S. RAY and E. LAHODA, Westinghouse Electric

Company LLC, USA

DOI: 10.1533/9780857097453.3.385

Abstract: This chapter provides background on current materials-related problems faced by the nuclear industry. These issues have become more important as the current fleet of nuclear plants ages and as life extensions of 20 years each are added onto the current 40 year life. Materials issues requiring research and development are presented in terms of the fuel, the primary boundary, the containment and other general issues.

Key words: nuclear, power plant, industry, materials, issues, fuel, rods, cladding, containment, primary, secondary, corrosion, cracking, buried, pipe, wiring, concrete, steel.

9.1 Introduction

As the light water reactor (LWR) nuclear fleet reaches and surpasses the original 40 year lifespan that it was licensed for and embarks on its next 20 years with visions of yet another 20 years beyond that, the need increases for a scientific underpinning of the understanding of the degradation of materials in a nuclear environment. The need to generate this scientific underpinning becomes more compelling when one considers that the orig­inal 40 year life had no scientific basis (INL, 2009) and that the materials designs were not based on irradiated materials in real life chemistry con­ditions (Majumdar, 2011). There are indeed many existing models and correlations for determining what may happen as materials in a nuclear environment age, but most are based purely on empirical data. The ability to extrapolate these models is under question by the industry and the NRC, which will not grant licenses based on extrapolated models. Far too often, researchers have discovered unexpected effects, both good and bad, which should not have occurred based on extrapolation of models.

This chapter focuses on the materials in a nuclear system from the inside out of a nuclear plant. First the initial fission boundary of the fuel (Fig. 9.1),

Zircaloy Zr based alloy

BWR Zry-2 (Zr-1.5Sn-0.12Fe-0.05Ni-0.1Cr) PWR Zry-4 (Zr-1.5Sn-0.15Fe-0.00Ni-0.1Cr)

9.1Nuclear fuel pellets and rods (Kazuya Idemitsu, Genshiryoku Zumenn Syuu, JAERO, p. 4, used by permission of the author).

both the fuel itself which contains most of the fission products, and then the fuel cladding which normally contains the rest of the fission products. Occasionally, the cladding leaks and the second boundary comes into play — the primary system of the pressurized water reactor (PWR) (Fig. 9.2) and the steam system of the boiling water reactor (BWR) (Fig. 9.3). After that, the boundary is the secondary system and the containment of the PWR or BWR. During postulated accident conditions, the innermost system (fuel and cladding) fails and then all that remains to avoid exposure to the public is the concrete and steel containment structure. Thus, a good understanding of all the containment systems is also needed.