On May 3, 1994, personnel at Rocky Flats reported that a six-inch berm surrounding a plenum glovebox deluge tank represents a potential criticality infraction. In the event of a fire, water from the deluge system could flush plutonium oxide out of the plenum and into the tank. The deluge tank contains borosilicate glass raschig rings as a fixed neutron poison; however, any overflow from the tank into the berm to a level greater than two inches could create a potential criticality. (ORPS Report RFO--EGGR-SOLIDWST-1994-0033)
Facility personnel identified the potential infraction while evaluating the requirements for a temporary containment to be installed in the area of the deluge tank. During the evaluation, engineers questioned the validity of previous nuclear safety calculations supporting the installation of the six-inch berm. Investigators reported that the berm was installed in the 1980s in response to environmental concerns and that nuclear safety issues associated with the installation may not have been adequately addressed.
Facility personnel believe there isn t any eminent danger because of past efforts at the facility to reduce the amount of plutonium oxide buildup in plenums. However, as a precautionary measure, they reviewed the berm configuration with criticality engineers and prepared a work control form in accordance with the integrated work control program and drilled holes in the berm wall so that level could not increase above two inches inside the berm. They also posted the area for a potential criticality infraction.
Management personnel continued to review the event and facility criticality engineers are performing a detailed analysis of the berm configuration. In Weekly Summary 93-35, NS reported an unusual occurrence at Rocky Flats when facility personnel determined that storage tanks containing raschig rings were not in compliance with Nuclear Material Safety Limit requirements. The non-compliance stemmed from a failure to perform required safety limit inspections of the raschig rings since 1989. (ORPS Report RFO--EGGR- SITEWIDE-1993-0005)
This recent event at Rocky Flats underscores the importance of ensuring that modification design control and review processes take into account nuclear safety issues as well as environmental impact concerns when modifications are being contemplated for an environmental issue. DOE 5480.24, Nuclear Criticality Safety, provides guidance for the basic elements and control parameters of programs for nuclear criticality safety at DOE facilities. It also states that the elements and control parameters of the DOE program shall satisfy the requirements of ANSI/ANS- 8.5, Use of Borosilicate-Glass Raschig Rings as a Neutron Absorber in Solutions of Fissile Material, and other related standards.
(Neil J. MacArthur - RPI (301) 540-2396)