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Review of Molten Salt Reactor Physics Calculations [Disc 2]
Review of Molten Salt Reactor Physics Calculations [Disc 2]
Review of Molten Salt Reactor Physics Calculations [Disc 2]
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25<br />
4. FISSION RRODUCTREWMEW<br />
I<br />
The MERC calculation includes 925 fission product nuclides in ex-<br />
plicit chains. However, many <strong>of</strong> these nuclides make extremely small<br />
contributions to the overall fission , product poison fractilsn.' To facilitate<br />
our ASSAULT and LTM calculations, it appeared desirable to include<br />
these small contributions in one or more pseudo-elements, with only the<br />
more important nuclides being treated explicitly.<br />
The long fission product treatment used in the advanced converter<br />
study (~~~~-3686) was chosen as tk basic 'kxnpleteW'ifission product<br />
description. This.description is pictured in Figi 4.1.<br />
Since the fluid&&l system in the MSBR allows some <strong>of</strong> the fission<br />
products to be stripped as gases or be removed in fuel processing, the<br />
above treatment needs to be modified to include those effects. The<br />
modifications made are discussed below. ,~<br />
'<br />
1. mJ&$9& Chain. 'All the nuclides in this chain plate out on<br />
metal.surfaces and are assumed to beg removed instantaneously.<br />
I 2. l%n. Assumed to be removed instantaneously by plating out on,<br />
metal surfaces.<br />
3 . "No-~~~R~ Chain. All the nuclides,beyond and including looEzu<br />
- plate out on metal surfaces. Instantaneous removal.was. assumed. Since<br />
the " MO half life is only 66.5 hr, i was assume$ that the 99 Mo.fission<br />
fissionyield produces "Tc instantly.<br />
4. 1311-13%e. Assumed t&t 13' I decays in&a&Q (8 day.half-life)<br />
to 13?Xe which is removed instantly by gas stripping.<br />
-.<br />
5. 13%e. Removed instantly by gas stripping.<br />
6. u3x,_&33&.. R emoved ' instantly by gas stripping.<br />
7* 135Xe<br />
l<br />
The-assum&ions <strong>of</strong> the MARC studies stated that a poison<br />
fraction <strong>of</strong>- O.O050.(fractional loss per neutron absorbed in fuel) would<br />
be assumed-for u5 Xe to alloifor.any absorption<strong>of</strong> xenonand krypton by -<br />
graphite. Since this assumption determines the 13%emconcentration, the<br />
135<br />
I precursor is not included in the chains.<br />
The reduced set <strong>of</strong> explicit; fission product chains is s&n in<br />
Fig. ic.2. Yield fractions for the explicit: nuclides are listed in Table<br />
4.1.
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