One of the problems that occurs in nuclear power stations is the accumulation of radioactive crud. (Wikipedia defines crud as a computer programming acronym representing [Create, Read, Update, Destroy] whereas some pioneers in the nuclear industry claim it stands for Chalk River Unidentified Deposits.)
Crud, formed from corrosion products and other particles floating in the cooling systems, is a problem when it becomes radioactive and deposits on surfaces in the cooling and steam-generating systems of reactors. Its presence greatly increases the dosage accumulated by maintenance workers and leads to significant costs.
The earliest attempts to remove the crud often required that the reactor was shut down for an extended period and chemicals would be added to the systems to remove the deposited film. The extended shutdown would be costly and also resulted in large volumes of radioactive liquid waste that would then have to be disposed. In the case of CANDU, the heavy water coolant would be downgraded and had to be purified.
In the late 1960’s teams at Chalk River, Whiteshell and Ontario Hydro collaborated to produce a new way of removing crud. This system, which came to be known as CAN-DECON (CANdu-DECONtamination), involves adding a small amount of the cleansing reagent to the primary cooling system of the reactor while it is shut down. The coolant circulates and works to remove the contaminated, radioactive film from the system surfaces and then passes through extremely fine filters which remove the particles combined with an ion exchange column that removes the dissolved contaminants and regenerates the reagent.
Typically, after 1-2 days circulating, the reagent has completed its task and no additional material is found in the filters or the ion resin. The coolant is then passed through a second Ion exchange resin where the reagent is removed, and the primary coolant is again returned to its pure state.
The process has the advantages of greatly reducing the reactor shut-down period and reducing the volume of the radioactive material to be disposed compared to the solid filters and ion exchange resins. With the CAN-DECON application, reductions of 10-12 are achieved in the radioactive load of the cooling systems.
The CAN-DECON process was first tested on the Nuclear Power Demonstration (NPD) reactor at Rolphton in 1973, and later that year at Gentilly-1. In 1975 decontamination was successfully achieved at the Douglas Point CANDU in just 72 hours.
International interest was almost immediate. The process was then licensed by AECL to W.P. London and Associates of Niagara Falls for wider application. A subsidiary company, London Nuclear Decontamination Limited (LNDL), was formed. Eric LeSurf, a long-time Chalk River researcher who had worked on the development of the process was
hired by LNDL as Technical Director for the program and led the application of CAN-DECON internationally.
Over the next decade the process was applied to the BRUCE-A CANDU units and also, with some modifications, to Boiling Water Reactors (BWR) and Pressurized Water Reactors (PWR) in Japan, Sweden and the USA.
Visitors to the Canadian Nuclear Heritage Museum can peruse various publications on the process as well as view a duplicate of a large painting presented to Eric LeSurf when he left AECL to join LNDL. The artist for the painting was the late Derek Lister, a long-time colleague of Eric’s at Chalk River who spent many years researching contamination transport in CANDUs before accepting a Research Chair at the University of New Brunswick.
