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Estimation of irradiation induced iodine pressure in an LWR fuel rod
244
Journal
of Nuclear
Materials 125 (1984) 246247 North-~olland~ Amsterdam
LETTER TO THE EDITORS ESTIMATION OF IRRADIATION INDUCED IODINE PRESSURE IN AN LWR FUEL ROD
1. Introduction
following equation:
It is generally accepted that the pellet-cladding interaction (PCI) failures in light water reactor (LWR) fuel rods are stress corrosion cracking (SCC) induced by fission products [l]. In post irradiation examinations of LWR fuel rods, high concentrations of fission product iodine were locally observed on the cladding inner surface opposite to pellet cracks and interfaces I;?]. Iodine causes SCC of zircaloy in laboratory tests (i.e., out-of-pile experiments) and the fractography of the cracks is very similar to that observed in the PC1 failure of zircaloy cladding of an irradiated fuel rod 131.This is the reason why iodine is believed to be responsible for PC1 failure. However, there still remains the question of the iodine-induced SCC mechanism, which concerns the existence of a sufficient amount of free iodine in an LWR fuel rod to cause SCC. On the basis of thermodynamic considerations, iodine should react with another fission product, cesium, and form an extremely stable compound, cesium iodide (CsI). CsI is more stab1e than the lowest zirconium iodide ZrI, so that cesium iodide cannot react with zircaloy [4]. To support the iodine-induced SCC mechanism, it is necessary to show how iodine is liberated from CsI to cause PC1 failures. Several concepts have been taken to explain the generation of free iodine [5,6]. In a previous paper [7], it was theoretically shown that the partial pressure of iodine should increase due to the radiolysis of gaseous CsI in the LMFSR fuel pin. In this work, the theoretical method mentioned in the previous paper is applied to estimate the partial pressure of iodine in an LWR fuel rod.
RTln P, +AGp(CsI,
g)+RTln
CS
CsI(s) = CsI(g).
ZCs(g) + UO,(s) -I-0, = Cs,UO,(s).
(4)
Substituting Pcsr and PC, into eq. (2), the iodine pressure is obtained. The calculated iodine pressure under non-radiation condition is - lO_” atm (- lo-l3 Pa) for the oxygen potential of - 100 kcaI/mol at 400 o C, and it is clear that the iodine pressure is too few to cause SCC. Recently, Gotzmann [6] has suggested that the cesium activity can be reduced by the formation of cesium molybdate Cs,MoO,, and as a result iodine pressure increases. The formation of Cs,MoO, in the fuel-cladding gap, however, has not been confirmed in post irradiation examinations of LWR fuel rods. In this work, the radiation effect was taken into account in order to estimate the iodine pressure under the condition close to the actual operation of the fuel rod. The gaseous reaction system of cesium iodine is written in more detail as follows,
Cs+l+Xk~C81+X, kd,
Cs(g) + I(g) = CsI(g). (1) The value of the iodine pressure is calculated by the
(3)
The pressure of Cs(g), PC,, can be calculated for the equilibrium between UO, and Cs&JO,,
kd,
The partial pressure of iodine in the fuel-cladding gap, neglecting radiation effect, is thermodynamically estimated as follows. The iodine pressure is determined by the gas phase ~~b~urn:
(2)
where AGP(Cs1, g) is the standard Gibbs energy of formation of gaseous CsI, and P,, PC, and PCs, are the pressures of iodine, cesium and cesium iodide, respectively. The R and T have usual meanings. The pressure of CsI(g), pcsi, is determined by the vapor pressure of CsI(s) on the cladding inner surface according to the reaction,
cs + I, 2 CSI + I, 2. Ektimation of iodine pressure
F,
