Utilizing Decay Heat via Steam Cycles to Produce Electric Power on Site to Eliminate Accidents Caused by Station Blackout in Nuclear Power Plants

Abstract

This invention fundamentally changes the basic design principles adopted over the last 50 years that addresses the basic root cause for the station blackout threat faced by all nuclear power plants. The Fukushima nuclear accident that occurred in Japan in 2011 could have turned benign had the plant implemented this invention. It uniquely utilizes the decay heat directly from the reactor core through steam cycles to produce useable power onsite with one or a number of steam turbines of less capacities in combination with compatible electric generators. Such arrangement is reliable to be the onsite energy source. The electric power produced by generators attached to these steam turbines could support necessary all safety functions. The result is that during the first week of urgent threat to the nuclear reactor, there will always be electric power available to run the safety equipment, computers, lighting and other vital devices continuously.

Claims

1. A nuclear power plant including major pieces of equipments: a separate and special steam turbine that has less the capacity of the main steam turbine; and a separate and special electricity generator connected to the said turbine that has less the capacity of the main generator; a steam line branched off the main steam line furnishing the steam to drive the said turbine; a relay arrangement connected to the said generator; a direct current conversion equipment connected to the said relay arrangement; an alternating current equipment connected to the said relay arrangement.

2. The nuclear power plant according to claim 1, comprising a valve in the said branched off steam line with a control device taking signal from a control signal switch, the said control signal switch takes signals generated by the reactor control rod positions.

3. The nuclear power plant according to claim 1, comprising a power relay control switch connected to the said direct current conversion equipment and connected to the offsite power line of converted direct current to deliver direct current to the plant direct current buses.

4. The nuclear power plant according to claim 3, comprising rechargeable batteries that connected to the said power control switch.

5. The nuclear power plant according to claim 1, comprising control valves for diverting steam from the said branched off stem line to the said steam turbine through a multistage arrangement considering the various levels of stem flows.

6. The nuclear power plant according to claim 5, comprising controls that delivering signals for the open sizes for the said control valves for modulating the steam flows from the said branched off steam line through the said multistage arrangement.

7. The nuclear power plant according to claim 1, the said branched off steam line branched off the main steam line furnishing the steam to drive the said turbine such that the steam is produced from the decay heat as the residual heat generated by the nuclear reactor core after shutdown.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0081] FIG. 1 shows the characteristics of the decay heat that is decreasing with time.

[0082] FIG. 2 is a structural diagram showing a boiling water reactor based nuclear power plant according to Embodiment 1.

[0083] FIG. 3 is a structural diagram showing a pressurized water reactor based nuclear power plant according to Embodiment 2.

[0084] FIG. 4 is a structural diagram showing the major equipments and devices with required arrangements and needed rechargeable batteries to eliminate the station blackout conditions for a nuclear power plant according to Embodiment 3.

[0085] FIG. 5 is a structural diagram showing the major equipments and devices with required arrangements and the needed multistage steam turbine to eliminate the station blackout conditions for a nuclear power plant according to Embodiment 4.

DETAILED DESCRIPTION OF THE INVENTION

Detailed Description of the Preferred Embodiments

Working Principles

[0086] When the reactor in a nuclear power plant is shut down, the initial decay heat level is rough at 6.5% of the previous operating power. Then it will decrease exponentially with time. The heat level will decrease to 1.5% in an hour, to 0.4% at the end of the first day, and to rough 2% at the end of a week. For a typical 1000 MWe nuclear plant, at the end of 3.sup.rd day the decay heat could still be available to generate electricity at roughly 2.8 MWe which is a significant power level for use on site. This invention overcomes the perceived impediments for utilizing the decay heat for this purpose. A decay heat of decreasing nature is illustrated by FIG. 1.

[0087] The engineering principle for this invention is illustrated by the arrangements described in the next example which is applicable to BWRs as well as PWRs. While only BWR and PWR examples are given, the invention is equally applicable to any reactor designs using water or heavy water as either the primary or secondary coolant.

[0088] For the first day after the reactor is shut down, at the end of the day the decay heat level will be at 0.5% of the full power level. A control system will set up and manage the arrangement that the steam produced during the first day either from a BWR directly or from steam generators of a PWR is channeled to a set of a multistage small size of turbine connected to generators to produce electricity. The number of the turbines and the streamlined generators used to produce electricity depends on the capacities adopted for this application. The generators are elected to be compatible with the amount of steam produced during the first day of shut down such that the steam production shall match with the electricity output that the five generators are capable of producing.

Embodiment 1

[0089] A nuclear power plant based on a boiling water reactor consists of a reactor vessel 5 with a reactor core 7. The reactor vessel is housed in a reactor containment as shown in FIG. 2. The feedwater lines 11 are delivering water to the reactor vessel to cool the reactor core 7. The heat generated by the reactor core 7 will convert the water inside the reactor vessel to steam. The steam produced in the reactor core 7 will go forward in the main steam line 16 and eventually to the main turbine that connected to the main generator to produced the electricity.

