as the secondary loop pump. The Silo Hall also has the “3Cs” function.
CAN
“THE CAN IS THE HEART OF THE POWER PLANT”
The Can contains the Pot, which are ThorCon’s term for the reactor, primary heat exchanger (PHX), and several tanks for fuel management.
At any one time, just one of the Cans of each module is producing power. The other Can is in cooldown mode. Every four years the Can that has been cooled is removed and replaced with a new Can. The fuelsalt is transferred to the Can, and the Can that has been operating goes into cooldown mode.
POT
“The POT pressure is very low. It’s <10 bar, about the same as the garden hose”
The outlet temperature of 704C results in an overall plant efficiency of more than 45%, and a nominal net electrical output per Can of 250 MW. To produce this power, the Can requires 1 tonne of uranium per year enriched to 19.7%. The Can has only one major moving part, the primary loop pump.
Primary Heat Exchanger
The PRIMARY HEAT EXCHANGER (PHX) is a twisted tube, hairpin heat exchanger shown in blue.
The PHX has several features:
1.Close to the counterflow
2.The spiraling flow inside the twisted tubes acts as a centrifuge, pushing colder, denser salt towards the tube wall which aids in heat transfer, but only if the fluid being heated is on the tube side.
3.Any plate out of the salt phobic fission products will be on the outside of the tube rather than the inside where it would be more likely to cause a plug.
4.Decontamination of the tube bundle will be facilitated by the fact that any fission product plate out will be on the tube exterior.
5.In the PHX, the secondary loop is at a higher pressure than the primary. This puts the tubes in tension where they are much stronger than in compression.
6.The ThorCon spec requires that the PHX tube sheets, and tubes be far stronger than the Secondary Heat Exchanger shell so that on over-pressure the SHX shell fails before the PHX tubes.
Primary Loop
1.Fuel is dissolved in the coolant. Fuel and coolant at the same temperature.
2.Flow is around 1.1m3/sec, 3300kg/sec, 20 second loop time, 560C to 704C
3.Cold fuelsalt flows down around the outer portion of the Pot.
4.Fuelsalt then flows up through the graphite moderator
5.Krypton and xenon have very low solubility and bubble out in the header tank where they are removed.
6.Pressure is modest 2 to 8 bar(a) with no phase change to increase it so ordinary thickness steel can be used.
Fuel Drain Tank
The FUEL DRAIN TANK (FDT) system discharges heat from the fuelsalt (inside the drain tank) to a stell wall cooled by water in natural circulation.
There are NO possibility of re-criticality in the FDT because it has no moderator so the fission chain reaction can not occurs.
3C FUNCTION
3C are: Control. Cooling, and Contain
- The control function is to stop the fission reaction
- Fission stops automatically with temperature increase (negative temperature coefficient) – Inherent safety design
- Drain the fuel from pot and primary loop to Fuel drain Tank (FDT) to stop the fission reaction
- The cooling function is to remove decay heat
- The colling system is a fully passive system for all the time and condition, even there is no power supply of AD/AC.
- The basement water is used as a heat transport medium.
- The basement water is used for reactor, fuel drain tank (FDT) and vault (spent fuel storage)
- Basement water naturally circulates up to expansion tank down to radiators, then back down to basement.
- The contain function is to keep radioactive material contained
- ThorCon uses multiple barrier containment
- All radioactive material is kept within three containment layers
- Can/FDT is the first gas tight barrier.
- Silo/radtank is the second gas-tight barrier
- The silo hall is the third containment barrier but it is not gas tight since it is man rated and has an HVAC and HEPA filter system like most containment building
SHX Hall
The SECONDARY HEAT EXCHANGER HALL (SHX Hall) is a part of the PMOD that contains the secondary loop, secondary heat exchanger, and several tanks for used fuel management.
Tanks that are located in the SHX Hall are:
1.Vault tank: Spent fuel storage
2.HUP tank: Off-gas flow storage until decay power is tolerable for cold traps
3.Secondary salt drain tank: To move secondary salt from secondary loop to a shielded area
4.Flush tank: two flush tank are prepared to allow double rinse
SGC Hall
The STEAM GENERATING CELL HALL (SGC Hall) contains the solar salt pump, the steam generator, and the steam reheater, and the quench tank.
The SGC is fitted with hatches at either end. These allow the steam generator and reheater loops to be withdrawn through these openings and replaced. There is also a hatch above the tertiary loop pump to facilitate its replacement. Personnel access to the SG cell with the hatches closed is through the aft bulkhead from the turbine hall.
The SGC basement is flooded but it is not connected to the silo hall/SHX cell basement. About 2 meters of ullage is maintained in this space. This allows the SGC basement to serve as a quench tank for the rest of the fission island.