There called urates.Its very normal.
Heres a quote from a care sheet that I like to go by.
Uric acid can be eliminated using substantial lower levels of water wastage than can systems based on urea, such as those of mammals. Therefore, tortoises, such as Russians, eliminate nitrogenous waste products with far greater water conservation. Its behavior is also programmed to reflect this need not to waste precious water. The semi-solid, white deposits are expelled urates. Tortoises are programmed not to use water in the bladder and to eliminate urates only if replenishment is available.
Hope this helps.