1

INPRO Dialogue Forum on Opportunities and Challenges in

Small Modular Reactors, 2-5 July 2019, Ulsan, Korea

Single Failure Proof Design of SMR

Fuel handling System

Roh, Myung-Sub Ph.D.

2

Contents

2

❑ SMR Perspectives

❑ Fuel Handling System of K-NPPs

❑ Incidents in Mockup Refueling Machine

❑ Current technology Status

❑ Summary

3 3

◆ Small and medium-sized or modular reactors are an option to fulfil the need for flexible power generation for a wider range of users and applications.

◆ Small modular reactors, deployable either as single or multi-module plant, offer the possibility to combine nuclear with alternative energy sources.

⚫ IAEA : < 300 MWe, “Plug & Play” at site

4 4

Name Type Coolant Neutron spectrum

Power (MWe)

Refueling (yr)

Developer Remarks

CAREM PWR H2O Thermal 27, 100300

1 INVAP (Argentina) Natural or Forced circ. No soluble Boron

WH-SMR PWR H2O Thermal 225 2 Westinghouse (USA) Forced circ.

NuScale PWR H2O Thermal 45 2 NuScale Power (USA) Natural circ.

KLT-40S PWR H2O Thermal 35 2 - 3 OKBM (Russia) Forced circ.

SMART PWR H2O Thermal 100 3 KAERI (Korea) Forced circ.

mPower PWR H2O Thermal 180 4 B&W (USA) Forced circ.No soluble Boron

HI-SMUR PWR H2O Thermal 160 3 Holtec (USA) Natural circ.No soluble Boron

PNMR BWR H2O Thermal 50, 100 10 Purdue Univ. (USA) Natural circ.

PBMR GCR He Thermal 165 On-line Eskom (S. Africa) Gen. IV

GT-MHR GCR He Thermal 285 6 - 8 GA (USA) Gen. IV

TWR LMR Na Fast 550, 1100 40 TerraPower (USA) Breeder / Breed & Burn

4S LMR Na Fast 10, 50 10 - 30 Toshiba (Japan) Breeder / Breed & Burn

SSTAR LMR Pb-Bi Fast 10 - 100 30 LLNL (USA) Breeder / Breed & Burn

HPM LMR Pb-Bi Fast 25 15 - 200 Hyperion Power (USA) Breeder

5 5

Refueling Machine

CEA change

Platform

Spent Fuel Handling Machine

Fuel Transfer System

Mast assembly

ContainmentFuel storage building

New Fuel Elevator

CEA Elevator

◆ Components of FHS▪ Refueling Machine(RM) : Insert New Fuel into RV, Taking-out of Spent Fuel from RV

▪ Spent Fuel Handling Machine(SFHM) : Taking-over and Storing Spent Fuel

▪ Fuel Transfer System(FTS) : Receiving Spent Fuel from RM and Transporting to SFHM

▪ New Fuel Elevator(NFE)

▪ Control Element Assembly Change Platform(CEACP)

▪ Control Element Assembly Elevator(CEAE)

6 6

6

◆ Fuel Handling and Storage

▪ SMART fuel is almost identical to the 17x17 standard PWR fuel except its height.

▪ Fuel-handling equipment of SMART is similar to that of the 900MWe PWRs, which are currently operating in the Rep. of Korea.

▪ The major components of the system are the refueling machine, the fuel transfer system, the spent fuel-handling machine, and the new fuel elevator, CRA change fixture, and fuel storage facility including pools, racks and associated systems.

▪ This equipment is provided to transfer new and spent fuel between the fuel storage facility, the containment building, and the fuel shipping and receiving areas during core loading and refueling operations.

▪ The principal design criteria specify the following:Fuel is inserted, removed, and transported in a safe manner. Subcriticality is maintained in all operations.

7 7

◆ Design Characteristics

▪ Each module installed in own isolated bay up to 12modules.

▪ Reactor building houses reactor modules, spent fuel pool and reactor pool.

▪ The NuScale design includes a proven safe and secure used fuel management system in fuel handling management and storage.

▪ 37 standard 17x17 PWR fuel assemblies (half height of Current PWR)

▪ 45MWe net power/module

Reactor Building

8 8

◆ Full scale Refueling Machine (RM) Installed in KPS Training Center

▪ RM: Taking-out of spent fuel from RV, and transporting to storage pool through FTS

▪ The mockup RM was designed and manufactured with the same structure and design standards as the actual nuclear power plant. It was supplied to 10 units and is in use now in Korea.

9 9

Hoist Drive System

◆ The hoist drive shaft in gearbox were broken twice on 16 Nov., 2018 and 18 March, 2019 respectively.▪ The simulated hoist drive gearbox (which has the function of transferring the

motor power to the hoist drum) installed at the KPS training Center. ▪ At that time, the dummy fuel rapidly dropped to 2m and 7m length and then

stopped by the fracture face friction force.

