ML24215A193

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LLC, Response to SDAA Audit Question Number A-16.3.3.1-5
ML24215A193
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Response to SDAA Audit Question Question Number: A-16.3.3.1-5 Receipt Date: 09/18/2023 Question:

SDAA generic TS Table 3.3.1-1 footnote (b) modifies the MODE 2 and MODE 3 Applicability of the following MPS Instrument Functions and for which Condition H applies:

1.b. High Power Range Linear Power DWSI actuation 3.b. High Intermediate Range Log Power Rate DWSI actuation 4.b. High Source Range Count Rate DWSI actuation 5.b. High Source Range Log Power Rate DWSI actuation 7.d. High Pressurizer Pressure DWSI actuation 9.a. Low Low Pressurizer Pressure reactor trip (Condition D) 9.b. Low Low Pressurizer Pressure DWSI actuation 10.b. High Pressurizer Level DWSI actuation 11.e. Low Pressurizer Level DWSI actuation 17.d. High Main Steam Pressure DWSI actuation (MODE 2 only) 19.c. Low Low Main Steam Pressure DWSI actuation 22.e. High Narrow Range Containment Pressure DWSI actuation 25.e. Low AC Voltage to EDAS Battery Chargers DWSI actuation 26.e. High Under-the-Bioshield Temperature DWSI actuation Footnote (b) states, When capable of withdrawal of more than one CRA and the RCS temperature above the T-3 interlock.

Bases page B 3.3.1-15 states, The WR RCS Thot T-3 interlock is active when WR [wide range]

RCS Thot is less than approximately 340 F.

(2) Consider clarifying second clause of footnote (b) similarly to the following markup (assuming the answer to (1) is RCS cold temperature) to ensure T-3 interlock is not active:

and the at least [two] RCS cold temperature channels indicate above the T-3 interlock (3) For the above listed Functions, the MODE 2 Applicability is modified by footnote (b). Why not NuScale Nonproprietary NuScale Nonproprietary

footnote (a) to modify MODE 2 because MODE 2 definition includes Any Indicated Reactor Coolant Temperature (RCTindic) 345 F?

Response

Original Response Item (2):

The phrase RCS temperature is used throughout GTS Section 3.3 to describe the temperature input to the various interlock functions. The APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY section of the GTS Section 3.3.1 Bases describes the interlocks referenced in GTS Section 3.3.1. That description includes the RCS temperature source used as input to the interlocks. There is no need to repeat the specific RCS temperature input in each reference to an interlock in GTS Section 3.3.

NuScale revises the following required action and footnotes to ensure consistency in the application of the phrase RCS temperature in the GTS Section 3.3 references to T interlocks:

GTS TS 3.3.1 Required Action N.1, GTS Table 3.3.1-1 footnotes (h), (o), and (p),

GTS Table 3.3.3-1 footnote (c), and GTS Table 3.3.4-1 footnote (d)

Item (3):

NuScale revises SDAA TS Table 3.3.1-1 MODE 2 applicability for the following MPS instrument functions from footnote (b) to footnote (a):

1.b. High Power Range Linear Power - DWSI 3.b. High Intermediate Range Log Power Rate - DWSI 4.b. High Source Range Count Rate - DWSI 5.b. High Source Range Log Power Rate - DWSI 7.d. High Pressurizer Pressure - DWSI 9.a. Low Low Pressurizer Pressure - RTS 9.b. Low Low Pressurizer Pressure - DWSI 10.b. High Pressurizer Level - DWSI 11.e. Low Pressurizer Level - DWSI NuScale Nonproprietary NuScale Nonproprietary

17.d. High Main Steam Pressure - DWSI 19.c. Low Low Main Steam Pressure - DWSI 22.e. High Narrow Range Containment Pressure - DWSI 25.e. Low AC Voltage to EDAS Battery Chargers - DWSI 26.e. High Under-the-Bioshield Temperature - DWSI NuScale revises SDAA TS Table 3.3.1-1 applicability for MPS instrument function 2.b. from MODE 1(b) to MODE 1(c).

