Distributions of fission products on PCI in spent PWR fuels using EPMA International Conference on Management of Spent Fuel from Nuclear Power Reactors

Distributions of fission products on PCI in spent PWR fuels using EPMA

International Conference on Management International Conference on Management of Spent Fuel from Nuclear Power Reactorsof Spent Fuel from Nuclear Power Reactors

Yang-Hong Jung Yang-Hong Jung

Republic of Korea Energy Research InstituteRepublic of Korea Energy Research Institute

IAEA-CN-178/08-05

PIE & Radwaste Division

ContentsContents

IntroductionIntroduction

Samples- 62,000 MWd/tU - at an average oxygen content region Samples- 62,000 MWd/tU –at an oxygen rich region Samples- 53,000 MWd/tU –failed fuel X-ray mapping image of CRUD sampling from 62,000 MWd/tU CRUD sampling from failed fuel using cross-section clad

Sample preparationSample preparation Result and discussionResult and discussion

ConclusionsConclusions


IntroductionIntroduction

The failed spent fuel rod with 53,000 MWd/tU and normal spent fuel rod with 62,000 MWd/tU from nuclear power plant were characterized to

compare and observe fission products in fuel-clad gap region by EPMA. Several recent studies have been conducted on fuel rod failures involving

PCI (Pellet-Clad Interaction) The results from these studies have established that PCI failures are due to

SCC(Stress Corrosion Cracking of the cladding) So, In this study we try to identified a number of fission products (I, Cs, Cd,

Xe, Kr) distribution at fuel-clad gab. The results of this study can be used in the interim dry cask storage

facilities for spent fuels which are being used in the Republic of Korea nuclear power plants.

EPMA technique offers the possibility of identifying and analyzing fission products in spent PWR fuel, although the small amounts expected to be present, and the background radiation, present a significant analytical challenge.


Fuel rodChopping

Pellet removalby drilling

Cladding profilewith parts of pellet

Mounting & Polishing

A thin diamond wheel was cut off from PWR fuel rod. The sample have been embedded in conducting resin and polished with

diamond paste of 1 ㎛ as a final stage. The Electron Probe Micro-Analysis(EPMA, SX-50R, CAMECA, France)

technique offers the possibility of identification and analyzing fission products.

Experimental and ResultsExperimental and ResultsSample preparationSample preparation

Schematic drawing of the sample preparation


Experimental and ResultsExperimental and Results

The failed spent fuel rod with 53,000 MWd/tU and normal spent fuel rod with

62,000 MWd/tU from nuclear power plant were discharged and cooled down

for 2 and 4 years, respectively.

Sample preparationSample preparation

Normal spent fuel 62,000 MWd/tUNormal spent fuel 62,000 MWd/tU

Failed spent fuel 53,000 MWd/tUFailed spent fuel 53,000 MWd/tU


An optical microscopy and SEM image of the 62,000 MWd/tU fuel rod

at an average oxygen content region The concentration of O, Zr, U on the marked point is illustrating the

general trend for release and redistribution in fuel-clad gap region. The quantitative line scan data taken from across fuel-clad gab shows

stable stats at an average oxygen region.

Experimental and ResultsExperimental and ResultsSamples- 62,000 MWd/tU - at an average oxygen content region

20 ㎛


Experimental and ResultsExperimental and ResultsSamples- 62,000 MWd/tU –at an oxygen rich content region

An optical microscopy, SEM and BSE image of the 62,000 MWd/tU

fuel rod at an oxygen content rich region . Quantitative analyses of O, Zr, U on the marked point .

20 ㎛


Samples- 62,000 MWd/tU –at an oxygen rich content region Experimental and ResultsExperimental and Results

The quantitative line scan data of O, Zr, U taken from across fuel-clad gap

shows stable states at an oxygen rich region. The quantitative line scan data of fission products Cs, Ce, Ba, Sr, I taken from

marked point. These results means, even at a high burn-up stat in the 62 GWd/tU,

the fuel-clad gab reliability seems to be appropriate conditions.



The Iodine and tellurium profiles exhibit stable states at an average oxygen

content region . But, tellurium profiles changed dynamically increased at an rich oxygen

content region .

Samples- 62,000 MWd/tU –at an oxygen rich content region

Fuel

Fuel

Clad

Clad


The gaseous cesium and xenon distribution are not so dynamically changed

between fuel-clad gap at an average oxygen region of 62,000 MWd/tU fuel rod Cerium and oxygen distribution are illustrating the general trend for release and

redistribution in fuel-clad gap region.

Experimental and ResultsExperimental and ResultsSamples- 62,000 MWd/tU

Qualitative concentration profile of Ce, O along the clad-fuel gap

Qualitative concentration profile of Cs, Xe along the clad-fuel gap

FuelClad

Fuel

Clad

O-Profile6 ㎛



The gaseous cesium and xenon distribution are not so dynamically changed

between fuel-clad gap at an oxygen rich region of 62,000 MWd/tU fuel rod The qualitative concentration profile along the clad-fuel gab obtained by

EPMA to conform the reliability of fission products behaviors at high burn up

fuel conditions and compare with at an average oxygen region and higher

oxygen region.

