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sel materials based on available information, research results, and plant surveillance data, and may use probabilistic fracture mechanics techniques. This analysis must be submitted at least three years before RTPTs is projected to exceed the PTS screening criterion.

(5) After consideration of the licensee's analyses, including effects of proposed corrective actions, if any, submitted in accordance with paragraphs (b)(3) and (b)(4) of this section, the Director, Office of Nuclear Reactor Regulation, may, on a case-by-case basis, approve operation of the facility with RTPTS in excess of the PTS screening criterion. The Director, Office of Nuclear Reactor Regulation, will consider factors significantly affecting the potential for failure of the reactor vessel in reaching a decision.

(6) If the Director, Office of Nuclear Reactor Regulation, concludes, pursuant to paragraph (b)(5) of this section, that operation of the facility with RTPTS in excess of the PTS screening criterion cannot be approved on the basis of the licensee's analyses submitted in accordance with paragraphs (b)(3) and (b)(4) of this section, the licensee shall request and receive approval by the Director, Office of Nuclear Reactor Regulation, prior to any operation beyond the criterion. The request must be based upon modifications to equipment, systems, and operation of the facility in addition to those previously proposed in the submitted analyses that would reduce the potential for failure of the reactor vessel due to PTS events, or upon further analyses based upon new information or improved methodology.

(7) If the limiting RTPTS value of the plant is projected to exceed the screening criteria in paragraph (b)(2), or the criteria in paragraphs (b)(3) through (b)(6) of this section cannot be satisfied, the reactor vessel beltline may be given a thermal annealing treatment to recover the fracture toughness of the material, subject to the requirements of § 50.66. The reactor vessel may continue to be operated only for that service period within which the predicted fracture toughness of the vessel beltline materials satisfy the requirements of paragraphs (b)(2) through (b)(6) of this section, with RTPTS ac

counting for the effects of annealing and subsequent irradiation.

(c) Calculation of RTPTS. RTPTS must be calculated for each vessel beltline material using a fluence value, f, which is the EOL fluence for the material. RTPTS must be evaluated using the same procedures used to calculate RTNDT, as indicated in paragraph (c)(1) of this section, and as provided in paragraphs (c)(2) and (c)(3) of this section.

(1) Equation 1 must be used to calculate values of RTNDT for each weld and plate, or forging, in the reactor vessel beltline.

Equation 1: RTNDT=RTNDT(U)+M+ARTNDT

(i) If a measured value of RTNDT(U) is not available, a generic mean value for the class of material may be used if there are sufficient test results to establish a mean and a standard deviation for the class.

(ii) For generic values of weld metal, values the following generic mean must be used unless justification for different values is provided: 0°F for welds made with Linde 80 flux, and -56°F for welds made with Linde 0091, 1092 and 124 and ARCOS B-5 weld fluxes.

(iii) M means the margin to be added to account for uncertainties in the values of RTNDT(U), copper and nickel contents, fluence and the calculational procedures. M is evaluated from Equation 2.

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(A) In Equation 2, ou is the standard deviation for RTNDT(U). If a measured value of RTNDT(U) is used, then ou is determined from the precision of the test method. If a measured value of RTNDT(U) is not available and a generic mean value for that class of materials is used, then ou is the standard deviation obtained from the set of data used to establish the mean. If a generic mean value given in paragraph (c)(1)(i)(B) of this section for welds is used, then ou is 17°F.

3The class of material for estimating RTNDTU) is generally determined for welds by the type of welding flux (Linde 80, or other), and for base metal by the material specification.

(B) In Equation 2, σ is the standard deviation for ARTNDT. The value of os to be used is 28°F for welds and 17°F for base metal; the value of σ need not exceed one-half of ARTNDT.

(iv) ARTNDT is the mean value of the transition temperature shift, or change in RTNDT, due to irradiation, and must be calculated using Equation 3. Equation 3: ARTNDT=(CF)f(0.28–0.10 log f)

(A) CF (°F) is the chemistry factor, which is a function of copper and nickel content. CF is given in Table 1 for welds and in Table 2 for base metal (plates and forgings). Linear interpolation is permitted. In Tables 1 and 2, "Wt-% copper" and "Wt-% nickel" are the best-estimate values for the material, which will normally be the mean of the measured values for a plate or forging. For a weld, the best estimate values will normally be the mean of the measured values for a weld deposit made using the same weld wire heat number as the critical vessel weld. If these values are not available, the upper limiting values given in the material specifications to which the vessel material was fabricated may be used. If not available, conservative estimates (mean plus one standard deviation) based on generic data may be used if justification is provided. If none of these alternatives are available, 0.35% copper and 1.0% nickel must be assumed.