NRC 12/19/23 Follow-Up Item (3)

Followup: Sometimes, instead of using T-# interlock the Bases use just T-#; should interlock always be used? Both mean T-# interlock setpoint temperature Followup: B 3.4.4 Applicability section first sentence has the passage: the LTOP enable interlock T-1 temperature specified in the Pressure and Temperature Limits Report (PTLR),

Consider whether to change to the LTOP enable T-1 interlock temperature or the LTOP enable temperature (T-1 interlock) ; be sure to address all such examples NuScale Response to 12/19/23 Follow-Up Item (3)

NuScale revises the Bases for GTS Sections 3.3 and 3.4 to clarify interlock descriptions.

NRC 2/6/24 Clarification of the 1/19/24 Discussion of Follow-Up Item (2):

The staffs notes on Item (2) say:

01/19/24 telcon with NuScale Item (2) - [NuScale stated] Mode change based on

[RCS] temperature indication, not interlock state; if interlock fails to unblock a supported Function, enter the Actions for affected channel [because MPS has no means of manually placing an automatic interlock in the required state if it failed to change state when the associated indicated parameter reaches the setpoint].

The staff requests that NuScale add this design point into the Bases where the role of interlocks supporting instrument Functions is discussed.

Regarding footnote (k) in Table 3.3.1-1, the staff had mentioned inserting water before level to be consistent concerning containment water level:

(k) With containment level below the L-1 interlock with reactor narrow range RCS temperature above the T-3 interlock, or with containment water level below the L-1 interlock with V-1 not active (both FWIVs open).

NuScale Nonproprietary NuScale Nonproprietary

MODES 2 and 3 for Function 19.b. Low Low Main Steam Pressure - SS NuScale Response to 2/6/24 Clarification of the 1/19/24 Discussion of Follow-Up Item (2):

NuScale revises Page B 3.3.1-11 of the Bases for GTS Section 3.3.1 to clarify the action to be taken should an MPS interlock fail to function correctly.

It was NuScales understanding, from the 1/19/24 discussion of Item (2), that insertion of water in front of level in footnote (k) was a confirmatory action. NuScale would ensure the change was incorporated into Revision 2 of the NuScale GTS. That change was processed and will be included in Revision 2 of the NuScale GTS. The markup of footnote (k) is included in this response.

Markups of the affected changes, as described in the response, are provided below:

NuScale Nonproprietary NuScale Nonproprietary

MPS Instrumentation 3.3.1 NuScale US460 3.3.1-4 Draft Revision 2 ACTIONS (continued)

CONDITION REQUIRED ACTION COMPLETION TIME L.

As required by Required Action C.1 and referenced in Table 3.3.1-1.

L.1 Be in MODE 2.

AND L.2 Be in MODE 3 and PASSIVELY COOLED.

AND L.3 Be in MODE 3 with RCS temperature below the T-2 interlock.

AND L.4 Isolate dilution source flow paths in the CVCS makeup line by use of at least one closed manual or one closed and de-activated automatic valve.

AND L.5 Open pressurizer heater breakers.

72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> 96 hours 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> 96 hours 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> M. As required by Required Action C.1 and referenced in Table 3.3.1-1.

M.1 Be in MODE 2.

AND M.2 Be in MODE 3 with RCS temperature below the T-3 interlock.

6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> 48 hours N. As required by Required Action C.1 and referenced in Table 3.3.1-1.

N.1 Reduce RCS Narrow Range temperature below the T-4 interlock.

6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />

MPS Instrumentation 3.3.1 NuScale US460 3.3.1-7 Draft Revision 2 Table 3.3.1-1 (page 1 of 8)

Module Protection System Instrumentation FUNCTION APPLICABLE MODES OR OTHER SPECIFIED CONDITIONS REQUIRED CHANNELS CONDITIONS

1. High Power Range Linear Power
a. RTS 1, 2(a), 3(a) 4 D
b. DWSI 1, 2(ab), 3(b) 4 H
2. High Power Range Positive and Negative Rate
a. RTS 1(c) 4 E
b. DWSI 1(cb) 4 H
3. High Intermediate Range Log Power Rate
a. RTS 1(d), 2(a), 3(a) 4 D
b. DWSI 1(d), 2(ab), 3(b) 4 H
4. High Source Range Count Rate
a. RTS 1(e), 2(a), 3(a) 4 D
b. DWSI 1(e), 2(ab), 3(b) 4 H
5. High Source Range Log Power Rate
a. RTS 1(e), 2(a), 3(a) 4 D
b. DWSI 1(e), 2(ab), 3(b) 4 H
6. High Subcritical Multiplication
a. DWSI 1(e), 2, 3 4

H (a) When capable of withdrawal of more than one CRA.

