By Ron Bousso LONDON (Reuters) – Shell will write down up to $5 billion following its decision to exit Russia, more than previously disclosed, while soaring oil and gas prices boosted trading activities in the first quarter, the company said on Thursday. The post-tax impairments of between $4 billion and $5 billion in the first quarter will not impact the company’s earnings, Shell said in an update ahead of its earnings announcement on May 5. Shell, whose market capitalisation is around $210 billion, had previously said the Russia writedowns would reach around $3.4 billion. The increase was du…