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The risk and conseauences of Puncture Scenario 1 (Case €3) will be presented for two
situations: 11 Case Bl (unmitigated) represents punmres occurrim in Room 147 or 170 while
dock doors are open: and 2) Case B2 (mitigated) represents punctures occurring at any other
time.
In summary, removal of analysis conservatism by assuming that onlv one TRU drum is
involved in the puncture event would continue to yield Risk Class I1 results for the CW for
Case B 1 (unlikely frequency, moderate consequences). No credit is taken in Case BI for the
expected inflow of air while dock doors are open that would tend to mitigate the puncture
scenario consequences. Crediting the Buildin,o 991 fizrered &aust verrtiZ&'on svstem and
fa&& co@+guration controls would reduce the CW risk to Risk Class 111 for Case B2 (unZik$y
frequency, low consequences).
Container ExDlosion Scenario 1 - "J Waste Box Container ExDlosion
Hydrogen generation in metal waste containers is postulated to lead to an internal
hydrogen explosion in a TRU waste container. The radioactive decay of the TRU waste material
interacts with hydrogenous waste materials and produces hydrogen and oxygen gases. The gases
are retained in the metal waste container and allowed to accumulate to the point where a
hydrogen explosion potential exists. Since as little energy as is associated with a static charge
can ignite flammable hydrogedoxygen mixtures, static charges generated by container
movements ignite the hydrogen. Therefore, the container explosion can OCCUT at any point in the
handlhg of the container (i.e., at the storage location, at the dock, and during transit). Since the
container loses its lid as part of the scenario, the material impacted by the event is no longer
confined. The scenario deals with an overpressure event that is conservatively assumed to
impact radioactive material in the form of a powder.
The postulated TRU waste box container explosion in the Building991 Complex is
considered to be an extremely unZikely event with moderate consequences for the MOI, high
consequences for the CW, and mdrate consequences for the IW. The CW risk class is Risk
Class II. The risk classes for the MOI and the IW are Risk Class LII, which are considered to be
acceptable.
Acceptability of the risk class results for the CW. in part, is based on the conservatism of I
the analysis (ie., modeling input assumptions, defense-in-depth protective features not
specifically credited). The rationale that the analysis of a waste box is a conservatism is as I
follows: (1) TRU waste boxes have not been the focus of hydrogen explosion issues at the Site;
(2) it is not clear that a TRU waste box has the potential to be involved in an internal hydrogen
explosion due to less radioactive material per unit volume, the type of wastes associated with
TRU waste boxes, and the significantly larger head space area; and (3) there are far fewer TRU
waste boxes than TRU waste drums, which makes the scenario less likely to occur in a TRU
waste box.
Also, there is conservatism in using the non-combustible contaminated solid release
fraction values from the DOE Handbook. These values are meant to be applied to rigid,
non-yielding contaminated surfaces where the venting gases can act against the rigid surface.
Revision 1
4.37 Mldhg 991 Complex FSAR
.%vtcrnbsr 1990 !