Q157. What are emergency siren signals and what action is to be taken for them?

A.     

SIGNAL	SIREN	ACTION
STAY IN	5 Sec. ON & 5 Sec. Off for 2 minutes	Close all windows & doors if inside the plant. If outside the plant, hold handkerchief on nose & proceed to nearest building.
EVACUATION	15 Sec On & 5 Sec Off for 5 minutes	Hold handkerchief on nose & gather in entrance hall.
ALL CLEAR	Continuous for 2 minutes	Resume normal work after clearance of Health Physics.

Q158. Why air is filtered before supply and before exhaust? What types of filters are used and why?

A.    Air is filtered before supply to avoid over loading of exhaust fan filters which are giving more radioactive dose while replacing. Air is filtered before exhaust to release minimum air activity through stack to avoid pollution. Before supply HDPE filters are used and after supply HEPA  & pre-filters are used.

Q159. What is meant by regeneration of MBU?

A.       In MBU, resin are provided for anions & cat-ions are collection. These resins are de-mineralizing the pond water. After some time, they are becoming inactive. The  process by which they are activated is called regeneration of MBU.

Q160.  How much vacuum is maintained in dissolver and why?

A.       1” of vacuum is maintained in dissolver cell to prevent spreading of air activity. Chopper cell exhaust fan is provided.

Q161.  What should be the quality of pond water?

A.        Pond water – PH-7, Contractive-0.5 to 1 micro-mhos/cm. Activity should less than 1000 MMCi/m³.

Q162.  What are the types of ventilation system?

A.     There are two types of ventilation systems. One is the system in which air is re-circulated after filtering or conditioning. In other system, air is passed through area and exhausted, a new air is provided in the area. In our plant this system is adopted. Supply fans are provided air and air is exhausted through E2 fans. This is also called series type ventilation.

Q163. Which are the ventilation fans associated with exhaust fan E2F3?

A.       V2F1/F2 ventilation fans are associated with exhaust fan E2F3. When E2F3 trips, V2F1/F2 also trips. These ventilation fans are supplying air to Access Galleries.

Q164. What are the protection devices used for compressor motor and unit?

A.       Motor is protected by dashpot relays against overload and earth fault conditions, by HRC fuse against

           short ckt conditions, by thermister against overheating of motor.

           Compressor unit is having protective devices as follows:

Low lub oil pressure	Pressure switch
Low cooling water flow	Float switch
High discharge air temperature	Thermostat
High cooling water outlet temperature	Thermostat

Q165. What are the conditions to be fulfilled for starting the boiler?

A.       Following conditions are to be fulfilled for starting the boiler:

           a. Normal water supply  -  Indicated by magnetic switch

           b. Furnace oil recirculation.

           c. Discharge damper should be open.

           d. Air vent valve should be open.

Q166. Why the fuel is stored in pond? How pond water is maintained?

A.       Fuel is stored in the pond because water is a good shielding material also waster is dissipating the

           heat if generated. Pond water is re-circulated through filters, through MBU for de-ionization & Push-

           pull ventilation is provided for pond.

Q167. What and how head end treatment is carried out?

A.       Head End Treatment: This treatment consists of : 1. Feed solution preparation, 2. Co-

          decontamination through portioning cycle, 3. U & Pu purification cycle.

Q168.  How air activities is controlled?

A.      Air activity is controlled by series type ventilation. Ventilation fans are supplying air in different areas. Air is going from low active area to high active area. Finally through cell exhaust is given via exhaust fans. Where extra exhaust is required in certain areas, separate fans are provided like chopper cell exhaust fans. Pu enclosure blower, glove box vacuum blower. In plant, negative air pressure is maintained to prevent spreading of contamination.

Q169.  Why and How two dosimeters are used?

A.       Two dosimeters are used when we have to measure Beta exposure and Gamma exposure separately at certain job. One dosimeter is given with sleeve and other is open. After performing a job reading of both dosimeters is taken. The dosimeter with sleeve gives the reading of Gamma exposure only while other dosimeter gives the total reading. Difference of the two dosimeter readings multiplied by certain factor (Mf>14) gives the Beta exposure of that particular worker.

Q170. What is meant by maintenance & what are various maintenance carried out? Explain difference between preventive maintenance & corrective maintenance.

A.       Maintenance is a action taken for increasing life of machine, for improving service of machine, for avoiding break down of machine, for replacement of worn-out parts of machine, for improving efficiency of machine and safe working of machine.

            Preventives maintenance is a preventives action to avoid breakdown of machine & to improve performance of machine which is a scheduled maintenance.

            Corrective maintenance of machine is done when there is a breakdown of machine which may come at any time.

Q171.  Explain maintenance practice of special work.

A.        a. Do proper planning of the job.

            b. Give clear instruction to person working.

            c. Arrange material before starting the work.

            d. Arrange one HP person for inspection.

            e. Keep one standby person ready.

            f . Take clearance from control room before starting the work.

            g. Keep constant supervision.

Q172.  Why 33 kv supply is preferred instead of 415 V in PREFR Plant?

A.      HT supply is preferred as it is reliable compared to 415 V supply as number of shutdowns are reduced. Losses of conductors are reduced when power is transmitted at high voltage. Also voltage regulation & efficiency is increased.   

Q173.  What is the standard clearance of 33 Kv from ground & from buildings when a line crosses a road,      what precautions are taken?

A.      Across the road – 20’, along the road – 19’, other area – 17’. Clearance from buildings – between phases – 36”, phase to earth – 24”, phase to ground wire – 48”.

Q174.  What are various earthings in practice? Explain which earthing is suitable for : a) rocky area where earth resistance is very high,  b) Industrial complex with lot of armoured cables?

A.        Mainly two types of earthings are in practice namely : pipe earthing & plate earthing.

 In Pipe Earthing, one GI pipe of approx. 2.25 mtrs is buried in ground at 2.25 mtrs below the ground. That pipe is connected to earthing conductor.

In Plate Earthing, plate of dimension 2’ x  2’ x  2mm  is buried in ground at 2.25 mtrs below the ground.

Rocky Area – Pipe earthing, Industrial structure – plate earthing.

Q175.  Why transformer rating is in KVA?

A.      As seen, Copper loss of a transformer depends upon the Current & Iron loss on voltage. Hence tatal transformer loss depends upon VA and not on phase angle between voltage and current. i.e. it is depend on load power factor. That is why rating of transformer is in KVA and not in KW.

Q176.  What is Vector Group?

A.        Position of primary and secondary winding in transformer.

Q177. What is Power Factor?

A.        It is a cosine ratio between the angle of voltage and current. 

Q178.  What is the effect of low power factor?

A.       Increased losses in alternator, exciter, distribution lines , transformers and in the consumers plant. This increased losses are caused by increased current for the same amount of power and strong fields are needed by the alternator furnish this power which causes under heating. Also increases M.D.

Q179.  What is static condenser?

A.        It is a device that stores up electrostatic energy by subjecting the insulation or the di-electric strength between two conducting elements to a voltage tress.

Q180.  What conditions are necessary for parallel operation of transformers?

A.        1. Voltage should be same with polarity.

            2. Phase sequence should be same.

            3. Vector group should be same.

            4. Impedance percentage should be same.

            5. Tap ratio should be same.

            6. Zero relative phase displacement.

Q181.  What is the cause of single phasing?

A.      1. Physical break in conductor, 2. blowing of fuse, 3. loose connection, 4. bad cable joint, 5. bad contacts in one pole of switch, contactor and ACB.