ML18005A699
| ML18005A699 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 10/28/1988 |
| From: | Watson R CAROLINA POWER & LIGHT CO. |
| To: | Ernst M NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| HO-880222-(O), NUDOCS 8811140074 | |
| Download: ML18005A699 (12) | |
Text
ENCLOSURE 3
Carolina Power lL Light Contpany OCT a 85~8 HARRIS NUCLEAR PROJECT P. O. Box 165 New Hill, North Carolina 27562 File Number:
SHF/10-13510 Letter Number:
HO-880222 (0)
Mr. Malcolm Ernst, Acting Regional Administrator United States Nuclear Regulatory Commission 101 Marietta Street, NW
- Atlanta, GA 30323 SHEARON HARRIS NUCLEAR POWER PLANT DOCKET NOo 50-400/LICENSE NO. NPF"63
RESPONSE
TO NRC SYSTEMATIC ASSESSMENT OF LICENSEE PERFORMANCE
Dear Mr. Ernst:
Carolina
- Power,
& Light Company (CP&L) has reviewed the Systemat'ic Assessment of Licensee Performance (SALP) Board report forwarded by your letter'f September 16,
- 1988, which evaluated CP&L's performance during the p'eriod of July 1,
- 1987, to June 30,
- 1988, for the Harris Plant.
CP&L has also considered the additional comments that the NRC presented to CP&L in the revie~
of the SALP report in a
meeting on.
September 27,
- 1988, and has several comments on this SALP report.
- First, CP&L is very pleased that the NRC recognizes the outstanding performance of the Harris Plant.
In particular, the SALP score recognizes that while only in the first cycle of operation, the Harris Plant is performing at a level equivalent to the best plants in Region II.
However, our expectations for future performance continue to increase.
In reviewing the SALP report and reflecting on the strengths and weaknesses presented in the September 27,
- 1988, meeting, there are several points on which CP&L wishes to make further comments.
These areas are discussed below.
RADIOLOGICAL CONTROLS The rating assigned to this functional area appears to be too heavily weighted by the NRC's conclusion that the Radiological Control and ALARA programs were not seriously challenged by the operational events in 'the SALP period.
We believe that this is an inappropriate way to judge the effectiveness of a
program.
.lt is CP&L's goal that the Radiological Controls function to the extent that individual s
exposure remain
Mr. Malcolm Ernst Page 2
ALARA and that plant total exposures remain less than median Eor coamercial PWRs in the U.
S.
This has beeri translated into a Harris goal. of 360 person-rem for 1988 (the SALP report page ll incorrectly quotes this goal as 260 person-rem).
An active program was in existence during the SALP period to assure that the dose.goal for 1988, including the refueling outage
- goal, was met.
In Eact, the dose. goal Eor the outage was reduced to 200 person-rem (from Self Reading Pocket Dosimeters) to support and emphasize the CPSL goal.
Notwithstanding three significant, unforeseen outage activities, the total exposure from SRPDs was 208.2 person-rem.
The three significant additional activities were the replacement of ex-core source range detectors (3.9 person-rem),
i'nvestigation of the Reactor Coolant System piping wall thickness (20.6 person rem) and repair of two Steam Generator head drains (3.2 person-rem).
The data from TLDs indicates that the total exposure recorded for the third quarter of
- 1988, the quarter with the majority of the outage
- dose, was approximately 154 person-rem.
While this proof oE the effectiveness of our programs was not available at the time that the SALP period ended>
the ALARA planning and reviews. were being done to assure the success of the outage from this perspective.
EMERGENCY PLANNING
~ The Harris Plant takes great 'pride in the efficiency. and overall quality of the Emergency Planning program.
Carolina Power 6
Light Company believes that the Emergency Planning programs for the Harris Plant improved during the SALP period and deserve a
higher score than a
SALP 2 ~
The SALP rating appears to be weighed 'primarily on the merits of four items.
'hese items were presented to CP&L as inspector Follow-up Items (IFIs) in the respective inspection reports; no violations were issued by the NRC against Emergency Pl.arming during the SALP period.
Further evaluation of the respective inspection reports indicates that the SALP report (1) misquotes
'the nature of the problem with the EOF ventilation system performance during the 1988 drill and (2) overstates the issue with the performance of dose calculations.
