Initial phase of Pu-238 production in Idaho National Laboratory
Section snippets
PFS program history and objectives
Pu-238 is an alpha emitter with a half-life of 87.7 years with a sufficient decay heat to power a deep space satellite or a space probe as a radioisotope thermoelectric generator (RTG). NASA missions: Mars’ Curiosity rover, the New Horizons spacecraft flyby of Pluto, and the most recent Perseverance launched to Mars, July 2020 were powered with a Pu-238 RTG. The capability to produce Pu-238 was lost in the late 1980s after the target irradiation reactors at the Savannah River Site were shut
ATRC operating conditions
The ATRC facility is a testing facility adjacent to the ATR, which runs at low power with nearly identical neutron profile to the ATR, see Table 1. Typically, nuclear material experiments are tested and mimicked in the ATRC before they are irradiated in the ATR to determine targets reactivity and safety by analysis of neutron flux and gamma background induced by the irradiation.
PFS-1 experimental design
Original dosimeters were shipped to the INL from the Pacific Northwest Laboratories (PNNL) in 1992, with detailed records of their weights, activities and measured doses, see Table 2, (U-235-U238Dosimeter R, 1992). They were unopened until preliminary measurements in 2017. The irradiation assembly in the ATRC consisted of four NpO2 dosimeters, in two separate dosimetry capsules, 1-X and 1-Y. It also included a number of other dosimetry wires, some were found in the INL, but others were ordered
Source production – details
Np-237 is a long-lived (>106 years) alpha radioisotope decaying to Protactinium (Pa-233) which decays to Uranium (U-233) in equilibrium (see Fig. 4). Almost all of the Np-237 feedstock was generated by reactors and refinement from past weapon activities (Preliminary Design Review, 2016). It decays in the combination of alpha, beta, and gamma emanations. The Np-237 most prominent gamma ray, 143.249(20) keV, has a branching ratio 0.443(8) % compared to over 38.5(4) % branching ratio for Pa-233
Summary
Careful pre- and post-irradiation measurements of NpO2 dosimeters and other sensors with and without Cd sleeve for thermal and epithermal neutron production in the ATRC reactor were performed by use of gamma spectroscopy to validate Pu-238 production in the INL.
The pre-irradiation average activity was determined from Pa-233 isotope's most intense gamma peak at 311 keV at 0.70(4)+-5% μCi/mg which was identical in the range of error with the nominal specific activity at 0.704 μCi/mg.
The
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The project was funded by DOE Office of Science, DE-AC07-05ID14517 contract for PFS ATR. It was released for publication thanks to the support of A. Zillmer and K. Lively from INL Nuclear Power and Isotopes Production Dept. We are grateful for the expertise provided by Dr. D. Nigg with experiment's plan design and N. Manwaring, for ATRC plan execution. We appreciate support of the RML laboratory, especially Dr. M. Reichenberger providing information about RML detectors/software, and technical
References (16)
- Atlas of Nuclear Resonances ENDF-VIII.0:...
- et al.
Meas. Of thermal neutron capture CS and res. Integral of the reaction 127I(n,γ)128I
J. Nucl. Sci. Technol.
(1999) - et al.
PCGAP Users Guide and Algorithm Desc
(2000) RML Data for Flux Run 17-4 in TP-04-17
(2017)- et al.
Production of plutonium-238 with minimum plutonium-236 concentration
J. of Nuclear Technology
(1972) CSM-10584 monitor procurement for INL
Rev.
(2017)