2U.S.NRC

United States Nuclear Regulatory Commission

Protecting People and the Environment

ACRS MEETING WITH

THE U.S. NUCLEAR

REGULATORY

COMMISSION

November 7, 2008
JU.S.NRC

United States Nuclear Regulatory Commission

Protecting People and the Environment

OVERVIEW

William J. Shack
Accomplishments

• Since our last meeting with the

Commission on June 5, 2008,

we issued 9 reports:

* Topics included:

-Security and aircraft impact

rulemaking for nuclear power

plants

-Selected chapters of the

ESBWR Design Certification

Application

3
-License renewal and stretch

power uprate applications

-TRACE thermal-hydraulic

system analysis code

-Quality assessment of

selected NRC research

projects

-PWR sump performance issues

4
New Plant Activities

" Established design-specific

(ABWR, APIOOO, EPR, ESBWR,

US-APWR) Subcommittees

* Chapter-by-chapter review of the

SER for the ESBWR design

certification application is

progressing

-Provided four interim letters

on 18 Chapters

5
* Reviewing topical reports

associated with the US-APWR

design

* EPR Subcommittee participated

in the Quadripartite (U.S.,

France, Japan, and Germany),

Working Group meeting on the

EPR design

* Continue to interact with the

NRO staff to establish schedule

for review of design certification,

early site permit, and COL

applications to ensure timely

completion of ACRS review.

6
Ongqoing/Future Activities

Advanced reactor research plan

" Combined license applications

* Design certification

applications

* Digital instrumentation and

control systems

" Early site permit application

(Vogtle)

" Extended power uprates

7
* Fire protection

* High-burnup fuel and cladding

issues

* Human reliability analysis

* License renewal applications

* Next generation nuclear plant

(NGNP) project

" PWR sump strainer resolution

" Research quality assessment

8
" Revisions to Regulatory Guides

and SRPs

" Safeguards and security matters

" Safety research program report

" Seismic issues

* State-of-the-Art Reactor

Consequence Analyses (SOARCA)

Project

* Waste management, radiation

protection, decommissioning, and

materials issues

9
Challenges in CY-2009

In CY-2009, ACRS will review

several significant matters,

including:

-Seven license renewal

applications

-AP1000 DCD amendment and

ESBWR DC application

Interim review of EPR and USAPWR DC applications

10
Interim review of four COL

applications

Final review of three extended

power uprate applications

Former ACNW&M activities -

significant issues in the areas of

Health Physics, Decommissioning,

Fuel Cycle, and Low-Level Waste

• At least 50 days of Subcommittee

meetings needed for items noted

above and other regulatory matters.

Any emerging issues would require

additional meetings

11
* Some meetings

conducted in pa

schedule, which

ability of membE

participate in all

interest to them

may have to be

rallel to meet

i may affect

,.rs to fully

I reviews of

* Maintain broad expertise,

experience, and diversity in

Committee membership

12
US.NRC

United States Nuclear Regulatory Commission

Protecting People and the Environment

PWR Sump Performance

Sanjoy Banerjee
Operating Experience

* Incidents in Barseback-2 (1992),

Perry-1 (1993), and Limerick-I

(1995) indicated significant plugging of BWR ECCS Strainers

* Parametric study of screen

blockage effects indicated need to

evaluate PWRs, leading to Generic

Letter 2004-02, which required

-Evaluation of potential for postaccident debris blockage and

prevention of recirculation

14
- Implementation of plant

modifications and corrective

actions to ensure system

functionality

15
Schematic of Flow Recirculation Loop

and Potential Debris Accumulation

Regions (Screens, Core, etc.)

16
Debris at Core Inlet

y

17
GSI-191 Progress

* All licensees have installed

significantly larger sump

screens

* Some licensees have replaced

fibrous insulation, changed

chemical buffers, modified

water management strategies

* Most licensees have conducted

sump screen head loss tests

18
Status Of Screen Head Loss Tests

" Plant-specific tests required: plants

have different layouts, debris

sources, chemical characteristics,

screen designs

" Guidance for conducting staff

reviews and protocols for test

procedures have been developed

" Staff's review of some tests have

been completed, others are in

progress

• Key issue: do scaled down proof

tests extrapolate adequately to plant

conditions?