I+I+Xk::12fX, kd,
(5)
(6) (7)
where X means the third body and He, Xe and Kr are supposed to play a role of X in the fuel rod. The kr,-kr, and kd,-kd, are the reaction rate constants. These constants were determined as a function of temperature
~22-311~/84/$03,00 Q Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
245
K. Konashi et al. / Irradiation induced iodine pressure in the previous work [7]. In the reactor, the dissociation of cesium iodide by the radiation of fission fragments is expected to take place in addition to the above three reactions (eqs. (S), (6) and (7)); CSI + ZE=,,
4 cs + I, kdd
(8)
where kd, is the reaction rate constant. The reaction represented by eq. (8) means that a molecule of CsI is excited by fission fragment impact into excited states and then a certain portion of the excited products decompose spontaneously to give free iodine atoms. The rate constant of the radiolysis, kd,, was determined for the condition of the LWR fuel rod in a manner similar to that obtained in the previous work [7]. Now, the reaction rate equations of the cesium-iodine system can be written as follows, d[Cs]/dr=
kd,[CsI][I]
+kd,[CsI][X]
+kd,[CsI]
-kr,[Cs][I,]
-kr2[Cs][I][X]. (9)
d[CsI]/dt
= -d[Cs]/dt,
d[I,]/dr=
kd,[CsI][I]
(IO) +kr,[I]*[X]
-krI[CslP21-k4LI[Xl,
3. Result and discussion Fig. 1 shows the result of the calculations. In this figure, the iodine partial pressures are plotted as a function of the reciprocal temperature of zircaloy cladding. The partial pressures of iodine calculated under radiation condition (solid line in fig. 1) are much higher than those under non-radiation condition (dashed line in fig. 1). It is apparent that the radiation of fission fragments contributes greatly to the increase in partial pressure of iodine in an operating LWR fuel rod. The present theoretical results were compared with experimental results in order to check whether the estimated iodine partial pressure could cause SCC. A known quantity of iodine was added to the inside of a sealed zircaloy tube in the out-of-pile SCC experiments [8-121, and so the iodine concentration could be calculated in terms of mass per volume or mass per exposed area. The minimum iodine concentration to induce the SCC of zircaloy has been obtained in the out-of-pile experiments [8-121. However, the iodine concentration in itself does not mean the chemical activity of iodine, since the iodine employed in the sealed tube reacts quickly with zirconium to form gaseous ZrI,. Therefore,
(11)
d[I]/dr=kr,[Cs][12]+kd,[CsI][X] +kd,[CsI]
(“C
+2kd,[I,][X]
700
-kd,[CsI][I]
-kr2[WII[Xl --2kr3[I12[Xl,
600
400
500 ’
(12)
where [ ] represents the concentration of the chemical species concerned. These rate equations were solved simultaneously under the given chemical, thermal and radiative conditions and then the partial pressure of iodine was determined. Calculations were performed for the case that the cesium-iodine systems reaches the equilibrium state in the LWR fuel-cladding gap. A typical LWR condition was considered as shown in table 1.
B
‘.
.\
‘\ ‘.
-15 -
“.,t(non-rad) ‘\ ‘\ ‘. ‘\
‘\
‘.
‘\
‘. -\
‘.
Table 1 Typical LWR conditions used in this work Radius of pellet Oxygen potential of fuel Linear heat rate Temperature difference across fuel-cladding gap Total gas pressure in fuel rod
0.5 cm - 100 kcal/mol 300 W/cm 2oo”c
;
10 atm
1
300 l-l
-4
‘\
L i0
I
12
14
,
-15 ‘.
‘Y
16 iO-‘/T(l/K)
Fig. 1. Radiation effect on the partial pressure of iodine as a function of reciprocal temperature of zircaloy cladding. Marks of closed squares represent the experimental critical P,‘s to cause SCC of zircaloy, which were obtained by other workers [8-121.
