TOKYO (Reuters) - A lack of preparation and poor communication at top levels after disaster struck were among the failures that turned a nuclear accident at Japan's Fukushima plant into the worst atomic crisis in 25 years, a panel probing the disaster said on Monday. The panel -- headed by an expert in why big mistakes are made -- said Tokyo Electric Power, the utility operating Fukushima's tsunami-wrecked Daiichi nuclear power plant, as well as regulators failed to sufficiently anticipate a massive tsunami and the devastating impact likely to result.