ML022140237

Summary of July 16-18, 2002, Public Meeting with NMC Staff Regarding Inputs for Use in the Pressurized Thermal Shock (PTS) Risk Analysis of Pnp

ML022140237
Person / Time
Site:	Beaver Valley, Calvert Cliffs, Oconee, Palisades
Issue date:	08/08/2002
From:	Woods H NRC/RES/DRAA
To:
References
TAC MB5392
Download: ML022140237 (15)

Text

August 8, 2002 LICENSEE: Nuclear Management Company, LLC (NMC)

FACILITY: Palisades Nuclear Plant (PNP)

SUMMARY

OF JULY 16-18, 2002, PUBLIC MEETING WITH NMC STAFF REGARDING INPUTS FOR USE IN THE PRESSURIZED THERMAL SHOCK (PTS) RISK ANALYSIS OF PNP (TAC NO. MB5392)

Background:

The Nuclear Regulatory Commission (NRC) staff and its contractors, with the active cooperation and participation of the nuclear industry, are currently conducting a reanalysis of the risk due to PTS at U.S. pressurized-water reactors (PWRs). The results will be used as part of the bases for a subsequent reevaluation (and possible change) of the PTS rule, 10 CFR 50.61. PNP is one of the four PWRs that has volunteered to participate in this effort.

At two of the four plants (Oconee and Beaver Valley), the NRC staff and its contractors are currently in the process of performing all portions of the reanalyses based, in part, on information obtained from those plants (i.e., they are performing the Probabilistic Risk Analysis (PRA), Human Reliability Analysis (HRA), Thermal Hydraulic (TH), and Probabilistic Fracture Mechanics (PFM) portions of those analyses).

At the other two plants (Palisades and Calvert Cliffs), the PRA/HRA portions of the analyses will be performed by the respective licensees and reviewed by the NRC staff and its contractors (the review will be based, in part, on information obtained from the licensees for those plants).

After modification (if necessary) by the licensees and/or the NRC staff and its contractors, the PRA/HRA will be used, along with TH and PFM analyses performed by the NRC and its contractors, to determine the risk due to PTS at those plants.

Discussion:

On July 16-18, 2002, the NRC Office of Nuclear Regulatory Research (RES) staff and their contractors (Sandia National Laboratory (SNL), Science Applications International Corp. (SAIC),

and Information Systems Laboratory (ISL)) met near the PNP site with NMC staff to discuss and quantify certain specific inputs to the PRA of hypothetical PTS events at PNP. Enclosure 1 is the meetings agenda and Enclosure 2 is the list of attendees.

The meeting started with an NRC RES staff discussion of the overall organization of the joint NRC RES and nuclear industry PTS risk analysis effort, showing how the PRA, HRA, TH, and PFM portions of the analyses will be utilized, along with their associated uncertainty analyses, to produce the final PTS-related risk for each of the four plants included in the study. Enclosure 3 is the slides that were prepared for this discussion.

The remainder of the meeting consisted of detailed discussions regarding TH PTS sequence binning. The binning process considers the tens of thousands of very low probability

sequences that might contribute to total PTS risk, and associates each sequence with one of the approximately 100 representative sequences for which a detailed TH analysis has been performed. This process is necessary because available resources cannot support a detailed TH analysis of every sequence. It is acceptable because the sequences are binned with (i.e.,

represented by) the TH analysis of a sequence judged to cause a slightly higher PTS risk.

Therefore, this process produces a total PTS risk that is slightly higher than would be predicted if detailed TH analyses were performed for each of the tens of thousands of sequences.

Most of the discussions involved minute details of the binning process below the significance level reported in this summary, except for the following more general items.

It was realized that certain of the PNP TH analyses intended to represent the most severe example of certain types of sequences had inadvertently assumed high pressure injection (HPI) throttling (i.e., flow reduction) occurred when the criteria for such throttling were met. Since throttling is a manual action, it had been intended that these most severe cases be analyzed assuming the operator failed to perform the throttling (throttling reduces the overcooling, resulting in lower PTS risk). It was therefore agreed that certain additional TH runs would be made to correct those cases where a significant nonconservative affect might have resulted from the throttling assumption. It was also agreed that certain TH analyses where safety relief valve setpoints were assumed to be slightly below their actual setpoints (this would result in a slight under-prediction of PTS risk) would be reanalyzed using their correct (higher) setpoint.