[0090] A branched off steam line 39 is directed to an Isolation Condenser 10 for passive cooling. Another branched off steam line is also designed to drive a steam driven turbine that could drive water pumps for other engineering applications. Note that not all BWRs incorporate an Isolation Condenser in their design as is discussed in the current example. Some include turbine driven standby emergency pumps (e.g., Reactor Core Isolation Cooling and/or High Pressure Coolant Injection). The invention is equally applicable to these BWR design variants.

[0091] The devices and equipment for this invention are added in a new branched off steam line 33, that is branched off the main steam line 16. A control valve 34 is installed as a switch to control the steam flow in Line 33. A valve control unit 35 is designed to take the control signals from Control Unit 8 that relies on the control rods that control the reactor power.

[0092] The branched off steam line 33 will be fed into a specially designed turbine 1 uniquely added for this invention. The turbine 1 is connected to a special generator 2 that produces electricity by the motion of the generator. The turbine 1 and the generator 2 are utilizing the steam generated by the decay heat to generate electricity such that the station blackout would never occur in a nuclear power plant.

[0093] The generator 2 that produces electricity is connected to an array arrangement 41. The electricity is then distributed by the array arrangements to the direct current (DC) buses 3 and the alternating current (AC) buses 4 for the electric equipments used in the plants.

Embodiment 2

[0094] A nuclear power plant based on a pressurized water reactor consists of a reactor vessel 5 with a reactor core 7. The reactor vessel is housed in a reactor containment as shown in FIG. 3. The hot legs 26 will take the coolant heated by the core 7 through steam generator tubes to steam generators 30 in which steam is produced. After the steam is generated and the coolant is cooled down by having transferred heat to steam generators, the coolant will be diverted to the cold legs through the pumping efforts by the Reactor Coolant Pumps 28 and the coolant will be further delivered into the reactor pressure vessel 5.

[0095] The feedwater lines 31 supply water to steam generators 30. The steam is produced utilizing the heat inside the steam generator tubes 29 from the water delivered from the feedwater lines 31. The produced steam is then sent through the main steam line 32 to the main turbine (not shown) connected to the main generators (not shown).

[0096] The unique devices and equipment for this invention are added in a new branched off steam line 33, that is branched off the main steam line 32. A control valve 34 is installed as a switch to control the steam flow in Line 33. A valve control unit 35 is designed to take the control signals from Control Unit 8 that relies on the control rods that control the reactor power.

[0097] The branched off steam line 33 will be fed into a specially designed turbine 1 uniquely added for this invention. The turbine 1 is connected to a special generator 2 that produces electricity by the motion of the generator. The turbine 1 and the generator 2 are utilizing the steam generated by the decay heat to generate electricity such that the station blackout would never occur in a nuclear power plant.

[0098] The generator 2 that produces electricity is connected to an array arrangement 41. The electricity is then distributed by the array arrangements to the direct current (DC) buses 3 and the alternating current (AC) buses 4 for the electric equipments used in the plants.

Embodiment 3

[0099] The unique devices and equipment for this invention are described by this embodiment as shown in FIG. 4. The turbine 1 is connected to a special generator 2 that produces electricity by the motion of the generator. The turbine 1 and the generator 2 are utilizing the steam generated by the decay heat to generate electricity such that the station blackout would never occur in a nuclear power plant.

[0100] The generator 2 that produces electricity is connected to an array arrangement 41. The electricity is then distributed by the array arrangements to the direct current (DC) buses 3 and the alternating current (AC) buses 4 for the electric equipments used in the plants. Normally during non-accident conditions, when a nuclear power plant is shutdown, the offsite power lines 17 are utilized to deliver power for the onsite use to run safety and non-safety equipments and devices. The offsite power 17 will go through a general control 20 and get converted to the direct current (DC) for onsite use with the connections to the DC buses 21. The general control will also branch off 18 the offsite AC power to the onsite AC power buses 19 through a connecting controls 23, 24 and distributes AC power to safety and non-safety equipments and devices 25.

[0101] When the reactor is shutdown, the decay heat presented at the beginning in the reactor is 6% of the full power. As time progresses, the decay heat will be decreasing. The decreasing characteristics is shown in FIG. 5. To compensate the less production of electricity at later time by this invention, rechargeable batteries 42 are used to store the higher electricity production at early stage using this invention.

Embodiment 4

[0102] The unique devices and equipment for this invention are described by this embodiment as shown in FIG. 5. The turbine 1 is connected to a special generator 2 that produces electricity by the motion of the generator. The turbine 1 and the generator 2 are utilizing the steam generated by the decay heat to generate electricity such that the station blackout would never occur in a nuclear power plant. The electricity is distributed by the array arrangements to the direct current (DC) buses 3 and the alternating current (AC) buses 4 for the electric equipments used in the plants.

[0103] The turbine 1 takes the steam delivered from a branched off steam line 16, 33 that is connected to the main steam line (not shown.) The steam is delivered to the turbine 1 through a multistage arrangement. This arrangement consists of several valves 37 and their associated controls 38 with a main valve 34 upstream of the steam line. Such main valve is controlled by a special control 35 that takes signals from a signal control switch 8. The signal controls switch 8 takes signals from the reactor control rod drives as the operations of this invention is initiated when the reactor is shutdown. The control unit 8 can be overridden by an external signal to begin the operations of this invention, a separate and isolated turbine and generator unit to produce electricity on site when all planned and installed power becomes unavailable.