CNNC said the fuel loading took place on 9 July, marking the first nuclear power unit under construction in China to accomplish fuel loading period this year.
Tianwan-5 is a 1,000-MW pressurised water reactor of the domestically developed CNP-1000 design. It is seen as a Generation II+ design and a precursor to Generation III designs. Another unit of the same design, Tianwan-6, is also under construction at the site.
Construction of Tianwan-5 began in December and of Tianwan-6 in September 2016.
There are also four Russia-procured VVER-1000 nuclear units in commercial operation at Tianwan.
A report this week by the China Nuclear Energy Association said China is expecting to build between six and eight new nuclear reactor units between 2020 and 2025.
The report, quoted by the state-run China Daily, estimated the total operational nuclear capacity at 70 GW by the end of 2025, with another 30 GW of capacity under construction.