Decontamination Processes for Restorative Operations and as a Precursor to Decommissioning: A Literature Review

Abstract

Pacific Northwest Laboratory (PNL) conducted an comprehensive literature review of actual reactor decontamination processes that are currently available. In general, any decontamination process should be based on the following criteria: effectiveness, efficiency, safety, and waste production. The information that was collected and analyzed has been divided into three major categories of decontamination: chemical, mechanical, and electrochemical. Chemical methods can be further classified as either low-concentration, singlestep processes or high-concentration, single-or multistep processes. Numerous chemical decontamination methods are detailed. Mechanical decontamination methods are usually restricted to the removal of a contaminated surface layer, whlch limits their versatility; several mechanical decontamination methods are described. Electrochemical decontamination. is both fast and easily controlled, and numerous processes that have been used in industry for many years are discussed. Information obtained from this work is tabulated in Appendix A for easy access, and a bibliography and a glossary have been provided. v SUMMARY There is an increasing realization by the public and the nuclear industry that decontamination of nuclear facilities is necessary for both continued operations and decommissioning. Processes used as a precursor to decommissioning may include more destructive measures than allowable for facilities that will be restored to operation; however, they are expected to have the potential for a greater degree of decontamination.This report is the result of a comprehensive literature review wherein the authors have collected and analyzed information on actual decontamination processes that are currently available. Processes that are acceptable for the primary system are reviewed, as are those that are acceptable for interior structural members (such as concrete or painted surfaces) and for exterior locations (such as concrete or soil). Applicability is based on such factors as extent of decontamination, corrosiveness, waste produced, and time required for application. Decontamination of activated materials such as fuel-cladding and bio-shield components is beyond the scope of this program except for possible removal of loose surface deposits.The information presented in this report is also tabulated in Appendix A for easy access. The information has been divided into three major groups: chemical decontamination methods, mechanical decontamination methods, and electrochemical decontamination methods.Chemical methods are further subdivided into low-concentration, singlestep processes and high-concentration, single-or multistep processes. Within these classifications the chemical processes can be summarized into six groups:• high pH oxidation and dissolution • high pH oxidation followed by low pH dissolution • low pH oxidation and dissolution • low pH oxidation followed by low pH dissolution • low pH dissolution • low pH reduction and dissolution.vii Mechanical decontamination methods usually...

Decontamination as a precursor to decommissioning. Status report Task 2: process evaluation. [PWR; BWR]

“…Corrosion testing was performed under both static (all alloys) and flow conditions (carbon steel only) as described earlier. Nelson 1981). There are, in some cases, significant effects of flow, pH, or concentration of key components which greatly change corrosion rates and are not always reported in the literature.…”

“…A comprehensive tabulation of the various chemical solutions used for a wide range of decontamination procedures is given in Table A.l of Nelson and Divine (Nelson 1981). A review of the solutions shows that there are anumber of chemicals common to various decontamination techniques.…”

“…The findings of this study are being published as topical reports which will be drawn together as a whole in a final comprehensive program report. The literature review has been published (Nelson 1981). The present report reviews the current status of Task 2, Process Evaluation, which is a laboratory scale examination of the major decontamination processes.…”

“…In reviewing the data available on the processes (Nelson 1981), it is apparent that they are not well described in terms of OF's, corrosion, safety or operating needs. There are exceptions such as Dow Chemical's NS-1 and the old standby AP-Citrox.…”

“…* H 3 P0 4 has also been used repetitively in the Hanford-N Reactor (Nelson 1981). Initially it was selected because of the large amounts of carbon steel in the system that had to be cleaned; but, the process is also ideally suited for Hanford-N Reactor and is relatively straightforward to use.…”