Hydro’s executive vice president of primary metals, Hilde Merete Aasheim, said redundancies would cost 200 million Krona, or about $30 million.

The closure would result in an ‘‘impairment charge’’ of about 1.2 billion Krona, or $200 million, relating to the value of the smelter in Hydro’s accounts.

Mr Aasheim said both items would be excluded from Hydro’s underlying earnings before income tax.

The cost of the redundancies would be more than offset by a release of working capital.

The smelter closure was described as a ‘‘proposal’’ last month but this week’s board decision in Norway clears the way for local management to start the shutdown.

‘‘The decision is a response to the weak macro-economic environment, with low metal prices, uncertain market outlook and overcapacity in the aluminium industry, in combination with a strong Australian dollar,’’ Mr Aasheim said.

About 150 people had already been laid off in recent months with the closure of one of the smelter’s three potlines and another 340-odd Hydro workers and another 50 or so contractors will lose their jobs in the full shutdown.

When the closure was announced, Hydro said the Kurri plant was losing about $7 million a month and trading conditions were unlikely to improve in the medium term.

Norsk Hydro is an aluminium and renewable energy company that employs about 20,000 people worldwide and has its headquarters in Oslo, Norway.