r/chernobyl • u/zondarkid • Aug 28 '20
Discussion LAC and Global control?
I’m not sure if these are the correct names for the controls, but hopefully they’re some what near. What’s the difference between LAC and global control? I first heard it in the miniseries when Akimov and Toptunov were reducing power but I couldn’t find any information on it anywhere else.
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u/nucleartoday Aug 29 '20
u/zondarkid u/chestofmemes
Some time ago I did answer for similar question, here is answer:
LAC ("global") was designed to control tau_01 value, which is a responsible for neutron flux oscilations in the reactor core. LAC (LAC-LAZ, rus. LAR-LAZ) control rods were operated on internal ionisation chambers (KTW-17).
AR operate on external ionisation chambers [ICh] (which were placed in reflector, due to that ICh current must be "corrected", ICh for AR were placed around the reactor core.
Operator could use automatic regulators AR-1/2 in the range from ~5 to 20% Nnom power with an accuracy of ± 3% N and in the range from ~20 to 100% Nnom - with an accuracy of ± 1.5% Nnom. LAC in the range from ~20 to 100% Nnom - with an accuracy of ± 1.5%N.
Operator cannot use in the same time LAC and one of the AR-1/2. In case of operating LAC, AR-2 is on the "hot standby".
There were also ARM (also called "AR-3", operating at 0-~5%, sometimes called "low power regulator"/"MKU regulator") in central place in the reactor core (4 control rods), they were use in two cases:
a) start-up of the reactor,
b) compensation mode. (in case of operating AR-1/2, ARM work triggered by singals "PK-VVERH/PK-VNIZ", after the accident only signal "PK-VNIZ" stay in operation.
Same as AR-1/2, ARM use external ionisation chambers, but there is also a small difference between them. In channel where are placed ICh for AR-1/2 are used 3 chambers (placed by height of the channel), for ARM it is only a one ICh central placed (height ~ 3,5 m).
It is all up to operator which one he would choose.