Incore monitoring method and incore monitoring equipment

• US 6,744,840 B2
• Filed: 09/27/2002
• Issued: 06/01/2004
• Est. Priority Date: 09/27/2001
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Hamada, Jun, Karino, Yoshiji
• Primary Examiner(s): Carone, Michael J.
• Assistant Examiner(s): MATZ, DANIEL R
• Application Number:
  US10/256,232
• Publication Number:
  US 20030128793A1
• Time in Patent Office: 613 Days
• Field of Search: 376/245, 376/254-255
• US Class Current: 376/254
• CPC Class Codes: G21C 17/108 Measuring reactor flux
• CPC Class Codes: Y02E 30/30 Nuclear fission reactors

Abstract

An incore monitoring method of a nuclear reactor, includes, measuring neutron flux levels at pitch levels corresponding to local power range monitor sensors arranged along an axial direction inside a detector assembly installed in a nuclear reactor; performing power calculation, including calculation of thermal characteristics, of fuel assembly group consisting of fuel assemblies adjacent to the corresponding detector assembly, based on indicated values of the local power range monitor sensors of the corresponding detector assembly at a first time, calculating thermal characteristics at a second, subsequent time in which the power calculation is not calculated, based on values indicated by the local power range monitor sensors and calculated thermal characteristics at the first time and values indicated by the corresponding local power range monitor sensors at the second time, and monitoring the calculated thermal characteristics.

Claims

1. An incore monitoring method of a nuclear reactor, comprising performing the following steps in order:

(1) measuring neutron flux levels at a plurality of pitch levels corresponding to a plurality of local power range monitor sensors arranged in an axial direction inside a detector assembly installed in the nuclear reactor;

(2) performing a power distribution calculation using a three-dimensional simulation to obtain a first calculation of thermal characteristics of a fuel assembly group consisting of fuel assemblies adjacent to the corresponding detector assembly, based on values indicated by the plurality of local power range monitor sensors of the corresponding detector assembly at a first time;

(3) performing during a first cycle at least one of (a) adjusting a reactor core flow rate for regulation reactor power and (b) operating control rods in the reactor core for regulation reactor core power;

(4) performing during said first cycle and after step (3) a plurality of second calculations of thermal characteristics in which the power distribution calculation is not performed, based on values indicated by the plurality of local power range monitor sensors at second times, subsequent to the first time, and based on the thermal characteristics calculated in the first calculation at the first time;

(5) monitoring during said first cycle and after steps (3) and (4), the plurality of thermal characteristics calculated during said first cycle in the plurality of second calculations;

(6) performing during a second cycle at least one of (a) adjusting a reactor core flow rate for regulation reactor power and (b) operating control rods in the reactor core for regulation reactor core power;

(7) performing during said second cycle and after step (6) said plurality of second calculations of thermal characteristics in which the power distribution calculation is not performed, based on values indicated by the plurality of local power range monitor sensors at third times, subsequent to the first and second times, and based on the thermal characteristics calculated in the first calculation at the first time; and

(8) monitoring during said second cycle and after steps (6) and (7), the plurality of thermal characteristics calculated during said second cycle in the plurality of second calculations.

2. The method as recited in claim 1, wherein:

at least one of steps (3) and (6) includes adjusting the reactor core flow rate; and

said method further comprises the step of;

suspending the adjusting of the reactor core flow rate when at least one of the monitored plurality of thermal characteristics calculated in the plurality of second calculations exceeds a limit.

3. The method as recited claim 1, wherein

at least one of steps (3) and (4) includes operating said control rods in said reactor core, said method further comprising the step of:

suspending the operating of the control rods when at least one of the plurality of thermal characteristics calculated in the plurality of second calculations exceeds a limit.

4. The method as recited in claim 1, wherein the first calculation and the plurality of second calculations are performed using a plurality of detector assemblies disposed adjacent fuel assemblies, said fuel assemblies being symmetrically disposed about a reactor core of the nuclear reactor so that each one quarter of the reactor core is identical with respect to the number and position of the fuel assemblies, and the plurality of local power range monitor sensors are non-symmetrically disposed adjacent to ones of the fuel assemblies so that each of the one quarter of the reactor core is different with respect to at least the position of the local power range monitor sensors.