(b) When capable of withdrawal of more than one CRA and the RCS temperature above the T-3 interlock.

(c)

With power above the N-2H interlock.

(d) With power below the N-2L interlock.

(e) When Intermediate Range Log Power less than N-1 interlock.

MPS Instrumentation 3.3.1 NuScale US460 3.3.1-8 Draft Revision 2 Table 3.3.1-1 (page 2 of 8)

Module Protection System Instrumentation FUNCTION APPLICABLE MODES OR OTHER SPECIFIED CONDITIONS REQUIRED CHANNELS CONDITIONS

7. High Pressurizer Pressure
a. RTS 1, 2(a), 3(a) 4 D
b. DHRS 1, 2, 3(f) 4 I
c. SSI 1, 2, 3(f) 4 I
d. DWSI 1, 2(ab), 3(b) 4 H
e. PHT 1, 2(g), 3(g) 4 G
8. Low Pressurizer Pressure
a. RTS 1(h) 4 N
b. SSI 1(h) 4 N
c. DWSI 1(h) 4 N
d. Pressurizer Line Isolation 1, 2, 3(i) 4 M
9. Low Low Pressurizer Pressure
a. RTS 1, 2(ab), 3(b) 4 D
b. DWSI 1, 2(ab), 3(b) 4 H
10. High Pressurizer Level
a. RTS 1, 2(a), 3(a) 4 D
b. DWSI 1, 2(ab), 3(b) 4 H
c. CVCSI 1, 2, 3 4

F (a) When capable of withdrawal of more than one CRA.

(b) When capable of withdrawal of more than one CRA and the RCS temperature above the T-3 interlock.

(f)

When not PASSIVELY COOLED.

(g) With pressurizer heater breakers closed.

(h) With narrow range RCS hot temperature above the T-4 interlock.

(i)

With RCS temperature above the T-3 interlock.

MPS Instrumentation 3.3.1 NuScale US460 3.3.1-9 Draft Revision 2 Table 3.3.1-1 (page 3 of 8)

Module Protection System Instrumentation FUNCTION APPLICABLE MODES OR OTHER SPECIFIED CONDITIONS REQUIRED CHANNELS CONDITIONS

11. Low Pressurizer Level
a. RTS 1, 2(a), 3(a) 4 D
b. CIS 1(h) 4 N
c. DHRS 1(h) 4 N
d. SSI 1, 2, 3(j) 4 I
e. DWSI 1, 2(ab), 3(b) 4 H
f.

CVCSI 1(h) 4 F

g. PHT 1, 2(g), 3(g) 4 G
12. Low Low Pressurizer Level
a. CIS 1, 2, 3(j) 4 K
b. CVCSI 1, 2, 3(j) 4 F
13. High Narrow Range RCS Hot Temperature
a. RTS 1

4 D

b. DHRS 1, 2, 3(f) 4 I
c. SSI 1, 2, 3(f) 4 I
d. DWSI 1

4 H

e. PHT 1, 2(g), 3(g) 4 G

(a) When capable of withdrawal of more than one CRA.

(b) When capable of withdrawal of more than one CRA and the RCS temperature above the T-3 interlock.

(f)

When not PASSIVELY COOLED.

(g) With pressurizer heater breakers closed.

(h) With narrow range RCS hot temperature above the T-4 interlock.

(j)

With RCS temperature above the T-2 interlock and containment water level below the L-1 interlock.

