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ON-LINE INTERROGATION OF PEBBLE BED REACTOR FUEL USING PASSIVE GAMMA-RAY SPECTROMETRY

CHEN, JIANWEI
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1096255485

Abstract Details

2004, PhD, University of Cincinnati, Engineering : Nuclear and Radiological Engineering.
The Pebble Bed Reactor (PBR) is a helium-cooled, graphite-moderated high temperature nuclear power reactor. In addition to its inherently safe design, a unique feature of this reactor is its multipass fuel cycle in which graphite fuel pebbles (of varying enrichment) are randomly loaded and continuously circulated through the core until they reach their prescribed end-of-life burnup limit (~ 80,000-100,000 MWD/MTU). Unlike the situation with conventional light water reactors (LWRs), depending solely on computational methods to perform in-core fuel management will be highly inaccurate. As a result, an on-line measurement approach becomes the only accurate method to assess whether a particular pebble has reached its end-of-life burnup limit. In this work, an investigation was performed to assess the feasibility of passive gamma-ray spectrometry assay as an approach for on-line interrogation of PBR fuel for the simultaneous determination of burnup and enrichment on a pebble-by-pebble basis. Due to the unavailability of irradiated or fresh pebbles, Monte Carlo simulations were used to study the gamma-ray spectra of the PBR fuel at various levels of burnup. A pebble depletion calculation was performed using the ORIGEN code, which yielded the gamma-ray source term that was introduced into the input of an MCNP simulation. The MCNP simulation assumed the use of a high-purity coaxial germanium detector. Due to the lack of one-group high temperature reactor cross sections for ORIGEN, a heterogeneous MCNP model was developed to describe a typical PBR core. Subsequently, the code MONTEBURNS was used to couple the MCNP model and ORIGEN. This approach allowed the development of the burnup-dependent, one-group spectral-averaged PBR cross sections to be used in the ORIGEN pebble depletion calculation. Based on the above studies, a relative approach for performing the measurements was established. The approach is based on using the relative activities of Np-239/I-132 in combination with the relative activities of Cs-134/Co-60 (Co-60 is introduced as a dopant) to yield the burnup and enrichment for each pebble. Furthermore, a direct consequence of the relative approach is the ability to apply a self-calibration scheme using the multiple gamma lines of Ba-La-140 to establish the relative efficiency curve of the HPGe detector. An assessment of the expected uncertainty components in this approach showed that a maximum uncertainty of less than 5% should be feasible. To confirm the above findings, gamma-ray scans were performed on irradiated PULSTAR reactor fuel assemblies at North Carolina Sate University. The measurements used a 40% efficient n-type coaxial HPGe detector connected to an ORTEC DSPECplus digital Gamma-Ray Spectrometer, and a data acquisition computer. The obtained results showed consistency with the predictions of the simulations including the observation of the I-132, Cs-134, Np-239 uncontaminated gamma lines. In addition, the Ba-La-140 lines were clearly observed confirming the ability to perform relative calibration of the spectrometer.
Ayman Hawari (Advisor)
155 p.
Engineering, Nuclear

Recommended Citations

Citations

  • CHEN, J. (2004). ON-LINE INTERROGATION OF PEBBLE BED REACTOR FUEL USING PASSIVE GAMMA-RAY SPECTROMETRY [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1096255485

    APA Style (7th edition)

  • CHEN, JIANWEI. ON-LINE INTERROGATION OF PEBBLE BED REACTOR FUEL USING PASSIVE GAMMA-RAY SPECTROMETRY. 2004. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1096255485.

    MLA Style (8th edition)

  • CHEN, JIANWEI. "ON-LINE INTERROGATION OF PEBBLE BED REACTOR FUEL USING PASSIVE GAMMA-RAY SPECTROMETRY." Doctoral dissertation, University of Cincinnati, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1096255485

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Cincinnati and OhioLINK.