Preliminary Evaluation of NMIS for Interrogation of Pu and HEU in AT400-RContainers at Mayak
Preliminary Monte Carlo simulations have demonstrated the sensitivity of the NMIS active interrogation method to the amount of uranium fissile material stored in AT400-R containers that are being proposed for use in the Mayak facility. Properties of the time-of-flight signature can be used to determine the absence of one of the uranium metal spheres or to determine if a different enrichment sphere is present in the container. The tail of the time-of-flight signature from induced fission is directly dependent on the amount of uranium 235 present in the containers, and a particular ratio of the correlated counts due to fission to the correlated counts due to transmission is nearly linear with 235U mass. These simulations demonstrate that the NMIS active method can be used to assay the amount of {sup 235}U with a sensitivity of coefficient of {approx}0.1 per kg {sup 235}U (approximately 10% change in the ratio per kilogram of {sup 235}U). These calculations have shown that these active measurements with a {sup 252}Cf source of 1 x 10{sup 6} fission per sec would require the order of a few minutes of data accumulation time for a container with two 8 kg spheres, and since NMIS operates in real time, 1.6 minutes of measurement time is required. This measurement time is short. The calculations for Pu have shown that NMIS in the passive mode (no Cf source) can determine the mass of Pu in AT400-R containers with short measurement times of a few minutes. The sensitivity of the proposed detectors to gamma rays should enhance this measurement method since the gamma rays from fission, induced or spontaneous, escape the container more easily than neutrons. In addition to the time correlation measurements, the multiplicity options of NMIS allow conventional multiplicity measurements that, depending on the type of detector, can include prompt gamma rays from fission. If gamma ray spectrometry is included in the NMIS processor, then one NMIS system can perform the desired NMC&A measurements for use at Mayak (i.e., HEU, Pu, and Pu isotopics). Higher order NMIS correlation measurements have promise for determining the Pu shape passively also if desired, but this requires four detectors. Active higher order measurements with Pu can separate out the effects of induced fission and spontaneous fission and thus may yield information on the ratio of {sup 239}Pu to {sup 240}Pu. Incorporation of gamma-ray spectrometry is discussed in Appendix A. These capabilities should be verified by measurements both with uranium and plutonium.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 885755
- Report Number(s):
- ORNL/M-6648/R4; TRN: US0604090
- Country of Publication:
- United States
- Language:
- English
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