ML090370140

Probabilistic Assessment of Flaw in Support of Calvert Cliffs Unit 2 Relief Request ISI-020

ML090370140
Person / Time
Site:	Calvert Cliffs
Issue date:	02/06/2009
From:	Ericksonkirk M NRC/RES/DE/CIB
To:	Pat Purtscher NRC/NRR/DCI/CVIB
References
Download: ML090370140 (3)

Text

February 6, 2009 MEMORANDUM TO: Patrick T. Purtscher, Materials Engineer Vessels & Internals Integrity Branch Division of Component Integrity Office of Nuclear Reactor Regulation FROM: Mark T. EricksonKirk, Sr. Materials Engineer Component Integrity Branch Division of Engineering Office of Nuclear Regulatory Research

SUBJECT:

PROBABILISTIC ASSESSMENT OF FLAW IN SUPPORT OF CALVERT CLIFFS UNIT 2 RELIEF REQUEST ISI-020 As we discussed, I requested that our contractors at the Oak Ridge National Laboratory (ORNL) perform a probabilistic fracture analysis using the FAVOR code of the single indication (Indication #1) that was found by ISI in Calvert Cliffs Unit 2 that did not satisfy the requirements of the flaw tables in 10CFR50.61a. Attachment A to this memo provides the problem specification that I sent to ORNL. Information in Attachment A was drawn from the documents provided by Constellation Energy that you provided to me following our conversation. To facilitate quick completion of our analysis we have used the transient set developed in our PTS work for the Palisades vessel. This use of Palisades transients to represent Calvert Cliffs Unit 2 is, in my view, justified for the following reasons:

1. Calvert Cliffs and Palisades are both vessels of Combustion Engineering design and construction, and

2. In our PTS work we found that the level of challenge produced by a comprehensive set of transients did not vary greatly even between the three vessel manufacturers (i.e.,

Westinghouse, Combustion Engineering, and Babcox and Wilcox). I would therefore expect even smaller variation between two Combustion Engineering plants.

Also, as detailed in Attachment A, ORNL performed the FAVOR analysis using an inner-diameter (ID) neutron fluence at the flaw location of 7.22x1019 n/cm2. Thus, our analysis does not account for the fact that the actual ID neutron fluence at the flaw location is only 60% of this peak value. This should be viewed as an implicit conservatism of our analysis.

Attachment B provides the detailed results of the FAVOR analysis that I received from Dr. Terry Dickson at ORNL. The results of Dr. Dicksons analysis can be summarized as follows:

• For Indication #1, only one of the 30 transients analyzed (a late re-pressurization transient) contributed anything to the through-wall cracking frequency (TWCF). The contribution of all other transients to the TWCF for Indication #1was zero because these transients were not severe enough to produce values of applied stress intensity factor that exceed the materials fracture toughness.

P. Purtscher

• The estimated contribution of Indication #1 to the TWCF of the vessel is vanishingly small. The FAVOR analysis provides a numerical estimate on the order of 10-17 TWCF per reactor year. This value is far below the 3x10-10 value that Constellation Energy has estimated to arise due to the entire flaw population in the Calvert Cliffs Unit 2 vessel, and is even further below the 1x10-6 limit that forms the basis of the reference temperature limits in 10CFR50.61a.

In summary, our analysis demonstrates that Indication #1 does not make any significant contribution to the risk of vessel failure arising due to PTS transients. Should you have any questions concerning this analysis, please do not hesitate to contact me.

Enclosures:

1: Problem Specification Sent to ORNL 2: Detailed Results Received from ORNL

ML090370650 OFFICE RES/DE/CIB NAME M. Kirk DATE 2/06/09