Specifically, the SALP report states that "during the recent emergency
- exercise, the ventilation failed to achieve the specified 0.125 inches
'of water differential pressure.
The licensee identified an inleakage path Erom the filter train drain valves."
Inspection Report 88-12 correctly identifies the situation that occurred during and after the exercise.
During the annuaL exercise, there was a problem maintaining
.the correct pressure in the EOF.
This was attributed to the ingress and egress at the EOF boundary doors.
After the drill, the pressurization system was tested and it successfull.y performed the required function.
The open drain Lines in the HVAC unit did not prevent successfuL operation of the EOF habitability system as implied in the SALP report on page 19.
With regard to the IFI on dose projection, the SALP stated that "dose projections were performed slowly and resulted in erroneous doses
'.n :wo
Mr. Malcolm Ernst Page 3
of three walk"throughs."
This statement overly simplifies the inspectors'indings and implies a gross programmatic breakdown.
The description of the problem as stated in Inspection Report 87"30 states that the three personnel tested demonstrated familiarity with the methods and two individuals made mathematical and table lookup errors in performing the manual dose projection.
However, Inspection Report 87-30 also ignores the fact that dose projections were successfully performed using the computerized method which is the preferred method.
In summary, even when taken as a group CP&L believes these IFIs do not appear to provide sufficient cause to rate Emergency Planning as a
SALP 2 rather than a
SALP l.
FIRE PROTECTION In the SALP
- report, the NRC makes the statement that "an apparent complacency on the part of the licensee, resulted in a lower category rating in this area."
We do not agree with this statement and wish to assure the NRC that complacency is not a factor in the performance of the fire protection program.
In fact, the improvements noted in the SALP report support CP&L's conclusion.
. SlB9lARY In the.
meeting that presented the SALP results to CP&L management, several very important points were discussed.
First was the need to investigate
- problems, especially those that involved mistakes by personnel, beyond the surface.
We heartily agree with this.
In particular for events which involved some level of "human performance" we are actively implementing an INPO Human Performance Evaluation System (HPES).
This evaluation technique will provide CP&L management with the insight to take better and more thorough actions to prevent recurrence of problems.
- Secondly, the NRC emphasized the fact that the SALP grading system is based on the expectation that improved performance is necessary to maintain the same score.
Carolina Power
& Light Company agrees with this approach and accepts the challenge to continue to improve our performance during the next SALP report period.
Yours very truly,
/c'Zfc~~M~
R. A. Watson Vice President Harris Nuclear Project DLT/lem cc:
Mr.
W.
HE Bradford Mr.
B i C. Buckley
November 21, 1988 ENCLOSURE 4 ERRATA SHFETS
~Pa e
Line 20 Now Reads
"...at 260 person-rem..."
Should Read
"...at 360 person-rem..."
Basis for change:
To properly quantify the licensee's 1988 collective radiation dose goal 19 38-41 "The licensee identified
.... drain valve."
"This failure was
... drain lines."
Basis for change:
To properly characterize the nature of an EOF ventilation system problem.
11 assessment period.
The licensee did experience 87 perso el contaminations during
- 1987, 48 of which were sk contaminations, The remaining 39 were clothing contami tions.
From January 1,
through June 30,
. 1988, the licens had experienced
.a total of 11 skin and 39 clothing cont inations.
The number of personnel contaminations is typical f a plant of similar size and age.
Licensee management support of, and involv ent in, the radiation protection program was adequate.
he radiological
'preparations and planning for the first r
ueling outage in July 1988, appeared to be generally corn ete and thorough.
Licensee management placed emphasis on k eping worker doses as low as reasonably achievable (ALARA), f llowing procedures, and complying with good radiation control ractices.
During calendar year
- 1987, the li nsee's collective dose was 33 person-rem which was well bel the PMR national average of
'368 person-rem.
The low collect ve dose was attributable to the fact that the facility is rel ively new and that there was no refueling outage during this eriod.
The collective dose goal for 1988, was set at 260 pe son-rem with 200 person-rem of that
~ total planned for the fQ t refueling outage.
As of June 30,
- 1988, the licensee had ended 7 person-rem.
