Integral isolation valve systems for loss of coolant accident protection

1. A nuclear island comprising:

a nuclear reactor including a nuclear reactor core comprising fissile material disposed in a reactor pressure vessel;

an emergency core cooling (ECC) system connected to the reactor pressure vessel through an ECC pressure vessel feedthrough;

a reactor coolant inventory and purification system (RCIPS) connected to the reactor pressure vessel to inject coolant into the reactor pressure vessel through a make-up line pressure vessel feedthrough and to extract coolant from the reactor pressure vessel through a let-down line pressure vessel feedthrough; and

an integral isolation valve (IIV) system including:

a passive IIV comprising a check valve built into a forged flange that is connected directly to the ECC pressure vessel feedthrough,

a passive IIV comprising a check valve built into a forged flange that is connected directly to the make-up line pressure vessel feedthrough, and

an active IIV comprising an active valve built into a forged flange that is connected directly to the let-down line pressure vessel feedthrough.

2. The nuclear island of claim 1 further comprising:

a residual heat removal (RHR) system having an RHR inlet connected to the reactor pressure vessel through an RHR pressure vessel inlet feedthrough and an RHR outlet connected to the reactor pressure vessel through an RHR pressure vessel outlet feedthrough;

wherein the IIV system further includes:

a passive IIV comprising a check valve built into a forged flange that is connected directly to the RHR pressure vessel outlet feedthrough, and

an active IIV comprising an active valve built into a forged flange that is connected directly to the RHR pressure vessel inlet feedthrough.

3. The nuclear island of claim 2 wherein the RHR system comprises an air- or water-cooled RHR heat exchanger.

4. The nuclear island of claim 2 further comprising:

a pressure sensor disposed in the reactor pressure vessel and configured to sense reactor coolant pressure; and

a reactor control system configured to close the active IIV connected directly to the RHR pressure vessel inlet feedthrough in response to the reactor coolant pressure sensed by the pressure sensor exceeding a threshold pressure.

5. The nuclear island of claim 1 further comprising:

a level sensor disposed in the reactor pressure vessel and configured to sense reactor coolant level;

a reactor control system configured to close the active IIV connected directly to the letdown line pressure vessel feedthrough in response to the reactor coolant level sensed by the pressure sensor falling below a threshold reactor coolant level.

6. A nuclear island comprising:

a nuclear reactor including a nuclear reactor core comprising fissile material disposed in a reactor pressure vessel that has a plurality of pressure vessel penetrations that exclusively carry flow into the reactor pressure vessel and at least one pressure vessel penetration that carries flow out of the reactor pressure vessel; and

an integral isolation valve (IIV) system including:

a plurality of passive IIVs each comprising a check valve built into a forged flange and not including an actuator, and

one or more active IIVs each comprising an active valve built into a forged flange and including an actuator,

wherein:

each pressure vessel penetration that exclusively carries flow into the reactor pressure vessel is protected by a passive IIV whose forged flange is directly connected to the corresponding pressure vessel penetration, and

each pressure vessel penetration that carries flow out of the reactor pressure vessel is protected by an active IIV whose forged flange is directly connected to the corresponding pressure vessel penetration.

7. The nuclear island of claim 6 wherein each pressure vessel penetration that carries flow out of the reactor pressure vessel exclusively carries flow out of the reactor pressure vessel.

8. The nuclear island of claim 6 wherein each active IIV further includes a manual backup for the actuator.

9. The nuclear island of claim 6 further comprising:

an emergency core cooling (ECC) system connected to the reactor pressure vessel through a pressure vessel penetration that exclusively carries flow into the reactor pressure vessel and is protected by a passive IIV whose forged flange is directly connected to the pressure vessel penetration.

10. The nuclear island of claim 6 further comprising:

a reactor coolant inventory and purification system (RCIPS) connected to the reactor pressure vessel to inject coolant into the reactor pressure vessel through a vessel penetration that exclusively carries flow into the reactor pressure vessel and is protected by a passive IIV whose forged flange is directly connected to the pressure vessel penetration.

11. The nuclear island of claim 10 wherein the RCIPS is further connected to the reactor pressure vessel to extract coolant from the reactor pressure vessel through a pressure vessel penetration that exclusively carries flow out of the reactor pressure vessel and is protected by an active IIV whose forged flange is directly connected to the pressure vessel penetration.

12. The nuclear island of claim 11 further comprising:

a residual heat removal (RHR) system having:

an inlet connected to the reactor pressure vessel through a pressure vessel penetration that exclusively carries flow out of the reactor pressure vessel and is protected by an active IIV whose forged flange is directly connected to the pressure vessel penetration, and

an outlet connected to the reactor pressure vessel through a pressure vessel penetration that exclusively carries flow into the reactor pressure vessel and is protected by a passive IIV whose forged flange is directly connected to the pressure vessel penetration.

13. The nuclear island of claim 6 further comprising:

a residual heat removal (RHR) system having:

an inlet connected to the reactor pressure vessel through a pressure vessel penetration that exclusively carries flow out of the reactor pressure vessel and is protected by an active IIV whose forged flange is directly connected to the pressure vessel penetration, and

an outlet connected to the reactor pressure vessel through a pressure vessel penetration that exclusively carries flow into the nuclear reactor pressure vessel and is protected by a passive IIV whose forged flange is directly connected to the pressure vessel penetration.

14. The nuclear island of claim 6 wherein the check valve of each passive IIV admits flow at above a threshold pressure into the reactor pressure vessel, while blocking flow otherwise.

15. The nuclear island of claim 6 wherein the active valve of each active IIV is a normally closed valve.

16. The nuclear island of claim 6 wherein the active valve of at least one active IIV is configured to be closed by reactor coolant pressure upon loss of actuator power.

17. A nuclear island comprising:

a nuclear reactor including a nuclear reactor core comprising fissile material disposed in a reactor pressure vessel;

a plurality of auxiliary systems in fluid communication with the reactor pressure vessel via pressure vessel penetrations wherein each said pressure vessel penetration is either a fluid inlet pressure vessel penetration carrying fluid into the reactor pressure vessel or a fluid outlet pressure vessel penetration carrying fluid out of the reactor pressure vessel; and

an integral isolation valve (IIV) system including:

at least one passive IIV comprising a check valve built into a forged flange and not including an actuator, and

at least one active IIV comprising an active valve built into a forged flange and including an actuator,

wherein:

each fluid inlet pressure vessel penetration is protected by a passive IIV whose forged flange is directly connected to the pressure vessel penetration, and

each fluid outlet pressure vessel penetration is protected by an active IIV whose forged flange is directly connected to the pressure vessel penetration.

18. The nuclear island of claim 17 wherein the plurality of auxiliary systems includes an emergency core cooling (ECC) system and a reactor coolant inventory and purification system (RCIPS).

19. The nuclear island of claim 18 wherein the plurality of auxiliary systems further includes a residual heat removal (RHR) system.