Qualitative concentration profile of Ce, O along the clad-fuel gap


Clad

Clad

Fuel

Fuel

Qualitative concentration profile of Cs, Xe along the clad-fuel gap

O-Profile20 ㎛


Experimental and ResultsExperimental and ResultsSamples- 62,000 MWd/tU - at an average oxygen content region

Xenon and cesium are fission products which are release from the central

parts of the pellet However, Xenon and oxygen concentration profiles illustrate the general trend

for release and cesium redistribution in fuel-clad gab.

Image mapping of Xe, Zr, O, U,Cs I on the fuel-clad gap

Cs

UO 20 ㎛U

Xe Zr

I

Cs



X-ray image of Xe, Zr, O, U, Cs, I The concentration of oxygen X-ray image is quietly different from at an

average oxygen content region

Image mapping of Xe, Zr, O, U, Cs, I on the fuel-clad gap


O

Cs

U

ZrXe

O 20 ㎛ I


Activated corrosion products, CRUD (Chalk River Unidentified Deposits) from BWR and PWR reactors deposit primarily on the outer surface of fuel rod.

On these surface, the deposits can lead to fuel rod failures and cladding breaches.

Also, it can become detached in cooling water and storage systems, causing additional radiation exposure to plant workers.

Zircalloy cladding is known to have a strong affinity for oxygen. In –reactor corrosion of the cladding typically produces a thin outer layer of

oxide 8-40 ㎛ in thickness. These deposits are distinguishable from oxide corrosion products dissolved

from structural material and piping which are transported into the core from the primary coolant

Experimental and Results-CRUDExperimental and Results-CRUD


Samples- 62,000 MWd/tU


Image mapping of O, Fe on the CRUD

SEM, BSE, X-ray image of CRUD sampling from 6200 MWd/tU SEM, BSE, X-ray image of CRUD sampling from 6200 MWd/tU

SE 10 ㎛ BSE 20 ㎛

BSE100 ㎛SE100 ㎛

O 50 ㎛

Fe 50 ㎛


Samples- 53,000 MWd/tU –failed spent fuel Experimental and ResultsExperimental and Results

CRUD sampling from failed fuel using cross-section cladCRUD sampling from failed fuel using cross-section clad

Quantitative Analysis points

O 10 ㎛C

B

Fe

Zr

Image mapping of Zr, B,O, Fe, C on the fuel-clad gap

PIE & Radwaste Division16 point quantitative analysis on crud region16 point quantitative analysis on crud region

Experimental and ResultsExperimental and ResultsSamples- 53,000 MWd/tU –failed spent fuel

EPMA quantitative analysis results were executed by dividing parts of crud

that was 8 ㎛ thick into 16 equal points These result was similar to Trevorite (NiFe2O4) is well known of crud main

compositions.

Fe

O

Ni

　100　70.044Total

0.0130.010.0180.013Zn

2.91716.1271.17718.651Ni

0.0080.0040.010.006Co

2.25828.6146.67632.454Fe

0.1540.5070.1410.547Mn

0.4060.7180.1890.693Cr

3.70854.0214.2517.68O

devaveragedevaverage

　

Atomic %Weight %　

NiFe2O3.x



X-ray image of Zr, O, U of the spent failed fuel rod with 53,000 MWd/tU The quantitative data of fission products taken from marked point The thickness of oxidation region was 13 ㎛ and metallic precipitates of Fe and

Sn were found. but the amounts were too low to be considered.

UO20 ㎛

Image mapping of Zr, O, U on the fuel-clad gap

Zr

O U



Distributions of fission products in PCI region. 25 beam points were set up. Point numbers from 1-18 points were placed on cladding side. High concentration of fission products was observed from 19-24 points

but Cs and Sr were observed over 1.0 wt %. It is almost same results of

Restani. He used SIMS and found that Sr and Cs were observed 1.2 wt%

and 1.0 wt% far from UO2 pellet by fission recoil.


ConclusionsConclusions

The spent failed fuel rod with 53,000 MWd/tU and normal spent fuel rod with

62,000 MWd/tU from nuclear power plant were characterized to compare and

observe fission products on the fuel-clad gap using EPMA. The gaseous cesium and xenon distribution are not so dynamically changed

between fuel-clad gap at an average oxygen region of 62,000 MWd/tU fuel rod,

quantitative line scan data illustrate the general trend of release and

cesium redistribution in fuel-clad gap region. Oxygen concentration profile at an average region is about less than 6 ㎛ compare to 20 ㎛ at higher oxygen region between clad to fuel gap. Tellurium

profiles changed dynamically increased at an oxygen rich content region. Oxide thickness is 13 ㎛ on the PCI region and the contents of the oxide layer

were 34 at.% of zirconium and 66.7 at.% of oxygen respectively in the failed

spent fuel rod with 53,000 MWd/tU. The results of this study can be used in the interim dry cask storage facilities for

spent fuels which are being used in the Republic of Korea nuclear power plants.


Thank youThank you

Documents

Distributions of fission products on PCI in spent PWR fuels using EPMA International Conference on Management of Spent Fuel from Nuclear Power Reactors