# Resurgence of a Nation's Radiation Science Driven by Its Nuclear Industry Needs
## 3 Exemplar Results
### Applications of the Re-Circulation Loop
#### 3.5.2 Gamma Radiation-Induced Corrosion  
Under pressurized water reactor (PWR) conditions, the in-pile corrosion response of zirconium alloy fuel cladding elements is significantly enhanced relative to that predicted by (radiation free) autoclave corrosion test data. The corrosion rate of zirconium alloys is predicted by using empirical models correlated to temperature, heat flux, and fast neutron flux and/or fluence. Although there are sound mechanistic reasons as to why neutron flux accelerates corrosion, such as microstructural damage to the underlying metal, it may not be the sole contributor to enhanced corrosion in-reactor. The majority of research into irradiation effects in zirconium alloys is based on simulating the effects of neutron irradiation damage; however, within a reactor, there are other forms of radiation, i.e., gamma radiation, which could affect corrosion behavior. There is limited knowledge on the effects of gamma radiation on zirconium alloy corrosion in the open literature, but there is evidence that a process related to photon dissolution of the protective barrier oxide layer enhances the in-reactor post-transition corrosion rates [56; 57]. Zirconium dioxide (ZrO2) is an n-type semiconductor and exposure to gamma radiation will lead to enhanced electronic conductivity via exciton (electron-hole pair) formation. In addition, gamma irradiation may also induce heterogeneous radiolysis within the porous oxide layer. Further details on these processes can be found in reference [58]. A key question is whether the incorporation of a gamma flux parameter will lead to an improved model for predicting zirconium alloy corrosion under reactor conditions.  
In this application, the high-temperature-high-pressure (HTHP) recirculation loop has been used to simulate PWR conditions and the mini-autoclave, with electrochemical feedthroughs, allowing in situ measurements during gamma irradiation of test specimens in the \({}^{60}\)Co gamma irradiator. The program to date has shown that gamma irradiation has an effect on the electrical conductivity of ZrO\({}_{2}\) and that heterogeneous radiolysis is possible in a post-transition oxide.  
Figure 11 shows the photo-voltage (PV) response of a pre-transition oxide and post-transition oxide under gamma irradiation at a test temperature of 150 \({}^{\circ}\)C. The PV is a measure of the open circuit potential (OCP) during gamma irradiation minus the OCP when gamma radiation is not present. The pre-transition oxide is dense and non-porous; the decrease in PV indicates the formation and separation of electron-hole pairs, which causes the PV to decrease with increasing gamma dose. When the gamma radiation is \"turned off\" the PV increases to its non-irradiated state, which indicates the recombination of these electron-hole pairs. The post-transition oxide is a thick, porous oxide and the increase in PV indicates an increase in oxidizing environment, which suggests that heterogeneous radiolysis is occurring within the porous oxide layer.  
These preliminary results support the working hypothesis that gamma radiation may have an effect on enhanced corrosion. Further experiments and analysis of the results will be required to ascertain whether gamma irradiation has a significant effect on enhanced corrosion behavior in-reactor.