Spent Fuel Transportation Package Response to the Baltimore Tunnel Fire Scenario

Abstract

On July 18, 2001, a freight train carrying hazardous (non-nuclear) materials derailed and caught fire while passing through the Howard Street railroad tunnel in downtown Baltimore, Maryland. The United States Nuclear Regulatory Commission (USNRC), one of the agencies responsible for ensuring the safe transportation of radioactive materials in the United States, undertook an investigation of the train derailment and fire to determine the possible regulatory implications of this particular event for the transportation of spent nuclear fuel by railroad.The USNRC met with the National Transportation Safety Board (NTSB) to discuss the details of the accident and the ensuing fire. Following these discussions, the USNRC assembled a team of experts from the National Institute of Standards and Technology (NIST), the Center for Nuclear Waste Regulatory Analyses (CNWRA), and Pacific Northwest National Laboratory (PNNL) to determine the thermal conditions that existed in the Howard Street tunnel fire and analyze the potential effects of those conditions on various spent nuclear fuel transportation package designs.The Fire Dynamics Simulator (FDS) code developed by NIST was used to determine the thermal environment in the Howard Street tunnel during the fire. The FDS results were used as boundary conditions for the COBRA-SFS and ANSYS ® computer models developed to evaluate the thermal performance of different package designs. The staff concluded that larger transportation packages resembling the TransNuclear Model No. TN-68 and HOLTEC Model No. HI-STAR 100 would withstand a fire with thermal conditions similar to those that existed in the Baltimore tunnel fire event with only minor damage to peripheral components. This is due to their sizable thermal inertia and design specifications in compliance with currently imposed regulatory requirements.For the TN-68 and the NAC International Model No. LWT (legal weight truck) transportation package, the maximum temperatures predicted in the regions of the lid and the vent and drain ports exceed the seals' rated service temperatures, making it possible for a small release to occur, due to CRUD that might spall off the surfaces of the fuel rods. While a release is not expected to occur for these conditions, any release that could occur would be very small due to a number of factors. These include (1) the tight clearances maintained between the lid and cask body by the closure bolts, (2) the low pressure differential between the package interior and exterior, (3) the tendency of such small clearances to plug, and (4) the tendency of CRUD particles to settle or plate out.USNRC staff evaluated the radiological con-sequences of the package responses to the Baltimore tunnel fire. The analysis indicates that the regulatory dose rate limits specified in 10 CFR 71.51 for accident conditions would not be exceeded by releases or direct radiation from any of these packages in this fire scenario. All three packages are designed to maintain regulatory dose rate limits even with a complete ...

Use of TRACE best estimate code to analyze spent fuel storage pools safety

“…Maine Yankee spent fuel storage racks material is aluminium with an emissivity of 0.55 and for the spent fuel rods an emissivity of 0.8 is taken, as it is recommended in reference (Adkins et al, 2009), for PWR fuel rods.…”

Spent fuel transportation risk assessment: transportation accident analysis

“…The NRC has conducted several analyses of historic fire accidents, making conservative assumptions regarding the placement of a cask within those fires. [8][9][10] In the case of the railroad tunnel fire similar to the Baltimore Tunnel Fire 8 and based on the rail event tree and the fire branch in Fig. 2, the conditional probability that a pool fire would occur in a tunnel is 7610 29 .…”

“…This probability does not include any information about the duration of that pool fire, but if it is assumed that all of these types of fires are as severe as the Baltimore Tunnel Fire, this number can be used to estimate the effect on the transportation risk assessment. Adkins et al 8 conservatively estimated that this fire could cause a release of 0?3 A 2 [An A 2 quantity of material is the radioactivity that can be carried in a type A cask (10 CFR Part 71 Appendix A). A member of the public exposed to an A 2 quantity would sustain a radiation dose that is acceptable (Ref.…”

Performance of metal and polymeric O-ring seals during beyond-design-basis thermal conditions

“…However, historical non-nuclear transportation fire incidents suggest that potential thermal exposures could exceed HAC fire. Examples are the Caldecott Tunnel fire in 1982 [2], the Baltimore Tunnel fire that occurred in 2001 [3], and the MacArthur Maze fire in 2007 [4]. The performance of package seals is important for determining the potential for release of radioactive material from a package during a beyond-design-basis accident because the seals, in general, have lower temperature limits than other package components.…”

“…An evaluation of the potential release of radioactive materials from three different transportation packages has been studied in detail by Adkins et al [3]. The evaluation used predicted temperatures from a simulation of the Baltimore Tunnel fire using the NIST Fire Dynamics Simulator (FDS) [5]as boundary conditions for numerical models to determine the temperature of various components of the packages, including the seals.…”