Interim Report on TREAT Test R8, a Seven-Pin Loss-of-Flow Test with Pressurized Pins -- Part 1
TREAT test R8 was the fifth in a series of R-series seven-pin tests supporting code development and analyses of the initiating phase of a hypothetical, unprotected loss-of-flow accident in an LMFBR. As in previous tests R4 through R7, the test fuel bundle was comprised of seven full-size FTR fuel pins containing fresh UO{sub 2} fuel. The specific objective of R8 was to examine the effects on sodium voiding and molten cladding behavior caused by release of pressurized plenum gas into the coolant channel. For this test, three of the seven fuel pins were pressurized with xenon gas to nominal end-of-life condition (4.14 MPa at 560° C); in contrast, all previous tests had been performed with helium fill gas at nominally one atmosphere pressure. Test R8 was performed May 7, 1976. The average fuel power was 31.8 kW/pin, and the axial power shape was 1.15 max-to-avg. The sodium inlet temperature was constant at 317°C (600°F) and the initial sodium flowrate was constant at 7.15 m/s. A flow coastdown was initiated after quasi-steady, prototypic thermal and hydraulic conditions were established. Sodium voiding began about 9.5 s into the coastdown when the rate of flow decay was about 11%/s and the coolant velocity was about 2.1 m/s (29% of initial flowrate). Inlet flow reversal followed at 10.2 sand initiated the sequence of cladding dryout, heatup, and pin failures. The pin failures appeared to be very coherent, occurring within a time span of about 20 ms. The plenum gas release resulted in pressurization of the coolant channel to about 4.1 atm, causing expulsion of both the upper and lower sodium slugs out of the core. (Lower slug expulsion had not been observed in the earlier tests.) The outward expulsions continued for about 0.7 s total. Gas escaping to the upper plenum prevented reentry of of the upper slug. The lower slug reversed direction and, after an additional 0.7 s, attempted to reenter the heated zone. A sodium vaporization event ensued which again expelled the inlet slug downward. Thereafter, sodium did not reenter the core, presumably due to formation of the inlet blockage. Posttest examination revealed a massive inlet blockage of steel in the lower reflector region, but no planar upper cladding blockage of the type found in earlier tests. The R8 test with pressurized pins was successful in demonstrating predicted channel pressurization, accelerated sodium voiding, and altered cladding motion not seen in previous R-series tests using unpressurized pins. This test demonstrated the need for modeling the effects of pressurized, noncondensible gas release, not previously handled in SAS. The test also serves as a data source for assessing future SAS modeling developments.
- Research Organization:
- Idaho National Lab. (INL), Idaho Falls, ID (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC07-05ID14517
- OSTI ID:
- 1130763
- Report Number(s):
- ANL/RAS 78-39
- Country of Publication:
- United States
- Language:
- English
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