ML20057C368

Forwards Rept of 930910 Telcon Re Assumption of No Superheat in Ssar Corium Shield Analysis

ML20057C368
Person / Time
Site:	05200001
Issue date:	09/17/1993
From:	Fox J GENERAL ELECTRIC CO.
To:	Poslusny C Office of Nuclear Reactor Regulation
References
NUDOCS 9309280275
Download: ML20057C368 (5)

Text

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4 l (

• . GENucle:r En:rgy GeneralDectnc Company 1 175 Cunner Avenue. San Jose. CA 95125 September 17,1993 Docket No. STN 52-001 j t

)

i

~I l

t Chet Poslusny Senior Project Manager Standardization Project Directorate -

Associate Directorate for Advanced Reactors .j and License Renewal -!

Office of the Nuclear Reactor Regulation l

Subject:

Submittal Supporting Accelerated ABWR Schedule - Effect of Debris I Superheat on Corium Shield i

Dear Chet:

l i

Enclosed is a report of a September 10,1993 telecon between GE and the NRC pertaining to  ?

the assumption of no superheat in the SSAR corium shield analysis. Based on the attached analysis, we believe that superheat does not impact the conclusion of the corium shield sizing l calculation and no change is required in the SSAR.

Please provide a copy of this transmittal to John Monninger.

Sincerely, M

Jack Fox Advanced Reactor Programs cc: Alan Beard (GE) l Carol Buchholz (GE)

Jack Duncan (GE)

Norm Fletcher (DOE)

Doug Mcdonald (GE) l l

JiW2fdl r: M 4rO l 9309280275 930917

.PDR A

ADOCK 05200C01 pm 9f6 V I

I . .

1 Effect of Debris Superheat on Corium Shield l During a tele-conference on Friday, September 10,1993 between GE 4 4

(Carol Buchholz, et al) and the Stafr(Rich Barret, et al), the Staff I l questioned the assumption of no superheat in the corium shield analysis l contained in Attachment ED of the ABWR SSAR. The question was the 1 result of a review of the analysis by personnel at Sandia. All other portions of the analysis were found to be acceptable.  ;

The Staff requested GE to consider superheats up to 200 C. GE does not 4 believe that this amount of superheat will occur during a severe accident.

Due to interactions with the vessel internals and the vessel bottom head, ,

the debris will exit the vessel at or very near its fusion point. Additionally, i the debris will transfer heat to the structures in the lower drywell l environment as it flows toward the sumps located on the periphery of the i

lower drywell. In GE's opinion, credible superheats are limited to a few l

degrees. j This analysis considers the effects of superheat on the corium freezing i process. First, the change in energy due to including superheat will be  ;

. calculated. Then, the impact on freezing time will be determined. Freezing i time can be used to correlate the length of channel required-the greater

the time required for freezing, the longer the channel. Since freezing time i dictates channel length for a given corium velocity and superheat is not  ;

j expected to affect velocity, the analysis will conclude at freezing time and not determine channellength.

]

2 a In the analysis contained in Attachment ED of the ABWR SSAR, it was .

4 shown that the channel length was limited by the eutectic material j formed by interaction of the core debris and concrete. The melting point of

the eutectic is approximately 1700 K. The melting point of unreacted core

! debris is expected to be 2500 K. The heat transfer from the eutectic to the *

shield wall is lower than for the unreacted state because of the smaller l temperature difference. The reduction in heat transfer increases the time

required for freezing to occur. Applying superheat to the core-concrete  !

) eutectic material is not appropriate because the interaction between the 1 concrete and the debris reduces the temperature to the fusion point. '

l Therefore, superheat will only be considered with the unreacted state (i.e.,

2500 K. fusion point).

l Chamre in Enerry  ;

. 1

Table 1 shows the change in energy which results from assuming different amounts of superheat.

i September 16,1993 dbm9321, p.1 f

, . ~ . . _ , . .._, e _

i Table 1 Change in Energy i

Superheat ('C) Change in Energy (%)

0 0 5 1 j 10 2 l 25 4 i l

l 50 9 ,

100 18 150 27 200 36 I

The energy comparison indicates that a significant amount of superheat

> (greater than 50 C) could impact the channel length. However, for ,

superheats on the order of a few degrees, there is negligible impact.

Change in Freezina Tima l

! A simplified analysis of the channel residence time required to ensure  :

l debris freezing can be used to determine the impact of debris superheat.  !

l Balancing the energy required to be removed from the debris to freeze arl

! the energy absorbed by the shield wall yields n

rf =%h. (1) l r where freezing time l

l rf =  !

e"f = energy required to be removed from the debris in order for  ;

l freezing to occur

=

Lc Pcm(h i +c p AT) where Le = half height of channel pcm = density of corium 1

September 16,1993 dbm9321, p. 2

hf = corium latent heat of fusion cp = corium specific heat AT = amount of superheat C= time averaged heat flux into shield wall (semi-infinite l body), see Equation (19ED-14)in the SSAR for the ,

instantaneous heat flux

~

2kw (T,-T;)

]santf I

where k, = thermal conductivity of shield wall l

T, = interface temperature, see Equation r (19ED-16) of the SSAR l Ti = initial temperature of shield wall j a, = thermal diffusivity of shield wall. l Combining all the portions of this equation yields  ;

2

.LcPcm(h i +cp AT))na, if= 2kw (T,-T i )

. (2) i The Table 2 is obtained by evaluating this equation for several different combinations of corium melt temperatures and superheats.  !

As can been seen in Table 2, the eutectic material, represented by a melting temperature of 1700 K and no superheat, has the longest required I time for freezing. This is the same result obtained in the SSAR. For the unreacted debris (melting temperature 2500 K) and superheats above 150 C, the interface temperature between the debris and the shield wall is slightly above the melting temperature of alumina (2288 15 K CRC Handbook of Chemistry and Physics,62 ed, p. B-74). However, since the melting of alumina is endothermic and the difference between the calculated temperature and the alumina fusion temperature is small, the impact on freezing is negligible.

September 16,1993 dbm9321, p. 3

i 4

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Table 2 ,

Change in Freezing Time Corium Melting Temperature (K) Superheat ( C) T,(K) ^

rf(sec) 1700 0 1560 7.1 2500 0 2180 3.1 .

2500 5 2180 3.2 .,

2500 10 2190 3.2 l 2500 25 2200 3.4 l '

2500 50 2220 3.6 2500 100 2250 4.0 2500 150 2290 4.5 -

2500 200 2320 5.0 ,

Concluainn l

Assuming that debris, which has not formed an eutectic material due to core-concrete interaction, is superheated does not impact the conclusion of the corium shield sizing calculation contained in Attachment ED of the  :

ABWR SSAR. The sizing calculation is limited by considering an eutectic material formed during core-concrete interaction which is not superheated. Therefore, no change is required to the SSAR.

September 16,1993 dbm9321, p. 4

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