For those who say we cannot use enriched uranium oxide fuels or thorium-plutonium MOX fuel in Wylfa, because the its too much hassle the safety case is too difficult...
I should point out that Wylfa currently runs on around 600 tonnes of uranium, with an unspecified fraction of this enriched from 0.7% Uranium-235 to slightly enriched 0.8% Uranium-235. The point being that a safety case has already been made in the past to change the fuel reactivity in the Wylfa Magnox reactor once before.
As I said before there are three options:
1. the AGR fuel cycle route - use stainless steel clad Uranium oxide pins (3 per existing Magnox fuel rod; perhaps around 130 tonnes of fuel enriched to the right level for criticality)
2. the Thorium-Plutonium MOX route - again using AGR steel clad pins ( 3 per existing Magnox fuel rod; perhaps around 110 tonnes of fuel enriched in plutonium to the right level for criticality)
3. Close down and decommission Wylfa Magnox Reactor 1 at the same time as Reactor 2 and give up on a UK based nuclear industry.
If Wylfa Magnox reactor (425MW net to grid) was run for 5 more years from 2017 (once refuelled) and given a concessionary rate for its electricity of £75 per MWh at 70% utilisation
The income would be
£75 * 425MW * 365 * 24 * 0.7 * 5 years = £977 million
Also with 500 MW of Biomass running for 10 years to 2025 at 70% utilisation with net £25 income after fuel costs
£25 * 500MW * 365 * 24 * 0.7 * 10 years = £767 million
Total income over 10 years = £1,744 million
From this must be taken:
1. Capital costs and loan costs for around 1500 MWt Biomass Combustor/Boiler Systems (£200 million ball park)
2. Wylfa Magnox Reactor 1 refuelling costs, regulatory and waste costs (£200 million ball park)
3. Wylfa Magnox Reactor 1 upgrade costs for materials experiments, regulatory and other reasons (£150 million ball park).
Capital costs £550 million
Site running costs in terms of staff etc, £80 million per year (say £1 billion over 10 years)
Ignoring other income and grants that would leave £200 million start up capital to invest in Generation IV nuclear.
My outline plan is for a Generation IV molten salt nuclear reactor building roughly the size and shape of the old Dragon Reactor at Winfrith. Maximum 33 metre outside diameter; up to 25 metres high from ground level, and up to 15 metres below ground, with the floor level above the reactor containment being around 5 metres above outside ground level. The inside working diameter of the building will be approximately 20 metres, as in the Dragon reactor building design.
I anticipate that up to 4 commercial 3.6 metre diameter integral molten salt reactors (each with a power output of 900 MWt) would eventually fit into such a building (one per quadrant). Giving a 3600 MWt output per reactor building of this type, and an electrical output of 1620MWe assuming a generation thermodynamic efficiency of 45%. This would be the equivalent output to an EPR of 4400 MWt and 37% thermodynamic efficiency, but in a much smaller sized building, using much less concrete than needed to build an EPR.
Each of these reactors would have a mixed mode heat transfer system with CO2 gas cooling (one third heat transport base load) and molten salt loop cooling (two thirds heat transport above that); both raising steam via appropriate heat exchangers/steam generators.
The gas cooling loop would be triply redundant each with a nominal 100 MWt heat transport capability, and would be bought off the self as a standard component. (12 being required per set of 4 integral molten salt reactors). The would have a passive heat removal capability to remove decay heat from the reactors under fail safe conditions when external power is lost.
The molten salt heat transfer loop will not need to operate passively as a reactor safety system in fail safe conditions. Therefore only one 600MWt molten salt transfer loop will be required per reactor. If it fails for any reason then the reactor will shut down, and be cooled by either active or (in worst case) passive CO2 gas cooling.
This design will allow a test molten salt nuclear reactor of 300 MWt or less to be cooled entirely using existing gas cooling technology, or a mixture of gas and active molten salt loop cooling as later test schedules demand.
This speeds up the development cycle as CO2 gas cooling technology is a safe, reliable and well understood technology used in the UK for many decades now. The CO2 gas heat transfer loop initially raises steam, prior to the steam temperature and pressure being raised to supercritical levels in the molten salt loop heat exchanger/steam generator (700/800 DegC). This will help prevent steam/water at too cold a temperature from entering the molten salt loop steam generator. If this molten salt loop steam generator fails the reactor will shut down and with active/passive gas cooling taking over.
All this new kit and a wide range of failure mode scenarios can be physically tested out prior to being used with an actual nuclear reactor, by electrically dumping large amounts of heat into a non-radioactive simulation integral molten salt reactor (physically simulating the heat generating properties of the nuclear reactor, as the heat transfer systems would see it).
I personally think the key to getting new Generation IV nuclear development of the ground quickly will be not to have to rely on new technologies (such as molten salt heat transfer loops) for safety and passive heat removal under power outage and other fail safe conditions. If only one molten salt heat transfer loop / steam generator need be built per reactor (because it has no safety heat transfer role, just an operational heat tranfer role), costs can be contained when up rating the size of the reactor between say 300 MWt and 900 MWt reactor power output.
I think this may be a better and ultimately safer route to take than using and relying on new supercritical CO2 gas cooling technologies say.