ML20209E026
| ML20209E026 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 01/27/1987 |
| From: | Russell J TENNESSEE VALLEY AUTHORITY |
| To: | |
| Shared Package | |
| ML20209B481 | List: |
| References | |
| 231.6(B), 231.6(B)-R02, 231.6(B)-R2, NUDOCS 8702040588 | |
| Download: ML20209E026 (15) | |
Text
.
TVA EMPLOYEE CONCERNS REPORT NUMBER:
231.6(B)
SPECIAL PROGRAM REPORT TYPE:
SEQUOYAH ELEMENT REVISION NUMBER: 2 TITLE:
FIRE PROTECTION SYSTEMS Quality Assurance Documentation PAGE 1 0F 14 i
REASON FOR REVISION:
1.
Revised to incorgorate TVA SRP and TAS comments; to add chronology; and to add Section 10, Corrective Action."
2.
Revised to incorporate additional TVA comments.
PREPARATION PREPARED BY:
Erh/
/ dm
//u/o (JIGtTURE ~
' DATE REVIEWS EVIEW C0 IltE a&avsaaA:JAL~~.NA i-zi-e r
SIGNATURE /
DATE TAS gI y
/19-f'F l
xxx i
t/. //E'/
SIG ATURE DATE CONCURRENCES i
ADO O
7 M
/-21-k7 CEG-H:
%[
/ 27 F7 SRP:
SIGNATURE DATE SIGNATURE
- DATE APPROVED BY:
M te[
Mk ECSP NANAGER DATE MANAGER OF NUCLEAR POWER DATE CONCURRENCE (FINAL REPORT ONLY) l
- SRP Secretary's signature denotes SRP concurrences are in files.
TVA EMPLOYEE CONCERNS REPORT NUMBER: 231.6(B)
SPECIAL PROGRAM REVISION NUMBER: 2 ll PAGE 2 0F 14 1.
CHARACTERIZATION OF ISSUES:
Issues:
Concern:
OCP-10.35-1 a.
Specification G-73 designates
" Discrepancy between G-73 design-fire protection drawings at BLN as ation of fire protection drawings required to be QA, but they are (0A) and engineering treatment of treated as non-QA by engineering.
fire protection drawings (as non-0A).
b.
Disposition of NCR 2675 ( App. A, 5.1)
"Also NCR 2675 (fire protection is specific to BLN and not generic cable deficiency) was invalid-to SQN.
ated based on verbal information received by telephone that con-tradicts design approved docu-ments."
7.
HAVE ISSUES BEEN IDENTIFIED IN ANOTHER SYSTEMATIC ANALYSIS? YES NO X Identified by Not Applicable Date Not Applicable 3.
DOCUMENT NOS., TAG NOS., LOCATIONS OR OTHER SPECIFIC DESCRIPTIVE IDENTIFICATIONS STAlto IN ELEMENT:
TVA General Construction Specification G-73 f
4.
INTERVIEW FILES REVIEWED:
l File QCP-10.35-1 was reviewed on November 8,1986, and found to l
contain the K-forms and " Form A" (ECTG M.1, Attachment F).
In
[
addition there was an attachment to the original K-form in which Engineering agreed to clarify and expand the applicability of some 0A requirements to areas the CI seemed most particularly concerned about (e.g., FPS detection circuits).
5.
DOCUMENTS REVIEWED RELATED TO THE ELEMENT:
l See Appendix A.
l 04730 - 01/20/87
TVA EMPLOYEE CONCERNS REPORT NUMBER: 231.6(B)
SPECIAL PROGRAM REVISION NUMBER: 2 PAGE 3 0F 14 WHAT REGULATIONS, LICENSING COMITMENTS, DESIGN REQUIREMENTS OR OTHER 6.
APPLY OR CONTROL IN THIS. AREA?
See Appendix A.
LIST REQUESTS FOR INFORMATION, MEETINGS, TELEPHONE CALLS, AND OTHER 7.
DISCUSSIONS RELAltu TD ELEMENT:
l See Appendix A.
P.
EVALUATION PROCESS:
Reviewed fire protection regulatory requirements applicable a.
to SQN.
b.
Reviewed TVA General Specification G-73 for inspection, testing, and documentation requirements for fire protection systems and features to establish QA docun.entation requirements.