19
ACRS Views On Screen Head Loss

Tests

* Tests in which all fine-scale debris

is entrained and carried to the

screen may be extrapolated to

plant scale

* Chemical effects are adequately

accounted for

* Further development of test

protocols and guidance is required

for tests in which a substantial part

of debris may settle upstream of

the screen

20
ACRS Views On Downstream

Effects

* Core is a second screen (in some

sense)

* Ex-vessel effects downstream of

the first screen are adequately

accounted for

* PWROG investigation of in-vessel

effects continuing. PWROG tests

must encompass a sufficiently

wide range of conditions, including

cold-leg breaks

21
* Fiber length characteristics and

loadings in tests must cover

conditions representative of the

first few flow passes through

core

* If debris is uniformly distributed

at core inlet, TRACE calculations

for cold-leg breaks provide

estimates of debris pressure

losses that may cause

overheating

22
STAFF'S CLOSURE PROCESS

Licensee Submits

GL 2004-02

Information zA Detailed Staff

Review

AL U11ILJRY

I Draft. RAIs Integration

• .. . . f

Review Team

ItL

I IRT

Determination ýMana~gement

J

I,

~~~1

Request Additional

Information

I

I

J

V

t Document

Licensee Closure

23
* Staff has proposed a systematic

process for closure of GSI-191

* Review process complicated by

requirements to be plant-specific

* Integration Review Team reviews

each submission in context of others

* ACRS endorses the proposed closure

process, and appreciates staff's

systematic and deliberate approach

to addressing a very complex

regulatory issue

24
rU.S.NRC.

United States Nuclear Regulatory Commission

Protecting People and the Environment

COMMITTEE VIEWS ON

POWER UPRATES FOR BWRs

Mario V. Bonaca
BWR Extended Power Uprates

* Impact of EPU is hig.hly plantspecific, necessitating focused

reviews on.

- Decreases in margins to

regulatory limits (e.g., ATWS

peak pressure, peak clad

temperature)

- Impacts on equipment and

component performance (e.g.,

steam dryer performance)

26
-Changes in core and fuel

performance (e.g.., fraction

of fuel operating near

thermal limits)

-Impact on systems relied

.upon to perform safety

function (e.g., containment

overpressure credit to

ensure adequate NPSH)

27
EPU Technical

" Steam Dryer

" Containment

Credit

Issues

Integrity

Overpressure

28
Steam Dryer Integrity

e Dryer Integrity Resolutions:

- Replacement/Instrumentation

- Use of new and evolving

analytical methods to predict

loads

- Installation. of branch lines to

dampen vibrations

- Reliance on power ascension

testing

29
* Only Quad Cities Unit 2 and

Susquehanna Unit I steam dryers

were instrumented

* Other licensees measure steam

line strain data and depend on

analytical acoustic-circuit model

to infer steam dryer pressure

loads

30
• To date, acoustic-circuit model

was benchmarked only against

Quad Cities Unit 2 measured

pressures

-This is limited validation for a

model addressing such a

complex set of conditions

31
9 ACRS accepted Hope Creek EPU

application steam dryer

evaluations in part because of

predicted large margin to the

stress limit

* Without further validation, we will

continue to expect large margin

to the stress limit in future

applications

32
Containment Overpressure Credit

" At EPU conditions, i

available NPSH

for safety systems is reduced

" For some plants, demonstrating

adequate NPSH for EPU operation

requires.

-Additional containment

overpressure credit

-Operator action to terminate

drywell cooling to increase

containment pressure

33
* In some cases, pump

cavitation is expected even

with overpressure credit

34
ACRS Position

• COP credit is acceptable.

-if justified by the approach in

RG 1.174, "An Approach for

Using PRA in Risk-Informed

decisions on Plant-Specific

Changes to the Licensing

Basis," or

-if there is no practical

alternative and if deterministic

analyses show required

overpressure is small and

duration limited to a few hours 35
Implications of Staff Position

* No limit on amount of

overpressure and duration is

needed, provided available

overpressure is supported by

conservative calculations

36
ACRS and Staff Positions

* Difference of opinion on the duration

and magnitude of acceptable

overpressure

* Issue was recognized in 1997 and

again in 2005

• Proposed Revision 4 to RG 1.82, "Water

Sources for Long-Term Recirculation

Cooling Following a Loss-of-Coolant

Accident," was supposed to address

this issue. Proposed Revision was not

issued

37
Browns Ferry Overpressure Credit

* For Browns Ferry Units 1, 2, & 3 EPU

(20%) Appendix R scenario,

containment overpressure credit of

up to 9.3 psi needed for 69 hours

SDrywell cooling is terminated to

maximize available overpressure

* Margin between available and

required overpressure is as low as

1.6 psi

38
Browns Ferry Unit I Uprate

In the February 16, 2007 Browns

Ferry Unit I report on 5% power

uprate, ACRS stated that granting

