ML20151V599

Requests NRC Approval of Util Proposed Reduction in IGSCC Insp Frequency for GL 88-01,Category D Welds in Support of Refueling Outage (RFO) 12

ML20151V599
Person / Time
Site:	Pilgrim
Issue date:	09/04/1998
From:	Alexander J BOSTON EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-88-01, GL-88-1, LTR.#2.98.126, NUDOCS 9809150028
Download: ML20151V599 (22)

Text

._ . . _ _ . . . _ _ _ _ . _ _ _ . _ . .. .

.- ~ O GL 88-01 Bassors W ,

Pilgrim Nuclear Power Station  !

, Rocky Hill Road Plymouth, Massachusetts 02360-5599 l

September 4,1998 BECo Ltr. #2.98.126 US Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Docket No. 50-293  !

License No. DPR-35 l

REQUEST FOR REDUCTION l'.4 GL 88-01 IGSCC INSPECTION FREQUENCIES FOR CATEGORY D WELDS DUE TO THE USE OF HYDROGEN WATER CHEMISTRY

References:

1. NRC Safety Evaluation Report on NEDC-31951P, dated January 18,1995.

2. BWROG Topical Report NEDC-31951P, dated April 1991.

3. Supplement 1 to BWROG Topical Report NEDC-31951P, dated April 8,1998.

-This letter requests NRC approval of Boston Edison Company (BECo) proposed reduction i in intergrannual stress corrosion cracking (IGSCC) inspection frequency for GL 88-01 '

Category D welds in support of refueling outage (RFO) 12.

The attachment describes Pilgrim Station's hydrogen water chemistry program, IGSCC inspection program, and provides information in response to NRC safety evaluation on l BWROG Topical Report NEDC-31951P (References 1,2 and 3).

BECo plans to implement the reduced IGSCC inspection frequency for Category D welds  ;

beginning RFO 12. RFO 12 is scheduled to commence on or about April 24,1999. NRC / ,

approval is requested by January 1999, in order allow sufficient time for scheduling of f 1

inservice and IGSCC examinations. /

Should you have any questions regarding this letter, please contact Walter Lobo at (508)  ;

830-7940.

f l

. Alexander egulatory Relations Group Manager i WGUlGsec

Attachment:

Reduction in IGSCC l' spe, tion Frequencies.

9809150028 980904 PDR o

P ADOCK 05000293:

PDRh

J. ,

• cc: Mr. Alan B. Wang, Project Manager Project Directorate 1-3

.- Office of Nuclear Reactor Regulation Mail Stop: OWFN 14B20 1 White Flint North 11555 Rockville Pike Rockville, MD 20852 U.S. Nuclear Regulatory Commission

' Region 1 -

475 Allendale Road -

King of Prussia, PA 19406 Senior Resident inspector Pilgrim Nuclear Power Station -

[

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ATTACHMENT REDUCTION IN IGSCC INSPECTION FREQUENCIES TABLE OF CONTENTS

1. Introduction

11. Hydrogen Water Chemistry Program A. HWC Performance Summary B. PNPS HWC Program

1. Hydrogen Water Chemistry System Description

2. Monitoring for HWC Effectiveness -

3. History of HWC at PNPS 111. PNPS IGSCC Welds inspection Program j

IV. Proposed IGSCC Inspection Schedule V. BWR Owner's Group Topical Report / Supplement 1 VI. Reduction in Radiological Exposure and Resources  ;

Vll. Conclusion Vill. Figures:

1. PNPS Cycle 12 ECP vs. MSLR Readings (Expanded View)

2. PNPS Cycle 12 ECP vs. Recirc H2, O2 & H2 Flow

3. PNPS Cycle 12 ECP vs. Alternate Parameters (Expanded View)

4. PNPS Cycle 12 ECP vs. MSLR Readings j l 5. PNPS Cycle 12 Power vs. Reactor Water Conductivity

6. PNPS H2 Injection Rate Requirements vs. Power i

I Page 1 of 13 l

l. Introduction On January 25,1988, the Nuclear Regulatory Commission (NRC) issued Generic Letter (GL) 88-01. This GL provided the Staff's position on Intergranular Stress Corrosion Cracking (IGSCC) in BWR austenitic stainless steel piping including weld examination frequencies. It also specified methods for applying for reduced examination frequencies when Hydrogen .

