Fission product release potential

Accident Type Steam Vented From Bldg. (1) Maximum Extent of Fuel Melting (2) Fission Product Release Potential (3) Applicable Remaining Back-up Systems... 

Under normal operating conditions, the performance of coated fuel particles is calculated by models defining several potential failure mechanisms. The HTGR fuel performance models calculate fission product release to the reactor coolant during normal operation from the following six sources ... 

The AHTR appears to have excellent safety attributes. The combined thermal capacity of the graphite core and the molten salt coolant pool offer a large time buffer to reactor transients. The effective transfer of heat to the reactor vessel increases the effectiveness of the RVACS and DRAGS to remove decay heat, and the excellent fission product retention characteristic of molten salt provides an extra barrier to radioactive releases. The low-pressure, chemically nonreactive coolant also greatly reduces the potential for overpressurization of the reactor containment building and provides an important additional barrier for fission product release. The most important design and safety issue with the AHTR may be the performance and reliability of the thermal blanket system, which must maintain the vessel within an acceptable temperature range. 

Condition IV events are faults that are not expected to take place, but are postulated because their consequences include the potential of the release of significant amoimts of radioactive material. They are the faults that must be designed against, and they represent limiting design cases. Condition IV faults are such that, without engineered Safety Measures and barriers to release, a significant fission product release to the environment may occur. 

The potential for containment isolation and containment bypass is lessened by having fewer penetrations to allow fission product release. In addition, normally open and risk important penetrations are fail-closed, thus eliminating the dependence on instrumentation and control (I C) and batteries. 

This potential design improvement would redirect the flow from the steam generator safety and relief valves to the IRWST. This would prevent or reduce fission product release from bypassing the containment in the event of a steam generator tube rupture event. 

A containment isolation failure occurs because of the postulated failure of the system or valves that close the penetrations between the containment and the environment. Containment isolation failure occurs before the onset of core damage. For such a failure, fission-product releases fi-om the reactor coolant system can leak directly from the containment to the environment with diminished potential for attenuation. Most isolation failures occur at a penetration that cormects the containment with the auxiliary building. The auxiliary building may provide additional attenuation of aerosol fission-product releases. However, this decontamination is not credited in the containment isolation failure cases. Accident sequences in which the contairunent does not isolate prior to core damage are grouped into release category Cl. 

The 117-N Building houses air filters used normally for filtering air from potentially contaminated areas in the 105-N Building. These filters will also be used after a severe accident involving significant fission product release. Effluent from the filters and some of the other parts of the 105-M Building is exhausted to the 116 N Air Stack. 

The fission product release assumed for these calculations should be based upon a major accident, hypothesized for purposes of site analysis or postulated from considerations of possible accidental events, that would result in potential hazards not exceeded by those from any accident considered credible. Such accidents have generally been assumed to result in substantial... 

Since for reactors in this group the potential of fuel damage and fission product release is related to the adequacy of the shut-down heat removal system, the requirement for and extent of an emergency plan feasibility has to be established on a case-to-case basis. 

At the same time the potential of NS, FSV and RC units was determined by potential of each of similar objects because even in case of neighboring NSs a simultaneous release of radioactivity (and, what is more, of fission products) from the primary circuit imder external impacts would be unlikely owing to several SNF safety barriers at each NS. Moreover, NS and MV waterborne storage locations are spread over different piers and bases. Magnitudes of radiation potentials of NS, CMB and RC... 

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