K. Konashi et al. / Irradiation induced iodine pressure
246
order to compare with the theoretical results, the iodine concentrations were transformed to the iodine pressure using thermodynamic data as follows [6]. First, the iodine concentrations can be converted to the partial pressures of ZrI, under the assumption that all iodine reacts with zirconium to produce gaseous ZrI,, in
P Zrl, = Llc./*w~~~
(13)
where PzrI is the partial pressure of ZrI,, I,,,,, is iodine conckntration and M is molecular weight of I,. From the ZrI, pressure thus estimated, the experimental critical iodine pressures were determined based on the following reaction, Zr(s) +41(g)
= ZrI,(g).
(14)
The values of the iodine pressure using the out-of-pile experimental results were also shown in fig. 1. The iodine pressures calculated theoretically under radiation condition are in excess of the critical values estimated from experimental results in fig. 1. From this, we can draw an interesting conclusion, that is, the free iodine liberated by radiolysis of CsI can cause the XC of zircaloy cladding. On the other hand, Shann and Olander [15] reported recently the minimum iodine pressure to be - 10e6 atm (- 10-l Pa). The high iodine pressure of - 10m6 atm (- 10-l Pa) might be obtained because of the following reason. In their experiments, iodine was supplied to the outside surface of the zircaloy tube in the form of a molecular beam. The iodine reacted with zirconium to form zirconium iodide in the small spot where the molecular beam impinged. Most of the formed zirconium iodide evaporated because of its high vapor pressure. The gaseous zirconium iodide escaped from the small reaction region and therefore did not contribute to the SCC of the zircaloy. On the contrary, the gaseous zirconium iodide can contribute to the SCC of zircaloy in the closed tube of an LWR fuel rod and so it should be possible for SCC to be caused by an iodine pressure of lower than 10m6 atm. Experimental approaches have been done to examine the radiation effect on iodine-induced SCC [13-151. Cubicciotti and Davis [13] have shown that free iodine is released from solid CsI by gamma radiation. They have proposed the gamma radiolysis of solid cesium iodide as a mechanism of liberating a sufficient amount of elemental iodine to produce SCC. Une [14], however, reported that the gamma radiolysis of CsI could not influence SCC in the in-pile test. Shann and Olander [15] also examined the hypothesis of Cubicciotti and Davis using the proton beam from a Van de Graaff accelerator. Negative findings were obtained in their experiment. It might be said from these experimental
results that the gamma radiolysis of CsI could not generate enough free iodine to cause the SCC of zircaloy. Davis and Adamson [16] tried to measure the partial pressure of iodine in an operating fuel rod. The results of these experiments showed no evidence for a significant pressure of free iodine in a fuel rod. On the other hand, Yamawaki et al. [17] have recently shown that gaseous CsI can react with iron in the radiation field of electrons, simulating that of fission fragments. The decomposition of gaseous CsI by charged particles was examined in their experiments. The results indicate that the gaseous CsI was decomposed by the electron bombardment and produced free iodine enough to react with iron. The present theoretical evaluation is supported by this experimental result.
4. Conclusion The free iodine partial pressure in an LWR fuel rod was theoretically evaluated taking the influence of the radiation field into account. The following three points are concluded by the present calculations: (1) The partial pressure of iodine calculated under radiation conditions corresponding to the operating LWR fuel rod can be calculated to be - 10e9 atm ( - 1O-4 Pa) at 400°C, which is much higher than that of the non-radiation condition - lo-‘* atm (- lo-l3 Pa). (2) The dominant process of dissociation of CsI in an operating fuel rod seems not to be normal thermochemical reactions but the radiolysis of the gaseous CsI by fission fragments. (3) The free iodine induced by irradiation can cause the SCC of zircaloy cladding.
Acknowledgements The authors are indebted to Dr. M. Yamawaki of University of Tokyo and Mr. H. Kaneko and Dr. N. Nakae for valuable discussions concerning this work.
References [l] B. Cox and J.C. Wood, in: Corrosion Problems in Energy Conversion and Generation, Ed. C.S. Tedmon (Proc. Electrochemical Sot., 1974) p. 275. [2] J.H. Davies et al., in: Proc. ANS Topical Meeting Water Reactor Fuel Performance, St. Charles, IL (1977) p. 230. [3] H.S. Rosenbaum, Electrochem. Tech. 4 (1966) p. 153.
