GENERIC SAFETY ISSUE

(GSI) 191, Debris-Induced

PWR Sump Clogging

Office of Nuclear Reactor

Regulation

October 25, 2006

Agenda

* Regulatory history

* Generic Letter (GL) 2004-02 status

* Key technical issues

* Research status

* Conclusions

.I
Regulatory History

*BWR strainer clogging issues

addressed in 1990s

*Bulletin 2003-01

*Generic Letter (GL) 2004-02

*Chemical effects testing results -

2005/2006

GL 2004-02 Status

" Licensees are making major

modifications to sumps

" Staff auditing licensee actions on a

sampling basis

* Strainer vendors conducting head loss

testing

* Staff and industry discussing water

management initiatives

2
Extension Requests

* Acceptance criteria in SECY-06-

0078

* Staff has approved 10 extensions,

all for relatively short durations

* All include relatively large

strainers in place before 12/31/07

Chemical Effects

* Tests indicate chemical effects

are a potential issue

* May need to refine chemical

loadings and/or other measures

* Solutions may involve more than

adding screen area

3
Coatings

* NRC testing indicates "chip" forms

not expected to transport

* Industry needs to show validity of

visual coatings examinations

* Joint (with EPRI) coating condition

assessment program

Downstream Effects

" Improved strainers appear to pass

very little debris

" Licensees modifying systems to

reduce susceptibility of

downstream components

" Owners Group developing topical

report on in-vessel effects

4
Research

* NRC-sponsored research results

are documented in numerous

NUREGs

* Review of licensee submittals

may lead to additional, focused

confirmatory research

Conclusions

" Installing larger strainers adds

substantial safety margin

" Licensees removing problem materials

" Resolution path identified

* Chemical effects issue complex

* Staff will decide on future research

* Anticipate closing the GSI in 2008

10

5
Acronyms

BWR - boiling water reactor

EPRI - Electric Power Research Institute

GL - Generic Letter

GSI - Generic Safety Issue

NRC - Nuclear Regulatory Commission

PWR - pressurized water reactor

6
- lp _

Commission Briefing. on GSI-191

Industry Perspectives

on GS-1,91

October 25, 2006

N EI
Industry Panel

* Tony Pietrangelo

VP Regulatory Affairs, NEI

* Joe Donahue

VP Nuclear Engineering and Services, Progress Energy

Chairman, PWR Owners Group Executive Committee

* Amir Shahkarami

Sr. VP Engineering and Technical Services, Exelon

2 E
Overview

SA highly conservative, deterministic approach

was developed to address GSI-191

* Conservative test methods are also being

applied

* Licensees are moving forward with significant

design and operational enhancements

* Industry wants -to achieve closure expeditiously
Evaluation Methodology (NEI-04-07)

* Developed as a conservative screening

tool to identify areas for licensee action

* Necessary to bound spectrum of plant

configurations and materials

* Did not include guidance on chemical

effects and downstream effects

• Resolution activities initiated in parallel

with joint industry/NRC chemical effects

testing P4EI

4
Examples of Bounding

Assumptions

* Instantaneous double-ended break of largest pipe at worst location (< 1 E-7/yr)

* Maximize head loss

* No credit for Leak Before Break

E Spherical zone of influence (uplto 28.6 D)

* All non-qualified coatings inside containment

assumed to fail

* 100% transport to screens NoE
Chemical Effects

* Joint industry/NRC tests demonstrated need to

consider chemical precipitants

* PWROG developed guidance for plant-specific

chemical effects- treatment

" Conservative estimation of precipitant formation

" Neglects inhibition effects

* Combination of high fiber load, high precipitant

formation leads to prediction of high head loss

* Industry pursuing range of actions to resolve

• Combination of refinements to methodology, test

protocols and design changes
Industry Resolution Activities

* Analysis and mock-up testing being

performed in. support of strainer

replacements

* Plant activities extend well- beyond

installation of larger strainers

* Plant-specific designs are a driver in the

resolution path taken

* Installation of new screens has begun

and will continue to 1st Quarter 2008 .

r E:

7
Licensee Actions Taken or Considered

SInstall very large screens

* Utilize alternate buffers_

* Install trash racks/debris interceptors

* Remove fibrous insulation

* Numerous compensatory actions

* Water management initiative

P4E I

8
PWROG Activities

* Industry guidance documents have been

developed to address

• Debris generation and transport

* Downstream effects evaluation

e Chemical effects

• Alternate buffers

* Conservative treatment of individual

phenomena and operational parameters

* Overall result is highly conservative

N~EI

9
Progress Energy Activities

* Crystal River

* Original sump screen:

* Design: Wire mesh with 1/4" square openings

* Size: 86 ft2.

