Surveillance Specimen Program

Only a few studies which suggest that MS is a potentially interesting tool for investigating the microstructural aspects of irradiation embrittlement of RPV steels have been performed so far [141-143], In the framework of the Extended Surveillance Specimen Program 24, specimens designed especially for MS measurement were selected and measured in the as-received state before being placed into the core of the operational nuclear reactor [144]. 

In the framework of the Extended Surveillance Specimen Program [144], several specimens that were originally prepared for Mbssbauer spectroscopy measurements. 

On the other hand, the first MS measurements performed on the Russian RPV steel 15Kh2MFA, irradiated with comparable neutron fluence ( = 6.7x10 n/cm En > 0.5 MeV) in the framework of the Surveillance Specimen Program, confirmed observable changes in the MS parameters. 

The Code specifies that surveillance capsules shall be located within the reactor vessel so that the specimen history duplicates as closely as possible the neutron spectrum, the temperature history and the maximum neutron flux experienced by the reactor vessel. A sufficient number of surveillance capsules shall be provided to monitor the effect of neutron radiation on the reactor vessel materials, that is, the transition temperature shift, ARTndt and the decrease in USE throughout its operating period. A minimum number of capsules is specified depending on the predicted ARTndt value of each testing material at the inside surface of the beltUne of the reactor vessel. In this section, the Japanese surveillance tests program is reviewed. The details of the JEAC 4201 can be found elsewhere (Tomimatsu et al., 2006). Table 4.8 summarizes major revisions of the JEAC 4201. 

In order to select the alloy best suited to this application, an extensive program of corrosion tests was carried out by ORNL (USA) on the available commercial nickel-base alloys and austenitic stainless steels [22,30—34]. These tests were performed in a temperature gradient system with various fluoride media and different temperatures (maximum temperature and temperature gradient). Chromium, which is added to most alloys for high-temperature oxidation resistance, is quite soluble in molten fluoride salts. Metallurgical examination of the surveillance specimens showed the corrosion to be associated with outward diffusion of Cr through the alloy. It was concluded that the chromium content shall be maintained as low as reasonably possible to keep appropriate air oxidation properties. The corrosion rate is marked by initial rapid attack associated with dissolution of Cr and is largely driven by the impurities in the salt [22,30—34]. This is followed by a period of slower linear corrosion rate... 

Comparative tests were run from a specimen of urine from a lawn sprayman containing 2.4 p.p.m. of PNP initially, which was treated with different preservatives and stored at room temperature and at 5°C. for 5 days. This experiment was conducted to establish the stability of this metabolite when left to stand at room temperature for as long as 5 days, conditions which were essential for a surveillance program. 

The effects of storage of a known concentrate of PNP under different degrees of temperature and with different preservatives added are shown in Table I. With formaldehyde added at room temperature the specimen degraded from 2.4 to 2.2 p.p.m. of PNP in 5 days, a decline that would not have seriously influenced the conclusions drawn in a surveillance program. This metabolite stability was subsequently confirmed in other urine samples. 

In this chapter, after giving an overview of the embrittlement of Western pressurized water reactor (PWR) reactor pressure vessel (RPV) beltline materials, together with the characteristics of PWR RPVs, such as their general specification, core region materials and the effects of variables on embrittlement, the surveillance database obtained from US, French and Japanese nuclear power plants (NPPs) and those from other countries is presented based on open literature. The surveillance program of each country is also briefiy described. Trends of surveillance data which will be obtained in the near future are described. The possibility of new data from reconstituted and miniature specimen techniques is described. 

Capsule holders are typically located circumferentially around the core to provide assurance that test specimens and monitors duplicate, as closely as possible, the irradiation history of the reactor vessel, including neutron spectrum, temperature history and maximum neutron fluence. Holders must be designed to avoid interference with in-service inspections required by Section XI of the ASME Code (ASME, 2010a). Most surveillance programs have the capsules located between the thermal shield and the reactor vessel wall with the vertical center at the core mid-plane. C-E, General Electric and B W designs have the holders attached directly to... 

ASTM E185-82 also provides the option of including correlation monitor material in the capsules. Correlation monitor material provides an independent check on the irradiation conditions because other specimens of the same correlation monitor material have been irradiated in other reactors and its response to irradiation (embrittlement characteristics) is well documented. An example of a common correlation monitor is Heavy Section Steel Technology (HSST) Plate 02 (an SA533 Grade B, Class 1 material). Correlation monitor material is also included in the surveillance program to provide a means of validating neutron fluence estimates for the surveillance capsules. The data obtained from correlation monitors should... 

The Charpy impact specimens from HAZ material are inserted in each surveillance capsule except the recent surveillance program. Although ARTnot values of HAZ material due to neutron exposure are not shown in the previously mentioned paper by Yamashita et al., ARTndt of HAZ material versus that of base material is given by Soneda et al. (2007) and is shown in Fig. 4.14. From this figure, ARTndt of HAZ material is almost the... 

In each surveillance program, fracture toughness specimens are usually optional and the number of specimens is still limited, even if these specimens are inserted in each surveillance capsule. Fracture toughness data can be... 

The irradiation surveillance program for System 80+ will be conducted to assess the neutrc n-induced changes in the RTj,j.,j, (reference temperature) and the mechanical properties of rne reactor vessel materials. Changes in the impact and mechanical properties of the material will be evaluated by the comparison of pre- and post-irradiation test results. The capsules containing the surveillance test specimens used for monitoring the neutron-induced property changes of the reactor vessel materials will be irradiated under conditions which represent, as closely as practical, the irradiation conditions of the reactor vessel. 

For surveillance programs including two base metal forgings, the total number of specimens shown in Table 5.3-1 will be... 

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