A nuclear reactor core comprising: a plurality of interchangeable components, wherein each interchangeable component of the plurality of interchangeable components is configured to affect a performance parameter of the core; and a plurality of configurable unit cells, wherein each configurable unit cell of the plurality of configurable unit cells is formed of a core block material, and wherein the plurality of configurable unit cells comprise: a standard unit cell comprising a first plurality of channels defined within the core block material, wherein each channel of the first plurality of channels is configured to engage an interchangeable component of the plurality of interchangeable components in an operating configuration; and a reactivity control cell comprising a second plurality of channels defined within the core block material, wherein each channel of the second plurality of channels is configured to engage an interchangeable component of the plurality of interchangeable components in the operating configuration, wherein at least one channel of the second plurality of channels is configured to engage a reactivity control rod; characterized in that the plurality of interchangeable components and the plurality of configurable unit cells (102, 104) are arranged in a plurality of rows, wherein at least one row of the plurality of rows overlaps an adjacent row of the plurality of rows such that unit cells of the at least one row and the adjacent row are offset from one another. a plurality of interchangeable components, wherein each interchangeable component of the plurality of interchangeable components is configured to affect a performance parameter of the core; and a plurality of configurable unit cells, wherein each configurable unit cell of the plurality of configurable unit cells is formed of a core block material, and wherein the plurality of configurable unit cells comprise: a standard unit cell comprising a first plurality of channels defined within the core block material, wherein each channel of the first plurality of channels is configured to engage an interchangeable component of the plurality of interchangeable components in an operating configuration; and a reactivity control cell comprising a second plurality of channels defined within the core block material, wherein each channel of the second plurality of channels is configured to engage an interchangeable component of the plurality of interchangeable components in the operating configuration, wherein at least one channel of the second plurality of channels is configured to engage a reactivity control rod; a standard unit cell comprising a first plurality of channels defined within the core block material, wherein each channel of the first plurality of channels is configured to engage an interchangeable component of the plurality of interchangeable components in an operating configuration; and a reactivity control cell comprising a second plurality of channels defined within the core block material, wherein each channel of the second plurality of channels is configured to engage an interchangeable component of the plurality of interchangeable components in the operating configuration, wherein at least one channel of the second plurality of channels is configured to engage a reactivity control rod; characterized in that the plurality of interchangeable components and the plurality of configurable unit cells (102, 104) are arranged in a plurality of rows, wherein at least one row of the plurality of rows overlaps an adjacent row of the plurality of rows such that unit cells of the at least one row and the adjacent row are offset from one another.