Excise exemption for prilled ammonium nitrate: no duty chargeable and no Modvat credit on melt derived material. Prilled ammonium nitrate obtained from ammonium nitrate melt is not excisable because the conversion does not produce new excisable goods; Collectors must ensure no Central Excise duty is levied and no Modvat credit of such duty is allowed, and pending assessments must be finalised accordingly.