of containment overpressure

credit during long-term loss-ofcoolant accident and 10 CFR Part

50 Appendix R fire scenarios at

120% of the original licensed

thermal power will require

support by more complete

evaluations

39
Browns Ferry Units 1, 2, & 3 COP

Credit

* Viable solutions minimizing need

for overpressure credit:

- Protect a second RHR train for

Appendix R scenario

- Use best-estimate calculation,

with uncertainties and biases

applied for the LOCA scenario

-Use more rigorous, risk

assessment for fire scenario to

demonstrate low risk

40
* TVA has recently provided

additional information to support

their request for overpressure

credit

* We will consider this new

information during our formal

review of the Browns Ferry EPU

Final Safety Evaluation

* Difference in staff and ACRS

positions needs to be resolved

41
Conclusion

* To understand the safety impact of

overpressure credit, more

information is needed than is

available solely from design-basis

analyses

" As a minimum, RG 1.82 should be

revised to state that when credit for

overpressure is requested,

additional analyses should be

performed to provide more realistic

estimates of the actual amount and

duration of containment

overpressure needed 42
* BWROG is developing a more

realistic methodology for

evaluating COP credit

* BWROG methodology is intended

to provide more consistent

evaluation of COP credit for EPU

applications

43
*U.S.NRC

United States Nuclear Regulatory Commission

Protecting People and the Environment

DEVELOPMENT OF

THE TRACE THERMALHYDRAULIC SYSTEM

ANALYSIS CODE

Said Abdel-Khalik
Background

" In the mid-1990s, a decision was

made to consolidate the agency

thermal-hydraulic analysis

capabilities into a single code

now called TRACE

" TRACE is intended to serve as themain tool for the confirmatory

analyses of a broad range of

thermal-hydraulic issues for

current and new reactor designs

45
* The consolidation proved to be

challenging, as anticipated

* The models, correlations, and

solution methodologies required

in-depth review and modification

* Extensive validation was

performed (data from about 500

experiments in 35 facilities)

46
2006 ACRS Report on the NRC

Safety Research Program

(NUREG-1635, Vol. 7)

• Highest priority should be given to

the integration of TRACE code

into the regulatory process

* Prioritization of technical

improvements might be aided

substantially by commissioning a

detailed peer review of TRACE

47
March 22, 2007 ACRS Report

o The schedule for documenting,

validating, and peer reviewing

TRACE should be accelerated -and

the work completed expeditiously

* The development of a

representative set of TRACE plant

models and user testing on

applications should also be

accelerated to facilitate timely

incorporation of TRACE into the

regulatory process

48
September 23, 2008 ACRS Report

* The recently completed peer review

identified no major deficiencies that

preclude the use of TRACE for

confirmatory analyses of postulated

LOCAs in current LWRs

* Several improvements have been

recommended by the peer reviewers

and the staff has proposed a plan to

address them. The ACRS agrees with

the recommended improvements and

the staff's plan

49
-Significant progress has been

made toward the incorporation of

TRACE into the regulatory

Process

*Further peer review should be

conducted to evaluate the

applicability of TRACE to new

LWR designs, as well as for

analysis of coupled reactor

physics-thermal hydraulics issues

related to EPUs and expanded

operating domains

50
* The capability to evaluate

uncertainties in its predictions

should be incorporated into

TRACE

* Continued development of TRACE

is necessary to keep pace with

evolving industry capabilities

51
Abbreviations

ABWR

ACNW&M

ACRS

ATWS

BWR

BWROG

CFR

COL

COP

DC

DCD

EPR

EPU

ESBWR

GSI

IRT

LOCA

LWR

NGNP

NPSH

NRC

NRO

PCT

PRA

PSI

PWR

PWROG

RG

RHR

SER

SRP

SOARCA

TVA

US-APWR

Advanced boiling water reactor

Advisory Committee on Nuclear Waste and Materials

Advisory Committee on Reactor Safeguards

Anticipated transient without scram

Boiling water reactor

Boiling Water Reactor Owners Group

Code of Federal Regulations

Combined license

Containment Overpressure

Design Certification

Design Control Document

Evolutionary Power Reactor

Extended Power Uprate

Economic Simplified Boiling Water Reactor

Generic Safety Issue

Integration Review Team

Loss-of-coolant accident

Light water reactor

Next Generation Nuclear Plant

Net positive suction head

Nuclear Regulatory Commission

Office of New Reactors

Peak clad temperature

Probabilistic risk assessment

Pounds per square inch

Pressurized water reactor

Pressurized Water Reactor Owners Group

Regulatory Guide

Residual heat removal

Safety evaluation report

Standard Review Plan

State-of-the-Art Reactor Consequence Analyses

Tennessee Valley Authority

United States 

- Advanced Pressurized Water Reactor

52