This Section summarises the major safety related modifications that have been implemented in the Ignalina NPP. This encompasses the important structural and procedural modifications implemented after the occurrence of the Chernobyl incident and the ongoing and projected modifications whose purpose is to bring the INPP safety criteria up to western safety standards.
13.1 Post-Chernobyl Modifications
After the Chernobyl accident, technical and organizational changes were prepared and implemented in order to improve the operational safety of all NPP’s with RBMK reactors. These changes had the following objectives:
Fig. 13.1 Redesign of the RBMK-1500 manual control rods  (all dimension are in cm)
The reduction of the positive steam reactivity coefficient at the Ignalina NPP, from +4.5b to +1b, was achieved by installing from no less than 52 additional absorber rods in the core, and increasing the effective reactivity reserve to from 53 to 58 manual control rods. In addition, replacement fuel enrichment has been increased to 2.4 %.
The increase in emergency protection system effectiveness was achieved by three independent means . In the first modification the old type of absorber rods were replaced by a re-designed type, in which the water column in the bottom part of the CPS channel has been eliminated (Fig. 13.1).
Secondly, the modernization of the CPS rods servodrive increased their speed of insertion into the core. This allowed a reduction of the insertion time from 18 seconds to 14 seconds. When these changes were implemented, the prompt effectiveness of the emergency protection system reached 0.9 b/s, which is about 8 times higher than the value before the Chernobyl accident.
The third stage of increasing the control and protection system effectiveness was to install a new design of the fast-acting scram rod in all the operating RBMK reactors. This new design eliminated the water which used to slow down the rod movement. The channel walls are now cooled by a thin film of water, while the rod moves in a gaseous environment.
The new design was tested at the Ignalina and St. Petersburg NPPs in 1987-88. Fig. 13.2  shows that as the 24 FAS rods are fully inserted in less than 2.5 s, achieving more than 2b of negative reactivity (left diagram). The diagram on the right shows the reduction in power when the FAS rods are inserted.
Fig. 13.2 Fast-acting scram system test, at reactor power N = 0.4Nnom 
1 - calculated, 2 - St. Petersburg NPP, 3 - Ignalina NPP
Besides the improvements mentioned above, several other important improvements were made which increased the CPS effectiveness:
All of these mean to improve the neutronic characteristics of the reactor and increase the emergency protection system effectiveness and thus diminish the chances of an uncontrolled increase in reactor power.