Water Chemistry (HWC) is in use. J In April 1991, the BWR Owners Group (BWROG) Improved Water Chemistry inspection Relief Committee submitted Topical Report NEDC-31951P to the NRC. This report requested a revised weld examination schedule for custenitic stainless steel piping for those BWRs committed to use Hydrogen Water Chemistry (HWC).

On January 18,1995 the NRC issued a Safety Evaluation Report (SER) approving NEDC- '

31951P.

7 On April 8,1998 the BWROG submitted Supplement 1 to Topical Report NEDC-31951P to the NRC. The supplement requested modifications to the NRC SER to allow BWROG to take credit for effective implementation of HWC. The NRC has requested that a " lead plant" be identified to apply for weld inspecuon relief taking into account the responses to the NRC SER Pilgrim Nuclear Power Station (PNPS) will be the " lead plant"in this effort.

PNPS has implemented a HWC Program utilizing a stress corrosion monitoring system and i alternate parameter monitoring with successful results. PNPS is requesting reduced examination frequencies for eleven Category D Recirculation System IGSCC welds beginning RFO 12. RFO 12 is scheduled to commence on about April 24,1999.

This document provides the justification for a revised inspection schedule in accordance with Supplement 1 to NEDC-31951P, taking into account the NRC SER. PNPS also currently meets the more restrictive requirements of the NRC SER.

Generic Letter 88-01 Scope of IGSCC Welds '

A total of 221 safety-related welds are included in the PNPS GL 88-01 IGSCC examination Program'. The 68 non safety-related welds in the reactor water clean-up system currently fall under the provisions of GL88-01, Supplement 1 and are outside the scope of the relief ,

l request. The number of safety-related welds and the categories as defined in GL 88-01 are l included in Table 1. ,

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' Ref: 1. BECo Response to GL 88-01, dated August 4,1988 (BECo Letter #88-119)

Ref: 2. BECo Response to NRC RAl, dated June 19,1989 (BECo Letter #89-084)

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-. -_ - - . _ - - -- . - . - -- - - - - -.~. - - - - _ _ -

TABLE 1: SAFETY-RELATED IGSCC WELDS (GL 88-01)

(INCLUDES RHR, RCS, CS, RWCU WELDS)  ;

Materials / Mitigation IGSCC inspection Extent No. of Safety- .

Process Category & Schedule Related Wolds Resistant MEterial A 25% every 10 years (at least 12% 169 in 6 years) i Non-Resistant Materials - B 50% every 10 years (at least 25% 0 Stress improvement (SI) in 6 years) within 2 years of operation ,

Non-Resistant Materials Si after 2 C All within .the next 2 refueling 2 3 years of operation cycles, then all every 10 years (at .

l least 50% in 6 years)  !

Non-Resistant Materials with no SI D All every 2 refuelinacycles 44 [

, Cracked Reinforced by W eld E 50% next refueling outage, then all 1 i l Overlay or Mitigated SI every 2 refueling cycles  !

Cracked inadequate or No Repair F All every refueling outage 0 i l Non-Resistant Not inspected G All next refueling outage 5 i The Table includes safety-related welds from residual heat removal, reactor coolant system, ,

core spray, and reactor water clean-up systems.  !

l PNPS has an aggressive inspection program that fulfills the requirements of GL88-01. l PNPS has performed 137 IGSCC (safety and non-safety) weld examinations since the GL88-01 inspection schedule was implemented and 82 examinations since HWC was initiated. The only cracking discovered was in RWCU piping prior to continuous use of HWC in September 1991. The safety-related portion of the RWCU system was replaced with i resistant material during the 1995 refuel outage while the non-safety-related RWCU piping falls under Supplement 1 of GL88-01. No pipe cracking has been observed in any safety-related system at PNPS since HWC was placed in continuous service.

II. Hydroaen Water Chemistry Proaram A. HWC Pe,-formance Summary HWC has been implemented at PNPS since September,1991 (beginning of Cycle 9). HWC can be placed into service at approximately 40% reactor power and injects 32 SCFM i hydrogen at 100% reactor power. HWC availability has averaged >80% above 200 Deg F ,

service temperature since that time. See Table 2 below.

Table 2: % HWC Availability .l Cycle Period  % HWC Ava .selity 9 8/91-4/93 ~75*

10 6/93-3/95 -80*

11 6/95-2/97 ~ 88*

12 4/97-8/98 93.3 estimated using hydrogen injection rate A Crack Arrest Verification System (CAVS) was implemented in January 1992 at PNPS to monitor the Reactor Recirculation System Electrochemical Corrosion Potential (ECP) levels and obtain crack growth data. Crack growta data is no longer obtained. CAVS has been i supplemented by a Stress Corrosion Monitoring System which was installed in May 1995 to

! facilitate hydrogen injection optimization. This system consists of in-situ ECP probes in the l

Reactor Recirculation piping. A Data Acquisition System (DAS) provides chemistry and ECP Page 3 of 13

' readings and stores tha data for later use.

