Restoration work for obstacle and upper core structure

in reactor vessel of experimental fast reactor “Joyo” (2)

Misao TAKAMATSU, Takashi ASHIDA, Tetsuhiko KOBAYASHI,

Hirotaka KAWAHARA, Hideaki ITO, Akinori NAGAI

Japan Atomic Energy Agency (JAEA)

IAEA-CN-199/103

MK-III

J O Y O

Contents

• Background and restoration

work plan

• Design and development of

principal equipment

• Summary

1

Background

and

restoration work plan

2

Background

Hold

down

shaft

Lower part of UCS

Fiber

scope

Bent irradiation

test S/A

(MARICO-2)Top of S/As

MARICO-2 : Material

testing rig with

temperature control

IVS : In-vessel storage

rack

IVS

� The top of irradiation

test subassembly

(S/A) “MARICO-2” had

bent onto the IVS.

� “MARICO-2” had

damaged the upper

core structure (UCS).

3

This incident requires replacement of UCS and retrieval of

MARICO-2 S/A for Joyo re-start

Cask

(2) Retrieval of

ed-UCS

Door valve

(3) Retrieval of

MARICO-2 S/A

(4) Installation of

n-UCS

L-R/P

S-R/P Temporary pit cover

Screw jack-up equipment

Guide tube

(1) Jack-up of

ed-UCS

UCS

Cask

MARICO-2

S/A

MARICO-2 S/A retrieval equipment

Wire jack-up equipment

Ed-UCS is extracted through

small-diameter part.

UCS

Outline of restoration work plan

Plant condition :

- Fuel S/As are remained in reactor vessel.

>>> Sodium level is maintained at 50 mm below top of fuel S/A.

- Temperature of sodium is approximately 200deg-C, and temperature of

cover gas is approximately 140~160deg-C. 4

ed-UCS : existing damaged UCS

n-UCS : new UCS

Structure of UCS

UCS

(during construction））））

Inner diameter of

through-hole

UCS Weight : 16.5 ton

Operation time of Joyo (1977～～～～2007) ：：：：70,798 h 5

Driving

mechanism

Holding

mechanism

Guide tube

Latch

mechanism

S/A

Appro

x.

11m Core

IVS

Hold-down shaft

UCS

MARICO-2

R/P

Core address during

irradiation (3E3)

Location of

disconnection work

(IVS No.16 (R16))

Guide tube

Guide sleeve

Handling head

Cable etc.

Transfer pot

Ref. Normal state

IVS

R/V

S/A

Structure of MARICO-2

6

Design and development of

principal equipment

7

Major subjects and measures

in ed-UCS jack-up and retrieval

Bolts

UCSR/P

Guide

sleeve

Sodium bridgeUCS UCS

Deformation of GS

Guide sleeve

(thickness : 5mm)interference

Contact

Thermal

shielding

plate

: Bolt

(18××××3)

UCS UCS

Excessive

bending

strength

caused by

sodium bridge

Deformation of guide sleeve due to sodium bridge Deformation of ed-UCS due to interference and

contact between ed-UCS and guide sleeve

UCS

Excessive resistance Deformation of bolts

To prevent deformation of ed-UCS and guide sleeve

>>> Investigation of allowable load is required.

To prevent interference and contact between ed-UCS and guide sleeve

>>> Strict inclination control and visual monitoring are required.

8

Investigation of allowable load

Allowable load is investigated using finite element analysis code

“Abaqus” with 3-D modeling.

Pulling

height

(mm)

Allowable

load (t)Resistance notes

0 ~ 2 0.72 Sodium bridge shearing forceJack-up speed

: <2mm/h*1

2 ~ 484 0.72 Sodium bridge shearing force

484 ~ 862 1.09Resistance caused by interference

between ed-UCS and guide sleeve

862 ~ 1.73Resistance caused by contact

between ed-UCS and guide sleeve

*1: Deformation at the point of force application of wringing force*2 is unlikely owing to its

thick structure. However, in the case that sodium bridge shearing is incomplete, there

may be a risk of guide sleeve deformation due to rapid release of the wringing force.

jack-up speed is limited to below 2 mm/h to prevent permanently deforming guide sleeve.

