Nuclear reactor and method of opening a nuclear reactor
A nuclear reactor includes a reactor pressure vessel housing plural fuel rods, the reactor pressure vessel having a vessel head. The reactor includes control rods. The control rods are inserted into the reactor between the fuel rods. The control rods are movable to control the power output of the reactor when it is critical, to generate power, and to put the reactor in a shutdown state. The reactor includes control rod drive mechanisms to move the control rods. The control rod drive mechanisms are controllable to release the control rods when a vessel opening operation is performed when the reactor is in the shutdown state and the vessel head is lifted upwards from the reactor pressure vessel so the control rods slide therethrough to remain stationary relative to the fuel rods. The reactor has a monitoring unit to identify whether a control rod is lifting with the vessel head.
1 . A nuclear reactor including:
a reactor pressure vessel housing plural fuel rods containing fissile material, the reactor pressure vessel having an upper, removable, vessel head;
control rods, each made of a neutron-absorbing material, the control rods being inserted into the reactor through the vessel head and between the fuel rods to control a rate of a fuel rods' fission reaction, whereby the control rods are movable over a first range of insertion positions relative to the vessel head to control a power output of the reactor when it is critical, to generate power, and to put the reactor in a sub-critical shutdown state; and
control rod drive mechanisms carried by the vessel head and operable to drive movements of the control rods;
wherein the control rod drive mechanisms are controllable to release the control rods when a vessel opening operation is performed when the reactor is in the shutdown state and the vessel head is lifted upwards from the reactor pressure vessel such that the control rods slide therethrough to remain stationary relative to the fuel rods to maintain the shutdown state;
wherein the reactor further comprises a monitoring unit to identify whether at least one control rod of the control rods is lifted with the vessel head and a control system, linked to the monitoring unt, and configured to terminate a lift of the vessel head during the vessel opening operation when the monitoring unit identifies the at least one control rod is being lifted with the vessel head.
2 . The nuclear reactor according to claim 1 , wherein the monitoring unit comprises any of: a plurality of position sensors; one or more neutron sensors; and one or more load sensors.
3 . The nuclear reactor according to claim 2 , wherein the monitoring unit includes:
the plurality of position sensors which detect the position of the control rods relative to the vessel head over the first range of insertion positions, and which further detect the positions of the control rods relative to the vessel head when the vessel head is lifted during the vessel opening operation and the control rods slide through the vessel head to identify whether the at least one control rod is lifted with the vessel head.
4 . The nuclear reactor according to claim 3 , wherein the control system is configured to control the vessel opening operation.
5 . The nuclear reactor according to claim 2 , wherein the monitoring unit includes the plurality of position sensors and each position sensor is formed by a row of induction coils which detect a local presence or an absence of a respective control rod.
6 . The nuclear reactor according to claim 1 , wherein the vessel head and any other components of the reactor lifted with the head form a reactor head package, and wherein the monitoring unit includes a load sensor which measures a weight of the reactor head package to identify whether the at least one control rod is lifted with the vessel head.
7 . The nuclear reactor according to claim 6 , wherein the control system is configured to control the vessel opening operation.
8 . The nuclear reactor according to claim 7 , wherein the control system is further programmed to compare the measured weight with a value of an expected weight of the reactor head package to identify from the measured weight whether the at least one control rod is lifted with the head.
9 . The nuclear reactor according to claim 1 , wherein the monitoring unit includes a neutron sensor which measures neutron population to identify whether the at least one control rod is lifted with the vessel head.
10 . The nuclear reactor according to claim 9 , wherein the control system is configured to control the vessel opening operation.
11 . The nuclear reactor according to claim 10 , wherein the control system is further programmed to compare the measured neutron population with a predetermined population level and/or to compare a rate of increase of the measured neutron population with a predetermined rate of increase to identify from the measured neutron population whether a control rod is lifted with the head.
12 . The nuclear reactor according to claim 1 , further including a control system which is programmed to control the vessel opening operation, the control system commanding termination of the vessel opening operation if it receives from the monitoring unit an indication that the at least one control rod is lifted with the head.
13 . The nuclear reactor according to claim 12 , wherein the control system returns the vessel head to the reactor pressure vessel if it receives from the monitoring unit an indication that the at least one control rod is lifted with the head.
14 . A method of opening a pressure vessel of a nuclear reactor;
wherein the reactor pressure vessel houses fuel rods containing fissile material and has an upper, removable, vessel head; wherein the reactor includes control rods, each made of a neutron-absorbing material, the control rods being inserted into the reactor through the vessel head and between the fuel rods to control a rate of a fuel rods' fission reaction, whereby the control rods are movable over a first range of insertion positions relative to the vessel head to control a power output of the reactor when it is critical and generating power, and to put the reactor in a sub-critical shutdown state; and wherein the reactor further includes control rod drive mechanisms carried by the vessel head and operable to drive movements of the control rods;
the method including steps of:
using the control rod drive mechanisms to move the control rods to an insertion position in which the reactor is in the shutdown state;
releasing the control rods from the control rod drive mechanisms;
lifting the vessel head upwards from the reactor pressure vessel such that the control rods slide therethrough to remain stationary relative to the fuel rods to maintain the shutdown state;
monitoring with a monitoring unit for identifying whether a at least one control rod of the control rods is lifting with the vessel head during the lifting of the head to open the pressure vessel; and
terminating, with a control system linked to the monitoring unit, the lifting of the vessel head when the monitoring unit identifies the at least one control rod is being lifted with the vessel head.
15 . The method of claim 14 , wherein terminating the lifting of the vessel head includes returning the vessel head to the reactor pressure vessel if the control rod is monitored to be lifted with the head.
16 . The method of claim 14 , wherein monitoring for identifying whether the control rod is lifted with the vessel head includes detecting the positions of the control rods relative to the vessel head, and comparing a rate of lift of the vessel head with the rates of change of the detected positions of the control rods relative to the head to identify from the detected positions the at least one control rod has been lifted with the vessel head.
17 . The method of claim 14 , wherein the vessel head and any other components of the reactor lifted with the head form a reactor head package, and the monitoring step includes measuring a weight of the reactor head package to identify whether the at least one control rod has been lifted with the vessel head.
18 . The method of claim 14 , wherein the monitoring for whether the control rod is lifting with the vessel head includes measuring neutron population to identify whether the at least one control rod has been lifted with the vessel head.