ML20207G318
| ML20207G318 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 08/11/1988 |
| From: | Murley T Office of Nuclear Reactor Regulation |
| To: | Ibser H CALIFORNIA STATE UNIV., SACRAMENTO, CA |
| References | |
| NUDOCS 8808240080 | |
| Download: ML20207G318 (8) | |
Text
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NG11Ing H. W. Ibser, Ph.D.
Professor of Physics California State University Sacramento, CA 95819
Dear Professor Ibser:
Thank you for your letter of March 19, 1977 to Chairman Lando W. Zech, Jr.,
reflecting your concern that the Rancho Seco reactor vessel is susceptible to pressurized themal shock (PTS) and that the NRC should be concerned because i
the individual in charge of Rancho Seco's restart program did not know the l
current value of the reference temperature, RT for the limiting material in the Rancho Seco reactor vessel.
Your lettehD[n,dicetes that SMUD has reported dif ferent values of reference temperature to the NRC and to Ms. Elaine Southard in letters dated January 23, 1986, and February 23, 1988, respectively.
l The pressurized thermal shock (PTS) rule in 10 CFR 50.61 "Fracture Toughness Requirements for Protection Against Pressurized Thermal Shock Events" established 1
screening criteria, which for Rancho Seco would be a reference temperature, RT of 270 F, beyond which it could not operate without a plant-specific sa$y, analysis acceptable to the NRC.
The rule also prescribed how to calculate RT The staff used the PTS subscript to distinguish procedures for caNblating reference temperature values to be compared to the PTS screening criteria from procedures used for other fracture analyses, e.g., RT NDT*
For Rancho Seco, SMUD repcrted to the NRC calculated value of RT of 217'F on January 23,1986 and 265'F on October 11, 2008, the expiration d$lk of the operating license. The NRC staff has accepted these values.
It should be understoodthattheprobabilityoffailureofavesselfromaPJSeventwhenits RT ye$h. reaches the screening criteria is still very low (5 x 10" per reactor 3
Nevertheless, in order to make sure nothing would happen to the reactor ves' sol, NRC requires the licensee whose reactor vessel is projected to exceed the PTS screening criteria before the end of its license to take corrective actions and conduct analyses to demonstrate that continued operation of this facility is safe.
The infomation reported by SMUD to Ms. Southard was the best estimate of the reference temperature for the controlling weld metal at a point one-fourth through the vessel wall thickness. That value of RT was cale.ulated using a different formula from that used to calculate RT HhbichwasreportedtoNRC.
We understand the difference in calculational me$kho,s and we agree with them.
In the course of investigating this matter we encountered some data en weld metal properties not previously considered.
Since it could have a bearing on Rancho Seco weld metal properties, we intend to conduct further analysis of the data and will make our findings public when completed.
Sincerely,
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Professor Ibser 2-AUG 111933 DISTRIBUTION:
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H. W. Ibser in the 1986 letter used the formula 10 the PTS rule.
Second, the calculations in the 1988 letter used 58'F as an estimate of the unirradiated reference L
temperature while the calculation in the 1986 letter used a generic mean value of 0"F.
Although the formulae for predicting the increase in reference temperature in the PTS rule and in RG 1.99, Revision 2, are similar, they should not be' indiscriminately applied. The staff believes that the best method for predicting the increase in reference temperature,,ili the fomula and tables in RG 1.99, Revision 2.
Therefore, the staff is proposing a change to the PTS rule to require that the increase in ref,er,ence temperature be calculated using the method in RG 1.99, Revision 2.
Jibwever, until the rule is changed, licensees must use the formulae in the PJS rule when they are responding to it.
Since the fomula and tables in JG,1.99, Revision 2, form the best method for predicting the increase in refeyence temperature, they should be useu to calculate values of reference temperature.
Therefore, in each letter SMUD used the correct method for calculatjng the increase in reference temperature because SMUD was responding to differerit subjects.
