Energy companies cannot be charged a fully commercial price for disposing of nuclear waste without "killing the prospect" of a new generation of reactors, a senior UK government adviser will warn today. The analysis will spur opposition to Britain's contentious drive to expand its nuclear capacity. Gordon Brown, the prime minister, will today underscore his determination to attract investors to build new reactors at his summit with Nicolas Sarkozy, the French president. The UK government has insisted that the utility companies vying to build a raft of new nuclear power stations will bear their "full share" of decommissioning and waste disposal costs. Ministers have agreed to cap the liability the companies will bear for the disposal of the waste but they insist it is "very unlikely" that the new plants will add to the estimated