K. Konashi et al. / Irradiation
[4] P. Hofmann
and J. Spino, J. Nucl. Mater. 102 (1981) 117. [S] D. Cubicciotti, R.L. Jones and B.C. Syrett, in: Proc. Zirconium in the Nuclear Industry; ASTM Fifth Conf. on Zirconium in Industry (1980). [6] 0. Gotzmann, J. Nucl. Mater. 107 (1982) 185. [7] K. Konashi, T. Yato and H. Kaneko, J. Nucl. Mater. 116 (1983) 86. [8] P. Hofmann and J. Spino, J. Nucl. Mater. 107 (1982) 297. [9] J.C. Wood, J. Nucl. Mater. 45 (1979) 105. [lo] C.C. Busby, R.P. Tucker and J.E. McCauley, J. Nucl. Mater. 55 (1975) 64. [ll] J.G. Weinberg, WAPD-TM-1048 (1974). Received
15 December
1983; accepted
6 March
1984
induced iodine pressure
247
[12] K. Une, J. Nucl. Sci. Technol. 14 (1977) 443. [13] D. Cubicciotti and J.H. Davis, Nucl. Sci. Eng. 60 (1976) 314. [14] K. Une, J. Nucl. Mater. 87 (1979) 207. [15] S.H. Shann and D.R. Olander, J. Nucl. Mater. 113 (1983) 234. [16] J.H. Davies, F.T. Frydenbo and M.G. Adamson. J. Nucl. Mater. 80 (1979) 366. [17] M. Yamawaki et al., J. Nucl. Sci. Technol. 20 (1983).
Kenji
Konashi,
Katsuichiro
Kamimura
and
Youji
Yokouchi Tokoi Works, Power Reactor und Nuclear Corporation, Tokui - mura, Ibaruki -ken, 319
Fuel Development
- I I Japan
Journal
of Nuclear
Materials 125 (1984) 246247 North-~olland~ Amsterdam
LETTER TO THE EDITORS ESTIMATION OF IRRADIATION INDUCED IODINE PRESSURE IN AN LWR FUEL ROD
1. Introduction
following equation:
It is generally accepted that the pellet-cladding interaction (PCI) failures in light water reactor (LWR) fuel rods are stress corrosion cracking (SCC) induced by fission products [l]. In post irradiation examinations of LWR fuel rods, high concentrations of fission product iodine were locally observed on the cladding inner surface opposite to pellet cracks and interfaces I;?]. Iodine causes SCC of zircaloy in laboratory tests (i.e., out-of-pile experiments) and the fractography of the cracks is very similar to that observed in the PC1 failure of zircaloy cladding of an irradiated fuel rod 131.This is the reason why iodine is believed to be responsible for PC1 failure. However, there still remains the question of the iodine-induced SCC mechanism, which concerns the existence of a sufficient amount of free iodine in an LWR fuel rod to cause SCC. On the basis of thermodynamic considerations, iodine should react with another fission product, cesium, and form an extremely stable compound, cesium iodide (CsI). CsI is more stab1e than the lowest zirconium iodide ZrI, so that cesium iodide cannot react with zircaloy [4]. To support the iodine-induced SCC mechanism, it is necessary to show how iodine is liberated from CsI to cause PC1 failures. Several concepts have been taken to explain the generation of free iodine [5,6]. In a previous paper [7], it was theoretically shown that the partial pressure of iodine should increase due to the radiolysis of gaseous CsI in the LMFSR fuel pin. In this work, the theoretical method mentioned in the previous paper is applied to estimate the partial pressure of iodine in an LWR fuel rod.
RTln P, +AGp(CsI,
g)+RTln
CS
CsI(s) = CsI(g).
ZCs(g) + UO,(s) -I-0, = Cs,UO,(s).