Reviewed TVA Design Criteria for SQN Fire Protection System c.
(FPS) and TVA Engineering Department Procedures to establish the requirements of and authority for assigning "Q" designations to FPS.
d.
Detennined validity of concern and established present disposition of issue.
9.
DISCUSSION, FINDINGS, AND CONCLUSIONS:
Chronology:
06/20/86:
TVA receives employee concern Discussion:
Ceneric Nature This concern is raised on BLN but addresses TVA Review of General Construction Specification G-73, " Inspection, Testing, and Documentation Requirements for Fire Protection Systems and Features" (hereinaf ter referred to as "G-73"), which is applicable to all plants and is, therefore, treated as generic to SQN.
04730 - 01/20/87
~-
s TVA EMPLOYEE CONCERNS REPORT NUMBER: 231.6(B)
SPECIAL PROGRAM REVISION NUMBER: 2 I
PAGE 4 0F 14 3
1 Background
I Fire protection dystem (FPS) design and documentation requirements have been a subject of development within the NRC over the last decade. This is a period that paralleled the design, construction, l
i startup, and initial operation of the SQN plant.
The SQN FPS was initially designed in accordance with Appendix A to BTP APCSB 9.5-1, " Guidelines for Fire Protection of Nuclear Power Plants Docketed Prior to July 1, 1976" (App. A, 5.g).
(This 1
l document has subsequently been incorporated into Branch Technical Position BTP.CMEB 9.5-1 but is commonly referred to as "BTP l
Appendix A;" a usage employed in this report.) On ' January 24, 1977 TVA forwarded to NRC a detailed comparison of the SQN fire protection program against the requirements of BTP Appendix A.
In its SER (App. A, 5.h), the NRC found that:
1 i
"Our conclusion... is that the Fire Protection Program at the Sequoyah plant was adequate and met Federal Design Criterion 3.
However, to further j
ensure the ability of the plant to withstand the damaging effects of fires that could occur, we t
requ< red and the applicant has committed to provide additional fire protection system improvements.
i l
These additional fire protection features have been i
?
completed for Unit I and will be completed for Unit 2 prior to Unit 2 fuel load."
Subsequent to this, the Code of Federal Regulations was modified by l
the addition of 10CFR50.48, " Fire Protection," (App. A, 5.d) and I
10CFR50 Appendix R. " Fire Protection Program for Nuclear Power l
Facilities Operating Prior to January 1, 1979," (App. A, 5.e).
These additions resulted in further modifications to SQN which are l
now nearing completion. A more comprehensive review of the FPS design change program is outlined in SQN Element Report 231.1, which covers such activities as the addition of sprinkler heads and spray piping header, revised calculations, and procedural changes.
Regulatory Requirements I
Cuhrentregulatoryguidancedoesnotclassifyfireprotectionasa
" safety system," per se. No fire protection, suppression, or detection apparatus initiates any safety function (f.e., emergency core cooling system, containment isolation, etc.). However, 1
certain portions of the FPS protect safety-related equipment and 04730 - 01/20/87 l -.-
TVA EMPLOYEE CONCERNS REPORT NUMBER: 231.6(B)
SPECIAL PROGRAM REVISION NUMBER: 2 PAGE 5 0F 14 are thereby considered to be in sufficient association with a safety function to warrant closer controls than would be the case with more conventihnal NFPA fire protection systems. For this reason, certain elements of fire protection usually have some selected QA requirements applied. This "Q/non-Q" mix is typically applied on a case-by-case basis for individual plants and may create an impression of inconsistency, which is possibly the case in this instance.
This confusion as to QA requirements may be further aggravated by the unique nature of fire protection systems. The traditional QA requirements, as outlined in 10CFR50 Appendix B, " Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants,"
(App. A, 5.1) are for systems and components that must act to fulfill a true " safety function," such as core cooling, containment of radioactive materials, and insertion of negative reactivity.
This definition extends to systems and components that must also act to support the basic safety function. These systems are generally termed " safety-related."