Liquid and gaseous'oactive effluents were within the dose limits specified i he Technical Specifications and 40 CFR 190, and within the r oactivity concentrations specified in 10 CFR 20.
Concentrati s did not exceed the 10 CFR 50 Appendix I ALARA limits.
o abnormal liquid or gaseous releases were reported duri 1987.
A summary of 1987 effluents is listed in Section V.K this report.
The chemi try program has become very effective.
The licensee has mad good use of contract chemistry personnel, as well as resour es from the corporate training center.
In the future, howe r,
the licensee plans to lessen the dependency on che istry contractors.
Since this plant was designed in the e
ly 1970's, some of the physical facilities, such as aboratories, are state-of-the-art where as other areas, such as sample
- rooms, are not.
- However, this has not affected acceptable performance by the licensee This was re-emphasi zed by the good agree-..er..
shown between
.he licensee's and
,'iRC's sample results for the NRC radiological and nonradiological (chemistry) confirmatory measurements programs.
During calendar year
- 1987, the license disposed of a total. of 3,700 cubic
. fee.
of solid radioac:ive waste containing 2.6 curies of eadioactivi:y.
This was well below the PMR national ave~age of 6,590 cubic feet fo~
a single unit site, but as s ated earlier, tnere was no major outage during tne oerioo.
assessment period.
The licensee did experience 87 personnel contaminations during
- 1987, 48 of which were skin contaminations.
The remaining 39 were clothing contaminations.
From January 1,
through June 30,
- 1988, the licensee had experienced a total of 11 skin and 39 clothing contaminations.
The number of personnel contaminations is: typical for a plant of similar size and age.
Licensee management support of, and involvement in, the radiation protection program was adequate.
The radiological preparations and planning for the first refueling outage in July 1988, appeared to be generally complete and thorough.
Licensee management placed emphasis on keeping worker doses as low as reasonably achievable (ALARA), following procedures, and complying with good radiation control practices.
During calendar year
- 1987, the licensee's collective dose was 33 person-rem which was well below the PMR national average of 368 person-rem.
The low collective dose was attributable to the fact that the facility is relatively new and that= there was no refueling outage during this period.
The collective dose goal for 1988, was set at 360 person-rem with 200 person-rem of that total planned for the first refueling outage.
As of June 30, 1988, the licensee had expended 7 person-rem.
Liquid and gaseous radioactive effluents were within the dose limits spec>fied in the Technical Specifications and 40 CFR 190, and within the radioactivity concentrations specified in 10 CFR 20.
Concentrations did not exceed the 10 CFR 50 Appendix I ALARA limits.'o abnormal liquid or gaseous releases were reported during 1987.
A summary of 1987 effluents is listed in Section V. K of this report.
The chemistry program has become very effective.
The licensee has made good use of contract chemistry personnel, as well as resources from the corporate training center.
In the future,
'owever, the licensee plans to lessen the dependency on chemistry contractors.
Since this plant was designed in the early 1970',
some of the physical facilities, such as laboratories, are state-of-the-art where as other areas, such as sample
- rooms, are not.
- However, this has not affected acceptable performance by the licensee.
This was re-emphasized by the good agreement shown between the licensee's and NRC's sample results for the NRC radiological and nonradiological (chemistry) confirmatory measurements programs.
During calendar year
- 1987, the license disposed of a total of 3,700 cubic feet of solsd radioactive waste containing 2.6 curies of radioactivity.
This was well below the PWR national average of 6,590 cubic feet for a single unit site, but as stated earlier, there was no major outage during the period.
inspection, it was noted that there was a
need for addit nal tr aining in use of dose assessment procedures by b th radiological personnel and reactor operators (who wou d make initial dose projections).
The dose calculations were performed slowly and resulted in erroneous doses in two of t ee walk-throughs.
Initially, the licensee indicated that t e expediency of these calculations was not
- relevant, as t re was no requirement stating dose projections had to be lculated within a
specified time period.
Further discussio s
between the licensee and Region II management resul,ted n
the licensee's acknowledgement of the need for timely dos projections.
The licensee then pursued aggressive train g
,and procedural corrective actions that were found to be ully adequate'during a
subsequent follow-up inspection.
The licensee was slow to impleme a
periodic maintenance program on Technical Support Cen er (TSC) door seals.
