(1) Adopting integrated self-pressurized water reactor.

(2) The primary circuit operational state is: the primary coolant is at low pressure; the reactor core has a low power density; the fuel in low temperature; while the coolant has a high average temperature. So not only the safety but also the economical steam is ensured. The third circuit steam pressure can reach 4MPa and thermal efficiency can come up to about 80% while the primary pressure is only 10 MPa.

(3) Adopting a water-water-steam technological process improves the operation reliability of the heat exchangers in the reactor. The middle circuit pressure is higher than the primary’s, so radioactivity leakage is prevented from the primary to the third. The size of the heat exchangers and related buildings is reduced.

(4) The reactor and the primary circuit have adoped an adopt integrated layout The inner diameter of the containment is only 16m, so the reactor building is reduced to a minimum and the nuclear island covers 2518m2, only 32% that of looped layout

(5) Large amount of concrete and steel will be reduced and the general cost will also be reduced because of the small constructive scale. And a half of million tons oil will be replaced every year. So the time to recover capital is estimated as about 7 years.

(6) High passive safety and reliability. About 20% thermal power can be removed by the natural circulation of coolant when the main pumps stop. So a core melt accident will not occur when the main pump motor electricity is lost It is almost impossibly difficult for radioactivity to leak into the third circuit because of the high pressure in the middle circuit The accident probability drops down because the systems are simplified and the number of valves and pumps also decreased. The water-water heat exchanger is more reliable than a steam generator in the reactor. All the above-mentioned can reduce unexpected plant shutdowns and improve the plant availability.

(7) The plant can be built near a city or a large enterprise because of the reactor’s high passive safety and two-layered containment.

(8) The plant layout is compact and the main and the auxiliary buildings take up less land, and the foundation loading is lightened. So it is favourable for the plant to be built on seabeach, soft soil or a seismic area.

(9) The main components of the reactor and the primary circuit can be manufactured and installed in the factory. On site installation and examination work become less. The nuclear island constructive scale is small. So the double-reactor constructive period can be shortened to 5 years.

(10) The shape of the main and the auxiliary buildings on the nuclear island is simple, it is easy to construct So the construction period is shortened.

Table 2 is the main performance comparison between the integrated and the looped pressurized water reactor. The parameters in table 2 indicate that this design meets the basic requirements of a nuclear co-generation plant

According to the above-mentioned, the small-sized nuclear co-generation plant is economically competitive. Referring to more than twenty users’ steam consumption, it is suitable to adopt 400-600MWt power for the single-reactor. For the nuclear co-generation plant, its main function is heat supply, while the amount of electricity supplied depends on how much the heat is supplied. To avoid causing a high turbine cost, the electric power proportion should not be too large. If the heat supply is the main function and the electricity supply is auxiliary, the three circuits and water-water-steam technological process should be adopted.

For the reactor choice, PWR and BWR have all been considered. But the former is put first to raise the reactor core temperature, produce medium pressure steam in the third circuit and expand the scope of steam supply. The reactor and the primary circuit adopt an integrated layout and forced circulation. It is more compact than BWR with natural circulation. It is more suitable that the operation pressure of the self-pressurized water reactor adopts lOMPa according to the steam parameter requirements of domestic chemical industry.

In accordance with the above discussion, for a small-sized nuclear co-generation plant, conclusions are made as follows:

(1) Adopt integrated, forced circulation, self-pressure-stabalized water reactor.

(2) Reactor operation pressure lOMPa.

(3) Single-reactor power 400-600MWt, maximum to 1000KWt.

(4) Adopt water-water-steam main technological process and electricity supply depends on steam supply.

(5) No boric acid and simplified system.

This design also suits a small nuclear electric power plant But the heat exchangers should be replaced by steam generators in the reactor vessel.

The design can also be used for centralized heat supply in a city. On condition of not changing the reactor and the auxiliary system, only decreasing operation pressure and temperature, and the steam generator being replaced by the heat exchangers in the third circuit, this design would turn to be nuclear heat supply plant, while the research and experiment are not needed furthermore.

Natural circulation and forced circulation should be compared further in the future and the control rod drive mechanism type needs improving. A core with a high conversion ratio in a small reactor is worth researching further.

In summary, a small nuclear heat and electricity co-generation plant could become an economic, safe and clean energy source in a city or a large enterprise in the future. Its basic capital investment is low, the construction period is short, it has a wide range of uses, it has good prospects and it should have a proper position in the energy resource development of China.