closure project manager - Document Request - U.S. Department of ...

i
’ i,
! U”
In summary, removal of analysis conservatism by using a TRU waste drum versus a
TRU waste box and irsirig more aDDroDriate ARF 2nd RF values would continue to yield
Risk Class 11 result for the CW. No credit is taken in Case 1 for the expected inflow of air while
dock doors are men that would tend to mitigate the container exdosion scenario consequences
Crediting the Huiiditzg 991 fiZtered exhartst vetrfilation system and facilitv confipiiration
controls would reduce the MOI and CW risk to Risk Class I\’ for Case 2 (exfrernelv ?mtikr?iy
frequency. low consequences).
NPmE Scenario 1 - DBE Event-Induced SpilJ
A DBE event is postulated to occur impacting the POC and TRU waste storage areas in
the Building 991 Complex. TRU waste containers stored in Building 991 are considered to be
susceptible to earthquake impacts. Containers that are impacted may be breached by falling
debris (e.g., overhead cranes; heating, ventilating, and air conditioning WAC) ducts; etc.) and
other overhead equipment that is not seismically rated. The building structure and roof is
expected to remain intact in a DBE event and stacked waste containers are not expected to topple
in a DBE event. The exposed upper tier of waste containers is assumed to be susceptible to
impact from the falling debris. The breached tantainers from the falling debris do not spill the
container contents from the breach since the breach is at the top or upper portion of the
container.
The postulated DBE scenario is considered to be an unZikzZj event with high
consesuences for the CW, moderate consequenlces for the MOI, and znoderate consequences for
the IW. The MOI and the Tw risk class for the scenario is Risk Class 11. The CW has Risk
Class I scenario results.
Acceptability of the risk class results for the CW and the MOI is based on the
conservatism that is assumed in the analysis. If‘ a median x/Q value (approximately an order of
magnitude reduction in atmospheric dispersion) were used in the analysis, the CW consequences
would be moderate and the MOI consequences would be low. This would yield a reduction in
the corresponding risk class for the CW and MO’I. Use of a more realistic MAR (k, a factor of
2 reduction in MAR) concurrent with a median >:/Q value yields the same results.
The DBE scenario does not take any credit for deposition and building retention of
radioactive material that is released during $he event. If the ventilation system is not
functioning, the ambient building leakpath factor is qualitatively judged to be less than 0.1 for an
intact facility. In the DBE event the building is assumed to remain intact. Assuming an ambient
building leakpath factor of 0.1 reduces the MOI consequences to low and the CW consequences
to moderate. This reduces the risk class to the MOI to Risk Class 111 and to the CW to Risk
Class II.
The damage ratios used in the analysis and the drum loading of the facility that is
assumed are both conservative. However, an order of magnitude conservatism from each of
these analysis assumptions is not likely. The mmbined effect of the two assumptions could
result in an order of magnitude conservatism that, if removed, would lower the risk class for the
MOI and for the CW.
Revision 1
September 1999
4-39 Building 991 Complex FSAR