Fire protection is not this kind of " active" safety-related system. Rather it is a passive system that ensures the availability of " active" systems; the physical systems equivalent of an insurance policy. While fire protection is essential, in terms of nuclear safety it is passive and, as such, does not warrant the full application of safety system QA. A " limited QA" application, as pointed out in BTP Appendix A, is sufficient.
l Specification G-73, a general construction specification prepared by Engineering to establish inspection, testing, and documentation requirements for fire protection systems and featurec (App. A, 5.c), recognizes this as evidenced by its reference to the limited QA program of 0EDC-QAI-6 (App. A, S.j).
It is not well understood that references to fire protection quality assurance include and apply these " limited QA" requirements.
G-73 QA Scope The evaluator first reviewed G-73.
This review was expected to establish the QA requirements to which the concerned individual (CI) was referring. Section 1.1 of G-73, " Scope," contains the following statement:
"This general construction specification establishes minimum inspection, testing. and documentation requirements for fire protection systems and features for TVA nuclear power plants to assure compliance with quality assurance requirements set forth by the fluclear Regulatory Commission (NRC)."
04730 - 01/20/87
TVA EMPLOYEE CONCERNS REPORT NUMBER: 231.6(B)
SPECIAL PROGRAM REVISION NUMBER: 2 PAGE 6 0F 14 Specification G-73 further states that this scope applies to "all TVA nuclear plantp". including SQN.
It should be noted that the G-73 scope statemr.nt contains no Engineering requirements.
This is consistent with G-73 being identified as a general construction specification."
G-73 Design Document Control In spite of being a general construction specification, Section 2.1 of G-73, " Design and Procurement Document Control," does refer to design document control requirements. This may have led the CI to believe that G-73 has scr.e jurisdiction over, in his, terms,
" engineering treatment of fire protection drawings (as non-QA)."
Section 2.1 of G-73 should be compared to the BTP Appendix A QA requirements for the control of fire protection system design and procurement documents.
From G-73:
" Measures should be established to ensure that the applicable NRC guidelines are included in fire protection design and procurement documents and that deviations from these documents are controlled."
From BTP Appendix A:
" Measures should be established to ensure that the guidelines of the regulatory position of this guide are included in design and procurement documents and that
~
deviations therefrom are controlled."
In discussions with TVA fire protection personnel ( App. A, 7.a), it was pointed out that Section 2.1 of G-73 was intended to provide a general background to the necessity of such requirements and used the words of BTP Appendix A to accomplish this.
It was further pointed out that the intent here is to establish a control over the Construction use of such documents and that it was never intended to establish Engineering requirements on the document's content.
Specification G-73 is intended for Construction and has no jurisdiction over design; only Engineering design standards, criteria, and procedures have that authority.
04730 - 01/20/87
TVA EMPLOYEE CONCERNS REPORT NUMBER: 231.6(B)
SPECIAL PROGRAM REVISION NLMBER: 2 PAGE 7 0F 14 G-73 QA Requirements l
G-73 Section 2.1 bo'ntains the phrase " applicable NRC guidelines."
No clarification is made as to what they may be and no criteria are offered as to how applicability could be established.
In Section 5 of G-73, " References," only the following NRC guidelines are listed:
"5.1 NRC Auxiliary Power Conversion Systems Branch
( APCSB), Branch Technical Position (BTP) 9.5-1,
' Guidelines for Fire Protection for Nuclear Power Plants Docketed Prior to July 1,1976.'
'~*
"S.2 Appendix A to APCSB BTP 9.5-1 "5.3 NRC Auxiliary Systems Branch ( ASB) BTP 9.5-1 (R1)
"5.4 National Fire Protection Association National Fire Codes "5.5 OEDC-QAI-6 ' Establishment of Limited QA Program' (R0 dated August 25,1981) (QAM 810827 012) f "S.6 TV.' General Construction Specification No. G-74,
' Ap,lication and Inspection Requirements for the Fireproofing of Structural Steel' (to be issued)"
References 5.1, 5.2, and 5.3 above contain QA requirements specifically tailored to fire protection systems. These requirements are outlined in Reference 5.5 above and, as explained previously, are appropriately different from those outlined in l
10CFR50 Appendix B.for nuclear safety systems.
There may be places where fire protection systems and nuclear safety systems interact.
An example would be where fire protection i
piping would constitute a flooding or impact hazard to the very safety equipment it is intended to protect.
In such instances, the seismic support to such piping would need to confonn to the requirements of 10CFR50 Appendix B, creating an overlap of and possible conflict between the 10CFR50 Appendix B QA program and the G-73 limited QA program.
