"Parametric Study of molybdenum-99 Production using a Sub-critical Low Enriched Uranium Assembly Design Proposed by Niowave, Inc.,"
M.S. Thesis, Nuclear Engineering, Texas A&M University, College Station, TX (2016).
The radioisotope, technetium-99m (99mTc with 6-hour
half-life), is used in over 80% of diagnostic medical imaging and
is the daughter product from the radioactive decay of the isotope,
molybdenum-99 (99Mo with 66-hour half-life).
99Mo is a fission product, with a fission yield of 6.1%,
and therefore can be produced by nuclear reactors or by other
methods. While 99Mo has been produced using highly
enriched uranium (HEU), there is an international interest to
produce this isotope using low enriched uranium (LEU) due to the
nuclear proliferation concerns of HEU. Niowave Inc. is a facility
that has plans to produce 99Mo in the United States. The
production of 99Mo in the U.S. ensures its seamless
availability to benefit the people who need 99mTc based
medical diagnostics in the country.
99Mo production was studied for an electron beam and
sub-critical LEU assembly design proposed by Niowave Inc. by
applying Monte Carlo radiation transport and coupled isotope
generation-depletion calculations. In addition, the production of
135Xe, 131I, 239Pu,
105Ru and 105Rh were also investigated. The
photoneutron source emanating from electronphoton- neutron
production scheme of Niowave was studied by varying neutron
moderators in the sub-critical system and LEU enrichment to predict
optimal production of 99Mo and other radioisotopes
products of interest. The neutron moderators that were considered
for this study are light water, heavy water and beryllium.
99Mo production rate was studied, the predicted value
for this study is ~9 kCi per week with a 235U enrichment
of 10% and light water as the neutron moderator. This amount of
99Mo production could meet 15% of the US demand from one
production facility. Studies found that water is the best neutron
moderator for the current design to maximize the production of
99Mo. The light-water-moderated system achieves highest
criticality level as well as a highest thermal neutron flux and
power, when compared to the other two candidates. Heavy water is a
better neutron moderator than beryllium for the current design,
however, it is not as good as water. Both, heavy water and
beryllium can achieve a similar performance as that of light water
moderator only if the 235U enrichment is higher than
19.9%, however the facility is limited to only using LEU fuel. Even
at 19.9% enriched fuel, heavy water and beryllium do not achieve
the neutron flux, power or 99Mo production levels when
water is used moderator in the system. In conclusion, the studies
conducted found that water is the best moderator candidate for this
design, maximizing the production of 99Mo.
Associated Project(s):Parametric Study of molybdenum-99 Production using a Sub-critical Low Enriched Uranium Assembly Design Proposed by Niowave, Inc.