JOIN USHe is survived by his wife Seetha, a son and a daughter.
Iyengar was renowned as a nuclear physicist with keen interest in developing indigenous experimental facilities.
He was the AEC chief and secretary, Department of Atomic Energy from 1990-93, his last official position before retirement. Later, he served briefly as scientific advisor to Kerala government in 1998, an official said.
A vocal opponent of the Indo-US nuclear agreement, Iyengar had been living a quiet, retired life in Mumbai's middle-class suburb of Deonar, in northeastern part of the city, since the past few years.
After graduating in physics from Trivandrum, Iyengar joined the famous Tata Institute of Fundamental Research in 1952 in Mumbai.
Three years later, he joined the then Atomic Energy Establishment, Trombay and was assigned to Chalk River Laboratories of the Canadian Atomic Energy Establishment.
After his return from Canada, Iyengar was involved in building several experimental facilities.
He was engaged in the design and setting up of the country's first fast reactor critical facility, Purnima-1, which achieved its first criticality May 18, 1972, paving the way for India's first peaceful nuclear experiment exactly two years later, on May 18, 1974, at Pokhran.
After serving in various capacities at the Bhabha Atomic Research Centre (BARC) Mumbai, Iyengar took over as its director in 1984.
During this time, he provided crucial leadership in resolving many technical challenges encountered in the commissioning of the indigenous research reactor Dhruva and directed the Indian Atomic Energy program during his tenure as AEC chairman.
Iyengar was conferred with various awards and honours in India and abroad, including the prestigious Bhatnagar Award in 1971 and the Padma Bhushan in 1975.