This potential jurisdictional problem is handled in G-73 Section 3.1.2:
" Systems, components, or features described in section 3.1.1 which come under the requirements of 10CFR50 Appendix B are exempt from the requirements of this specification. The 10CFR50 Appendix B Quality Assurance Program applies instead of this construction specification." (Emphasis added.)
04730 - 01/20/87
TVA EMPLOYEE CONCERNS REPORT NUMBER: 231.6(B)
SPECIAL PROGRAM REVISION NUMBER: 2 PAGE 8 0F 14 The " systems, components... [and] features described in G-73 Section 3.1.1" are,:
"a.
Mechanical fire suppression systems (including carbon dioxide and Halon);
"b.
Fire detection systems including detectors, panels, central processing units, alarm stations, actuation circuits, and related wiring; "c.
Mechanical and electrical fire barrier penetration seals and fire stops; "d.
Heating, ventilating, and air-conditioning system fire and smoke dampers, fire and smoke damper controls, and duct fireproofing; "e.
Fire doors, frames, hardware, and related control circuits; "f.
Emergency lighting systeins (eight-hour battery packs);
"g.
Emergency communication systems (portable radios and fixed repeater systems); and l
"h.
Fire barriers and fire retardant cable coatings."
Since G-73 specifically defers jurisdiction where 10CFR50 Appendix B applies, it follows that G-73 applies only in lin:ited Q and non-Q fire protection areas. However, G-73 does not establish the QA
" designation of fire protection drawings" as stated in the l
This position is further strengthened in Section 3.2 of l
concern.
l G-73, " Fire Protection QA Boundaries," where identification of FPS l
QA boundaries is specifically deferred to the Engineering design drawings:
" Fire protection QA boundaries shall be defined by EN l
DES on design drawings. All design drawings where this construction specification is applicable shall have a
'Q' or 'Q*' in the title block or Drawing Information System as required by EN DES-EP 4.25 and a note similar l
to that shown below which states the applicability of this specification and any exclusions thereto:
0473D - 01/20/87
TVA EMPLOYEE CONCERNS REPORT NUMBER: 231.6(B)
SPECIAL PROGRAM REVISION NUMBER: 2 i
PAGE 9 0F 14 "All construction activities for the fire protection system and/or features shown on this' series bf drawings shall be conducted in accordance with TVA General Construction Specification No.
G-73, ' Inspection, Testing, and Documentation Requirements for Fire Protection Systems and Features.' "
The choice of the word "shall" in the above gives the impression that this paragraph is establishing an EN DES requirement'in spite of the fact that specification G-73 has no jurisdiction over EN DES. The use of the more explanatory term "will" (e.g., "QA boundaries will be defined by EN DES") followed by the more demanding term "shall" in the appropriate places (e.g., "All construction activities... shall be conducted...") would probably have prevented the confusion that led the CI to believe i
that G-73 designated " fire protection drawings (QA)." In fact, G-73 does not designate any QA requirements for "the engineering treatment of fire protection drawings." G-73 only covers Construction activities in this area, an issue separate and distinct from Engineering requirements. Since G-73 does not have jurisdiction in Engineering affairs, there can be no discrepancy between "the G-73 designation" and "the engineering treatment" as expressed in the concern. Minor wording changes in G-73 would make this clear.
l FPS Design Criteria ihe question remains as to where Engineering does express the QA requirements for the SQN FPS. Further investigation found two TVA n Criteria covering SQN FPS. The first, originally dated Desig/72 and revised 09/06/85, is SQN General Design Criteria 09/26 SQN-DC-V-7.5 (App. A, 5.a).
This document covers the High Pressure, the CO, and the Aqueous Foam FPS. Section 4.0, 2
" Quality Assurance," of this document carries the following instruction:
"The fire protection systems are covered by a limited Quality Assurance Program when they provide protection for structures which contain safety-related systems or components. Refer to Quality Assurance (QA) List (Appendix A to Construction Specification N2G-877), System 26 (HPFP) and System 39 (C0 ) for components in the QA program.
