退役核燃料干式贮存混泥土护箱受高温作用之效应研究

Effects of temperature on concrete cask in a dry storage facility for spent nuclear fuels

退役核燃料干式贮存设施主体由混凝土构成,混凝土得在长时期内承受残余核燃料释出的衰变热,加上台湾地区特殊的环境气候条件,混凝土材料可能产生劣化。依据核能安全混凝土结构物的材料规定的配比,我们制作了混凝土试样,用实验室模拟法研究干式贮存混凝土护箱在高温环境作用下可能出现的损害或劣化,甚至耐久性变差等。利用非破坏性检测方法(超音波试验、动弹性模数试验及反弹锤试验等),观察混凝土受持续高温作用下的结构致密性及内部是否产生裂缝,而影响混凝土的质量及耐久性安全。研究结果表明,混凝土干式贮存设施在高温(94℃)长期作用下,其抗压强度所受影响有限,不致损及混凝土结构承载之能力;其超音波波速及动弹性模数在初期会略有降低,而后趋于稳定;混凝土受热环境作用后体积产生收缩,且温度越高收缩量越大,但不随受热历时增加而再有明显收缩;就抵抗高温作用而言,添加卜作岚材料的混凝土优于纯水泥混凝土。

In the dry storage of spent nuclear fuels,concrete cask serves both as a shielding and a structural containment.The concrete in the storage facility is expected to endure the decay heat of the spent nuclear fuel during its service life.Thus,effects of the sustaining high temperature on concrete material need be evaluated for safety of the dry storage facility.In this paper,we report an experimental program aimed at investigating possible high temperature effects on properties of concrete,with emphasis on the mechanical stability,porosity,and crack-resisting ability of concrete mixes prepared using various amounts of Portland cement,fly ash,and blast furnace slag.The experimental results obtained from concrete specimens exposed to a temperature of 94oC for 90 days indicate that：（1） compressive strength of the concrete remains practically unchanged;（2） the ultrasonic pulse velocity,and dynamic modulus of elasticity of the concrete decrease in early stage of the high-temperature exposure,and gradually become stable with continuing exposure;（3） shrinkage of concrete mixes exhibits an increase in early stage of the exposure and does not decrease further with time;（4） concrete mixes containing pozzolanic materials,including fly ash and blast furnace slag,show better temperature-resisting characteristics than those using only Portland cement.