Lomi decontamination process

Aspden, R. G., Grand, T. E PWR full-reactor coolant system decontamination. Materials evaluation after three cycles of exposure to the LOMI decontamination process. Report EPRI NP-75I2-M (1991)... 

A fundamental study was conducted to analyze the mechanism of decontamination, as a part of the efforts to develop regenerative LOMI decontamination process. Most of the chemical reactions between picolinate and metal ions such as V, Fe, Ni and Co in the LOMI decontamination system have been known fast chelation reactions so that the chemical reactions can be represented with thermodynamic equilibrium. 

The chemical species in the LOMI decontamination system above pH 5 has not been well investigated. In this study, the reduction mechanism of the V(III) - picolinic acid system based on the results obtained from cyclic voltammetry with various scan rates was investigated as a part of the efforts to develop the regenerative LOMI decontamination process. 

One of the most frequently reported decontamination processes is the Lomi process (Low Oxidation State Metal Ions), which was originally developed by the British CEGB for removal of corrosion product deposits from the fuel bundles of the Steam Generating Heavy Water Reactor (SGHWR). Since Fe " always is the... 

LOMI [Low oxidation metal ions] A process for decontaminating parts of nuclear reactors by washing with aqueous solutions of low-valency transition metal ions. Developed at the Berkley laboratories of the UK Atomic Energy Authority in the early 1980s. 

With oxides containing higher chromium contents, the Lomi process proceeds very slowly since vanadous picolinate is not able to reduce Cr(III). If the chromium concentration in the oxide exceeds 15%, the dissolution rates will become unacceptably low. Therefore, in such applications, the Cr(III) must first be oxidized to Cr(VI) by an appropriate preoxidation step (AP and NP steps, see below). In order to save this time-consuming additional step, attempts have been made to replace V(II) by another reducing cation. Only a combination of Cr(II) with nitrilo triacetic acid or with EDTA shows a faster reaction, but it suffers from insufficient thermal stability thus, it cannot be used in the decontamination of systems and circuits. 

Other full-system decontaminations (e. g. of the Steam Generating Heavy Water Reactor) have been performed using the Rjrco reagent or the Lomi process with and without the NP pretreatment step. The results of these operations were satisfactory as regards decontamination factors and materials compatibility at the circuit surfaces, as well as at the fuel assemblies. 

Experiments performed in an SGHWR loop showed that specimens of stainless steel SS 304, Inconel 600 and Zircaloy-4, previously decontaminated with the Lomi or the NP/Lomi processes, recontaminate within a few months to their preceding activity levels (Bridle et al., 1986). Surfaces which had been decontaminated with the Lomi process alone experienced a faster recontamination than those treated with the NP/Lomi process. This difference may be explained by the fact that application of the NP/Lomi process results in a complete removal of the surface oxide layer, leaving behind a surface which shows less tendency to attract suspended corrosion product particles. 

Experimental work by Nuclear Electric on water reactor decontamination techniques has actually ceased. The LOMI and NP/POD processes which were developed at Berkeley have been licensed for a large number of partial circuit decontaminations, particularly in the USA. 

Experimental work by Nuclear Electric on water reactor decontamination techniques has effectively ceased. The LOMI and NP/POD processes which were developed at Berkeley have been licensed to various commercial companies and have been used for a large number of partial circuit decontaminations, particularly in the USA. The AP/LOMI process has been validated for full circuit decontaminations on BWRs and is in the process of being validated for PWRs. In the USA full circuit decontamination studies are being coordinated by EPRI and we maintain a close interest in this work. It is planned to carry out a full circuit decontamination of Indian Point 2 in 1995. 

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