  It is often considered that a massive torus with solar mass or so surrounding
a stellar-mass black hole may be a central engine of a gamma-ray burst. We
study the properties of such massive accretion tori (or disks) based on the
$\alpha$ viscosity model. For surface density exceeding about $10^{20}$ g
cm$^{-2}$, which realizes when about a solar-mass material is contained within
a disk with a size of $\sim 5 \times 10^6$ cm, we find that (1) luminosity of
photons is practically zero due to significant photon trapping, (2) neutrino
cooling dominates over advective cooling, (3) pressure of degenerate electrons
dominates over pressure of gas and photons, and (4) magnetic field strength
exceeds the critical value of about $4 \times 10^{13}$ G, even if we take 0.1 %
of the equi-partition value. The possible observable quantum electrodynamical
(QED) effects arising from super-critical fields are discussed. Most
interestingly, photon splitting may occur, producing significant number of
photons of energy below $\sim 511$ keV, thereby possibly suppressing e$^\pm$
pair creation.
