The research problem of in-core detector placement optimization is applied to Indian Advanced Heavy Water Reactor (AHWR). AHWR is a 300 MWe thorium fuel based vertical pressure tube type thermal reactor with heavy water as moderator and boiling light water under natural circulation as coolant. The core radius of AHWR is neutronically large and is more likely to experience spatial flux tilts. In such large nuclear reactors, for better regulation and protection, neutron flux is monitored by Online Flux Mapping System (OFMS) at regular intervals. OFMS provides detailed neutron flux distribution information to the operator and is used to ensure that the design parameters such as hot channels, zonal power, channel power, etc are well within their prescribed limits. For effective monitoring of neutron flux inside the reactor, the most ideal way is to place in-core SPNDs at all possible locations. However, such placement is not pragmatic given high maintenance and operational costs. Therefore, it is important to optimize the number and locations of in-core SPNDs so as to retrieve as much information as possible.

Recently, a clustering technique called Bond Energy Algorithm (BEA) has been used to optimize sensor locations in nuclear reactors and in other areas such as structural health monitoring, product design and development, etc. This technique uses correlation as the parameter for grouping SPNDs as clusters. Higher correlation among SPNDs corresponds to greater redundancy. Therefore, selection of SPNDs with minimal association can provide more independent information of the reactor configuration. BEA calculates bond energy among all SPNDs based on a correlation matrix and then transforms them into blocks of sub-matrices. Each sub-matrix is considered as one group within which SPNDs are strongly correlated. Optimal SPNDs locations can be determined from the sub-matrices directly.

The accuracy of the neutron flux estimation is dependent not only on placement of in-core SPNDs but also on the mathematical model of the reactor and the flux reconstruction technique. The typical algorithms for flux reconstruction available in literature are Flux Synthesis Method (FSM) and Modified Flux Synthesis Method (MFSM). Both the algorithms use in-core SPND readings and eigenmodes of the reactor configuration to reconstruct the flux distribution. FSM uses eigenmodes of the nominal reactor configuration whereas MFSM uses the fundamental eigenmode of the actual reactor configuration and other higher eigenmodes of the nominal configuration thereby improving accuracy. A Subspace Iteration (SSI) scheme has been employed to generate several eigenmodes simultaneously which have been used in an Improved MFSM (IMFSM) for reconstruction, for the proposed research work.   

AHWR houses in-core detector units with SPNDs distributed axially to monitor the three-dimensional neutron flux distribution. This paper attempts to optimize the number and locations of SPNDs through application of BEA and validate the SPNDs for various operational reactor configurations using FSM, MFSM and IMFSM.


Optimization of In-Core Detector Locations in AHWR Using Bond Energy Algorithm

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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