ML102460566

NSP000017-Revised Testimony of Steven Skoyen-NUREG-1765 Excerpts

ML102460566
Person / Time
Site:	Prairie Island
Issue date:	09/03/2010
From:	Office of Nuclear Regulatory Research
To:	Atomic Safety and Licensing Board Panel
SECY RAS
Shared Package
ML102460550	List: IR 05000282/2009009 IR 05000282/2009011 IR 05000282/2009015 Information Notice 2009-11, NSP000059-Revised Prefiled Testimony of Northard/Petersen/Peterson-NRC Information Notice 2009-11 L-PI-10-027, NSP000046-Revised Testimony of Northard/Petersen/Peterson-NSPM Response to NRC Annual Assessment Letter for Calendar Year 2009 ML102460551 ML102460552 ML102460553 ML102460554 ML102460555 ML102460556 ML102460557 ML102460558 ML102460559 ML102460560 ML102460562 ML102460563 ML102460564 ML102460565 ML102460566 ML102460568 ML102460569 ML102460615 ML102460616 ML102460617 ML102460618 ML102460619 ML102460620 ML102460621 ML102460624 ML102460625 ML102460626 ML102460627 ML102460628 ML102460629 ML102460630 ML102460631 ML102460633 ML102460634 ML102460635 ML102460636 ML102460637 ML102460638 ML102460639 ML102460715 ML102460716 ML102460718 ML102460719 ML102460720 ML102460722 ... further results
References
50-282-LR, 50-306-LR, ASLBP 08-871-01-LR-BD01, RAS 18550 NUREG-1765
Download: ML102460566 (2)

Text

SKOYEN EXHIBIT 17 NSP000017 NUREG-1765 Basis Document for Large Early Release Frequency (LERF)

Significance Determination Process (SDP)

Inspection Findings that May Affect LERF U.S. Nuclear Regulatory Commission Office of Nuclear RegulatoryResearch Washington, DC 20555-0001

If the breach in the drywell pressure boundary results in a leakage2 to the environment greater than 200 x La it can constitute a large early release. Drywell sprays, if available, reduce the amount of the release. Data generated in the IPE program and reported in published PRAs suggests that for BWRs with Mark I containments, on average, about one-third of the core damage frequency consists of early containment failure sequences and about a third of the early containment failure sequences are large releases. Hence on average, about 0.1 of the core damage frequency in BWRs with Mark I containments constitutes LERF. Thus if a finding implies the existence of a breach in the drywell pressure boundary that would result in a drywell leakage rate > 200 x La, the large release probability of 0.1 increases essentially to 1.0. The conversion factor for Type B findings is, therefore, approximately (1.0-0.1) = 0.9 for findings of this type. This assumption neglects the effect of pool scrubbing for those sequences in which the in-vessel release passes through the suppression pool.

The risk significance can be determined by using the relationship given in Section 2.3 and assuming a total CDF of 10"S/ry for BWRs:

ALERF = 0.9 x I1V x (multiplier based on duration of degraded condition)

Using the multipliers given in Section 2.3 for each of the three (degraded condition) durations the following three ALERFs and the corresponding risk significance categories are obtained:

Duration ALERF Significance Category

> 30 days 9 x10"6 yellow 30-3 days 9 x10-7 white

< 3 days 9 x10s green If a finding identifies a degraded condition that involves a breach of the drywell pressure boundary that can potentially result in a leakage rate in excess of 200 x La and the duration of the degraded condition is also determined, one of the significance categories given above can be assigned to the finding.

2 Several studies, including NUREG/CR-4330, "Review of Light Water Reactor Regulatory Requirements," NUREG 1493, "Performance-Based Containment Leak-Test Program," and NUREGICR-6418, "Risk Importance of Containment and Related ESF System Performance Requirements," have been performed to determine the risk significance of various levels of containment leakage. While the results vary by plant and containment type, a containment leak rate of about 100 volume percent per day appears to constitute an approximate threshold beyond which the release may become significant to LERF. Design basis leakage from containment is determined by regulatory requirements to assure the containment leakage will be below the maximum allowable leak rate (denoted as Lj)set by Title 10 of the Code of FederalRegulations Part 100 dose limits that is incorporated in the plant technical specifications. Typical values of L, are 0. 1 containment volume percent per day for PWRs and 0.5 volume percent per day for Mark I and Mark II BWRs, and 0.2 volume percent per day for Mark III BWRs. Thus a LERF significant leakage rate from containment would be a rate greater than or equal to about 1000 1, for PWRs, 200 L, for Mark I and II BWRs, and 500 L. for Mark III BWRs. The 100 volume percent per day leakage rate is approximately equivalent to a hole size in containment of 2.5 - 3 inches in diameter for PWRs with large dry containments, 2 inches for PWRs with ice condenser containments, I inch for BWRs with Mark I and II containments, and 2.5 inches for BWRs with Mark III containments (Palla, 2001).

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