Flux-shifting reactivity control system

Abstract

A control assembly for a nuclear reactor includes a first reactivity control assembly having a first neutron modifying material, a second reactivity control assembly having a second neutron modifying material, and at least one drive mechanism coupled to the first neutron modifying material and the second neutron modifying material. The first neutron modifying material and the second neutron modifying material are selectively repositionable relative to a fuel region of the nuclear reactor. The at least one drive mechanism is configured to provide the first neutron modifying material and the second neutron modifying material in different directions through the fuel region thereby shifting a flux distribution within the fuel region away from the second neutron modifying material.

What is claimed is: 
     
         1 . A method comprising:
 sustaining a nuclear fission reaction within a fuel region of a nuclear reactor core, the nuclear reactor core having first moveable control assemblies insertable into a first side of the fuel region of the nuclear reactor core and second control assemblies insertable into a second opposing side of the fuel region of the nuclear reactor core, wherein the sustaining operation includes
 moving at least one assembly of the first and second control assemblies into a first insertion configuration of the first and second control assemblies within the fuel region of the nuclear reactor core; and 
 moving at least one assembly of the first and second control assemblies into a second insertion configuration of the first and second control assemblies within the fuel region of the nuclear reactor core, wherein the first and the second insertion configurations sustain the nuclear fission reaction. 
   
     
     
         2 . The method of  claim 1 , further comprising:
 wherein the nuclear fission reaction yields a first neutron flux distribution dependent on the first insertion configuration of the first and second control assemblies; and   wherein the nuclear fission reaction yields a second neutron flux distribution dependent on the second insertion configuration of the first and second control assemblies.   
     
     
         3 . The method of  claim 2 , wherein the second nonzero neutron flux distribution is satisfied by a target total neutron flux over a predetermined period of time. 
     
     
         4 . The method of  claim 2 , wherein the first flux distribution differs axially from the second nonzero flux distribution. 
     
     
         5 . The method of  claim 2 , wherein the first flux distribution differs radially from the second nonzero flux distribution. 
     
     
         6 . The method of  claim 1 , further comprising:
 moving at least one assembly of third moveable control assemblies insertable into a third side of the nuclear reactor core section, the third moveable control assemblies being insertable into the nuclear reactor core section at a different angle than the first and second control assemblies.   
     
     
         7 . The method of  claim 1 , wherein the moving operation further comprises:
 moving at least one assembly of the first control assemblies and at least one assembly of the second control assemblies in at least a first direction, wherein the axial distance between the at least one moved assembly of the first control assemblies and the at least one moved assembly of the second control assemblies remains substantially constant during the moving operation.   
     
     
         8 . The method of  claim 1 , wherein the moving operation further comprises:
 moving at least one assembly of the first control assemblies and at least one assembly of the second control assemblies, wherein the distance between the at least one moved assembly of the first control assemblies and the at least one moved assembly of the second control assemblies is core symmetric.   
     
     
         9 . The method of  claim 1 , wherein the moving operation further comprises:
 moving at least one assembly of the first control assemblies and at least one assembly of the second control assemblies, wherein the axial distance between the at least one moved assembly of the first control assemblies and the at least one moved assembly of the second control assemblies changes during the moving operation.   
     
     
         10 . The method of  claim 1 , wherein the nuclear fission reaction is a standing wave reaction. 
     
     
         11 . The method of  claim 10 , wherein the first control assemblies and second control assemblies are disposed on substantially opposing sides of the standing wave reaction. 
     
     
         12 . The method of  claim 1 , wherein at least one of the first or second control assemblies include a poison. 
     
     
         13 . The method of  claim 1 , wherein the second neutron flux distribution is satisfied by a target total neutron flux over a predetermined period of time in a predetermined fuel region within the nuclear reactor core section. 
     
     
         14 . A system comprising:
 a nuclear reactor core including a fuel region;   first control assemblies insertable into a first side of the fuel region, the first control assemblies moveable into a plurality of first insertion configurations; and   second control assemblies insertable into a second opposing side of the fuel region, the second control assemblies moveable into a plurality of second insertion configurations, wherein at least one of the first insertion configurations and at least one of the second insertion configurations sustain a nuclear fission reaction.   
     
     
         15 . The system of  claim 14 , further comprising:
 one or more drive mechanisms operably coupled to the first control assemblies and second control assemblies and configured to move the first control assemblies into a first insertion configuration and second control assemblies into a second insertion configuration to sustain the nuclear fission reaction in the fuel region according to a target nonzero neutron flux distribution.   
     