The in-situ Recirculation Syst::m ECP measurements and chemistry data are used in the HWC program to verify that ECP remains below - 230 millivolts on the standard hydrogen electrode (mVSHE) scale during reactor operation.

It is important for ECP to remain below -230 mV (SHE) since the threshold for IGSCC mitigation is ECP levels below -230 mV (SHE). During the current cycle (12), the ECP values in the recirculation system have been below -230 mV (SHE) >80% of the time service temperature was above 200 Deg F. This is confirmed by both ECP and alternate parameter .

measurements  !

In accordance with NEDC-319151P Supplement 1, alternate operational parameters, namely Reactor Recirculation System dissolved oxygen, Reactor Water Conductivity, and Feedwater hydrogen injection rate are continuously monitored to verify ECP below -230 mVSHE  ;

Alternate diagnostic parameters, namely Reactor power, Reactor Recirculation System  ;

dissolved hydrogen and Main Steam Line Radiation (MSLR) levels are also measured to confirm and supplement the operational parameters.

At the current hydrogen injection rate, ECP levels, and HWC availability, IGSCC mitigation of the recirculation system is accomplished. This is confirmed by the weld examination results during the Refueling Outages 9,10 and 11 which revealed no new IGSCC indications since the implementation of HWC.

B. PNPS Hydroaen Water Chemistry Proaram I l

PNPS has a HWC program established in 1991 in accordance with EPRI Guidelines.

1. Hydroaen Water Chemistry System Description The HWC System consists of Extended Test System (ETS), Electrolytic Hydrogen Water Chemistry System (EHWCS), and the Stress Corrosion Monitoring System.

The Extended Test System (ETS) provides the means for injecting hydrogen into the reactor via the suction side of the reactor feed pumps and oxygen into the off gas utilizing boitled gas (hydrogen tube trailers and oxygen tank).

The Electrolytic Hydrogen Water Chemistry System (EHWCS) is a permanently 1 installed hydrogen and oxygen injection system utilizing the electrolytic generation of hydrogen and oxygen. This is the primary means of injecting hydrogen into the i feedwater. The ETS system, which is more expensive to operate, is the backup i injection system. j

)

The Stress Corrosion Monitoring System (SCM) consists of the following:

a) A Crack Arrest verification system was started in 1992. The CAVS is an on-line monitoring system receiving reactor water from the discharge of the 'B' reactor recirculation loop, it consists of 3 autoclaves and a water chemistry panel. Two of -

the autoclaves were used for crack growth monitoring of representative plant components. These autoclaves provided initial testing information and are no longer used. A third autoclave contains 2 Copper / Copper Oxide and 1 Platinum reference ECP probes.

b) An ECP assembly installed at the suction decontamination flange to the "A' loop recirculation pump. Originally installed in 1995, it was replaced in April 1997 for use in cycle 12. It consists of 2 Iron / Iron Oxide and 2 Platinum reference electrodes. The platinum probes are still functional, while the iron probes lasted approximately 8 months before failure. Both iron and platinum probes have been Page 4 of 13 i

utilized to b:nchmark altsrnate parametsrs. The CAVS probes were also benchmarked against Recirculation system in-situ probes. However, only Recirculation probes are being used for the purposes of obtaining relief in accordance with Supplement 1 to NEDC-31951P.

c) A Water Chemistry Panel which accepts water from the same recirculation sample line that supplies the autoclaves and directs it past sensors which measure dissolved oxygen, dissolved hydrogen and conductivity.

1 d) Data Acquisition Systems (DAS) displays and trends ECP, water chemistry measurements, hydrogen injection rate and power. The balance of plant computer is utilized to trend Main Steam Line Radiation Levels (MSLR).

2. Monitorina for HWC Effectiveness ECP measurements at PNPS have provided the primary means of determining HWC j availability and effectiveness. However, ECP probes are expected to fail before the end of cycle 12 (April 1999). Therefore, it is desirable to be able to use alternate parameters to confirm that ECP is indeed below -230 mV (SHE) for > 80% of the time service temperature is >200 Deg F. i Data as presented in the attached graphs (Figures 1 through 5) shows the correlation between alternate parameters and ECP in accordance with NEDC-31951P Supplement 1 for the current Cycle 12 at PNPS.