1010

◆ The Incident Inspection and shaft fracture section

▪ The 1st Break : In the course of checking whether there is a mechanical integrity, suddenly, the hoist box turbulence and the dummy fuel fastened to the hoist is dropped down about 2m and Stopped at 1m above the floor point. It was found that the cross shaft in hoist drive gearbox was broken.

➢ After 1st incident, the function was restored by replacing the original gearbox assembly with a new gearbox assembly of the same manufacturer with a same model.

▪ The 2nd Break : After the first breaking failure and the trial training operation were completed, the same failure occurred in the same area at 2019. 03. 18 17:43, and the dummy fuel assembly fell down by about 7 m. At that time, the dummy fuel assemblage that had fallen still stopped without colliding with the simulated lower core support plate.

1st broken Phenomenon 2nd broken Phenomenon

No. 1-2 Fracture No. 2-2 FractureNo. 2-1 FractureNo. 1-1 Fracture

1111

◆ Overload Torque Observation and Analysis

▪ The manufacturer's guaranteed shaft torque is 40.2Nm at 2000rpm based on shaft material S45C.

▪ As result of real-time monitoring of the actual operation value (electric current value, torque, number of revolutions), It is measured, the maximum torque value applied to the actual motor shaft was 21Nm.

▪ Here, considering the speed reduction ratio of the gearbox of the hoist gear 2: 1 (the torque applied to the shaft is doubled as the number of revolutions of the broken shaft is reduced), the maximum torque acting on the broken gearbox cross shaft will be 42Nm.

▪ As a result, it is revealed that the first and second breaks of the broken shaft of the hoist gearbox are caused from the repeated overrunning of the overload (See Attach. #3 &4).

#3 : Torque Value #4 : Current Value

Ratio 2:1

1212

◆ Design change of hoist braking device

▪ The current RM's brake system has a double braking system at one end of the shaft. However, in any case, such as the middle break of the shaft, it is necessary to distribute the braking device to both ends of the drum in order to prevent any falling of the nuclear fuel assembly.

▪ Two (2) brakes installed on one side of the current drive motor are installed on both sides of the hoist drum to introduce a redundancy concept so that one brake (A) can stop at one brake (B) shown in next page “Conceptual Design of Improved System”.

◆ Addition of Single Failure Proof (SFP) emergency braking system

▪ An additional emergency braking system should be installed to prevent the falling ofthe fuel assembly even if the braking force is lost due to the breakdown of the electric dive brakes and the gearbox shaft is break simultaneously.

▪ This can be achieved by introduction of Single-Failure-Proof-System, COSAS, which compliant with U.S.NRC, NUREG-0554, "Single-Failure-Proof-System" and NUREC-0612, "Control of heavy load at NPP“.

➢ COSAS (Crane Operation Safety Assurance System) ;

It provides independent emergency path for stopping and holding the load in the event of any single

failure in the hoist drive train by stopping the wire rope drum. The failure detected by monitoring improper wire rope spooling, and then the system actuates the emergency drum brake if drive train discontinuity of component failure occurs (shown on P. 14).

1313

Ele

ctric

Moto

r기어박스

Bra

ke

A

기어감속

장치

드럼

Gear

Speed

Reduce

r

Bra

ke

B

Manual

opera

tion

handle

B

Manual operation

handle A

Mech

anic

al

bra

kin

g d

evic

e

(COSAS)

Mechanical

Encoder

Gear

Box

Bra

ke

A

기어감속

장치

드럼

Gear

Speed

Reduce

r

Bra

ke

B

Manual

opera

tion

handle

B

Manual operation

handle A

Mech

anic

al

bra

kin

g d

evic

e

(CO

SA

S)

Mechanical

Encoder

Gear

Speed

Reduce

r

◆ Conceptual Design of Improved System

Dru

m

1414

Overspeed Switch

Mechanical Encoder

Wire Drum Reducer for Drum

Manual Handle

Main Brake

Trigger unit

Reducer forMechanical

EncoderEmergency Brake Clutch

Motor Signal Shaft

Dual Wire- Rope

Wire- Rope Spooling Error Detector

◆ Adding Single Failure Proof Redundancy to Hoist/Brake System

1515

1. Single Failure Proofed Hoist for Refueling Machine and Spent Fuel

Handling Machine has been developed and proved by verification

test, which can significantly contribute to safety improvement of Fuel

Handling System.

2. Considering the current situation of Korean NPPs related with the

overflowing spent fuel storage problem, the importance of safety

improvement of the Fuel Handling System by immediate adopting of

Single Failure Proofed Hoisting system can not over-emphasized.

3. The goal of SMR design, which is being developed around the world,

is to enhance safety. Especially, in the nuclear fuel handling system,

multiple safety devices such as a single failure proof are needed for

the FHS because longer up and down fuel moving distance by

adopting a longer integrated reactor.

16