ML090370666

Enclosure 2 - Detailed Results Received from ORNL

ML090370666
Person / Time
Site:	Calvert Cliffs
Issue date:	02/06/2009
From:	NRC/RES/DE/CIB
To:
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Download: ML090370666 (5)

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Enclosure 2 ENCLOSURE 2 Detailed Results Received from ORNL Problem Statement In a recent application to NRR, the Calvert Cliffs (CC) Nuclear Power Plant (Unit 2) requested an extension of its in-service-inspection interval from 10 to 20 years. As part of this request, NRR has required that CC assess if flaws found in the RPV beltline are bounded by the flaw tables in 10CFR50.61a. The documents provided by CC demonstrate that one flaw is not bounded by the 10CFR50.61a flaw tables.

The goal of this analysis is to use FAVOR to determine if this single flaw found in CC, which is not bounded by the 10CFR50.61a flaw tables, would significantly contribute to the risk assessment results of Calvert Cliffs.

FAVOR (07.1) Analysis Details

The 07.1 version of FAVOR was applied to perform a probabilistic fracture mechanics (PFM) analysis for the specified flaw geometry, residing in a plate region with the specified embrittlement-related properties, subjected to the 30 transients for Palisades that were applied in the PTS re-evaluation program.

The 07.1 version of FAVPFM was modified such that each RPV would contain exactly one flaw, in every case the specified flaw geometry: an embedded flaw with its inner crack tip located 0.40 inch from the clad-base interface, a through-wall thickness of 0.60 inches, and a length of 0.95 inch (aspect ratio (l / a) of 3.17). Also, the 07.1 version of FAVPFM was modified such that all of the flaws would be axially oriented (normally half of the embedded flaws in plate material are assumed to be axially oriented and half are assumed to be circumferentially oriented).

The PFM analysis was performed for 50,000 RPVs; therefore, there were a total of 50,000 flaws in the analysis. The flaw geometry was constant for all RPVs; however, RT NDT was calculated for each RPV using appropriately sampled values of chemistry and neutron fluence. Figure 1 illustrates the probability distribution of RT NDT at the inner crack tip of the specified embedded flaw geometry determined by sampling from the specified embrittlement-related properties.

FAVOR (07.1) Analysis Results The conditional probability of crack initiation (CPI) was zero for all transients except transient 48. The CPImean for transient 48 was 5.52e-11. The CPFmean was the identical value, i.e., all initiated flaws propagated thru the wall to failure. The integrated results were that the mean value of the frequency of crack initiation and thru-wall crack frequency were identical and were equal to 3.57e-17. The 95 th percentile of both the CPI and the CPF distributions were zero.

As a check for consistency of the full FAVOR analysis discussed in the preceding paragraph, the deterministic minimization option of FAVOR was used for each of the 30 Palisades Enclosure 2 transients to determine how high the simulated value of RT NDT needs to be such that the conditional probability of crack initiation becomes greater than zero of the flaw/transient combination analyzed. This value is called the "Minimum RT NDT for Crack Initiation," or RT NDT(min-init), a name intended to say that all higher simulated values of RT NDT will produce some finite probability of crack initiation and, depending on the transient, vessel failure. Figure 2 illustrates, for Transient 48, that at RT NDT(min-init) the applied K I time history becomes tangent to (or just touches) and time history of the minimum value of fracture initiation toughness (K Ic). Transient 48 is a late re-pressurization transient, as illustrated in Figure 3.

Table 1 contains the incipient value of RT NDT(min-init) for each of the 30 Palisades transients. Transient 48 has the lowest value of RT NDT(min-init). Of the 50,000 flaws simulated in the FAVOR analysis, there were two flaws predicted to have a conditional probability of crack initiation (CPI) greater than zero, i.e., there were only two simulated values of inner crack tip RT NDT that exceeded the values of RT NDT(min-init) in Table 1. These two simulated inner crack tip RT NDT values were 199.22

°F and 208.84

°. Each of these exceeds the RT NDT(min-init) for transient 48, but they are both below the RT NDT(min-init) values for all other transients. Consequently, only transient 48 contributes to the crack initiation and vessel failure probabilities in this analysis.

RT NDT (F) -150-100-50050100150200250denstiy (%)

0 1 2 3

4sample size = 50,000 RT NDT mean = 108.97 F neutron fluence = 7.22 x 10 19 Copper = 0.11 wt %Nickel = 0.56 wt % Phosphorus = 0.007 wt %

Manganese = 1.45 wt %

RTNDT(u) = 10 F \Eason 2006 RT NDT correlation applied lowest simulated RT NDT = -135.53 F highest simulated RT NDT = 208.84 F Figure 1 - Probability distribution of RT NDT at the inner crack tip of the specified embedded geometry determined by sampling from the specified embrittlement-related properties

Table 1 - Values of incipient crack tip RT NDT for 30 Palisades transients (warm pre-stress in effect) for axially oriented flaw Transient ID number Minimum RT NDT for Crack Initiation RT NDT(min-init)

(°F) 2 673.51 16 423.11 18 477.30 19 342.91 22 407.48 Enclosure 2 Transient ID number Minimum RT NDT for Crack Initiation RT NDT(min-init)

(°F) 24 376.34 26 376.34 27 322.13 29 378.21 31 288.73 32 348.02 34 339.33 40 230.52 42 673.51 48 198.9949 378.21 50 312.60 51 281.32 52 339.09 53 354.38 54 271.38 55 332.15 58 235.87 59 302.21 60 294.94 61 356.29 62 237.38 63 224.68 64 246.80 65 224.84 Enclosure 2 Illustration of incipient value of inner crack tip RTNDT when specified flaw geometry is subjected to Palisades transient 48 transient time (minutes) 050100150200250 K I and K Ic (ksi in 1/2) 0 10 20 30 40 50 60 70applied K I at inner crack tip minimum K Ic represented by Weibull "a" parameter for inner crack tip = 199 F Figure 2 - Illustration of the incipient value of RT NDT for Palisades transient 48. The incipient value of RTNDT creates a point of tangency between the applied K I time history and the minimum value of fracture initiation toughness K Ic time history as represented by the Weibull "a" parameter. Enclosure 2 01002003004005006000.00.51.01.52.02.53.0050100150200250300Palisades transient 48 coolant temperature (F) pressure (ksi) transient time (min)

T(t) P(t) Figure 3 - Palisades transient 48 is a late re-pressurization transient