In certain selected cases, it was agreed that new bins will be created that are identical to existing bins except that TH calculations for the new bins will be performed assuming the reactor at hot, full operating temperature and pressure, but producing zero power (called hot zero power, or HZP - these conditions exist during startup from an extended period of shutdown, e.g., for refueling). PTS analyses typically are made assuming full power operation for an extended period because those conditions exist a majority of the time. However, even taking into account that HZP conditions exist only about 2 percent of the time (which reduces the likelihood that a PTS event will occur starting with those conditions), a PTS event at HZP could be more severe (i.e., more likely to cause vessel failure) because the nuclear core would not contain as much stored heat and would not generate as much heat from fission product decay following shutdown, both of which would worsen the cooldown, making the PTS event more severe. These additional bins will enable the added risk due to HZP to be included for the selected cases.

==

Conclusion:==

The NRC staff and its contractors expressed appreciation for the cooperation and support of the NMC staff during the meeting. The NRC staff believes that the meeting provided a significant contribution to the process of performing improved PTS risk analyses at PNP.

This meeting was not an inspection. Instead, it was an information gathering meeting with a licensee who has volunteered to cooperate with NRCs PTS reevaluation effort. As such, no open items were identified that require future actions or NRC approvals.

/RA/

Hugh W. Woods, Senior Task Manager Probabilistic Risk Analysis Branch Division of Risk Analysis and Applications Office of Nuclear Regulatory Research Docket No. 50-255

Enclosures:

1. Meeting Agenda

2. List of Attendees

3. Slides prepared for the meeting cc: w/encls: See next page DOCUMENT NAME:g:\pts\3rdpalmtgmins.wpd OAR in ADAMS? (Y or N) Y ADAMS ACCESSION NO.: TEMPLATE NO. RES-Publicly Available? (Y or N) Y DATE OF RELEASE TO PUBLIC Immediate SENSITIVE? N To receive a copy of this document, indicate in the box: "C" = Copy without enclosures "E" = Copy with enclosures "N" = No copy OFFICE DRAA/PRAB DRAA/PRAB DRAA/PRAB NRR/DLPM/LPD3 NAME H. Woods* M. Cunningham* S. Newberry* D. Hood*

DATE 07/07/25/02 07/29/02 07/30/02 08/1/02

• See previous concurrence (RES File Code) RES -2C-1A DISTRIBUTION:

PUBLIC PDIII-1 Reading Attachment ML02 BSheron Package (both of above) ML02 JZwolinski/S. Black FEltawila SBajwa HWoods, RES WReckley DBessette, RES RBouling MCunningham JStrasma, RIII MMayfield MRing, RIII SMalik DHood NChokshi AVegel, RIII JRosenthal Enclosure 1 AGENDA July 16, 17, & 18, 2002 Meeting Inputs for use in the Pressurized Thermal Shock (PTS) Risk Analysis of Palisades July 16:

8:00-8:15 Introduction and Purpose of Meeting H. Woods, NRC/RES 8:15-9:45 Discussion of Thermal Hydraulic PTS Sequence A. Kolaczkowski (SAIC),

Binnning for Input to FAVOR Probabilistic D. Whitehead (SNL), and Fracture Mechanics Code B. Brogan, et. al. (NMC) 9:45-10:00 Break 10:00-11:30 Continuation of Discussion (Same) 11:30-12:30 Lunch 12:30-2:45 Continuation of Discussion (Same) 2:45-3:00 Break 3:00-4:30 Continuation of Discussion (Same) 4:30-5:00 Questions from the Public July 17:

8:00-4:30 Continuation of Discussion (Same)

(with breaks and lunch, as above) 4:30-5:00 Questions from the Public July 18:

8:00-11:30 Continuation of Discussion (Same)

(with break as above) 11:30-12:00 Questions from the Public

Enclosure 2 LIST OF ATTENDEES PUBLIC MEETING WITH NMC STAFF REGARDING INPUTS FOR USE IN THE PRESSURIZED THERMAL SHOCK (PTS) RISK ANALYSIS OF PNP JULY 16-18, 2002 NAME ORGANIZATION Roy Woods NRC/RES Donnie Whitehead Sandia National Lab. (SNL)

Alan Kolaczkowski Science Applications International Corp. (SAIC)

Don Fletcher Information Systems Laboratory (ISL)

Brian Brogan Nuclear Management Company, LLC (NMC)

Gary Pratt Nuclear Management Company, LLC (NMC)

Frank Yanik Nuclear Management Company, LLC (NMC)

John Kneeland Nuclear Management Company, LLC (NMC)

Dave Blanchard Nuclear Management Company, LLC (NMC)