MPS Instrumentation 3.3.1 NuScale US460 3.3.1-10 Draft Revision 2 Table 3.3.1-1 (page 4 of 8)

Module Protection System Instrumentation FUNCTION APPLICABLE MODES OR OTHER SPECIFIED CONDITIONS REQUIRED CHANNELS CONDITIONS

14. High RCS Average Temperature
a. RTS 1

4 D

b. DWSI 1

4 H

15. Low RCS Flow
a. DWSI 1, 2, 3 4

H

16. Low Low RCS Flow
a. RTS 1, 2(a), 3(a) 4 D
b. DWSI 1, 2, 3 4

H

17. High Main Steam Pressure
a. RTS 1, 2(a) 4 per SG D
b. DHRS 1, 2, 3(f) 4 per SG I
c. SSI 1, 2, 3(f) 4 per SG I
d. DWSI 1, 2(ab) 4 per SG H
e. PHT 1, 2(g), 3(g) 4 per SG G
18. Low Main Steam Pressure
a. RTS 1(h) 4 per SG N
b. SSI 1(h) 4 per SG N
c. DWSI 1(h) 4 per SG N

(a) When capable of withdrawal of more than one CRA.

(b) When capable of withdrawal of more than one CRA and the RCS temperature above the T-3 interlock.

(f)

When not PASSIVELY COOLED.

(g) With pressurizer heater breakers closed.

(h) With narrow range RCS hot temperature above the T-4 interlock.

MPS Instrumentation 3.3.1 NuScale US460 3.3.1-11 Draft Revision 2 Table 3.3.1-1 (page 5 of 8)

Module Protection System Instrumentation FUNCTION APPLICABLE MODES OR OTHER SPECIFIED CONDITIONS REQUIRED CHANNELS CONDITIONS

19. Low Low Main Steam Pressure
a. RTS 1, 2(a), 3(a) 4 per SG D
b. SSI 1, 2(k), 3(k) 4 per SG I
c. DWSI 1, 2(ab), 3(b) 4 per SG H
20. High Steam Superheat
a. RTS 1

4 per SG D

b. SSI 1

4 per SG I

c. DWSI 1

4 per SG H

21. Low Steam Superheat
a. RTS 1(l) 4 per SG D
b. SSI 1(l), 2(m), 3(m) 4 per SG I
c. DWSI 1(l) 4 per SG H

(a) When capable of withdrawal of more than one CRA.

(b) When capable of withdrawal of more than one CRA and the RCS temperature above the T-3 interlock.

(k)

With containment water level below the L-1 interlock with reactor narrow rangeRCS temperature above the T-3 interlock, or with containment water level below the L-1 interlock with V-1 not active (both FWIVs open).

(l)

With V-1 not active (both FWIVs open).

(m) With containment water level below the L-1 interlock and with V-1 not active (both FWIVs open).

MPS Instrumentation 3.3.1 NuScale US460 3.3.1-12 Draft Revision 2 Table 3.3.1-1 (page 6 of 8)

Module Protection System Instrumentation FUNCTION APPLICABLE MODES OR OTHER SPECIFIED CONDITIONS REQUIRED CHANNELS CONDITIONS

22. High Narrow Range Containment Pressure
a. RTS 1, 2(a), 3(a) 4 D
b. CIS 1, 2, 3(i) 4 M
c. DHRS 1, 2, 3(i) 4 M
d. SSI 1, 2, 3(i) 4 M
e. DWSI 1, 2(ab), 3(b) 4 H
f.

CVCSI 1, 2, 3(i) 4 F

g. PHT 1, 2(g), 3(n) 4 G
23. Low Reactor Pressure Vessel Riser Level
a. ECCS 1(o), 2(o) 4 I
24. Low Low Reactor Pressure Vessel Riser Level
a. ECCS 1, 2, 3(f) 4 I

(a) When capable of withdrawal of more than one CRA.

(b) When capable of withdrawal of more than one CRA and the RCS temperature above the T-3 interlock.

(f)

When not PASSIVELY COOLED.

(g) With pressurizer heater breakers closed.

(i)

With RCS temperature above the T-3 interlock.

(n) With RCS temperature above the T-3 interlock and pressurizer heater breakers closed.

(o) With wide range RCS cold temperature above the T-5 interlock.

MPS Instrumentation 3.3.1 NuScale US460 3.3.1-13 Draft Revision 2 Table 3.3.1-1 (page 7 of 8)

Module Protection System Instrumentation FUNCTION APPLICABLE MODES OR OTHER SPECIFIED CONDITIONS REQUIRED CHANNELS CONDITIONS

25. Low AC Voltage to EDAS Battery Chargers
a. RTS 1, 2(a), 3(a) 4 per bus L
b. CIS 1, 2, 3 4 per bus L
c. DHRS 1, 2, 3(f) 4 per bus L
d. SSI 1, 2, 3(f) 4 per bus L
e. DWSI 1, 2(ab), 3(b) 4 per bus L
f.

