DOE 2000. - Waste Isolation Pilot Plant - U.S. Department of Energy

WIPP RH PSAR DOE/WIPP-03-3174 CHAPTER 5
After examining the nature of the 17 individual hazardous events selected as candidates for quantitative
analysis, and for minimization of repetitiveness, the events were grouped into "categories" of events with
similar characteristics. The grouping resulted in 9 specific accidents (72-B) and 8 specific accidents (10-
160B) that would be analyzed quantitatively. The accidents are listed in Table 5.1-9.
Following the ranking and binning process, applicable safeguards were identified for each event. Once
the existing protection was identified, the adequacy of that protection was qualitatively judged. Based on
the level of protection provided by the existing controls, follow-up items were listed in the form of
Action Items or Recommendations. Action Items are those items which, in the judgement of the HAZOP
Team, must be implemented to increase the safeguards or to verify the function of existing safeguards.
Recommendations are those items which, in the judgement of the Team, would enhance the existing
safeguards and must be addressed, but not necessarily implemented. Implementation of
Recommendations is, however, strongly encouraged. The Action Items and Recommendations are
summarized in Tables 8 and 9 respectively of DOE/WIPP-99-2303 4 and
WSMS-WIPP-00-0006. 5
5.1.5 Prevention of Inadvertent Nuclear Criticality
The intent of a criticality safety program is to prevent the accumulation of fissile and fissionable material
and neutron moderating or reflecting materials in quantities and configurations that could result in an
accidental nuclear criticality.
To ensure adequate margins of criticality safety for adherence to DOE O 420.1, 22 the WIPP facility was
designed so that during each operation involving fissile material K eff does not exceed a value of 0.947 (at
the 95 percent probability level) for the most reactive set of conditions considered credibly possible. The
calculation of K eff includes the effect of neutron interaction and reflection between fissile elements and
dimensional variations resulting from fabrication tolerances and changes due to corrosion and mechanical
distortion. As discussed below, these calculations indicate the combination of conditions enabling the
K eff limit of 0.947 to be exceeded for the RH waste forms handled at the WIPP facility is incredible.
5.1.5.1 WIPP Nuclear Criticality Safety Program Elements
The WIPP nuclear criticality program elements consist of mass limits control, TRU waste disposal
configuration control, and analytical verification of subcriticality.
Mass Limits Control
The WIPP RH WAC 10 limits the fissile or fissionable radionuclide content of RH TRU waste, including
allowance for measurement errors, to 325 Fissile-Gram Equivalent (FGE) for a RH waste canister.
TRU Waste Disposal Configuration Control
In addition to the mass limits control, geometry controls are required for the emplacement and/or
in-transit handling disposal configurations. Canisters will be stored in horizontal positions in the walls of
the Underground disposal rooms with an analyzed minimum center-to-center spacing of 30 in
(76 cm). 29
5.1-17 January 22, 2003