Enclosure 3 Slides Prepared for the Meeting

PRA/HRA & TH for PTS Rule Revision Roy Woods Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission Presented at Palisades Nuclear Plant Covert, MI July 16, 2002

Development of Technical Basis to Revise PTS Rule 10 CFR 50.61 Use Public Meetings to Identify Use Public Meetings to Identify Areas in 10CFR 50.61 that need Open Technical Questions in:

Re-assessment (RG 1.99 Rev.) --Identify and Bin PTS Events (PRA)

--Embrittlement Correlations --Thermal Hydraulics

--Margin Terms, etc. --Probabilistic Fracture Mechanics

--Overall Uncertainty Analysis Staff Develops Proposed Changes Collect Information, Develop Methods, To 50.61 Areas. Potentially Use Do Specific Analyses, Involve Public, to

--Fully Participatory Rule Making with --Resolve Open Questions Public Involvement --Involve PRA in All Aspects Identify & Bin Events (PRA) Thermal Hydraulics Probabilistic Fracture Mechanics Re-assess PTS Risk Acceptance

--Use IPTS 3-plant study --Use expert panel and --Revise Flaw Distributions Criterion

--Update plant-specific PRAs, --Limited TH analyses to estimate --Revise Embrittlement Correlations --Base on Risk Informed Guidance if available (1) Effect of TH improvements --Revise Fracture Toughness Models --Consider LERF, Effect on Containment

--Update Events Frequencies (2) Uncertainty bounds in TH results --Material Property Variability --Develop Commission Papers (INPO, plant info, etc.) --Develop Up-to-date Fluence Maps, etc.

Public Meetings to Resolve Public Meetings to Gain Understanding on Outstanding Issues Developed Methods and Input Parameters PROPOSE TECHNICAL BASIS FOR Calculate Vessel Fracture Frequency Re-evaluate PTS Screening

--Mean Value and Variance Criterion REVISION TO 10 CFR 50.61 --Sensitivity & Uncertainty Analyses --Use Vessel Fracture Frequency

--Specific Regulatory Approach --Evaluate IPTS and Other Plants --PTS Risk Acceptance Criterion

--Risk Informed --Evaluate SECY 82-465 Analyses --Generic Sensitivity Analyses Results

--Can it be Performance Based? --Evaluate Effect on Containment PRA/HRA Objective Support development of technical basis for revised rule

 Ensure overall process is coherent, risk-informed 6 Appropriate integration of T/H, PFM, and PRA/HRA 6 Consistent treatment of uncertainties

 Update old PTS/PRA studies 6 Reflect changes to study plants 6 Reflect changes to PRA state of the art, knowledge base 6 Update HRA 6 Address other plants Overall Analysis Framework Overall PTS/PRA/HRA Analysis Approach

 Estimate PTS-induced through-wall crack frequencies (TWCFs) for 4 plants, including uncertainties 6 Develop PTS/PRA/HRA models for Oconee and Beaver Valley 6 Review PTS/PRA/HRAs for Calvert Cliffs and Palisades 6 Resolve inconsistencies, generalize results to population

 Develop TWCF vs. RTPTS relationship, e.g.,

PTS/PRA/HRA Analysis Status

 Oconee

 Kickoff meeting: March, 2000

 Initial PRA/HRA & TH results: December, 2000

 Review meeting at Duke Energy: January, 2001

 Model revised, preliminary TWCF: Dec., 2001

 Final TWCF: July, 2002

 Beaver Valley

 Kickoff meeting: July, 2000

 Initial PRA/HRA & TH results: April, 2002

 Review meeting at FENOC: May 14, 2002

 TWCF results: August, 2002

 Palisades

 Kickoff meeting: March, 2001

 HRA Quant. meeting Nov., 2001

 Initial PRA/HRA & TH results: April, 2002

 TWCF results: September, 2002

 Calvert Cliffs

 Early meeting August, 2001

 Kickoff meeting June 5-7, 2002

 TWCF: February, 2003 Meeting Objectives

 Discuss draft results of PTS PRA/HRA and TH analyses for Palisades

 Finalize TH binning of results for input to PFM calculations (FAVOR code)

(Backup Slide)

Characteristics of Events that Cause a PTS Challenge

 Embrittlement

- irradiation sensitive steel

- years of exposure to high energy neutrons

 Presence of a crack or flaw

- critical size and orientation

- located in embrittled region

 Vessel rapidly cooled

 Vessel remains at a sustained low temperature

 Primary system remains at high pressure, or is repressurized