Novel In-Situ Technique for Inspection of Deep Borehole Casing Emplacement and Cement Annulus Integrity

Spent Nuclear Fuel (SNF) disposition remains one of the forefront problems in the nuclear energy industry. One of the concepts being actively investigated is the encasement of SNF casks in deep wellbores with bentonite, concrete seals, and concrete casings. However, deep geological formations have temperatures and pressures in excess of 150°C and 50 MPa respectively, and thus pose a great risk of concrete seals and/or casings becoming compromised during emplacement or at a later stage. Thus, techniques for the verification of in-situ wellbore seals and concrete casing integrity is of vital importance to ensure the safety of the SNF disposition program. Statement of How this Problem is Being Addressed: Here we propose a novel well-logging technique to be executed as part of the overall cement program in deep borehole disposition. In our method, the casing and seal concrete is modified using special agents and subsequently irradiated in-situ with an isotopic source. Following the irradiation, specialized radiation detectors are used to measure signal emitted from the seal concrete. Based on variations in the observed signal, density/porosity, voids and other compositional defects in the concrete can be localized and quantified. What is to be done in Phase I: In Phase I, we will demonstrate the feasibility of our approach through simulations and testing in order to evaluate the optimal cementitious mixture, agent concentration, as well as detector material and design. Phase I will culminate in a working technical model that shows the method’s feasibility as well as detection and environmental limits. Phase II efforts will focus on building a physical prototype of the system to be used in the field as well as further optimization of the detector. Commercial Applications and Other Benefits: The proposed method is of immediate applicability for the inspection of on-site dry storage casks. In addition to radioactive waste disposal, the proposed technique has far reaching applications including the oil and gas industry, carbon sequestration, and geothermal energy. Keywords: neutron activation, cement annulus inspection, radiation detector, borehole logging detector, density tool.