The following alternate operational parameters were benchmarked against ECP:

Feedwater hydrogen injection rate (Figures 1,2 and 4).

Reactor Recirculation dissolved oxygen (Figures 2 and 3).

The following alternate diagnostic parameters are used as confirmatory measurements:

Reactor Recirculation dissolved hydrogen (Figures 2 and 3).

Main Steam Line Radiation Levels (Figures 1 and 4).

Reactor power (Figure 5) was used to confirm that the hydrogen injection rate is correct for the power level. Reactor conductivity (Figure 5) is used to determine HWC availability if it increases to above 0.2 US/cm.

Figures 1 and 3 provide correlation data during the first 5 months of cycle 12 when multiple ECP readings were available and to show more clearly the response of  !

alternate parameters to ECP changes.

Hydroaen Iniection Rate vs. ECP ECP changes with the hydrogen injection rate. Refer to figures 1,2 and 4 which show this relationship. For instance, if the hydrogen injection rate is reduced to 0, ECP values clearly move above -230 mV (SHE). If the ECP does not change with the injection rate it is because the injection rate has not changed enough to affect water chemistry.

Reactor Recirculation Water Dissolved Oxvaen ECP changes with reactor water dissolved oxygen. Refer to figures 2 and 3 which show that as ECP increases above -230 mV (SHE), dissolved oxygen increases.

When ECP is <-230 mV (SHE) oxygen measurements are very low (<1.0 ppb) and are considered " buried" or as low as can be measured.

Page 5 of 13

. - .- .. .. - - -_ - - - ~ - .

Reactor Recirculation Water Dissolved Hydroa n Reactor water dissolved hydrogen at PNPS is used as a confirmatory measurement i . to the hydrogen injection rate. Also, it is used to correct raw platinum ECP measurements. Refer to figures 2 and 3 which show that as hydrogen injection rate decreases so does the dissolved hydrogen reading.

Main Steam Line Radiation Levels (MSLR)

Main Steam Line Radiation Levels change significantly when hydrogen injection rate ,

and ECP change. In general at PNPS, if enough hydrogen is being injected to reduce  ;

ECP to <-230 mV (SHE), then radiation levels increase by approximately 4 times <

over normal water chemistry (NWC) conditions. A significant change in MSLR  ;

readings is used to confirm that ECP has indeed changed. See figures 1 and 4.

Reactor Power Hydrogen injection requirements vary with power level. PNPS has previously  !

determined the hydrogen requirements during "HWC Ramp Testing" in cycle 11 (figure 6) and reconfirmed this in cycle 12. Therefore, Reactor Power is monitored  !

along with hydrogen injection rate to confirm enough hydrogen is being injected, l Reactor Water Conductivity Reactor water conductivity is monitored to satisfy PNPS Technical Specifications, to trend overall reactor water conditions and to determine HWC availability in accordance with the SER to NEDC-31951P. If conductivity increases to above 0.2 l US/cm, then credit for hydrogen is not taken. The periods where conductivity is above l 0.2 US/cm is very infrequent and accounts for <1% of total HWC availability that is lost. Refer to figure 5 which shows conductivity trended over cycle 12. j l

HWC Availability i Using either ECP or alternate parameters, HWC availability is determined by the following equation:

% HWC availability = (Hours ECP <-230 mV & Conductivity <0.2 US/cm X 100 (Hours service temp >200 Deg F)

Refer to Table 3 below indicating % HWC availability for the last four cycles at PNPS.

Table 3: % HWC Availability Cycle  % HWC  % HWC Availability Availability  !

(Using alternate (Using ECP parameters) measurements) 9 ~75

• 56 10 ~80

• 75 11 ~88

• 86.7 12 93.3 92.3

• Estimated.  !

l ECP derived availability is lower than with e ing alternate parameters because ECP measurements where not always available. A. rnate parameter derived availability for cycles 9,10 and 11 are estimated using hydrogen tjection rate.

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Regardless of how availability is derived, cycle 12 availability is above 80% as being proposed by Supplement 1 to NEDC-31951P. If ECP probes continue to function until the end of the cycle, then it is projected that a two cycle HWC availability average of > 90% will be attained. This means that PNPS will meet the requirements of the SER to NEDC-31951P as well.

