June 9, 2021

MAYAK DEVELOPED MEASUREMENT METHODS FOR PLUTONIUM IN HOLD-UPS AND SCRAP

An article on measuring plutonium at Mayak prepared by four Mayak experts appeared in December 2020 in a journal published by Rostechnadzor's Scientific and Engineering Center for Nuclear and Radiation Safety (SEC NRS). The article highlights that such measurements are essential for material control and accounting (MC&A) and provides details on measurement methods and equipment used for the measurements.

Below is an outline of the article. Full text (in Russian) is available in the online version of the SEC NRS journal.

The article covers measurements of quantities of plutonium in hold-ups remaining in processing equipment, plutonium remaining in filters, as well as in nuclear waste. The article states that such measurements are essential to MC&A, including accounting for plutonium in nuclear waste and accurate calculation of inventory difference. The measurements are also essential for nuclear safety, control of the technological processes, and nuclear waste management.

Measurements of uranium and plutonium in hold-ups and scrap were an essential part of the U.S.-Russian nuclear security cooperation. Mayak developments show that Russia continues paying substantial attention to this topic.

Mayak developed five measurement methods for measuring plutonium in hold-ups, scrap, and filters of various types. The measurement methods are based on either neutron coincidence counting or measuring gamma spectrum using MKS-AT6101 spectrometers with various detectors manufactured in Belarus and certified in Russia. The methods were certified as required by Russian legislation on measurement uniformity.

The development and certification of measurement methods for hold-ups and nuclear waste is a complex task. The main issue is the need for reference standards, the development of which is challenging. The standards are needed for calibration of measurement equipment, estimation of variables that impact the measurement result, and measurement quality control. The development of reference standards is challenging due to the variety of shapes and dimensions of hold-ups and waste, as well as their physical state, nuclear material content and isotopic composition, and admixtures that may impact measurement results. An additional challenge is a need for the use of significant quantities of nuclear material to fabricate certain reference standards.

Mayak used the following approach to address the challenges described above:

– Using data from numerical simulation and recent experiments to define detector characteristics and take variables impacting the measurements into account instead of using reference standards;
– Validating measurement methods using attested objects (specifically fabricated samples containing plutonium with well-known characteristics) or reference measurement methods.

Sources:
1. Khorun A. A., Semenov M. A., Galuzin D. D., Romadova S. I. Development and Application of Nondestructive Measurements of Nuclear Materials in Depositions, Aggregations, and Wastes. Nuclear and Radiation Safety, 2020, no. 4 (98), p. 3–12
2. Record on Type Approval of Measuring Instruments for MKS-AT6101 Spectrometers in Federal Measurements Uniformity Registry