The short answer is it adds a bit more into the rewards pool each block. The exact amount is a little complicated, but the formula is 65% of the new inflation that is generated each block.
At block 7,000,000 Hive had a 9.5% inflation rate, which decreases at a rate of 0.01% every 250k blocks. We are currently on block 56,713,563, so the inflation rate is 7.52%.
The inflation is based on the virtual supply of HIVE, which is currently 412,688,638.
If you take the current virtual supply times the current inflation, you get an estimated annual inflation of 31,034,185 HIVE. (Note this is estimated because the virtual supply will change over time.)
If you take the annual inflation amount and divide it by 365, you will get a daily inflation amount of 85,025 HIVE. This is a rough estimate of how much new HIVE is generated by the protocol each day.
There is a new block every 3 seconds, so that means there are 28,800 blocks per day. 85,025 HIVE per day divided by 28,800 blocks is about 2.95 new HIVE per block.
The rewards pool gets 65% of that, so about 1.92 new HIVE is added to the rewards pool each block based on the current inflation rate and virtual supply. I believe this is the answer you are looking for :)
The amount that the rewards pool is worth will go up or down with the price of HIVE though. For example, there is currently 808,277 HIVE in the rewards pool worth approximately $371k. If the price of HIVE were to 2x, then the same rewards pool would be worth $742k.
The last thing to keep in mind is that the rewards pool is being used for payouts each block too, so as new rewards are being added to the pool, rewards are also being subtracted too. The formula for payouts is very complex, although basically it aims to keep the pool in a state of equilibrium where the amount going out is roughly equal to the amount coming in.
Hope that helps!