3. Hydroaen Water Chemistry History at PNPS l

(a) Implementation of Hydroaen Water Chemistry at PNPS PNPS found IGSCC indications in the reactor recirculation system in 1983.

As a result, the IGSCC susceptible 304SS reactor coolant piping was replaced with IGSCC res:stant 316SS in 1984 (RFO 6). However, remaining alloy 182 (INC66) safe-end weld material was still susceptible to IGSCC as well as 304SS recirculation inlet thermal sleeves.

Hydrogen Water Chemistry was implemented to control the reactor water chemistry environment for inhibiting IGSCC. HWC was implemented in stages as presented below.

(b) " Mini-test" of May 1985 l

General Electric (GE) conducted a " mini-test" at PNPS and determined that l

23 SCFM hydrogen should be injected at 100 percent power to reduce the ECP in the recirculation system to less then -230 mV (SHE). This is equivalent to 0.87 ppm hydrogen in the feed water. The mini-test also showed that the main steam line radiation monitor readings increased - 4 l times normal background. The recirculation water conductivity decreased ,

significantly from a normal conductivity of ~0.2 uS/cm to 0.09 US/cm, and

, oxygen decreased from ~200 ppb to ~2 ppb.

l (c) CAVS Operation Since January 1990 The CAVS system was placed in operation on January 15,1990 for "! ire I conditioning". The normal water chemistry baseline crack growth rates for the three crack growth specimens were established prior to the use of hydrogen water chemistry. There were two periods where crack growth rates were l collected under normal water chemistry (NWC) conditions 0-300 hrs and l ~1400-2400 hrs. (See Figure 2,3 and 4). The alloy 182 specimen (INC66) lnitially showed a typical growth rate of 11.7 micro-in/hr when compared to l laboratory data. By the end of the NWC baseline period. INC66 showed a steady crack growth rate of 10.6 micro-in/hr (93 mils /yr).

l The 304SS/ alloy 82 specimen (SSINC) initially showed a crack growth rate of l 14.3 micro-in/hr that is close to the rate of 21.4 micro-in/hr, which the GE j PLEDGE crack growth model predicts for type 304SS under the initial conditions of stress intensity, EPR value, conductivity and ECP value. By the end of the NWC baseline period SSINC growth rate leveled off to an average i of 2.4 micro-in/hr (21 mils /yr).

The 304SS Pilgrim recirculation piping specimen (PRPS1) initially showed insignificant growth ai O.9 micro-in/hr. By the end of the NWC baseline period the growth rate leveled off to 1.4 micro-in/hr (12 mils /yr).

The low crack growth rates for the two 304SS specimens reflect the very good water chemistry condition maintained at PNPS during the baseline Page 7 of 13

p::riod i.e. rcactor conductivity of 0.09 us/cm. The ECP measured during the baseline period was in a range of +120 to +150 mV (SHE) d) First Cycle with HWC Since September 1991 PNPS started Crcle 9 with HWC. The H2 injection rate was set at 23 SCFM.

The ECP autoclave was out of service for required repairs. Reactor water conductivity and dissolved oxygen decreased to ~0.065 us/cm and ~2 ppb respectively. Even though CAVS was out of service, there was a high confidence that ECP values were <-230 mV (SHE). This was based on achieving reactor water chemistry parameters maintained during the mini-test.

This was later confirmed when the CAVS was placed into service in January 1992, and ECP values of <-400 mV (SHE) were recorded.

HWC availability, was 56% by utilizing ECP measurements and estimated at

~75% using hydrogen injection rate. ECP derived availability is lower than that derived with alternate parameters because ECP measurements where not always available.

i All three crack growth specimen readings remained viable th ough July 1992  !

at which time the SSINC and PRPS1 specimen values became unstable.

This is believed to be due to the specimens reaching the end of their design life. Until that time, crack growth data indicated a decrease in the crack ,

growth rate under HWC conditions. 1 The first cycle under HWC presented an opportunity to measure ECP and crack growth under various plant power levels and operating conditions. ECP i and crack growth is presented here for various plant condition. i

1) Normal steady-state Full Power Operation - PNPS operated at full power ,

utilizing HWC the majority of the time. The programmed rate for hydrogen '

injection at 100% was 23 SCFM. Typical ECP measured values were <-400 mV (SHE) decreasing to <-500 mV (SHE) during extended periods of i operation. The crack growth rates fell to the range of <2 mils /yr. I

2) Less than Full Power Operation - The rate of hydrogen injection is programmed to follow power. The required hydrogen necessary to maintain

<-230 mV (SHE) decreased as power decreases. The ECP has been measured at 50% power during a condenser backwash and was still <-230 mV (SHE).