     
         16 . The system of  claim 14 , further comprising a drive mechanism including an actuator coupled to the first control assemblies and second control assemblies and configured to selectively reposition the first control assemblies and second control assemblies relative to the fuel region. 
     
     
         17 . The system of  claim 15 , wherein the target nonzero neutron flux distribution is a total neutron flux over a predetermined period of time. 
     
     
         18 . The system of  claim 15 , wherein the target nonzero neutron flux distribution is a total neutron flux over a predetermined period of time in a predetermined portion of the fuel region. 
     
     
         19 . The system of  claim 15 , wherein the target neutron flux distribution corrects one or more axial asymmetries in a neutron flux distribution in the nuclear reactor core. 
     
     
         20 . The system of  claim 15 , wherein the target flux distribution differs axially from a neutron flux in the nuclear reactor core. 
     
     
         21 . The system of  claim 15 , wherein the target flux distribution differs radially from a neutron flux in the nuclear reactor core. 
     
     
         22 . A nuclear fission reactor comprising:
 means for sustaining a nuclear fission reaction within a fuel region of a nuclear reactor core, the nuclear reactor core having first moveable control assemblies insertable into a first side of the fuel region of the nuclear reactor core and second control assemblies insertable into a second opposing side of the fuel region of the nuclear reactor core;   means for moving at least one assembly of the first and second control assemblies into a first insertion configuration of the first and second control assemblies with the fuel region of the nuclear reactor core and for moving at least one assembly of the first and second control assemblies into a second insertion configuration of the first and second control assemblies within the fuel region of the nuclear reactor core, wherein the first and the second insertion configurations sustain the nuclear fission reaction.   
     
     
         23 . The nuclear fission reactor of  claim 22 , wherein the means for moving further comprises repositioning means for selectively repositioning the first control assemblies and second control assemblies relative to the fuel region. 
     
     
         24 . The nuclear fission reactor of  claim 22 , further comprising:
 means for detecting a current neutron flux distribution within the fuel region.   
     
     
         25 . The nuclear fission reactor of  claim 23 , wherein the means for detecting a current neutron flux distribution includes a neutron flux monitor. 
     
     
         26 . The nuclear fission reactor of  claim 23 , wherein the means for detecting a current neutron flux distribution includes a temperature sensor. 
     
     
         27 . The nuclear fission reactor of  claim 23 , wherein the means for detecting a current neutron flux distribution includes a neutron flux model. 
     
     
         28 . The nuclear fission reactor of  claim 22 , further including means for moving at least one assembly of a third control assembly into a third insertion configuration of the first, second, and third control assemblies within the nuclear reactor core section to yield a third nonzero neutron flux distribution dependent on the third insertion configuration of the first, second, and third control assemblies. 
     
     
         29 . The nuclear fission reactor of  claim 22 , wherein the means for moving at least one assembly of the first and second control assemblies into a second insertion configuration of the first and second control assemblies within the nuclear reactor core section to yield a second nonzero neutron flux distribution dependent on the second insertion configuration of the first and second control assemblies includes a first actuator coupled to the at least one assembly of the first control assembly and a second actuator coupled to the at least one assembly of the second control assembly. 
     
     
         30 . The nuclear fission reactor of  claim 22 , further comprising control means for controlling the means for moving at least one assembly of the first and second control assemblies into a second insertion configuration of the first and second control assemblies within the nuclear reactor core section to yield a second nonzero neutron flux distribution dependent on the second insertion configuration of the first and second control assemblies. 
     
     
         31 . The nuclear fission reactor of  claim 30 , further comprising wherein the second nonzero neutron flux distribution is satisfied by a target neutron flux distribution. 
     
     
         32 . The nuclear fission reactor of  claim 31 , wherein the target neutron flux distribution is a total neutron flux over a predetermined period of time. 
     
     
         33 . The nuclear fission reactor of  claim 31 , wherein the target neutron flux distribution is a total neutron flux over a predetermined period of time within a predetermined portion of the fuel region. 
     
     
         34 . The nuclear fission reactor of  claim 31  wherein the target nonzero flux distribution corrects one or more axial asymmetries in a neutron flux distribution. 
     
     
         35 . The nuclear fission reactor of  claim 22 , wherein the nuclear fission reaction is a standing wave reaction. 
     
     
         36 . The nuclear fission reactor of  claim 35 , wherein the first and second control assemblies within the fuel region of the nuclear reactor core are disposed on substantially opposing sides of the standing wave reaction. 
     
     
         37 . The nuclear fission reactor of  claim 22 , wherein the first and second control assemblies within the fuel region of the nuclear reactor core include a poison.