Replacement sump screen:

* Design: Concentric rolled and perforated plates

(tophat design) with 1/8" diameter holes

* Size: 1140 ft2 (thirteen times larger than original)

* 50% screen head loss margin reserved for chemical

effects

* Separate flow diverter and debris interceptor

upstream of screen

* Status: Installed in fall 2005 N E!

.10
Progress Energy Activities

Crystal River Tophat Strainers

NrEI

11
Progress Energy Activities

m H. B. Robinson

* Original sump screen:

* Design: Wire mesh with 7/32" square openings

* Size: 116 ft2

* Replacement sump screen:

* Design: Tophat with 3/32" diameter holes and integral

woven mesh to minimize debris penetration

* Size: 4200 ft2 (thirty-six times larger than original)

* >50% screen head loss margin reserved for chemical

effects

* Status: Will be installed in spring 2007

12
H. B. Robinson Strainer Layout

N

w.ma  ̧I

ftAmEA

Plaw .

*$At Us WWI

Ic'mk

3⁄4.

t \.~ X4

.7

K
Progress Energy Activities

* Material head loss testing

" Screen penetration testing.

" Coating destruction pressure (ZOI) testing

" Chemical effects

* Working closely with NEI.and PWROG to

resolve chemical effects issue

* Additional testing may be required to quantify

head loss impact

* Using industry predictive spreadsheet to identify

actions most effective in reducing chemical

precipitates

P4E.I

14
EXELON PWRs

. Byron Station Units 1 and2

" Braidwood Station Units 1

" Three Mile Island Unit 1

and 2

* Salem Units 1 and 2

NEI

15
EXELON Activities

, Byron & Braidwood Stations

Original sump screen:

* Design: Wire mesh with 3/16" square openings

* Size: 150 ft2 total both sumps

• Replacement sump screen

* Design: "Pocket" design with 1/12" holes

* Size: 3000 ft2/sump, 6000 ft2 total

, Design complete including head loss and chemical

effects testing

* Status:

* Byron - Unit 1 : installed Sept. 2006

* Braidwood - Unit 2 : will be installed Oct. 2006

* Byron - Unit 2 : will be installed April 2007

, Braidwood - Unit 1 : will be installed Oct. 2007 NEI

16

I
EXELON Activities

Byron & Braidwood Stations

Additional Hardware Modifications

* Remove/replace fiberglass insulation within ZOI

with Reflective Metal Insulation

, Install trash racks for large debris interception

* Replace ECCS throttle valve trim

* Operational Modifications

* Improved loose debris surveillances

* EOP changes for increased cool down rates for,.

Small Break LOCA (Bulletin 2003-01) N E1

17
EXELON Activities

ByronlBraidwood Replacement Sump Screen

,r I

II

1A%
EXELON Activities

* Salem Units 1 and 2

Original sump screen:

* Design: Wire mesh with 1/8,x1/8" square openings

* Size: 85 ft2

• Replacement sump screen

* Design: "Pocket" design with 1/12" holes

* Size: 5000 ft2 total

* Screen design complete

* Chemical effects testing scheduled for Nov. 2006

* Status:

* Unit 2 will be installed October 2006

* Unit 1 will be installed February 2007 NEI

19
EXELON Activities

* Salem Units 1 and 2

• Additional Hardware Modifications:

* Remove/replace Calcium Silicate and Min

K insulation within ZOI with Reflective

Metal Insulation

* Install trash racks for large debris

interception

* No equipment modifications anticipated

to address Downstream Effects

20
Salem Replacement Strainers

Outside Shield

Strainer Pockets

Flow Channel

NE !

21
Closure = Reasonable Assurance

of Long Term Cooling

" GSI-191 in context

" Low risk significant event

" Significant safety enhancements

" Chemical effects is the challenge

* No silver bullet

" Screens sized with margin

* Working with staff on more realistic treatment

* Closure is recognition that the above actions

achieve reasonable assurance

22