Reduced Pressure Principle Backflow Preventer Evaluation and Use at Oak Ridge National Laboratory

Abstract

The necessity for prudent conservation of potable water, the need for protecting water supplies from contamination, and the increased cost of dual water distribution systems serving an expanding nuclear complex, generated an interest at Oak Ridge National Laboratory in the reduced pressure principle backflow preventer. This device, despite its advantages of economy and convenience, has been only partially accepted as a substitute for air-gap separation in preventing pollution of potable water.Previous tests generally reported dynamic or maltreatment conditions. To provide additional assurance of the safety of the device, a reduced pressure principle backflow preventer was tested under five different static conditions. A solution of manganese and potassium nitrates was used as a nonradioactive tracer. Activation and radiochemical analyses having a sensitivity of -0.2 parts per billion of manganese proved there was no detectable backflow from the discharge side to the supply side. Potassium analyses also showed no detectable backflow, but with a lesser sensitivity.The "Protection Factor" (P.F.) for the device is defined as:Reagent concentration in the discharge zone Reagent concentration in the supply zone due to backflow ' P.F. =The minimum protection factor proven in these tests based upon the limit of the sensitivity of manganese analysis is 6.5 x lo8. This factor provides a rational basis for installation where the concentration of radioactivity or other contaminant can be estimated, measured or limited.Criteria for RPPBP installations at ORNL include purchase specifications, inspection requirements, approvals required for use in three levels of hazard, installation requirements and maintenance considerations.

Guide criteria for laboratory evaluation of backflow prevention devices for protection of potable water supplies

“…standards was studied at Oak Ridge National Laboratory around 1965. [8] The following paragraphs are excerpts from the Introductory section of the report on these studies: The flow characteristics and pressure loss requirements of these devices are of prime consideration In Insuring their functional operation.…”

Evaluation of backflow prevention devices :

“…Although the standards for devices do not consider these realistic conditions, such tests have been performed on one model of RPBD by the Oak Ridge National laboratory (ORNL) using the procedures of activation analysis [36] . The RPBD passed this test which had a sensitivity of about 0.2 parts per billion of manganese.…”