The licensee
- agreed, in June of 1986 to perform such maintenance.
In August
- 1987, the licensee c
ld not confirm whether such a
program had been implemented.
In September
- 1987, the licensee implemented a procedure
@6, utinely test the TSC pressure and habitability systems.
+4 The TSC fs powered by separate sources.
In preparation for the ERF Appraisal, licensee determined the need for an addltlonal power sRWu e ln the event of a station blackout and determined that +
endor-supplied diesel generator could be supplied and made operational in approximately 25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br />.
The licensee agreed o reanalyze the need for an additional power supply given t e potential impact of loss of TSC function on station black t.
The Emerge cy Operations Facility (EOF) is located approximately 3,400 me ers from the plant.
The facility is equipped with emergen y ventilation (HEPA and charcoal) to maintain the area under ositive pressure.
This degree of protection exceeds NRC cri ria, which specifies the need for only HEPA filters.
The li nsee's evaluation of direct radiation dose showed doses w uld be maintained below GDC 19 criteria.
Quring the recent'ergency
- exercise, the ventilation failed to achieve the specified
- 0. 125 inches of water differential pressure.
The licensee identified an inleakage path from the filter train drain valves.
The licensee committed to nstall isola ion valves on the drain lines'he licensee implemented an appropriate p flic information program that included dissemination of a public information brochure in the form of a
- calendar, place.-..ent of public information decals on public telephones and in.ormation signs.
In addition, the
)icensee conoucted annual media education
19 inspection, it was noted that there was a
need for additional training
>n use of dose assessment procedures by both radiological personnel and reactor operators (who would make initial dose projections).
The dose calculations were performed slowly and resulted in erroneous doses in two of three walk-throughs.
Initially, the licensee indicated that the expediency of these calculations was not relevant, as there was no requirement stating dose projections had to be calculated within a
specified time period.
Further discussions between the licensee and Region II management resulted in the licensee's acknowledgement of the need for timely dose projections.
The licensee then pursued aggressive training and procedural corrective actions that were found to be fuglly adequate during a subsequent follow-up inspection.
The licensee was slow to implement a periodic maintenance rogram on Technical Support Center (TSC) door seals.
The icensee
- agreed, in June of 1986, to perform such maintenance.
In August 1987, the licensee could not confirm whether such a
program had been implemented.
In September 1987, the licensee implemented a procedure to routinely test the TSC pressure and habitability systems.
The TSC is powered by two separate sources.
In preparation for the ERF Ap'praisal, the licensee determined the need for an additional power source in the event of a station blackout and determined that a vendor-supplied diesel generator could be supplied and made operational in approximately 25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br />.
The licensee agreed to reanalyze the need for an additional power supply given the potential impact of loss of TSC function on station blackout.
The Emergency Operations Facility (EOF) is located approximately 3,400 meters from the plant.
The facility is equipped with
. emergency ventilation (HEPA and charcoal) to maintain the area under positive pressure.
This degree of protection exceeds NRC criteria> which specifies the need for only HEPA filters.
The licensee s ev'aluation of direct radiation dose showed doses would be maintained below GDC 19 criteria.
During the recent emergency
- exercise, the ventilation failed to achieve the specified
- 0. 125 inches of water differential pressure.
This fai lure was due to inadequate control of the EOF access doors.
During a subsequent test conducted for NRC observation, proper pressurization was demonstrated.
The licensee did identify,
- however, a potential source of inleakage through filter drain
- valves, and instituted corrective action to install isolation valves in these drain lines.
The licensee implemented an appropriate public information program that included dissemination of a public information brochure in the form of a calendar, placemen<
of public information decals on public telephones and information signs.
In addition, the licensee conducted annual media education
t4
~C CELERATED DISTRIBUTION DEMONSTRATION 'YSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)
ACCESSION'BR:8811140074 DOC.DATE: 88/10/28 NOTARIZED: NO FACIL:50-400 Shearon Harris Nuclear Power Plant, Unit 1, Carolina AUTH.NAME AUTHOR AFFILIATION WATSON,R.A.
Carolina Power
& Light Co.
RECIP.NAME RECIPIENT AFFILIATION ERNST,M.
