Characterization of Radiation Fields for Assessing Concrete Degradation in Biological Shields of NPPs

Abstract

Abstract. Life extensions of nuclear power plants (NPPs) to 60 years of operation and the possibility of subsequent license renewal to 80 years have renewed interest in long-term material degradation in NPPs. Large irreplaceable sections of most nuclear generating stations are constructed from concrete, including safety-related structures such as biological shields and containment buildings; therefore, concrete degradation is being considered with particular focus on radiation-induced effects. Based on the projected neutron fluence values (E > 0.1 MeV) in the concrete biological shields of the US pressurized water reactor fleet and the currently available data on radiation effects on concrete, some decrease in mechanical properties of concrete cannot be ruled out during extended operation beyond 60 years. An expansion of the irradiated concrete database is desirable to ensure reliable risk assessment for extended operation of nuclear power plants.

Review of the Current State of Knowledge on the Effects of Radiation on Concrete

“…Remec et al (2016b) showed that, for the neutron spectra in the biological shield of two-loop and three-loop (the number of reactor cooling circuits) PWRs, neutrons with energies above 0.1 MeV contribute more than 95% of all atom displacements in several widespread aggregate minerals, while neutrons with energies above 1 MeV cause only about 20 to 25% of the total atom displacements, as shown in Fig. 1 (Remec et al 2016a). The conclusions were similar when, instead of atom displacements, neutron-induced absorbed dose in minerals was considered.…”

Structural effects of radiation-induced volumetric expansion on unreinforced concrete biological shields

“…These rather deep damage penetration are the result of the very high total flu-ence exposure assumed: 10 +12 n.cm −2 s −1 which leads to a total fluence of about 1.6 × 10 +21 n.cm −2 after 50 years of operation. Such a flux is one to two orders of magnitude higher than the estimated bounding value for PWR CBSs (Esselman and Bruck, 2013;Remec et al, 2014 Finally, Andreev and Kapliy (2014) were the first to develop an 1Dcylindrical model accounting for the radiation-induced deformation and, the loss of elastic modulus induced by temperature and irradiation. However, the fluence (up to 5 × 10 +24 n.cm −2 , the temperature (500 • C) and the ge-…”

“…Hence, BWRs CBS are likely to be relatively immune to irradiation effects since the effets of radiation on concrete mechanical and physical properties are observed for fluence above 1.0 × 10 +19 n.cm −2 . The flux attenuation (Remec et al, 2014) in ordinary concrete is about one order of magnitude per ≈ 12 to 15 cm (5 to 6 in.). Hence, radiation-induced effects are expected to be predominant primarily in the same region depending on the actual fluence at the CBS inner diameter although constrained radiation-induced volumetric expansion (RIVE) could potentially develop detrimental stresses deeper in the CBS wall.…”

“…The interest of Mirhosseini et al' approach is to conduct structural failure analysis of NPP RC components using a nonlinear finite element tool. However, the use of membrane elements for modeling irradiated-CBSs (or RPVSSs) is particularly debatable because of the actual thickness to height ratio of such component and because of the presence of radiation fields profile (Remec et al, 2014) through the member thickness. Modeling nonuniform thermo-hygro-radiological effects in the CBS requires either the use of multilayers shell elements or 3D-volume elements, or 2D-surface element r-z in a cylindrical model, or 1D-r segment element in a radial-cylindrical model.…”

“…Where k and µ are, respectively, the local bulk and the shear moduli of the material and ε * is usually the unrestrained thermal expansion. The latter can be replaced by any other form of physically or chemically induced expansion, i.e., the macroscopic expansion/contraction of concrete resulting from the effects of temperature elevation; shrinkage; and RIVE: code from the DOORS3.2a code system, which includes one-, two-and threedimensional discrete ordinates neutron and photon transport codes (Remec et al, 2014;Field et al, 2015). Hence it is not possible to obtain an analytical solution of the ODE, Eq.…”