ML19212A534
| ML19212A534 | |
| Person / Time | |
|---|---|
| Issue date: | 06/16/1977 |
| From: | Levine S NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Case E, Minogue R Office of Nuclear Reactor Regulation, NRC OFFICE OF STANDARDS DEVELOPMENT |
| References | |
| RIL-012, RIL-12, NUDOCS 7912140488 | |
| Download: ML19212A534 (2) | |
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l JUN16t7t Isi /.Ui 22 DI 3: 22 CFFICE OF THE ggg;n D.C.
l 8D ORANDUM FOR:
E. G. Case. Acting Directer L'/
Office of Nuclear Reactor Regulation R. 8. Itinogue. Director '
Office of Standards Development FRON:
Saul Levine. Director Office of Nuclear Regulatory Research
SUBJECT:
RESEARCH INFOR'MTION LETTER - 12. MODIFICATIONS TO PRESSURE VESSEL FAILURE PROBASILITY PREDICTION This memorandum transmits the results of the modifications incorporated in the OCTAVIA computer code (Research Infomation Letter dated February
- 25. 1977) as discussed in meetings between RES and NRR and as referenced in the letter (Case to Levine, dated March 24.1977). The modifications involve:
1.
The capability to handle residual stresses. Coding was incorporated in OCTAYIA to handle residual stresses which can be a constant or can vary with flaw size.
2.
An upper limit to be imposed on the toughness. Coding uns incorporated to allow the user to impose an upper bound on the toughness.
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3.
The capability to handle uncertainties in the toughness.
The OCTAYIA code was modified to calculate the 95% and 5% confidence bounds on the toughness as derived from thebasicHSSTdata(ORNL-TM-4914). The best fit to the data was also updated based on regression analyses.
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The user also has the option of inputting his own confidence bounds or best fit.
The draft reports which are enclosed describe the above mdifications and sensitivity studies which have been m de on the effects of these modifications. The Surry 1 vessel has been re-evaluated with the modified versions of OCTAYIA and the median pressure vessel failure probabilities are shown in Tables 1 and 2.
Table 1 is for a copper content of 0.25% which was used as the present copper content in Surry 1; Table 2 is for a reduced copper content of 0.11. Figure 1 is a plot associated with Table 1.
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E. G. Case and R. B. Minogue,
From Table 1, the median failure probabil per vessel years for an operating temperature of 110{ty is 5 x 10~7 and the current age cf Surry taken to be approximately 2.5 years; the failure probability increases to 3 x 10 5 per vessel year after 40 years. These numbers compare with 6 x 10-7 per vessel year for 2.5 years and 3 x 10-5 per vessel year after 40 years reported in the previous OCTAVIA Research Infomation Letter. Table 2 shows the 1 to 2 order of magnitude reduction in failure probability due to reduced copper content. The effect of copper content is similar to that in the previous OCTAVIA calculation.
For the input data used, the modified OCTAVIA results generally agreed e' thin a factor of 2 with the previous results from OCTAVIA.
Ongsaal Signed DI sau11mine J Saul Levine, Director Office of Nuclear Regulatory Research
Enclosures:
1.
Calculation of Pressure Vessel Failure Probabilities for Surry 1 2.
Sensitivity Studies on Residual Stress and Toughness Limits 3.
The OCTAVIA Computer Code: PWR Reactor Pressure Vessel Failure Probabilities Due to Operationally Caused 4
Pressure Transients Distribution:
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