Region 2, Ofc of the Director
SUBJECT:
Responds to NRC 880916 SALP rept for Jul 1987 -June 1988.
DISTRIBUTION CODE:
IE40D COPIES RECEIVED:LTR L ENCL L SIZE:
TITLE: Systematic Assessment of Licensee Performance (SALP) Report NOTES:Application for permit renewal filed.
DOCKET 05000400 I
05000400 p RECIPIENT ID CODE/NAME PD2-1 LA BUCKLEY,B INTERNAL: ACRS AEOD/DSP/TPAB DEDRO NRR/DLPQ/HFB 10 NRR/DOEA/EAB ll NRR/DREP/RPB 10 NRR/DRIS/RSGB 9
NRR/DRIS/SIB 9A NUDOCS-.ABSTRACT OGC/HDS 1 RGN2 FILE 01 EXTERNAL:, H ST LOBBY WARD NRC PDR COPIES LTTR ENCL RECIPIENT ID CODE/NAME PD2-1 PD AEOD/DOA COMMISSION NRR MORISSEAU,D NRR/DLPQ/PEB 11 NRR/DREP/EPB 10 NRR/DRIS DIR 9A NRR/DRIS/SGB 9D NRR/PMAS/ILRB12 OE IEBE N,J G
02 LPDR NSIC COPIES LTTR ENCL 1
5 1
1 1
1 1
1 1
1 A
NOIR 'I0 ALL "RIDS" RECIPIENTS:
A PIZASE HELP US K) REDUCE WASTE.'XMRCT 'IHE DOCUMEPZ CORI'.ROL DESK, ROOM Pl-37 (EXT. 20079)
IO EIZMZNATE KXlR HAHE FROH DISTVUEPZION
~ FOR DOCtM&IS KNJ DONiT NEEDf D
S TOTAL NUMBER OF COPIES REQUIRED:
LTTR 33 ENCL
CPRL Carolina Power 8 Light Company HARRIS NUCLEAR PROJECT P.
O.
Box 165 New Hill, North Carolina 27562 N50 File Number'.
SHF/10-13510 Letter Number'HO-880222 (0)
Mr. Malcolm Ernst, Acting Regional Administrator United States Nuclear Regulatory Commission 101 Marietta Street, NW
- Atlanta, GA 30323 SHEARON HARRIS NUCLEAR POWER PLANT DOCKET NO. 50-400/LICENSE NO. NPF-63
RESPONSE
TO NRC SYSTEMATIC ASSESSMENT OF LICENSEE PERFORMANCE
Dear Mr. Ernst:
Carolina Power
& Light Company (CP&L) has reviewed the Systematic Assessment of Licensee Performance (SALP) Board report forwarded by your letter of September 16,
- 1988, which evaluated CP&L's performance during the period of July 1,
- 1987, to June 30,
- 1988, for the Harris Plant.
CP&L has also considered the additional comments that the NRC presented to CP&L in the review of the SALP report in a
meeting on September 27,
- 1988, and has several comments on this SALP report.
- First, CP&L is very pleased that the NRC recognizes the outstanding performance of the Harris Plant.
In particular, the SALP score recognizes that while only in the first cycle of operation, the Harris Plant is performing at a level equivalent to the best plants in Region II.
However, our expectations for future performance continue to increase.
In reviewing the SALP report and reflecting on the strengths and weaknesses presented in the September 27,
- 1988, meeting, there are several points on which CP&L wishes to make further comments.
These areas are discussed below.
RADIOLOGICAL CONTROLS The rating assigned to this functional area appears to be too heavily weighted by the NRC's conclusion that the Radiological Control and ALARA programs were not seriously challenged by the operational events in the SALP period.
We believe that this is an inappropriate way to judge the effectiveness of a
program.
It is CP&L's goal that the Radiological Controls function to the extent that individual's exposure remain 8811140074 38102-'DR ADOCK 05000400 P
eric
~o MEK/BIO-8802220/1/OS1
Mr. Malcolm Ernst Page 2
ALARA and that plant total exposures remain less than median for commercial PWRs in the U.
S.
This has been translated into a Harris goal of, 360 person-rem for 1988 (the SALP report page 11 incorrectly quotes this goal as 260 person-rem).