2
" NOTE:
After completion of a trial period, Appendix A will l
be removed from Specification N2G-877 and a final QA list will be issued as design drawings."
i r
0473D - 01/20/87
TVA EMPLOYEE CONCERNS REPORT NUMBER: 231.6(B)
SPECIAL PROGRAM REVISION NUMBER: 2 PAGE 10 0F 14 The second design criteria document is SQN-DC-V-24.0 (App. A, 5.b) and is initially dated 05/01/85 and revised 07/02/85. These criteria cover the FPS for " Safe Shutdown Capability" and define where such fire protection must be located and to which systems Appendix R applies. SQN-DC-V-24.0 makes specific reference to Appendix R of 10CFR50 (App. A, 5.e).
However, SQN-DC-V-24.0 does not contain any reference to the QA requirements of 10CFR50 Appendix B.
Since Appendix R also makes no reference to Appendix B, SQN-DC-V-24.0 is consistent with the governing regulatory requirements.
This means that the most definitive source of FPS QA boundary identification and the QA requirements that apply thereto is the
" final QA list... issued as design drawings" per the requirements of SQN-DC-V-7.5 as quoted above.
From this it is clear that:
a.
G-73 defers jurisdiction to 10CFR50 Appendix B wherever they overlap b.
G-73 is exclusively a construction specification that defers to and depends upon the FPS QA boundaries to be defined by Engineering in other documents or drawings Engineering establishes SQN FPS QA requirements in c.
design criteria and identifies QA boundary requirements on design drawings On these bases, therefore, there cannot be " Discrepancies between G-73 designations... and engineering treatment of" SQN FPS QA requirements as claimed in the concern.
Findings:
Engineering treatment of SQN FPS is a mix of both Q (including limited Q) and non-Q requirements. This is consistent with regulatory requirements for SQN FPS.
Specification G-73 does not designate fire protection QA requirements and specifically defers such jurisdiction to other documents.
Specification G-73 also defers identification of QA boundaries to Engineering design drawings. Design Criteria SQN-DC-V-7.5 are the definitive present source of SQN FPS QA boundary identification and requirements. SQN FPS design drawings, in conformance with SQN-DC-V-7.5, establish QA boundaries and have clear jurisdiction over G-73.
No " discrepancies," per se, can therefore exist between the two.
0473D - 01/20/87
TVA EMPLOYEE CONCERNS REPORT NUMBER: 231.6(B)
SPECIAL PROGRAM REVISION NUMBER: 2 PAGE 11 0F 14
==
Conclusion:==
G-73 is a constrdclion specification prepared by Engineering that specifically defers jurisdiction of Quality Assurance issues, including designation of QA boundaries, to Engineering. This precludes the existence of discrepancies between G-73 and Engineering " treatment of fire protection drawings (as non-QA)."
Engineering drawings establish the proper QA treatment of SQN FPS.
The concern is not factual, as stated, but the confusion between Paragraphs 3.1.2 and 3.2 in G-73 as to whether or not QA requirements are deferred to other documents should be corrected.
- 10. CORRECTIVE ACTION TVA has submitted a corrective action plan (App. A, 5.k) which includes a commitnent to revise G-73 in a manner that will eliminate the confusion which led to the expression of this concern. No substantive changes to the SQN FPS QA program are required. The corrective action is satisfactory to the evaluation team.
0473D - 01/20/87
~
TVA EMPLOYEE CONCERNS REPORT NUMBER: 231.6(B)
SPECIAL PROGRAM REVISION NUMBER: 2 PAGE 12 0F 14 APPENDIX A 5.
DOCUMENTS REVIEWED RELATID TO THE ELEMENT:
TVA General Design Criteria SQN-DC-V-7.5, " Fire Protection a.
Systems," R1, (09/06/85) b.
TVA General Design Criteria SQN-DC-V-24.0, " Fire Protection of Safe Shutdown capability," (05/01/85)
TVA General Construction Specification G-73, " Inspection, c.
Testing and Documentation Requirements for Fire Protection System and Features," R1, (03/14/84) d.
10CFR50.48, " Fire Protection," (05/23/85) 10CFR50 Appendix R. " Fire Protection Program for Nuclear e.
Power Facilities Operating Prior to January 1, 1979" f.
Letter from J. E. Gilliland, TVA, to R. S. Boyd, NRC, " Docket Nos. 50-327, 50-328, 50-390, 50-391," (DES 770126 029),
(01/24/77) g.
