Mpai (136
Cs) =Mu x 136/235 Y
mFcs [1 - exp (-X(
136Cs)x]Otrzymane wielkości przedstawia tabela 4.9. Po przemnożeniu masy poszczególnych nuklidów zawartej w paliwie przez ich frakcje uwolnienia do szczeliny^ otrzymamy (tabela 4.7):
Podstawiając do wzoru (3.1) współczynniki z tabeli 3.2 oraz dane charakterystyczne dla prętów typu WWER-1000, tj. p = 11,2 MPa, V
geom= 5,81 cm
3, A
acz= 239,5 cm
2i 7trozerwania)= 900°C,p
zew„ = 0,1 MPa, otrzymamy VB = 5,81 x 11,2/0,1 = 650,5 cm3oraz frakcję uwohiioną natychmiast po rozerwaniu koszulki:
/B = MB( C S ) / M0( C S )
= 3,49 x 650,5 (0,05/239,5)
0>8exp (-7420/1173) / 0,05 = 0,1617
Uwolnienia cezu w drodze dyfuzji ze szczeliny w ciągu następnej minuty określamy podstawiając do wzoru (3.2, 3.3) parametry określone przez Lorenza w tab. 3.2 oraz dane charakterystyczne dla AUCH w reaktorach WWER, mianowicie szerokość szczeliny W = 32,5 um, ciśnienie/? = 0,1 MPa, t- 1/60 h. Przyjmujemy, że temperatura szczeliny w tym okresie wynosi T- 1200°C.
Wówczas:
Ro = 1,9 x 103 x 32,5/0,1 x 1,09 x 10'3 exp (- 19800/1473)
/D =MD(Cs)/A/0(Cs) = 1 - exp (-3,83 x \0A 160 / 0,05) = 5,95 x 10"4 Powyższe wielkości zestawiono w tabeli 4.10.
Łącznie frakcja zasobu cezu w szczelinie wydzielona w ciągu 1 minuty po rozerwaniu koszulki i wzroście temperatury do 1200°C (w szczelinie) wyniesie/(Cs, wyp) =/B +fo = 0,1623.
Jod, paliwo wypalone
Frakcję jodu wydzielonego z paliwa wypalonego obliczamy według tej samej metodyki, tj. dla nuklidów 1 3 M 3 5I z aktywności zawartej w paliwie, a dla l 2 9I (X - 1,37 x 10"15 s"1) i trwałego
ITT
I z wydajności na 1 akt rozszczepienia. Uzyskaną masę przedstawia także tabela 4.9.
Odpowiednie frakcje jodu uwolnione na zewnątrz pręta wyniosą, po podstawieniu do wzorów (3.1)-(3.3):
fB = 0,2600; fD = 0,00174; fu = 0,2617
Tabela 4.10. Uwolnienia izotopów jodu i cezu ze szczeliny pod koszulką według wzorów Lorenza (3.1) - (3.3) Założenia:
grubość szczeliny 32,5 mm;
ciśnienie gazu 11,2 MPa (paliwo wypalone), 9,74 MPa (paliwo świeże);
ciśnienie zewnętrzne 0,1 MPa;
objętość gazowa 5,81 cm3 * 11,2/0,1 = 650,5 cm3 (paliwo wypalone); 5,81 * 9,74/0,1 = 565,7 cm3 (paliwo świeże);
temperatura rozerwania 900°C = 1173 K;
temperatura dyfuzji 1200°C = 1473 K;
masa jodu i cezu wg tabel 4.8 - 4.9.
Pierwiastek Paliwo świeże
I (127 + 129 + 131 + 132 + 133 + 134 +135)
Cs (133 + 134 + 135 + 136 + 137) Paliwo wypalone
I Cs
Uwolnienie
natychmiastowe fę Uwolnienie dyfuzyjne
fn, min'1 Uwolnienie łączne po 1 minfu 0,9205
0?7889
7,08 x io"J i 3,33 x 1O'J
0,9276 0,7922 0,2600
0r1617
1,74 x 10°
5,95 x 10"* 0,2617 0,1623
Paliwo świeże
Dla paliwa świeżego przyjęto frakcje uwolnień do szczeliny, uzyskane przez Pawlenkę [44] dla rozszczelnionych prętów paliwowych. W paliwie nie utlenionym będą to wartości oczywiście zawyżone (patrz rozdział 4.3), niemniej jednak ze względów bezpieczeństwa przyjmiemy je do obliczeń. Wówczas:
M0(I) = 5,3xl0-€g(tab.4.8);
i frakcje uwolnień z pręta paliwowego otrzymane według (3.1) - (3.3) przy/? = 9,74 MPa i
= 565,7 cm3 wyniosą:
/„(I) = 0,928;
/„(Cs) = 0,79.
Stałe produkty rozszczepienia
Dla stałych produktów rozszczepienia (Sr, Eu, Ba, Ce) przyjmiemy fu = 1 0 "
telluru przyjmujemy/, = 1/40 zgodnie z kodem CORSOR [61].
6. Przy powyższych założeniach uzyskano wyniki podane w tabelach 4.11 i 4.12.
Tabela 4.11. Wydzielenie produktów rozszczepienia z wypalonego paliwa WWER-1000 podczas awarii z utrzymaniem paliwa w temperaturze 1400°C przez 60 s
W przypadku
1,92 >ApjJ
3,8 x
J& (tab. 4.31 0,024
Tabela 4.12, Wydzielenie produktów rozszczepienia ze świeżego paliwa WWER-1000 podczas awarii z utrzymaniem paliwa w temperaturze 1400°C przez 60 s
Nuklid
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