An active program was in existence during the SALP period to assure that the dose goal for 1988, including the refueling, outage
- goal, was met.
In fact, the dose goal for the outage was reduced to 200 person-rem (from Self Reading Pocket Dosimeters) to support and emphasize the CPSL goal.
Notwithstanding three significant, unforeseen outage activities, the total exposure from SRPDs was 208.2 person-rem.
The three significant additional activities were the replacement of ex-core source range detectors (3.9 person-rem),
investigation of the Reactor Coolant System piping wall thickness (20.6 person-rem) and, repair of two Steam Generator head drains (3.2 person-rem).
The data from TLDs indicates that the total exposure recorded for the third quarter of
- 1988, the quarter with the majority.of the outage
- dose, was approximately 154 person-rem.
While this proof of the effectiveness of our programs was not available at the time that the SALP period ended; the ALARA planning and reviews were being done to assure the success of the outage from this perspective.
EMERGENCY PLANNING The Harris Plant takes great pride in the efficiency and overall quality of the Emergency Planning program.
Carolina Power 6
Light Company believes that the Emergency Planning programs for the Harris Plant improved during the SALP period and deserve a
higher score than a
SALP 2.
The SALP rating appears to be weighed primarily on the merits of four items.
These items were presented to CPGL as inspector Follow-up Items (IFIs) in the respective inspection reports',
no violations were issued by the NRC against Emergency Planning during the SALP period.
Further evaluation of the respective inspection reports indicates that the SALP report (1) misquotes the nature of the problem with the EOF ventilation system performance during the 1988 drill and (2) overstates the issue with the performance of dose calculations.
Specifically, the SALP report states that "during the recent emergency
- exercise, the ventilation failed to achieve the specified 0.125 inches of water differential pressure.
- The licensee identified an inleakage path from the filter train drain valves."
Inspection Report 88-12 correctly identifies the situation that occurred during and after the exercise.
During the annual
- exercise, there was a problem maintaining the correct
. pressure in the EOF.
This was attributed to the ingress and egress at the EOF boundary doors.
After the drill, the pressurization system was tested and it successfully performed the required function.
The open drain lines in the HVAC unit did not prevent successful operation of the EOF habitability system as implied in the SALP report on page 19.
With regard to the IFI on dose projection, the SALP stated that "dose
" projections were performed slowly and resulted in erroneous doses in two MEM/HO-8802220/2/OS1
Mr. Malcolm Ernst Page 3
of three walk-throughs."
This statement overly simplifies the inspectors'indings and implies a gross programmatic breakdown.
The description of the problem as stated in Inspection Report 87-30 states that the three personnel tested demonstrated familiarity with the methods and two individuals made mathematical and table lookup errors in performing the manual dose projection.
However, Inspection Report 87-30 also ignores the fact that dose projections were successfully performed using the computerized method which is the preferred method.
In summary, even when taken as a group CP&L believes these IFIs do not appear to provide sufficient cause to rate Emergency Planning as a
SALP 2 rather than a
SALP 1.
FIRE PROTECTION In the SALP
- report, the NRC makes the statement that "an apparent complacency on the part of the licensee, resulted in a lower category rating in this area."
We do not agree with this statement and wish to assure the NRC that complacency is not a factor in the performance of the fire protection program.
In fact, the improvements noted in the SALP report support CP&L's conclusion.
SUMMARY
In the meeting that presented the SALP results to CP&L management, several very important points were discussed.
First was the need to investigate
- problems, especially those that involved mistakes by personnel, beyond the surface.
We heartily agree with this.
In particular for events which involved some level of "human performance" we are actively implementing an INPO Human Performance Evaluation System (HPES).
This evaluation technique will provide CP&L management with the insight to take better and more thorough actions to,prevent recurrence of problems.
- Secondly, the NRC emphasized the fact that the SALP grading system is based on the expectation that improved performance is necessary to maintain the same score.
Carolina Power
& Light Company agrees with this approach ana accepts the challenge to continue to improve our performance during the next SALP report period.
Yours very truly,
/ZEMLYA~
R. A. Watson Vice President Harris Nuclear Project DLT/lem cc:
Mr. W. H. Bradford Mr. B. C. Buckley MEM/H0-8802220/3/OS1