(B) f is the best estimate neutron fluence, in units of 1019 n/cm2 (E greater than 1 MeV), at the clad-base-metal interface on the inside surface of the vessel at the location where the material in question receives the highest fluence for the period of service in question. As specified in this paragraph, the EOL fluence for the vessel beltline material is used in calculating KRTPTS.

(v) Equation 4 must be used for determining RTPTS using equation 3 with EOL fluence values for determining ᎪᎡᎢers.

4 Data from reactor vessels fabricated to the same material specification in the same shop as the vessel in question and in the same time period is an example of "generic data."

5 Surveillance program results means any data that demonstrates the embrittlement

Equation 4: RTPTS=RTNDT(U)+M+ARTPTS

(2) To verify that RTNDT for each vessel beltline material is a bounding value for the specific reactor vessel, licensees shall consider plant-specific information that could affect the level of embrittlement. This information Icludes but is not limited to the reactor vessel operating temperature and any related surveillance program3 results.

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(i) Results from the plant-specific surveillance program must be integrated into the RTNDT estimate if the plant-specific surveillance data has been deemed credible as judged by the following criteria:

(A) The materials in the surveillance capsules must be those which are the controlling materials with regard to radiation embrittlement.

(B) Scatter in the plots of Charpy energy versus temperature for the irradiated and unirradiated conditions must be small enough to permit the determination of the 30-foot-pound temperature unambiguously.

(C) Where there are two or more sets of surveillance data from one reactor, the scatter of ARTNDT values must be less than 28°F for welds and 17°F for base metal. Even if the range in the capsule fluences is large (two or more orders of magnitude), the scatter may not exceed twice those values.

(D) The irradiation temperature of the Charpy specimens in the capsule must equal the vessel wall temperature at the cladding/base metal interface within +25°F.

(E) The surveillance data for the correlation monitor material in the capsule, if present, must fall within the scatter band of the data base for the material.

(ii)(A) Surveillance data deemed credible according to the criteria of paragraph (c)(2)(i) of this section must be used to determine a material-specific value of CF for use in Equation 3. A material-specific value of CF is determined from Equation 5.

trends for the limiting beltline material, including but not limited to data from test reactors or from surveillance programs at other plants with or without surveillance program integrated per 10 CFR Part 50, Appendix H.

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(B) In Equation 5, "n" is the number of surveillance data points, "A" is the measured value of ARTNDT and "fi" is the fluence for each surveillance data point. If there is clear evidence that the copper and nickel content of the surveillance weld differs from the vessel weld, i.e. differs from the average for the weld wire heat number associated with the vessel weld and the surveillance weld, the measured values of ARTNDT must be adjusted for differences in copper and nickel content by multiplying them by the ratio of the chemistry factor for the vessel material to that for the surveillance weld.

(iii) For cases in which the results from a credible plant-specific surveillance program are used, the value of o

to be used is 14°F for welds and 8.5°F for base metal; the value of σ need not exceed one-half of DRTNDT.

(iv) The use of results from the plantspecific surveillance program may result in an RTNDT that is higher or lower than those determined in paragraph (c)(1).

(3) Any information that is believed to improve the accuracy of the RTPTS value significantly must be reported to the Director, Office of Nuclear Reactor Regulation. Any value of RTPTS that has been modified using the procedures of paragraph (c)(2) of this section is subject to the approval of the Director, Office of Nuclear Reactor Regulation, when used as provided in this section.

TABLE 1.-CHEMISTRY FACTOR FOR WELD METALS, °F

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TABLE 1.-CHEMISTRY FACTOR FOR WELD METALS, °F-Continued

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the Construction of Nuclear Power Plant Components," edition and addenda as specified by § 50.55a, Codes and Standards.

(2) "Pressurized Thermal Shock Event" means an event or transient in pressurized water reactors (PWRS) causing severe overcooling (thermal shock) concurrent with or followed by significant pressure in the reactor vessel.