(4)
Substituting Pcsr and PC, into eq. (2), the iodine pressure is obtained. The calculated iodine pressure under non-radiation condition is - lO_” atm (- lo-l3 Pa) for the oxygen potential of - 100 kcaI/mol at 400 o C, and it is clear that the iodine pressure is too few to cause SCC. Recently, Gotzmann [6] has suggested that the cesium activity can be reduced by the formation of cesium molybdate Cs,MoO,, and as a result iodine pressure increases. The formation of Cs,MoO, in the fuel-cladding gap, however, has not been confirmed in post irradiation examinations of LWR fuel rods. In this work, the radiation effect was taken into account in order to estimate the iodine pressure under the condition close to the actual operation of the fuel rod. The gaseous reaction system of cesium iodine is written in more detail as follows,
Cs+l+Xk~C81+X, kd,
Cs(g) + I(g) = CsI(g). (1) The value of the iodine pressure is calculated by the
(3)
The pressure of Cs(g), PC,, can be calculated for the equilibrium between UO, and Cs&JO,,
kd,
The partial pressure of iodine in the fuel-cladding gap, neglecting radiation effect, is thermodynamically estimated as follows. The iodine pressure is determined by the gas phase ~~b~urn:
(2)
where AGP(Cs1, g) is the standard Gibbs energy of formation of gaseous CsI, and P,, PC, and PCs, are the pressures of iodine, cesium and cesium iodide, respectively. The R and T have usual meanings. The pressure of CsI(g), pcsi, is determined by the vapor pressure of CsI(s) on the cladding inner surface according to the reaction,
cs + I, 2 CSI + I, 2. Ektimation of iodine pressure
F,
I+I+Xk::12fX, kd,
(5)
(6) (7)
where X means the third body and He, Xe and Kr are supposed to play a role of X in the fuel rod. The kr,-kr, and kd,-kd, are the reaction rate constants. These constants were determined as a function of temperature
~22-311~/84/$03,00 Q Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
245
K. Konashi et al. / Irradiation induced iodine pressure in the previous work [7]. In the reactor, the dissociation of cesium iodide by the radiation of fission fragments is expected to take place in addition to the above three reactions (eqs. (S), (6) and (7)); CSI + ZE=,,
4 cs + I, kdd
(8)
where kd, is the reaction rate constant. The reaction represented by eq. (8) means that a molecule of CsI is excited by fission fragment impact into excited states and then a certain portion of the excited products decompose spontaneously to give free iodine atoms. The rate constant of the radiolysis, kd,, was determined for the condition of the LWR fuel rod in a manner similar to that obtained in the previous work [7]. Now, the reaction rate equations of the cesium-iodine system can be written as follows, d[Cs]/dr=
kd,[CsI][I]
+kd,[CsI][X]
+kd,[CsI]
-kr,[Cs][I,]
-kr2[Cs][I][X]. (9)
d[CsI]/dt
= -d[Cs]/dt,
d[I,]/dr=
kd,[CsI][I]
(IO) +kr,[I]*[X]
-krI[CslP21-k4LI[Xl,
3. Result and discussion Fig. 1 shows the result of the calculations. In this figure, the iodine partial pressures are plotted as a function of the reciprocal temperature of zircaloy cladding. The partial pressures of iodine calculated under radiation condition (solid line in fig. 1) are much higher than those under non-radiation condition (dashed line in fig. 1). It is apparent that the radiation of fission fragments contributes greatly to the increase in partial pressure of iodine in an operating LWR fuel rod. The present theoretical results were compared with experimental results in order to check whether the estimated iodine partial pressure could cause SCC. A known quantity of iodine was added to the inside of a sealed zircaloy tube in the out-of-pile SCC experiments [8-121, and so the iodine concentration could be calculated in terms of mass per volume or mass per exposed area. The minimum iodine concentration to induce the SCC of zircaloy has been obtained in the out-of-pile experiments [8-121. However, the iodine concentration in itself does not mean the chemical activity of iodine, since the iodine employed in the sealed tube reacts quickly with zirconium to form gaseous ZrI,. Therefore,
(11)
d[I]/dr=kr,[Cs][12]+kd,[CsI][X] +kd,[CsI]
(“C
+2kd,[I,][X]
700
-kd,[CsI][I]
-kr2[WII[Xl --2kr3[I12[Xl,
600
400
500 ’
(12)
where [ ] represents the concentration of the chemical species concerned. These rate equations were solved simultaneously under the given chemical, thermal and radiative conditions and then the partial pressure of iodine was determined. Calculations were performed for the case that the cesium-iodine systems reaches the equilibrium state in the LWR fuel-cladding gap. A typical LWR condition was considered as shown in table 1.
