Noun, する verb, and の adjective
るいせき
日本政府が巨額の国債を累積していることについて、あなたはどのようにお考えですか。
How do you think the Japanese government accumulated such a great amount of national debt?
Accumulate and accumulate make accumulation!
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.