ML14231B210
| ML14231B210 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 08/18/2014 |
| From: | Marc-Anthony Murray South Texas |
| To: | NRC/SECY |
| SECY/RAS | |
| References | |
| 79FR16105 00012, NOC-AE-14003108, NRC-2008-0332, NRC-2012-0041, NRC-2012-0042, NRC-2012-0043, PR-050, PR-052 | |
| Download: ML14231B210 (3) | |
Text
STI 33840383 August 18, 2014 NOC-AE-14003108 10CFR50.46c Secretary, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001 ATTN: Rulemakings and Adjudications Staff South Texas Project Units 1 and 2 Comments on Proposed Rule 10CFR50.46c Docket ID NRC-2008-0332
Reference:
NEI Industry Response to 10 CFR 50.46c Draft Rule Language, August 2014 STP Nuclear Operating Company (STPNOC) has reviewed the proposed 10CFR50.46c rule change and participated with industry in the preparation of the referenced industry comments.
STPNOC agrees with the industry that the rule imposes significant burden and substantial revision to the proposed rule is needed, and generally endorses the industry comments.
As the pilot for the risk-informed approach for the assessment of the effect of debris, STPNOC has additional comments on the proposed risk-informed provision for assessment of debris effects.
The proposed rule has a very detailed definition for the debris evaluation model. STPNOC agrees with the industry position that the definition needs to be simplified to emphasize that this is an input to the PRA, and the PRA, not the debris evaluation model, should be the primary focus of the risk-informed approach.
In the STPNOC pilot licensing application, the PRA for the risk contribution from debris is done by obtaining conditional failure probabilities as top events representing the failure of the Emergency Core Cooling System (ECCS) in the recirculation mode. These top events are derived from an uncertainty quantification that propagates the various engineering models describing transport and deposition of debris in the sump pool, ECCS strainers, and the reactor core. Importantly, they are not an evaluation of risk that is traditionally the product of frequency and consequence. Only the PRA has all the needed information to evaluate the risk from debris.
As with other critical elements of the PRA model of record, the requirements for adequacy of the uncertainty quantification (top event probabilities or basic events) should be part of the PRA Standard (ASME PRA standard) and adopted in RG 1.200. The mechanisms and processes needed to ensure an adequate risk assessment already exist in other guidance documents making redefinition unnecessary in the rule itself.
PR-10 CFR Parts 50 and 52 79 FR 16105 12
NOC-AE-14003108 Page 2 of 3 STPNOC recommends that the definition should be rewritten to define a debris risk assessment consisting of a PRA meeting the required elements of accepted guidance (e.g. RG 1.200) that is capable of evaluating the risk to the cooling function of the ECCS from debris and the effects of chemical formation, including any debris generated from, or present during, a postulated LOCA.
Paragraph (d)(2) of the proposed rule is unclear and can be read to mean that the debris evaluation model is part of the ECCS evaluation model. That reading would then apparently extend the documentation requirements of Paragraph (d)(3) to the debris evaluation model. If so, then it appears that the rule language goes well beyond the intent described in Section VI.F of the Federal Register notice, which would apply existing standards for risk-informed analyses (i.e., RG 1.200). STPNOC recommends that the rule clearly separate the requirements for the risk informed debris assessment from the requirements for the ECCS evaluation model. This can be accomplished by assigning the requirements for the debris assessment their own paragraph (which would fit better in Paragraph (e)), and remove the reference to them from Paragraph (d)(2).
Paragraph (e)(1) requires the risk-informed approach to demonstrate compliance with paragraph (d)(1)(ii). The risk-informed evaluation may identify scenarios that result in core damage, which would be assigned to failure in the PRA in a risk-informed approach; i.e., there would be scenarios for which compliance to (d)(1)(ii) cannot be demonstrated, although their risk contribution would be small. Consequently, STPNOC recommends that the wording in (e)(1) be revised to change demonstrate compliance with (d)(1)(ii) to address the requirements of (d)(1)(ii).
Paragraph (e)(3) requires the application to establish an acceptable long-term peak cladding temperature limit as a condition for approval (presumably the same PCT required in (g)(1)(v)).
The context of the rule implies, but does not specifically state, that not exceeding this PCT is a success criterion for the risk-informed evaluation. The rule should not establish a PCT as a PRA success criterion, but allow the application of core damage success criteria established in the PRA (e.g., CDF and LERF). STPNOC recommends deleting this proposed requirement.
STPNOC strongly endorses the industry comments with regard to eliminating the reporting requirements of Paragraph (m) and having instead an NRC endorsed industry standard document. The industry approach would enable licensees to take advantage of existing programs and procedures, such as their corrective action programs, design control procedures, reporting procedures, Maintenance Rule implementing procedures, etc. STPNOC also notes that the requirement in Paragraph (m)(4) for a licensee to submit a license amendment request for a condition where there was a failure to meet an acceptance criterion of Paragraph (e)(1) would require the submittal even if the nonconforming condition was restored to the approved licensing basis condition. No license amendment should be required if a nonconforming condition is corrected and restored. STPNOC recommends the requirement for the license amendment be clarified accordingly.