3) ECP at Full Power vs H2 Injection Rate - The H2 injection rate was kept at 23 SCFM at 100% power. During surveillances and maintenance periods in steam affected areas, the hydrogen injection rate was manually lowered to 13.5 SCFM to reduce dose to individuals, however, ECP was still maintained

<-230 mV (SHE). This is generally for very short periods, typically less than 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. No increase in crack growth occurred, and reactor water chemistry ,

remained unchanged.

4) Hydrogen Interruption Periods - At certain times, the hydrogen injection system (ETS) was secured at 100% power. During this period, ECP rapidly ,

rose to positive levels indicative of normal water chemistry following an j interruption of hydrogen. Typically, reactor water conductivity increased to a level of 0.3 us/cm, and pH decreased to about 6.2. This is due to the same chromate ion phenomenon as reported by other BWRs with HWC. Chromate levels typically increase from a HWC level of <11 ppb to between 80 and 150 Page 8 of 13

ppb d:p:nding on tha length of time hydrogen has been inject:d prior to tha interruption.

. 5) E//ect of Conductivity on ECF - There has been no documented effect of conductivity on ECP at PNPS.

6) Plant Shutdown - Hydrogen injection is normally secured at ~40% power on a shutdown. It takes approximately 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for the plant to cool down to a cold shutdown condition of <212 F.

(e) Second Cycle with HWC - June 1993 in June 1993, after Refueling Outage 9, PNPS started its second cycle (Cycle

10) with HWC. ECP is typically maintained in the <-400 mV (SHE) range. All crack growth specimen readings were unstable showing indeterminate crack lengths indicating they had reached the end of their useful lives. PNPS has no plans to replace or repair the specimens since their usefulness has been realized in demonstrating the benefit of HWC in reducing crack growth in susceptible plant materials.

In July 1993, improvements in measuring dissolved oxygen yielded reactor water values of <0.5 ppb which are typical of current values.

HWC availability was 75% using ECP measurements and estimated at -80%

using hydrogen injection rate. ECP derived availability is lower than with using  ;

alternate parameters because ECP measurements where not always l available.

(f) Third Cycle with HWC June 1995 ECP probes were installed in RFO 10 (May 1995) in the Reactor Recirculation System and in the vessel in an LPRM. A " ramping test" was performed in June 1995 where the hydrogen injection rate was varied to find the optimum )

injection rate to protect both the reactor vessel lower internals and the reactor recirculation piping. It was determined that 32 scfm is the optimum injection rate for PNPS at 100 % power. Alternate parameters such as those proposed by NEDC-31951P Supplement 1 were also obtained in conjunction with ECP measurements. CAVS ECP measurements were also " calibrated" against in-situ ECP values.

i l

An 86.7 % HWC availability was maintained by the end of the cycle based on  !

ECP rr.easurements and was estimated to be ~88% using hydrogen injection l rate. ECP derived availability is lower than that derived with alternate l l parameters because ECP measurements where not always available.

(g) Current Status of HWC(Cvele 12)

Hydrogen is injected virtually 100 percent of the time PNPS is above 40%

reactor power. The hydrogen injection rate is maintained at 32 scfm (1.2 ppm in feedwater) while at 100% power. The cycling of hydrogen going above -230 l mV (SHE) has been greatly reduced as evidenced by HWC availabilities to-date of 92.3 % using ECP readings and 93.3% using alternate parameters.

It is expected that Recirculation System ECP measurements will not be available by the end of the cycle (April 1999) so alternate parameters will be relied upon to determine HWC availability. If reactor recirculation dissolved Page 9 of 13

l

- oxyg:n r:mrins b: low ~2.0 ppb and th3 required hydrog:n is inject:d for ths power level, then ECP will be assumed to be < -230 mVSHE.

(h) Future Status of HWC Plans are to evaluate the replacement of the Reactor Recirculation System ECP probes in RFO 12 (April 1999). The CAVS system is being evaluated for -

shutdown to limit PNPS personnel dose and since in-situ probes are more representative of in-the -pipe conditions. 3 Also, a reliable correlation of in-situ ECP to alternate parameters has been established.

Ill. PNPS IGSCC Weld Inspection Proaram l l

A. BECo Response to GL 88-01

[

Boston Edison's response to Generic Letter 88-01 actions is contained in BECo l Letter 88-119 (dated August 18, 1988) and supplemented by BECo Letter 90-140 .

