Page 249 - Dynamics and Control of Nuclear Reactors

250 APPENDIX B Advanced reactors

use of reactor vessels with smaller thickness compared to LWRs. Any chemical
interaction of sodium with water must be avoided and is a safety issue to be consid-
ered in the design of heat exchangers.

B.6.3 Molten salt reactors
In a molten salt reactor (MSR) the system uses molten salt to transfer heat from the
reactor primary side, to an intermediate heat exchanger, and then to the balance-of-
plant side of the system for electricity production and/or industrial heat applica-
tions [23, 24].Ina salt-cooled reactor, the core is stationary with solid fuel
and liquid salt is used as the coolant. In a salt-fueled reactor, the fuel is dissolved
in a liquid salt and the liquid fuel circulates through the primary and the interme-
diate loops. The Department of Energy adopted the term “fluoride salt-cooled high-
temperature reactor” (FHR) in 2010 to distinguish fluoride salt-cooled MSRs from
salt-fueled MSRs.
Liquid salt-fueled reactors are called molten salt reactors or MSRs. Potential
future molten salt reactors include thermal reactors and fast reactors. The thermal
version uses graphite as the moderator. In both types, the fuel is dissolved in a molten
salt. MSRs operate at low pressure with the ability for on-line refueling, thus avoid-
ing the need for reactor shut down for regular refueling. In the molten salt breeder
reactor (MSBR) design, the conversion of Th-232 first results in Protactinium-233
and, consequently, has the problem of loss of U-233 production through neutron cap-
tures in Pa-233 as described in Section B.1.1. The MSBR addresses this problem by
removing and sequestering the molten salt stream that contains Pa-233. The MSBR’s
unique use of fertile material dissolved in a fluid enables a solution to the problem of
U-233 losses by captures in Pa-233.

B.6.4 Heavy water reactors
The Advanced Heavy Water Reactor (AHWR) is a new heavy water design from
India [25–27]. It uses light water coolant that boils in vertical channels located in
a tank of heavy water moderator. Coolant flows by natural circulation.
The AHWR is designed to use thorium for power production. The cylindrical fuel
bundle contains 54 rods, an inner circle with 30 rods containing ThO 2 and an outer
circle with 24 rods containing ThO 2 and PuO 2 .
Since other reactors with similar features had stability problems, detailed sta-
bility studies have been performed for theAHWR. TheAHWRhas aphysically
separate and stationary moderator from the boiling coolant like the Russian RBMK
(Chernobyl) reactor. The AHWR has boiling coolant as in BWRs. Both of these
reactors have stability issues. Stability studies for the AHWR indicate adequate
stability margins.