Bhavesh,
my share

CAN WE USE WRC107 FOR SPHERICAL VESSEL?
Answer- YES

IF YES THAN WHAT SHOULD BE THE VESSEL COSINE VECTOR,NOZZLE COSINE VECTOR

Answer- Depends on nozzle location, lets take example of Vertical vessle with horizontal nozzle(projection towards -x direction).

vessel cosine: 0,-1,0
Nozzle cosine: 1,0,0

CAN WE CHANGE DIAMETER OF VESSEL OR SELECT SPHERICAL VESSEL OPTION
Answer: diameter can be changed however D/d ratio should be in criteria.