Shielding Calculations for the BDMS UF6 Mass Flow Meter
We performed Monte Carlo calculations of the neutron and gamma ray spectra and neutron and gamma dose rates outside the shielding of the UF{sub 6} mass flowmeter. The UF{sub 6} mass flowmeter and the UF{sub 6} mass flowmeter are the two main components of the Blend Down Monitoring System (BDMS) equipment. The BDMS equipment is designed to continuously monitor the UF{sub 6} enrichment and mass flow rates in processing pipes at uranium facilities. The UF{sub 6} mass flowmeter incorporates four {sup 252}Cf neutron sources, surrounded by a polyethylene shielding block. The uranium fission products generated by the {sup 252}Cf neutrons are detected down the pipe, thus confirming the UF{sub 6} mass flow rate. The dose calculations used both U.S. and Russian gamma and neutron fluence-to-dose conversion coefficients. The purpose of these calculations was to facilitate proper interpretation of the neutron dose rate measurements from rem meters (e.g., rem balls) outside of BDMS shielding. An accurate determination of the dose rate is particular interest in that it enables dose rates to be compared with the applicable regulatory limit. The calculations show that neutrons outside of BDMS shielding are significantly reduced in energy, i.e., the spectrum is shifted (i.e., moderated) towards lower energies and contains significantly larger amount of neutrons in the energy range below 100 keV. Results of the calculations indicate that neutron dose rate measurements taken outside of BDMS shielding are overestimated by 25% to 55%, depending on the location around BDMS, when using either Russian or U.S. dose conversion coefficients. For an accurate neutron dose rate evaluation, application of an appropriate correction factor to the neutron dose rate measurements is necessary.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15013412
- Report Number(s):
- UCRL-ID-145377; TRN: US0600863
- Country of Publication:
- United States
- Language:
- English
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