Safety consequences of local initiating events in an LMFBR

Abstract

III. REACTOR-OPERATING EXPERIENCE 13 IV. ANALYSIS OF POTENTIAL MODES OF FAILURE PROPAGATION 17 A. Fission-gas Release. V. OPERATION WITH DEFECTED FUEL 45 A. Fission Products Released from Failed Pins to Coolant 45 B. Sodium-Fuel Chemical Reaction 46 VI. SUMMARY AND CONCLUSIONS 50 9. Lower and Upper Gas-Liquid Interface inside an FFTF Fuel Subassembly vs Time after Simultaneous Rupture of 10 or More Fuel Pins at the Outlet Region of the Core, Assuming Zero Gas-flow Resistance 29 10. The Effects of Support Length L and Peak Pressure p Q on Moment M max 31 11. The Effects of Fuel-pin Radius and Temperature on Moment: t = 0.014 in 31 12. The Effects of Fuel-pin Radius and Temperature on Moment: t = 0.010 in 32 13. Flow Passing through a Porous Bed 36 14. Maximum Porous-bed Thickness to Produce Coolant Boiling for Various Bed Porosities and Particle Sizes 37 15. UO 2 Particle Sizes from Interactions with Sodium 38 16. Model of Coolant-channel Blockage 38 17. Coolant-temperature Increase Downstream of a Blockage 39 18. Detection of an Inlet Blockage 40 19. Flow-blockage Model 40 20. Bubble Growth and Collapse for Local Boiling behind a 50% Flowarea Blockage in an FFTF Subassembly 41 21. Velocity of Coolant Stream Required to Sweep Out Fuel Debris. . 44 22. Fuel-element Swelling vs Time after Failure 47

Analytical investigation of certain aspects of LMFBR subassembly-failure propagation

“…From the previous discussion of initiating faults, areas of concern in subassembly-to-subassembly failure propagation can be grouped into several modes: (1) the response of the adjacent subassembly to strictly mechanical loads, (2) the response of the adjacent subassembly to strictly thermal loads, and (3) the response of the adjacent subassembly to combined thermal and mechanical loads. Few analytical investigations to predict the capability of an adjacent subassembly duct to withstand external mechanical loadings have been documented.…”

Studies on LMFBR subassembly boundary integrity

“…above h~s been discussed ·iri a previous report . 1 This report c~ncentrates.only on the second area, and presents a discussion of the initiating events and failure modes which may potentially lead to a breach of the subassembly-boundary integrity. A breach of the subassemblyboundary integrity in this report is defined as a condition in which the subassembly duct is ruptured or severely deformed.…”

“…The initial f.aults were represented by three categories of accident source: (1) random fuel-pin failure, (2) fuel-pin operatiuu aL overpower, and (3) debris in the primary coolant system. 1-'uel-pin damage aml failure-propagation modes associated with these initial faults were analyzed: (1) fission-gas release, (2) local MFCis, and (3) local blockages in the fuel-pin bundle.…”

“…1-'uel-pin damage aml failure-propagation modes associated with these initial faults were analyzed: (1) fission-gas release, (2) local MFCis, and (3) local blockages in the fuel-pin bundle. Based on these analyses, as well as experimental results and reactor operating expe.rience, it was concluded that fuel pin failure propagation is unlikely to occur and, if occurring, is inherently self-limiting.…”

“…Since the presence of liquid sodium would prevent fuel from attaining such high temperatures, such a situation could exist only after sodium voiding has occurred and the subassembly remains voided for a few seconds. In a previous report on local initiating events, 1 it was shoWn that local.coolant boiling due to a local blockage or a local MFCI is not expected to propagate to the entire subassembly and that restoration of the coolant flow would be expected even if only on an intermittent basis. Therefore, it is not expected that any local initiating event in the fuel subassembly will lead to whole subassembly voiding and subsequent meltdown.…”