ML19294C175
| ML19294C175 | |
| Person / Time | |
|---|---|
| Issue date: | 07/09/1979 |
| From: | Bessette D Advisory Committee on Reactor Safeguards |
| To: | Shewmon P Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-SM-0150, ACRS-SM-150, NUDOCS 8003070279 | |
| Download: ML19294C175 (6) | |
Text
unasov UNITED STATES
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"o NUCLEAR REGULATORY COMMISSION f
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I ADVISORY COMMITTEE ON REACTOR SAFEGUARDS
/44 #/5"M WASHINGTON D. C. 20555 o
g
%, m.e f July 9, 1979 kw Dr. Paul Shewmon, ACRS Member AND ZIRCALOY AT HIGH TEMPERATURES
SUMMARY
OF REACTIONS BETWEEN U02 and zircaloy occurs at high (T > 1000C)
Chemical interaction between UO2 is reduced and zircaloy is oxidized.
temperatures. The result is that UO2 The reaction depends on whether or not good contact exists between fuel and cladding.
If good contact does not exist, reaction will not occur.
If good contact exists, the reaction is practically independent of contact pressure.
Reaction rate is controlled by rate of oxygen diffusion in zircaloy and in the ok -Zr(0) phase that is formed. The reaction follows a parabolic time law.
Rate of internal cladding oxidation can be as high as external oxidation.
Three reactions layers form from the cladding / fuel interaction. This results in the following structures.
cladding Zr-4 9
initial pellet / clad boundry III 4-Zrf 0) y e
) U:63 a/o II (U,Zr) alloy
) Zr:18 a/o
) 0:19 a/o
) U:0.6 a/o I
d-Zr(0)a+
-U
) Zr:81 a/o
) 0:18 a/o 00 fuel 2
In terms of size, layer II (U,Zr alloy) is thinnest, followed by I (4 -Zr(0)a +d-U) and III (4 -Zr(0) b.
Figure 1 shows the reaction layers growth as a function of time for four temperatures (1000C, 1100C, 1200C, and 1300C). Figure 2 shows reaction layers growth as a function of temperature.
Figure 4 Figure 3 gives U-Zr-0 phase diagrams for T + 1000C and T + 1500C.
gives the Ir-0 phase diagram.
The U,Zr alloy layer that is formed has a relatively low melting temperature of ~1300C (2370F). For T)1300C this layer can flow under the influence of an applied stress.
E70 8003070
For the TMI-2 event it is hard to say how much, if any, melting of the U,Zr Before 1300C is reached, the fuel rod should burst, alloy layer occurred.
If the steam has adequate access thus allowing inflow of steam into the rod.
to the U,Zr layer, the V,Zr will oxidize and melting temperature will increase.
$,3 D. E. Bessette ACRS Fellow Attachments:
Figs. 1-4
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Time [ min]
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at different te=peratures. There is practically no influence y
of simulated fission products (Cs,I,Tc) on the depth of the interaction zones (see 1200 C specimens) y
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t 1000'C L = Liquid i
---Extrapolated due to insufficient data Based on sufficient data
-- U Og 3
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Zr INEL-A 2043 Fig 3 Equilibnum phase diagrams for the U Z:4 ss stem at 1000 and 1500'C -
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