(3) "Reactor Vessel Beltline" means the region of the reactor vessel (shell material including welds, heat affected zones, and plates or forgings) that directly surrounds the effective height of the active core and adjacent regions of the reactor vessel that are predicted to experience sufficient neutron radiation damage to be considered in the selection of the most limiting material with regard to radiation damage.

(4) "Initial RTNDT" means the reference temperature for a reactor vessel material as defined in the ASME Code, Paragraph NB2331. RTNDT means the reference temperature as adjusted for the effects of neutron radiation for the period of service in question.

(5) "RTprs" means the reference temperature calculated by the method given in paragraph (b)(2) of this section for use as a screening criterion.

(b) Requirements.

(1) For each pressurized water nuclear power reactor for which an operating license has been issued, the licensee shall submit projected values of RTPTs for reactor vessel beltline materials by giving values for the time of submittal, the expiration date of the operating license, the projected expiration date if a change in the operating license has been requested, and the projected expiration date of a renewal term if a request for license renewal has been submitted. The assessment must use the calculative procedures given in paragraph (b)(2) of this section. The assessment must specify the bases for the projection, including the assumptions regarding core loading patterns. The submittal must list the copper and nickel contents, and the fluence values used in the calculation for each beltline material. If these quantities differ from those submitted in response to the original PTS rule and accepted by the NRC, justification must be provided. If the value of RTPTs for any material in the beltline is projected to exceed the PTS screening criterion before the expiration date of the operating license or the proposed expiration date if a change in the license has been requested, or the end of a renewal term if a request for license renewal has been submitted, this assessment must be submitted by December 16, 1991. Otherwise, this assessment must be submitted with the next update of the pressure-temperature limits, or the next reactor vessel material surveillance report, or 5 years from the effective date of this rule, whichever comes first. These submittals must be updated whenever there is a

significant change in projected values of RTPTS, or upon a request for a change in the expiration date for operation of the facility.

(2) The pressurized thermal shock (PTS) screening criterion is 270°F for plates, forgings, and axial weld materials, or 300°F for circumferential weld materials. For the purpose of comparison with this criterion, the value of RTPTs for the reactor vessel must be calculated as follows, except as provided in paragraph (b)(3) of this section. The calculation must be made for each weld and plate, or forging, in the reactor vessel beltline. Equation 1. RTÂT=I+M+ARTPTS

(i) "I" means the initial reference temperature (RTNDT) of the unirradiated material measured as defined in the ASME Code, Paragraph NB-2331. Measured values must be used if credible values are available; if not, the following generic mean values must be used: 0°F for welds made with Linde 80 flux, and 56°F for welds made with Linde 0091, 1092 and 124 and ARCOS B-5 weld fluxes.

(ii) "M" means the margin to be added to cover uncertainties in the values of initial RTNDT, copper and nickel contents, fluence and the calculational procedures. In Equation 1, M is 66°F for welds and 48°F for base metal if generic values of I are used, and M is 56°F for welds and 34°F for base metal if measured values of I are used.

(iii) ARTPTS is the mean value of the adjustment in reference temperature caused by irradiation and should be calculated as follows:

Equation 2: ARTPTS=(CF)f(0.28–0.10 log f)

(iv) CF (°F) is the chemistry factor, a function of copper and nickel content. CF is given in table 1 for welds and in table 2 for base metal (plates and forgings). Linear interpolation is permitted. In Tables 1 and 2 "Wt-% copper" and "Wt-% nickel" are the best-estimate values for the material, which will normally be the mean of the measured values for a plate or forging or for weld samples made with the weld wire heat number that matches the critical vessel weld. If these values are not available, the upper limiting values given in the material specifications to which the vessel was built may be used. If not available, conservative estimates (mean plus one standard deviation) based on generic data1 may be used if justification is provided. If none of these alternatives are available, 0.35% copper and 1.0% nickel must be assumed.

(v) "f" means the best estimate neutron fluence, in units of 1019 n/cm2 (E greater than 1 MeV), at the clad-base-metal interface on

1 Data from reactor vessels fabricated to the same material specification in the same shop as the vessel in question and in the same time period is an example of "generic data."

167-027 0-96--23

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