Zenith National Insurance Corp. in Woodland Hills will eliminate approximately 100 positions, or 6 percent of its workforce, to streamline its administrative cost structure in its workers’ compensation operations. Employees affected by the workforce cuts will receive severance payments, professional outplacement assistance and a special health insurance benefit in which Zenith will pay full premiums for up to 18 months. Because of the cuts, Zenith anticipates a one-time charge of approximately $5 million in the first quarter of 2009. This charge includes termination benefits of approximately $4.3 million, lease termination costs of approximately $0.3 million and miscellaneous costs of approximately $0.4 million, the company reported. These actions are expected to result in more than $10 million ($6.5 million after tax) of annualized expense savings, according to Zenith.