i must repeat : the MS will NEVER transmit its IMSI. Only the TMSI. The VLR will then make the link between TMSI and IMSI.
BTW, after LU, it is probable the TMSI is going to be changed to a new value.
T3212 = 10mn : lots of SDCCH congestion all over your network, very poor CSSR, not even talking about the MSC/VLR overload and the HLR overload…
Do Not Do It.