Refueling pool

M. The SCS is designed to transfer refueling pool water back to the IRWST following refueling operations. 

These failures could be caused by the refueling canal drain valves being closed, or the fine mesh strainer left in the refueling pool during operation preventing the water spray from returning to the containment emergency sump. 

A watertight seal is installed between the reactor vessel flange and the floor of the refueling pool during the refueling operation. The seal is removed before reactor operation. 

Provisions are made to test the seal after installation and before flooding the refueling pool. 

The contaimnent, auxihary building, refuelling pool, and spent fuel pool are designed to seismic Category I requirements to thus provide their integrity in the event of a safe shutdown earthquake. 

On discharge from the reactors the fuel is stored for an initial cooling period in a pool at the reactor site. BWR pools are filled with demineralised water, whereas PWR pools are fdled with a dilute (typically 0.2M) boric acid solution. The boric acid in PWR pools results from mixing the boronated water in the reactor vessel with the bulk poolwater during refuelling operations. This chemistry results in BWR pools operating at approximately pH 5.8-7 and the PWR pools at pH 4.5-6. Most of these pools operate at, or below, 40°C. 

Reactor pool flooding to refuelling and core mapping 59 ... 

Fuelhandling accidents Fuel assembly jamming or breaking off during its installation in the spent fuel pool by the refuelling machine BDBA... 

Fig. 2.2. Elevation view of the AHTR with metallic internals (AHTR-MI) for normal operation (left) and refueling (right) modes. IHX = intermediate heat exchanger DHX = decay heat exchanger PHX = pool heat exchanger Source Peterson and Zhao, 2006.)...

Since the reactor operates at a power that is significantly less than the rated power (about 40-60%, and because the same power level enables loop tests to be conducted), the actual average operation time of the FAs in the core is about six months. The spent FAs are then extracted from the core and allowed to cool in the reactor s coohng pool. All refuelling operations are performed under water. 

The spent fuel pool of the MIR reactor is a pit 11 m in diameter and filled with distilled water (about 20001). The pool walls are lined with stainless steel 1X18H10T. All the equipment and apphances for spent product storage are made of the same steel. Leaktight boxes can be used to store FAs with breached cladding. The refuelling tools are made of both stainless steel and SZAV-6 aluminium alloy. 

During reftielling operations the containment dome and the reactor vessel head are removed, and the cavity above the dome is filled with water. The reactor internals are lifted out in sections, and placed in the water-filled cavity. The refuelling is carried out with a conventional refuelling machine from the reactor service room. Fresh fuel is brought into the cavity from a fresh fuel storage in the reactor building, and the spent fuel is removed to an adjacent spent fuel pool at the reactor service room floor level. 

The upper containment pool has a shield wall with a removable gate between the reactor well, the fuel holding pool, and the fuel transfer pool. With the gate inserted in the slot, the upper containment pool can be drained for work at the pressure vessel flange level. With the pools full of water, the gates are removed during refueling operations to permit the transfer of fuel and equipment between pools. 

The purpose of the second layer of the shield is to slow down and absorb the neutrons. Water makes the best neutron shield for this purpose followed by plastics and then concrete due to their relative hydrogen contents. This is the reason spent fuel pools are deep pools and why the reactor vessel is submerged imderwater during refueling. The water serves an important role in cooling the fuel rods as well, but the depth of the pools is dictated by the need for shielding. 

I) Concrete containment 2) Containment steel shell 3) Polar crane 4) Reactor pressure vessel S) Control rod drive mechanism 6) Spent fuel pool 7) Refuelling machine 8) Steam generator 9) Pressurizer 10) Pressurizer relief tank 11) Main coolant pump 12) Main steam line 13) Feedwater line 14) Concrete shield IS) Accumulator 16) Personnel lock 17) Mate rials lock 18) Lifting gantry 19) Fresh fuel assembly storage 20) Borated water storage tank 21) Residual heat cooler 22) Component cooler 23) Safety injection pump (By courtesy of Siemens/KWU)... 

Refuelling machine 2) Reactor wet well 3) Reactor pressure vessel 4) Control rod drive mechanisms S) Main coolant pumps 6) Containment 7) Air recirculation system 8) Pipe floors 9) Fuel pool cooling heat exchanger 10) Pressure suppression pool II) Residual heat removal cooler 12) Lock (By courtesy of Siemens/KWU)... 

Damage of a fuel assembly during handling in the spent fuel pool (e. g. during refuelling)... 

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