Crisil has upgraded the Rs 1.91 billion non-convertible debenture programme of Tata Chemicals to 'AA+' with a stable outlook from 'AA' with a positive outlook. The upgrade is within the high safety grade. Crisil said the upgrade reflected the benefits that would accrue to Tata Chemicals following its acquisition of Hind Lever Chemicals, which is expected to reduce debt and interest costs.