B
‘.
.\
‘\ ‘.
-15 -
“.,t(non-rad) ‘\ ‘\ ‘. ‘\
‘\
‘.
‘\
‘. -\
‘.
Table 1 Typical LWR conditions used in this work Radius of pellet Oxygen potential of fuel Linear heat rate Temperature difference across fuel-cladding gap Total gas pressure in fuel rod
0.5 cm - 100 kcal/mol 300 W/cm 2oo”c
;
10 atm
1
300 l-l
-4
‘\
L i0
I
12
14
,
-15 ‘.
‘Y
16 iO-‘/T(l/K)
Fig. 1. Radiation effect on the partial pressure of iodine as a function of reciprocal temperature of zircaloy cladding. Marks of closed squares represent the experimental critical P,‘s to cause SCC of zircaloy, which were obtained by other workers [8-121.
K. Konashi et al. / Irradiation induced iodine pressure
246
order to compare with the theoretical results, the iodine concentrations were transformed to the iodine pressure using thermodynamic data as follows [6]. First, the iodine concentrations can be converted to the partial pressures of ZrI, under the assumption that all iodine reacts with zirconium to produce gaseous ZrI,, in
P Zrl, = Llc./*w~~~
(13)
where PzrI is the partial pressure of ZrI,, I,,,,, is iodine conckntration and M is molecular weight of I,. From the ZrI, pressure thus estimated, the experimental critical iodine pressures were determined based on the following reaction, Zr(s) +41(g)
= ZrI,(g).
(14)
The values of the iodine pressure using the out-of-pile experimental results were also shown in fig. 1. The iodine pressures calculated theoretically under radiation condition are in excess of the critical values estimated from experimental results in fig. 1. From this, we can draw an interesting conclusion, that is, the free iodine liberated by radiolysis of CsI can cause the XC of zircaloy cladding. On the other hand, Shann and Olander [15] reported recently the minimum iodine pressure to be - 10e6 atm (- 10-l Pa). The high iodine pressure of - 10m6 atm (- 10-l Pa) might be obtained because of the following reason. In their experiments, iodine was supplied to the outside surface of the zircaloy tube in the form of a molecular beam. The iodine reacted with zirconium to form zirconium iodide in the small spot where the molecular beam impinged. Most of the formed zirconium iodide evaporated because of its high vapor pressure. The gaseous zirconium iodide escaped from the small reaction region and therefore did not contribute to the SCC of the zircaloy. On the contrary, the gaseous zirconium iodide can contribute to the SCC of zircaloy in the closed tube of an LWR fuel rod and so it should be possible for SCC to be caused by an iodine pressure of lower than 10m6 atm. Experimental approaches have been done to examine the radiation effect on iodine-induced SCC [13-151. Cubicciotti and Davis [13] have shown that free iodine is released from solid CsI by gamma radiation. They have proposed the gamma radiolysis of solid cesium iodide as a mechanism of liberating a sufficient amount of elemental iodine to produce SCC. Une [14], however, reported that the gamma radiolysis of CsI could not influence SCC in the in-pile test. Shann and Olander [15] also examined the hypothesis of Cubicciotti and Davis using the proton beam from a Van de Graaff accelerator. Negative findings were obtained in their experiment. It might be said from these experimental
results that the gamma radiolysis of CsI could not generate enough free iodine to cause the SCC of zircaloy. Davis and Adamson [16] tried to measure the partial pressure of iodine in an operating fuel rod. The results of these experiments showed no evidence for a significant pressure of free iodine in a fuel rod. On the other hand, Yamawaki et al. [17] have recently shown that gaseous CsI can react with iron in the radiation field of electrons, simulating that of fission fragments. The decomposition of gaseous CsI by charged particles was examined in their experiments. The results indicate that the gaseous CsI was decomposed by the electron bombardment and produced free iodine enough to react with iron. The present theoretical evaluation is supported by this experimental result.
