* Sudden departure a blow to MUFG succession plans
* Move not expected to have immediate impact on management
* MUFG expected to name Kanetsugu Mike as successor -sources (Adds detail, context)
By Taro Fuse and Taiga Uranaka
TOKYO, May 23 (Reuters) - The head of the Bank of Tokyo-Mitsubishi UFJ (BTMU), the core business of Japan's biggest "megabank," has decided to step down for health reasons barely a year into the job, sources told Reuters on Tuesday.
President and CEO Takashi Oyamada's departure disrupts parent Mitsubishi UFJ Financial Group's (MUFG) meticulous succession planning but is not expected to have an immediate impact on the management of Japan's largest lender by assets.
The MUFG board is expected to name Deputy President Kanetsugu Mike as Oyamada's replacement on Wednesday, said the sources, one of whom was involved in the decision and two of whom were briefed on the change.
The sources would not elaborate on Oyamada's health condition and an MUFG spokesman declined to comment. Oyamada, who took the helm of BTMU in April last year, had widely been seen as a successor to Nobuyuki Hirano as head of the MUFG holding company.
Like Oyamada, successor Mike is a career insider, having joined Mitsubishi Bank in 1979. He served as head of MUFG's global business group until this month.
MUFG is renowned for its careful grooming of candidates for top posts. But the sudden change is not expected to have an immediate impact because MUFG chief Hirano remains in charge of the financial conglomerate and its 300 trillion yen ($2.7 trillion) in assets. ($1 = 111.1100 yen) (Editing by William Mallard and David Goodman)