A discussion of the plans for the HyperKamiokande detector was given by Gabriella Catanesi. Hyper-K would be a multi-purpose experiment, not just doing neutrino oscillation physics, but also offering nucleon decay discovery potential, and neutrino astrophysics.
There are two tanks of 260 kton total volume, 10 times the SuperKamiokande fiducial volume. 60 meters in height by 74 in diameter. The location is very close to the Kamioka mine, under mount Nijugo-yama. The baseline from T2K is the same.
The detector will benefit from a continuous upgrade of the neutrino beam from J-PARC until 2030. Also a near detector upgrade is under consideration by T2K. One problem is the statistics this will provide, but another is a strong reduction of systematics in the T2K-II era. The project is to upgrade the detector by adding new TPCs.
Adding cherenkov detectors at 1 or 2 km from the source would provide further reduction of systematic uncertainties. There are two proposals at the moment: one an off-axis angle-spanning orientation, and another is a Gd-loaded magnetized muon-range detector. The systematics one wants are down to 3-4%, which is what one needs in Hyper-Kamiokande.
The experiment in 10 years of running would be doing electron-neutrino appearance measurements achieving discrimination of different values of delta as a function of neutrino energy. HK could exclude sin(delta_CP)=0 and demonstrate CP violation at discovery-level significance for 62% of the delta_CP values, with resolutions on the parameter varying from 7 to 21%.