(dated November 15, 1990). The IGSCC susceptible welds within the scope of GL 88-01 are included in Table 4 below:

TABLE 4: IGSCC Related Welds IGSCC Description - Number of Safety Number of Number of Category Related Wolds Safety Related Non-Safety  :

Excluding RWCU RWCU Related Welds  !

(RWCU)  !

A Resistant Material 115 54 19 B Non-resistant 0 0 0 material, SI within 2 years of operation C Non-resistant 0 2 1 material, St after 2 years of operation D Non-resistant 41 3 3 materials, no St E Cracked, 1 0 0 reinforced by weld overlay or mitigated by St F. Cracked, 0 0 0 inadequate or no repair G Non-resistant 4 1 45 materials, not inspected TOTALS 161 60 68 Total IGSCC susceptible safety-related welds: 221 Total IGSCC susceptible non-safety related welds: 68 TotalIGSCC susceptible welds: 289 Page 10 of 13

Explanation of Cateaory Welds Category A: The Category A welds are a result of pipe replacement programs which replaced most of the susceptible pipe in the Drywell (PDC 84-56; 82-62) and a pipe replacement program in the RWCU System (PDC 91-39; 92-33). Welds that were difficult to replace remain, but the major portion of the piping has been changed. Relief is not applicable to these welds.

Category B: There are no Category B welds at PNPS.

Category C: These two welds are located in RWCU and are a result of mechanical stress improvement of existing welds. They are a 304SS-to-316SS weld for i replacement and a pipe-to-penetration weld which was left due to construction i difficulties. Relief is not requested for these welds.

r Category D: The population of safety related Category D welds is currently 44 welds. l Schedule relief is requested for 11 of these 44 wolds. Only Category D welds in the reactor recirculation system are candidates for relief at this time. The l non-safety related welds in RWCU are not considered within the scope of

• examination since the provisions of Generic Letter 88-01, Supplement 1 became applicable during the 1995 refuel outage.

Category E: One cracked and overlayed weld exists at the RPV-N9A-1 safe-end weld.

This weld has been examined three times since the overlay with no apparent growth. Relief is not requested for this weld.

Category F: There are no Category F welds at PNPS.

Category G: Five welds are considered inaccessible for examination. These welds are  ;

inside containment penetrations. Relief is not applicable to PNPS Category G welds. i B. IGSCC Inspection Results l PNPS has performed 137 IGSCC (safety and non-safety related) weld examinations ,

since the GL #88-01 inspection schedule was implemented and 82 examinations  !

since HWC was initiated. Four instances of IGSCC (1 safety-related,3 non-safety i related) were discovered in July 1991 in RWCU piping welds. .This was prior to the  !'

continuous use of HWC. No subsequent piping cracks have been observed in any system at PNPS since HWC was placed in continuous service.

IV. Proposed IGSCC Inspection Schedule

}

This request for NRC approval only applies to the eleven Category D nozzle safe-end welds of the reactor recirculation system. Increasing the inspection interval by a  !

factor of 2 (i.e. from two to four years) is proposed as shown in Table 5 below based on the proven effectiveness of HWC at PNPS.

Page 11 of 13

l TABLE 5: PROPOSED GL 88-01 SCHEDULE FOR RECIRCULATION WELDS j Materials / Mitigation IGSCC Inspection Extent & Number of Proposed

. Process Category Schedule Welds Changes Resistant materials A 25% every 10 years (at 61 N/A least 12% in 6 years) t Non-resistant materials B 50% every 10 years (at 0 N/C l (stress improvement [Sl] least 25% in 6 years) within 2 years of operation)

Non-resistant materials SI C All within the next 2 0 N/C after 2 years of operation refueling cycles, then all every 10 years (at least 50% in 6 years)

Non-resistant materials with D  ; All every 2 refueling .11 '  ; All every 4 -

- no SI . , ]

i cycles l

_ refueling . ,

cycles Cracked reinforced by weld E All every 2 Refueling 0 N/C overlay or mitigated Si cycles i Cracked inadequate or no F All every refueling 0 N/C j repair outage Non-resistant not inspected G All next refueling outage O N/C The specific category D Recirculation welds are listed below (Figure 11: ISI-l-2RA and B )

Drawings, attached):

