There is a reference to kalaapa in "Abhidhammatha Sangaha: A Comprehensive Manual of Abhidhamma" by Ven. Aacariya Anuruddha and translated by Ven. Bhikkhu Bodhi with commentary by Ven. Sayadaw U Silananda and Ven Rewatadhamma.
You can also read about kalaapa here: http://www.accesstoinsight.org/lib/authors/khin/wheel231.html and do a text search for "kalapa".
- "The real meaning of Anicca is that Impermanence or Decay is the inherent nature of everything that exists in the Universe — whether animate or inanimate. The Buddha taught His disciples that everything that exists at the material level is composed of "Kalapas." Kalapas are material units very much smaller than atoms, which die out immediately after they come into being. Each kalapa is a mass formed of the eight basic constituents of matter, the solid, liquid, calorific and oscillatory, together with color, smell, taste, and nutriment. The first four are called primary qualities, and are predominant in a kalapa. The other four are subsidiaries, dependent upon and springing from the former. A kalapa is the minutest particle in the physical plane — still beyond the range of science today. It is only when the eight basic material constituents unite together that the kalapa is formed. In other words, the momentary collocation of these eight basic elements of behavior makes a man just for that moment, which in Buddhism is known as a kalapa. The life-span of a kalapa is termed a moment, and a trillion such moments are said to elapse during the wink of a man's eye. These kalapas are all in a state of perpetual change or flux. To a developed student in Vipassana Meditation they can be felt as a stream of energy."
There is an alternative tradition that does not take the abhidhamma as the word of the Buddha. Abhidhamma was developed after the Blessed One's parinibbaana and went through a period of development over 200-300 years until ancient Theravada Buddhists established the canonical texts. The abhidhamma doctrine was developed further in the commentaries which were not written down in the form that we have them now until about 1500 years ago by Ven. Buddhaghosa. During the past 1500 years many sub-commentaries have been written about the abhidhamma.
These days meditation teachers take various stands regarding the abhidhamma intepretation of the Dhamma. Some teachers ignore the abhidhamma and don't comment on it. Some teachers openly say that the abhidhamma distorts the Buddhadhamma. And yet other teachers teach in conformity with the orthodox abhidhamma doctrine. Ven. Pa Auk Sayadaw is in the later group.