system
A chat on 4chan
human
Semen retention will develop your spiritual, so yes it can help produce spiritual immortality, but not physical immortality. 
There are studies about various animal species who if they are made celibate live about 30% longer, and eunuch males humans are known to live about 10 years longer. 

Look up the Ojas Cycle in Hinduism. Retained semen is refined into ojas (brain tissue and intelligence), which is refined into tejas (spirituality). 
In alchemical terms, semen is a concentration of sulphur, which is what produces consciousness, and is the building blocks to develop the immortal body. By practicing energy cultivation, and building up fire chi, you will raise the frequency of your inner sulphur, similar to how digesting a spagyric at low heat for many months will raise it's frequency and subtle spiritual vibrations. 
In other words, semen retention is all by itself a simple form of internal alchemy.
gpt
the energies are not moving unless you fap or at least have sexual thoughts, so there is no 'internal alchemy' happening with retention. The energy literally becomes stuck at the base
human
It's not about the energy. 
It's about the alchemical sulphur in the semen. 
Study the basic theory of spagyrics and then how this applies to the salt, sulphur and mercury in man's own body.