ORNL-TM-7207 - the Molten Salt Energy Technologies Web Site
ORNL-TM-7207 - the Molten Salt Energy Technologies Web Site ORNL-TM-7207 - the Molten Salt Energy Technologies Web Site
128 the letter, of NRC requirements, particularly where methods of compliance are concept-specific. Any special issues that might arise from public consideration of an MSR license probably would be closely associated with those features of the reactor concept that affec% its safety and environmental attributes. A number of these features and attributes have been identified in earlier S ~ C ~ ~ O R S Owe , major difference between more conventional reactors and MSRs is in the confinement of radioactive fuel and fission products. The barriers to fission-product release in LWRs are (I) the fuel element clad- dingp (2) the reactor coolant pressure bounda~y (RCPB) (ioee9 the primary- Poop vessels, components, and piping), and (3) the reactor c~~tairnent, This arrangement relies heavily on the ECCS to prevent cladding failure in the event of coolant loss by failure of the RCPB. Iqithsut adequate ENS performance, a failure of the WCPR conceivably @odd leave the fis- sion produets with only one level of confinement intact. A different situation would prevail in an MSR because the fission- p~~duct confinement barriers are different. The relevant barriers in an MSR are (1) the RCPB, (2) the sealed reactor cells or primary csntaiment, and (3) the reactor containment building or secondary containment. Be- cause the fuel is a circulating liquid that is also the primary ~o~lant, there is no thin fuel clad that could fail quickly on EQSS of co~lfng or in a reactor power/temperature transient. ~hras, an entire class of po- tential accidents could be eliminated from the licensing consideration. Failure of the RCPB in an MSR would cause no sh~rt-term threat to either of the remaining two barriers to fission-product release. 'Flze ultimate requfrements for longer-tern protection of the fission-product barriers cannot be defined without extensive system design and safety analysis, but preliminary considerations suggest 'chat the requirements may not be extensi%re, Although radioactive materials would have three levels of confine- ment during norm1 operation, a different condition could exist during maintenance operations that required opening of the primary containment, * Failure of the WCPR is one sf the mechanisms for initiating a Psss- of-coolant accident (LOCA>. *
129 particularly if such activities were undertaken after an RCPB failure. However, in a shutdown situation, substantial confinement can be achieved through access limitation and controlled ventilation because, as shown by MSRE experience, fission products are not readily released and dis- persed from stagnant salt. Thus, whether fission-product confinement would be a net favorable or unfavorable factor for a BMSR in a licensing proceeding is not clear at this time. At the end of reactor life, a DMSR without fuel processing would contain the entire fissio~-pr~duct inventory associated with the 30-year operating history of the plant. Some of the volatile nuclides, especially 85Kr and 3H, would have been accumulated in storage containers outside the primary circuit, and the noble metals would have plated out on surfaces in the primary circuit. The inventories of these nuclides, which would not be strongly affected by nuclear burnup, would be about the same as those produced in a solid-fuel reactor wPth the same thermal power level and duty factor. However, because the BMSR would generate only about two- thirds as much thermal power as an EWR for the same electrical output, it would produce a ~o~~espondingly smaller inventory of fission products. Most of the other fission products and all the transuranium nucltcles wou%dl remain with the fuel salt in a DMSR. The inventories of these mate- rials would be further reduced by nuclear burnup resulting from exposure of the nuclides to the neutron flux in the reactor core. This effect would be particularly important for the high-cross-section nucPides such as the major plutonium isotopes. Consequently, the net production of plu- tonium would be much smaller for a DMSR than for a comparable solid-fuel reactor, but the production of higher actinides would be much greater be- cause of the long effective fuel exposure time. Although a DMSW WQUI~ produce a much smaller total inventory of some important nuclides over its lifetime than an LWR, the actual in-plant in- ventory could be substantially higher for the DMSR because there would be no periodic removal during refueling operations. (There would also be no major shipments of highly radioactive spent fuel from the plant during its lifetime arid no out-of-reactor storage of suck materials until after the final shutdown.) Thus, if a major release of in-p%ant radionuclides could occur, the consequence might be more serious in a DMSR than in an
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128<br />
<strong>the</strong> letter, of NRC requirements, particularly where methods of compliance<br />
are concept-specific.<br />
Any special issues that might arise from public consideration of an<br />
MSR license probably would be closely associated with those features of<br />
<strong>the</strong> reactor concept that affec% its safety and environmental attributes.<br />
A number of <strong>the</strong>se features and attributes have been identified in earlier<br />
S ~ C ~ ~ O R S Owe , major difference between more conventional reactors and<br />
MSRs is in <strong>the</strong> confinement of radioactive fuel and fission products. The<br />
barriers to fission-product release in LWRs are (I) <strong>the</strong> fuel element clad-<br />
dingp (2) <strong>the</strong> reactor coolant pressure bounda~y (RCPB) (ioee9 <strong>the</strong> primary-<br />
Poop vessels, components, and piping), and (3) <strong>the</strong> reactor c~~tairnent,<br />
This arrangement relies heavily on <strong>the</strong> ECCS to prevent cladding failure<br />
in <strong>the</strong> event of coolant loss by failure of <strong>the</strong> RCPB. Iqithsut adequate<br />
ENS performance, a failure of <strong>the</strong> WCPR conceivably @odd leave <strong>the</strong> fis-<br />
sion produets with only one level of confinement intact.<br />
A different situation would prevail in an MSR because <strong>the</strong> fission-<br />
p~~duct confinement barriers are different. The relevant barriers in an<br />
MSR are (1) <strong>the</strong> RCPB, (2) <strong>the</strong> sealed reactor cells or primary csntaiment,<br />
and (3) <strong>the</strong> reactor containment building or secondary containment. Be-<br />
cause <strong>the</strong> fuel is a circulating liquid that is also <strong>the</strong> primary ~o~lant,<br />
<strong>the</strong>re is no thin fuel clad that could fail quickly on EQSS of co~lfng or<br />
in a reactor power/temperature transient. ~hras, an entire class of po-<br />
tential accidents could be eliminated from <strong>the</strong> licensing consideration.<br />
Failure of <strong>the</strong> RCPB in an MSR would cause no sh~rt-term threat to ei<strong>the</strong>r<br />
of <strong>the</strong> remaining two barriers to fission-product release. 'Flze ultimate<br />
requfrements for longer-tern protection of <strong>the</strong> fission-product barriers<br />
cannot be defined without extensive system design and safety analysis,<br />
but preliminary considerations suggest 'chat <strong>the</strong> requirements may not be<br />
extensi%re,<br />
Although radioactive materials would have three levels of confine-<br />
ment during norm1 operation, a different condition could exist during<br />
maintenance operations that required opening of <strong>the</strong> primary containment,<br />
* Failure of <strong>the</strong> WCPR is one sf <strong>the</strong> mechanisms for initiating a Psss-<br />
of-coolant accident (LOCA>.<br />
*
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