Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_12983929_1 ( construction_start VARCHAR, net_power VARCHAR, unit VARCHAR )

### Question ###
When did the construction of the unit Chinon B1 with net power of 905 MW start?

### Accurate SQL ###

SELECT construction_start FROM table_12983929_1 WHERE net_power = "905 MW" AND unit = "Chinon B1"