SMUD indicates that different values of unirradiated reference temperatures for Rancho Seco's limitMg weld metal results from its interpretation of the PTS rule and its evalpation of test data from the heavy section steel technology (HSST) pyogram at the Oak Ridge National Laboratory. However, our Cdlculations indicate that even with an unirradiated reference temperature of 58'F, the Ranchoe$eco reactor vessel will not reach the screening cri*arion for several yearstAherefore, the licensee would have several years to complete the actionsrequjredinthePTSrule.
The NRC staff is rigorously pursuing this evaluation,and will reach a decision in the near future well before the Rancho Seco reference temperature gets anywhere near the screening criterion.
Sincerely,
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Thomas F. Murley, Director Office of Nuclear Reactor Regulation
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0FFICIAL RECORD COPY DRSP 5520 document name:
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H. W. Ibser, Ph.D.
Professor of Physics California State University Sacramento, California 95819
Dear Professor Ibser:
In your letter dated March 19, 1988, to Chairman Lando W. Zech, Jr., you indicate that the NRC should be concerned because Sacramento Municipal Utility District's (SMUD's) current Chief Executive Officer, Nuclear, G. CarVAdognini (or his staff) does not know the current value of the reference temperature, leNr, for the limiting material in the Rancho Seco reactor vesse).
RT Your indicates that SMUD has reported different values of reference tem-perature to the NRC and to Ms. Elaine Southard in letters dated 41anuary 23, The staff has determined that the differ,fach of these 23, 1988, respectively.
Our evaluation of 1986, and February letters is attached.
ent values of reference temperature are appropriate because the subject of each letter is different. Therefore, the reference temperature may be ca culated differently, and the SNUD responses appear credible.
The only significant difference.between the information presented in each of these letters is the unirradiated reference temperature for the limiting
.ncho Seco reactor vessel weld metal.
The staff is #' valuating the licensee's engineering justification for the values; however, tpe staff has performed its own calculations, which are surrn1arized in the attac)iment.
Using a conservative value for the unirradiated.'eference temperature,/ 3everal years without fear our calculations indicate that the Rancho Seco reactor vessel may be operated fo of vessel' rupture from a pressurized thermal shoc'k (PTS) event, and the licensee would have several years to complete the actions' required by the PTS rule in 10 CFR 50.61.
Sincerely, Thomas E. Murley, Director Office of Nuclear Reactor Regulation
Enclosure:
As stated DISTRIBUTION:
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/ /88 0FFICIAL RECORD COPY 5520 document name:
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4 H. W. Ibser, Ph.D.
Professor of Physics California State University Sacramento, CA 95819
Dear Professor Ibser:
In your letter to Chairman Lando W. Zech, Jr., dated March 19, 1988, you indicate that the NRC should be concerned, because SMUD's current Chief Executive Officer, Nuclear, G. Carl Adognini [or his staff] does not know the current value of the reference temperature, RT for the limiting material in the Rancho Seco reactor vessel. Ycur lettepDJn,dicates that SP.UD has reported different values of reference temperature to the NRC and to Ms. Elaine Southard in letters dated January 23, 1986 and February 23, 1988, respectively.
Our evaluation of each of these letters is contained in Attachment 1.
We have determined that the different values of reference temperature are appropriate, because the subject of each letter is different; therefore, the reference temperature may be calculated differ = rely.
Hence, the SMUD responses appear
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The only significant difference between the information present'ed in each of these letters is the unirradiated reference temperature for' the limiting Rancho Seco reactor vessel weld metal. We are presently evaluating the Licensee's engineering justification for the values. Howevsr, we have performed our own calculations, which are summarized in Attachment 1.
Using a conservative value for the unirradiated reference temperature, our calculations indicate tnat the Rancho ieco reactor vessel may be oper'ted for several years a
without fear of vessel rupture from a PTS event and the' licensee would have several years to complete the actions required by the' PTS rule, 10 CFR 50.61.
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Thomas E. Murley, Director Office of Nu'elear Reactor Regulation Enclosure
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As Stated
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