*2: Pushing force by atmospheric pressure with assuming that contacting surface of ed-

UCS has been vacuumed by tight contact (3.37t)

9

Measure for inclination control

(Ex. Jack-up equipment)

吊吊吊吊りりりり蓋蓋蓋蓋

Required Max. load : 400kN

( total load of three screw jack )

1100mm

Servomotor

Screw jackVertical

displacement

measuring

device

Base mechanism

of screw jack

Handle

Jack

holder base

Manual :

0.025mm/rotation

Auto :

0.017～～～～1mm/s

Level measuring

deviceHanging plate

Load

measuring

device

Three screw jacks are

located uniformly in a

concentric configuration.

Guide tube

Temporary

pit cover

Temporary boundary

R/P UCS

Jack-up

equipment

Screw jack

Assuming conservative 2.5 mm gap between ed-

UCS and GS (safety factor: 2), allowable inclination

is estimated as 0.6925 mm/m (0.039 deg).

Achieve strict control of inclination

>>> Applying three-point suspension

>>> Inclination monitoring with level- and load-

measuring devices

10

Ex-vessel function test of jack-up equipment

Dummy UCS

Dummy guide tube

Screw jack

Screw jack

Hanging plate

Guide pin

11

Dummy

guide sleeve

R/P

UCS fitting area

monitoring

equipment

UCSRef. Ex-vessel test

result using video-scope

Dummy UCS

（（（（O.D. : 1010mm)

Observation image

using video-scope

UCS fitting

area

UCS

Bottom of R/P

Video-scope

- Endurance of dose : 1000Gy

- Max. Temp. : 100 deg-C

- O.D. : 6mm

- View angle : 40 deg

- Lighting : LED

Improvement of

picture quality

UCS

Bottom of R/P

Dummy

guide sleeve

(I.D. : 1070mm)

Visual monitoring equipment for UCS replacement

Ex. UCS fitting area

monitoring equipment

12

Major subjects and measures

in MARICO-2 S/A retrieval

- it was confirmed that MARICO-2 S/A is stuck in transfer pot

owing to its deformation.

>>> Retrieval equipment for MARICO-2 S/A is designed to

retrieve MARICO-2 S/A together with transfer pot.

- To avoid contact, ed-UCS cannot be set just above MARICO-2

S/A.

* Retrieval is performed using hole through which ed-UCS is

extracted

>>> Offset arm to reach MARICO-2 S/A is designed as part of

MARICO-2 S/A retrieval equipment.

13

Large R/P

Small R/P

MARICO-2 S/A

UCS

Location of R/P

during restoration work

Retrieval

equipment

MARICO-2 S/A

Pantograph mechanism

Latch finger mechanism

Pantograph

Latch finger

Schematic diagram of

MARICO-2 S/A retrieval equipment

Pantograph and latch finger

mechanism are developed on

basis of remote control

techniques demonstrated in

fuel handling machine. 14

Dummy

S/A

Latch

fingerDummy

transfer pot

Transfer pot

70mm

MARICO-2

S/A

Insertion of latch finger

UCSHold-

down

shaft

Fiberscope

Latch

finger

Latch

fingerLatch

finger

MARICO-2

S/A

Pulling up MARICO-2 S/A

MARICO-2

S/A

Latch

finger

Preliminary in-vessel testPreliminary in-vessel test was conducted to demonstrate latch

finger performance.

15

- In this preparation work for restoration of Joyo, a series of

equipment has been successfully designed and developed.

[UCS replacement]

> Allowable loads are investigated.

> Measures to achieve strict inclination control are established.

[MARICO-2 S/A retrieval]

> Pantograph and latch finger mechanism are developed on basis of remote

control techniques demonstrated in fuel handling machine.

Summary

Current status and future plan

- n-UCS and all necessary equipment are currently being

manufactured.

- A full ex-vessel test is scheduled in 2013 to verify

performance of equipment and establish final work procedure

- Replacement of UCS and retrieval of MARICO-2 S/A will be

conducted in 2014.

Restoration work on Joyo will provide valuable experience and

insight into further improvements and verification of repair

techniques for sodium-cooled fast reactors.16