2R-N2A-1 12" inlet nozzle 2R-N2F-1 12" inlet nozzle 2R-N18-1 28" outlet nozzle 2R-N2B-1 12" inlet nozzle 2R-N2G-1 12" inlet nozzle 2R-N2C-1 12" inlet nozzle 2R-N2H-1 12" inlet nozzle 2R-N2D-1 12" inlet nozzle 2R-N2J-1 12" inlet nozzle 2R-N2E-1 12" inlet nozzle 2R-N2K-1 12" inlet nozzle The reduction in examination frequency is consistent with the BWROG Topical Report and will only apply to eleven Category D welds in the Recirculation System. There are ten 12 inch inlet nozzle safe-end welds and one 28 inch outlet nozzle safe-end welds (Category D welds) in the recirculation system of which all are currently examined every two fuel cycles. ,

Relief from the current schedule is requested to allow a 4 fuel cycle interval.

This request does not change the Technical Specification leakage monitoring program that l meets Generic Letter 88-01. Also, requests for relief on RWCU, RHR, and CS welds are not included since there are no Electrochemical Corrosion Potential (ECP) measurements  ?

performed on RWCU, RHR and Core Spray Systems.

l i

Page 12 of 13

'V. BWROG Topical Report and Supolemant 1 T.te BWROG NEDC-31951P, the SER of NEDC-31951P and Supplement 1 to

. .lEDC-31951P is hereby incorporated and endorsed as applicable to this relief '

request. The technical content of this submittal concerning the PNPS experience with HWC is consistent with the BWROG Topical Report, SER and Supplement 1 relating to revised piping inspection schedules. The PNPS HWC program conforms with the above references as follows: ,

BWROG Tooical Report / SER/Sucolement PNPS Status '

1 Criteria

1. ECP measurements should be less than - 1) ECP has been maintained at less than

• 230 mV(SHE) and conductivity below -230 mV SHE as confirmed by in-situ '

0.2 us/cm. ECP measurements and benchmarked by attemate parameters.)

2) Reactor coolant conductivity has been maintained below 0.2 US/cm. HWC availability has been decreased when greater than 0.2 uS/cm.

2. HWC availability should be greater than Hydrogen availability to-date is 93.3 %

80% for the fuel cycle preceding relief since April 1997 (RFO 12) request when above 200 deg F. when above 200 Deg F.

3. Short interruptions of hydrogen injection No credit was taken for the HWC are acceptable when the length of each " Memory" effect.

interruption is less than 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> and ECP remains Selow 0.3 us/cm i

VI. Reduction in Radioloaical Exposure and Resources PNPS has estimated the ALARA benefits anticipated during future refueling outages based on reduction in inspection frequency. The revised inspection frequency would reduce exposure by 15 man-rem each fuel cycle, and will reduce BECo expenditures in the range of $300,000 per refueling outage without compromising the underlying objective of the IGSCC program.

l Vil Conclusion I i

This Request is in conformance with the BWROG Topical Report NEDC-31951P, j SER to NEDC-31951P and Supplement 1. This does not compromise the underlying '

objective of the IGSCC program and is within the scope of NRC Generic Letter 88-  !

01.

PNPS, through the continuous monitoring of chemistry and plant parameters, has demonstrated that an availability of > 80% is attainable. Also, weld inspection results confirm that this availability and possibly below is all that is necessary to prevent measurable crack growth and qualify for a factor of two improvement.

If in-situ ECP probes continue to function until the end of the cycle, then it is projected that a two cycle HWC availability average of > 90% will be attained. This means that PNPS will meet the requirements el the SER to NEDC-31951P and requests inspection relief on this basis as well.

Vill. Figures (Enclosed)

Page 13 of 13

1 PNPS Cycle 12 ECP vs. MSLR Readings (Expanded View) a 400 35 WW $e 4 %^ ,- -

300 l < ' '

o l > i 30 l

200 - l 100 j 25 o , ,

l < ,

r o c < '

I 5 1,

" O tueup i ,l 5 20 a ECP(mVSHE) h E E o MSLR(mR/Hr) j -230 mV(SHE)

{ -100 ,,

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g . ,

i

-300 ' '

10 a ,

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-600 0 3/31/97 4/20/97 5/10/97 S/30/97 6/19/97 7/9/97 7/29/97 8/18/97 9/7/97 9/27/97 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 i

Figure 1

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i PNPS Cycle 12 ECP vs. Recirc 02, H2 & H2 Flow

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0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 Figure 2

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l PNPS Cycle 12 ECP vs. MSLR Readings 1

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- Figure 4

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