The r a d i a l d i s t r i b u t i o n of t h e f u e l temperature a t t h e o u t l e t of t h e channels i s shown i n Fig. 12 f o r the reference conditions a t 10 Ptw.
This
d i s t r i b u t i o n includes t h e e f f e c t s o f t h e d i s t o r t e d power-density d i s t r i bution (Fig. k ) and t h e r a d i a l v a r i a t i o n s i n f u e i v e l o c i t y .
A t the refer-
ence conditions t h e main-core i n l e t temperature i s 1177,3"Fand t h e xixed mean temperature leaving t h a t regior: i s 2220.8*F0 The a d d i t i o n a l heat required t o raise t h e r e a c t o r o u t l e t temperature t o 1223'F
i s produced i n
Vne p e r i p h e r a l regions above t h e main p a r t o f t h e core.
Also shown on
Fig. 1 2 f o r comparison i s t h e o u t l e t temperature d i s t r i b u t i o n f o r an i d e a l ized core with a uniform f u e l f r a c t i o n and uniform f i e 1 v e l o c i t y .
For t h i s
case t h e radial power d i s t r i b u t i o n vas assumed t o follow t h e Bessel f'unct i o n , J0(2.4 r / R ) 9 which vanished a t t h e i n s i d e o f t h e core s h e l l .
The
d i s t r i b u t i o n was normalized t o t h e same i n l e t and mixed-mean o u t l e t t e m p e r a t u r e s t h a t were calculated for t h e main portion of t h e l4SRE c o r e . Nuclear MeaE Temperature A t zero power t h e f u e l temperature is e s s e n t i a l l y constant throughout
t h e r e a c t o r and, a t power it assumes t h e d i s t r i b u t i o n discussed i n t h e preceding s e c t i o n .
The nuclear mean temperature of t h e f u e l i s defined as
t h e uniform f u e l temperature which vould produce t h e same r e a c t i v i t y chmge from t h e zero-power condition as t h a t produced by t h e a c t u a l f u e l temperature distribution. The nuclear average temperature of t h e f u e l i s obtained by weighting t h e l o c a l temperatures by t h e l o c a l nuclear importance f o r a f u e l texpera-
ture change.
The importance function, G ( r , z ) ,
includes t h e e f f e c t of f u e l
volume f r a c t i o n as w e l l as a l l n u c l e w e f f e c t s (see p . 22 e t s e q . ) .
There-
fore
J'
G(r,z) dv
V
I n carrying o u t t h e indicated i n t e g r a t i o n f o r t h e MSRE, both t h e numerator m d denominator o f (7
were s p l i t ir.to 11 terms, one f o r t h e main p a r t of
t h e core and one for each of the fuel-bearing p e r i p h e r a l regions. p c r f p h e r d rci;ims, tk.2 3 ~ ~C,eqcra;t.ac 2, ic cach rcgio::
For t h e
vas zss-mcd constant