Appendix A to BTP APCSB 9.5-1, " Guidelines for Fire Protection of Nuclear Power Plants Docketed Prior to July 1, 1976," (08/76) h.
SQN Safety Evaluation Report, Section 9.5, " Fire Protection
~
Systems," NUREG 0011, Supp 1, (02/80) 1.
10CFR50 Appendix B, " Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants" j.
TVA OEDC-QAI-6, " Establishment of Limited QA Program,"
(08/25/81) l k.
TCAB-064, Corrective Action Plan for Element Report 231.06, (S03 870116 801), (01/17/87) 1.
NCR 2675, Nonconforming Condition Report, (12/20/83) 0473D - 01/20/87
r TVA EMPLOYEE CONCERNS REPORT NUMBER: 231.6(B)
SPECIAL PROGRAM REVISION NUMBER: 2 PAGE 13 0F 14 APPENDIX A (Cont'd) 6.
WHAT REGULATIONS, LICERSING COMMITMENTS, DESIGN REQUIREMENTS OR OTHER
%PPLY OR CONTROL IN THIS AREA?
a.
10CFR50.48, " Fire Protection" b.
10CFR50 Appendix A, " General Design Criteria" 10CFR50 Appendix R, " Fire Protection Program for Nuclear c.
Power Facilities Operating Prior to January 1, 1979" d.
NRC Branch Technical Position: Auxiliary Powe'r Conversion System Branch BTP APCSB 9.5-1, " Guidelines for Fire Protection for Nuclear Power Plants," (05/76)
Appendix A to BTP APCSB 9.5-1, " Guidelines for Fire e.
Protection of Nuclear Power Plants Docketed Prior to July 1, 1976," (08/76) 7.
LIST REQUESTS FOR INFORMATION, MEETINGS, TELEPHONE CALLS, AND OTHER FITCUSSIONS RELATED TO ELEMENT:
Telephone conference, D. L. Damon, Bechtel, with H. A.
a.
Mahinan and R. Winbrow, TVA, IOM 544, (01/13/87) l l
l t
l I
0473D - 01/20/87
TVA EMPLOYEE CONCERNS REPORT NUMBER: 231.6(B)
SPECIAL PROGRAM REVISION NUMBER: 2 PAGE 14 0F 14 I
I CATD LIST The following CATD' identifies and provides corrective action for the findings included in this report:
231.06-SQN-1 (12/24/86; CAP revised 01/13/87) l 04730 - 01/20/87
n..
,y
. $)
REFERENCE
- ECPS120J-ECPS121C TENNESSEE VALLEY AUTHORITY PAGE 126 FREQUENCY
- REQUEST OFFICE OF NUCLEAR PDHER RUN TIME - 12:S7:19
)
)
ONP - ISSS - RHM EMPLOYEE CONCERN PROGRAM SYSTEM (ECPS)
-RUN DATE - 12/02/86 LIST OF EMPLOYEE CONCERN INFORMATION CATEGORY: EN DES PROCESS 4 UUTPUT SUBCATEGORY: 23106 FIRE PROTECTION QA DESIGNATION
)
KEYHORD A
)
S GENERIC H
APPL QTC/NSRS P
KEYHORD B CONCERN SUB R PLT BBSH INVESTIGATION S
CONCERN KEYWORD C NUMBER CAT CAT D LOC FLQB REPORT R
DESCRIPTION KEYHORD D.
,)
)
BNPQCP10.35-1 EN 23106 N BLN YYYY SS DISCREPANCY BETHEEN G-73 DESIGNATION REPORT OF FIRE PROTECTION DRAHINGS (QA) A ND ENGINEERING TREATMENT OF FIRE PRO 3
3 TECTION DRAHINGS (AS NON-QA).
ALSO 4>
NCR 2675 (FIRE PROTECTION CABLE DEFI CIENCY) HAS INVALIDATED BASED ON VER BAL INFORMATION RECEIVED BY TELEPHON
's) r
$)
E THAT CONTRADICTS DESIGN APPROVED D OCUMENTS.
~
1 CONCERNS.FOR CATEGORY EN SUBCATEGORY 23106 f)
)
v')
3 s
)
3
').
a
)
l'
)
)
.)
t