5. The method as recited in claim 1, further comprising:

calculating thermal characteristics of one local power range monitor sensor based on values indicated by local power range monitor sensors being symmetrical to, and at the same pitch level of, the respective local power range monitor sensor in terms of a quarter of the reactor core in rotation or in an axis, provided the respective local power range monitor sensor outputs no signal.

6. The method as recited in claim 1, further comprising:

calculating thermal characteristics of a faulty local power range monitor sensor based on a mean value of values indicated by local power range monitor sensors being symmetrical to, and at the same pitch level of, positions adjacent to the respective faulty local power range monitor sensor in terms of a quarter of the reactor core in rotation or in an axis.

7. The method as recited in claim 1, wherein the first and plurality of second calculations of thermal characteristics includes a linear heat generation rate, and the method includes monitoring the linear heat generation rate.

8. The method as recited in claim 7, further comprising:

providing an alert signal when a maximum linear heat generation rate based on the monitored linear heat generation rate exceeds a predetermined limit.

9. The method as recited in claim 7, wherein

at least one of steps (3) and (4) includes operating said control rods in said reactor core, said method further comprising the step of:

acquiring a function designating a changing rate of the linear heat generation rate corresponding to the plurality of local power range monitor sensors with parameters of a changing rate of values indicated by the respective plurality of local power range monitor sensors and a position status of the control rod, based on values indicated by the plurality of local power range monitor sensors and the linear heat generation rate of the respective plurality of local power range monitor at the first time and second times, respectively, and;

correcting the calculated linear heat generation rate based on the function.

10. The method as recited in claim 7, further comprising:

calculating at least some of the plurality of second calculations of the thermal characteristics at a plurality of pitch levels of the plurality of local power range monitor sensors; and

calculating thermal characteristics at a pitch level in which no local power range monitor sensor exists based on the calculated thermal characteristics at the corresponding pitch levels.

11. The method as recited in claim 1, wherein the thermal characteristics includes a critical power ratio, and the method includes:

monitoring the critical power ratio calculated at the second times; and

providing an alert signal when a minimum critical power ratio based on the monitored critical power ratio exceeds a predetermined limit.

12. The method as recited in claim 11, wherein

at least one of steps (3) and (6) includes adjusting the reactor core flow rate;

and said method further comprises the steps of;

acquiring a function showing a correlation of a critical power and the reactor core flow rate based on the critical powers and the reactor core flow rate at the first time and second times; and

correcting the calculated critical power ratio based on the function.

13. Incore monitoring equipment of a nuclear reactor, comprising:

a detector assembly configured to be installed in the nuclear reactor, including local power range monitor sensors to measure neutron flux levels at a plurality of pitch levels;

a three-dimensional simulator for calculating a power distribution including a first calculation of thermal characteristics of a fuel assembly group consisting of fuel assemblies adjacent to the corresponding detector assembly, based on values indicated by the plurality of local power range monitor sensors of the corresponding detector assembly at a first time;

a control rod operation unit for operating control rods in a reactor core of the nuclear reactor to regulate reactor power, and for suspending operation of the control rods when the monitoring unit detects the thermal characteristics exceeds a predetermined limit;

a recirculation flow control unit for adjusting a reactor core flow rate to regulate reactor power, and for suspending adjustment of the reactor core flow rate when the monitoring unit detects the thermal characteristics exceeds a predetermined limit;

a calculating unit for performing during a first cycle and after operation of at least one of said control rod operation unit and said recirculation flow control unit, a plurality of second calculations of thermal characteristics in which the power distribution calculation is not performed, based on values indicated by the plurality of local power range monitor sensors at a second time, subsequent to the first time, and based on the first calculated thermal characteristics at the first times;

said calculating unit operative for performing during a second cycle, subsequent to said first cycle, and after operation of at least one of said control rod operation unit and said recirculation flow control unit, said plurality of second calculations of thermal characteristics in which the power distribution calculation is not performed, based on values indicated by the plurality of local power range monitor sensors at a third time, subsequent to the second time, and based on the first calculated thermal characteristics at the first time;

a monitoring unit, operative, after said calculating unit performs said plurality of second calculations during said first cycle, for monitoring said plurality of thermal characteristics calculated during said first cycle; and

said monitoring unit operative, after said calculating unit performs said plurality of second calculations during said second cycle, for monitoring said plurality of thermal characteristics calculated during said second cycle.