4. Conclusion The free iodine partial pressure in an LWR fuel rod was theoretically evaluated taking the influence of the radiation field into account. The following three points are concluded by the present calculations: (1) The partial pressure of iodine calculated under radiation conditions corresponding to the operating LWR fuel rod can be calculated to be - 10e9 atm ( - 1O-4 Pa) at 400°C, which is much higher than that of the non-radiation condition - lo-‘* atm (- lo-l3 Pa). (2) The dominant process of dissociation of CsI in an operating fuel rod seems not to be normal thermochemical reactions but the radiolysis of the gaseous CsI by fission fragments. (3) The free iodine induced by irradiation can cause the SCC of zircaloy cladding.
Acknowledgements The authors are indebted to Dr. M. Yamawaki of University of Tokyo and Mr. H. Kaneko and Dr. N. Nakae for valuable discussions concerning this work.
References [l] B. Cox and J.C. Wood, in: Corrosion Problems in Energy Conversion and Generation, Ed. C.S. Tedmon (Proc. Electrochemical Sot., 1974) p. 275. [2] J.H. Davies et al., in: Proc. ANS Topical Meeting Water Reactor Fuel Performance, St. Charles, IL (1977) p. 230. [3] H.S. Rosenbaum, Electrochem. Tech. 4 (1966) p. 153.
K. Konashi et al. / Irradiation
[4] P. Hofmann
and J. Spino, J. Nucl. Mater. 102 (1981) 117. [S] D. Cubicciotti, R.L. Jones and B.C. Syrett, in: Proc. Zirconium in the Nuclear Industry; ASTM Fifth Conf. on Zirconium in Industry (1980). [6] 0. Gotzmann, J. Nucl. Mater. 107 (1982) 185. [7] K. Konashi, T. Yato and H. Kaneko, J. Nucl. Mater. 116 (1983) 86. [8] P. Hofmann and J. Spino, J. Nucl. Mater. 107 (1982) 297. [9] J.C. Wood, J. Nucl. Mater. 45 (1979) 105. [lo] C.C. Busby, R.P. Tucker and J.E. McCauley, J. Nucl. Mater. 55 (1975) 64. [ll] J.G. Weinberg, WAPD-TM-1048 (1974). Received
15 December
1983; accepted
6 March
1984
induced iodine pressure
247
[12] K. Une, J. Nucl. Sci. Technol. 14 (1977) 443. [13] D. Cubicciotti and J.H. Davis, Nucl. Sci. Eng. 60 (1976) 314. [14] K. Une, J. Nucl. Mater. 87 (1979) 207. [15] S.H. Shann and D.R. Olander, J. Nucl. Mater. 113 (1983) 234. [16] J.H. Davies, F.T. Frydenbo and M.G. Adamson. J. Nucl. Mater. 80 (1979) 366. [17] M. Yamawaki et al., J. Nucl. Sci. Technol. 20 (1983).
Kenji
Konashi,
Katsuichiro
Kamimura
and
Youji
Yokouchi Tokoi Works, Power Reactor und Nuclear Corporation, Tokui - mura, Ibaruki -ken, 319
Fuel Development
- I I Japan