The Applications of Surface Modifications to Lower the Stress Corrosion Cracking Sensitivity of 304/304l Stainless Steel Canister for Storage of Wasted Nuclear Fuel(1/3)

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Project title

Code/計畫編號

MOST109-2221-E019-023-MY3

Project Coordinator/計畫主持人

Leu-Wen Tsay

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Department of Optoelectronics and Materials Technology

Website

https://www.grb.gov.tw/search/planDetail?id=13532723

Year

2020

Start date/計畫起

01-08-2020

Expected Completion/計畫迄

31-07-2021

Bugetid/研究經費

1226千元

ResearchField/研究領域

能源工程

304/304L stainless steel (SS) have been used to construct dry-storage canister for wasted nuclear fuel. For the storage of wasted nuclear fuel, there have been built up 25 canisters at nuclear power station 1, and 9 canisters at nuclear power station 2. The occurrence of stress corrosion cracking (SCC) of 304/304L canister in Cl-containing environment is a concern of some people in Taiwan. Therefore, the construction of highly reliable and durable dry-storage canister to win the trust of people is an important issue. In this study, various surface modifications are proposed to applied to the regions of high SCC susceptibility, especially in the regions around the weld metal of dry storage canister in salt-spray condition. Shot peening is applied to retard the SCC cracking in the first year study. Fine particle shot peening can introduce high residual compressive stress, but does not cause a rough surface, which has harmful effects on the SCC resistance. Two step shot peening will be performed to further lower the surface roughness of a 304/304L weld and achieves high residual compressive stress. To modify the surface properties of structural components, thermal spray and cold spray technologies are used extensively to provide different coatings on the exterior. To match the demands of various applications, a variety of coating materials have been developed for specific situations, eg., anti-corrosion, anti-wear. In this work, spray coating of IN625 and Fe-Cr-Mo-C-B amorphous by High Velocity Oxy-Fuel process and cold spray on the 304 weld will be carried out to improve the corrosion/ SCC resistance. To introduce high compressive stress, shot peening will be applied before surface coating. The bonding strength of the coating will be measured. Salt spray tests are used to evaluate the corrosion/SCC resistance of the specimens with different coatings in the second and third year of this project. The effects of coating parameters on the apparent density, porosity and corrosion/SCC resistance of the specimens are investigated. In the end of this work, optimum process variables will be provided according to the results of salt spray tests. Moreover, the mechanism of SCC and the degradation of alloy with various surface modifications will be explored. 國內核電廠已產生之核廢燃料棒，現階段乾式儲存有其必要性且最切合實際需求，目前核一已完成25座、核二已完成9座乾儲設施，若能進一步安全無慮延長乾儲使用年限，國際也同步研究廢燃料棒再處理技術，若干年後這些廢燃料疑慮則將順應解決。考量不銹鋼護筒建置過程中，304/304L不銹鋼冷加工及銲接施工成型，冷加工造成不銹鋼相變化及引入應力，銲接導致熱影響區敏化及引發高殘留張應力，臨海環境可能導致不銹鋼護筒誘發應力腐蝕。為進一步改善目前已建置304不銹鋼護筒抗應力腐蝕能力，提升已建置及未建置不銹鋼護筒可靠性，本研究為選用表面改質方式，包括微粒子珠擊、熱噴覆及冷噴覆方式，施作在304/304L不銹鋼乾儲銲道鄰近區域，這區域原本就是不銹鋼應力腐蝕最可能產生位置，只要能抑制應力腐蝕裂縫不會產生在銲道鄰近區域，不銹鋼護筒安全性即可進一步再強化，降低國內各方對不銹鋼護筒安全性疑慮。本研究規劃三年度研發時程:第一年度目標將發展較佳微粒子珠擊(fine particle shot peening)參數，利用高速50微米微粒子撞擊工件而引入表面壓應力，並量測壓應力對深度變化，此外使用小於10微米粒子再進行第二次珠擊，得以降低工件表面粗糙度到Ra 1微米，並可保有較高之表層殘留壓應力，來提升304/304L不銹鋼抗鹽霧應力腐蝕。第二及第三年度以高速火焰噴覆及冷噴塗製程，將IN625及Fe-Cr-Mo-C-B非晶粉末，噴覆至304不銹鋼銲道及鄰近區域，噴覆前仍實施50微米微粒子珠擊，評估結合微粒子珠擊及噴塗兩種製程之效益，並比較傳統珠擊與微粒子珠擊對噴塗層鍵結結合強度之影響。

Keyword(s)

304/304L不銹鋼乾儲
應力腐蝕破裂
微粒子珠擊
高速火焰噴覆
冷噴覆
304/304L SS
dry canister
stress corrosion cracking
fine particle shot peening
salt spray
HVOF
cold spray

DSpace CRIS

The Applications of Surface Modifications to Lower the Stress Corrosion Cracking Sensitivity of 304/304l Stainless Steel Canister for Storage of Wasted Nuclear Fuel(1/3)

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