 In contrast to the NRC's decision, Ma believed that computer codes used to analyze the modified design were not precise enough and some of the materials used were too brittle.A US consultant engineer has also criticized the AP1000 containment design arguing that, in the case of a design-basis accident, it could release radiation; Westinghouse has denied the claim.The NRC completed the overall design certification review for the amended AP1000 in September 2011.