CVCSI 1, 2, 3 4 per bus L

g. PHT 1, 2(g), 3(g) 4 per bus L
h. ECCS 1, 2, 3(f) 4 per bus L
26. High Under-the-Bioshield Temperature
a. RTS 1, 2(a), 3(a) 4 L
b. CIS 1, 2, 3 4

L

c. DHRS 1, 2, 3(f) 4 L
d. SSI 1, 2, 3(f) 4 L
e. DWSI 1, 2(ab), 3(b) 4 L
f. CVCSI 1, 2, 3 4

L

g. PHT 1, 2(g), 3(g) 4 L

(a) When capable of withdrawal of more than one CRA.

(b) When capable of withdrawal of more than one CRA and the RCS temperature above the T-3 interlock.

(f)

When not PASSIVELY COOLED.

(g) With pressurizer heater breakers closed.

MPS Instrumentation 3.3.1 NuScale US460 3.3.1-14 Draft Revision 2 Table 3.3.1-1 (page 8 of 8)

Module Protection System Instrumentation FUNCTION APPLICABLE MODES OR OTHER SPECIFIED CONDITIONS REQUIRED CHANNELS CONDITIONS

27. High RCS Pressure - Low Temperature Overpressure Protection
a. LTOP 3(p) 4 J

(p) With wide range RCS cold temperature below the LTOP enable temperature specified in the PTLR (T-1 interlock) and both reactor vent valves closed.

ESFAS Logic and Actuation 3.3.3 NuScale US460 3.3.3-6 Draft Revision 2 3.3.3-1 (page 1 of 1)

ESFAS Logic and Actuation Functions ACTUATION FUNCTION APPLICABLE MODES OR OTHER SPECIFIED CONDITIONS REQUIRED DIVISIONS CONDITIONS

1. Emergency Core Cooling System (ECCS) 1, 2, 3(a) 2 C
2. Decay Heat Removal System (DHRS) 1, 2, 3(a) 2 C
3. Containment Isolation System (CIS) 1, 2, 3 2

D

4. Demineralized Water Supply Isolation (DWSI) 1, 2, 3 2

E

5. CVCS Isolation (CVCSI) 1, 2, 3 2

F

6. Pressurizer Heater Trip 1, 2(b), 3(b) 2 G
7. Low Temperature Overpressure Protection (LTOP) 3(c) 2 A
8. Secondary System Isolation (SSI) 1, 2, 3(a) 2 C
9. Pressurizer Line Isolation 1, 2, 3(d) 2 F

(a) When not PASSIVELY COOLED.

(b) With pressurizer heater breakers closed.

(c)

With wide range RCS cold temperature below the LTOP enable temperature specified in the PTLR (T-1 interlock) and both reactor vent valves closed.

(d) With RCS temperature above the T-3 interlock.

Manual Actuation Functions 3.3.4 NuScale US460 3.3.4-4 Draft Revision 2 Table 3.3.4-1 (page 1 of 1)

Manual Actuation Functions MANUALLY ACTUATED FUNCTION APPLICABLE MODES OR OTHER SPECIFIED CONDITIONS REQUIRED DIVISIONS CONDITIONS

1. Reactor Trip System 1, 2(a), 3(a) 2 C
2. Emergency Core Cooling System 1, 2, 3(b) 2 D
3. Decay Heat Removal System 1, 2, 3(b) 2 D
4. Containment Isolation System 1, 2, 3 2

I

5. Demineralized Water Supply Isolation 1, 2, 3 2

E

6. CVCS Isolation System 1, 2, 3 2

F

7. Pressurizer Heater Trip 1, 2(c), 3(c) 2 G
8. Low Temperature Overpressure Protection 3(d) 2 H
9. Secondary System Isolation (SSI) 1, 2, 3(b) 2 D

(a) When capable of CRA withdrawal.

(b) When not PASSIVELY COOLED.

(c)

With pressurizer heater breakers closed.

(d) With wide range RCS cold temperature below the LTOP enable temperature specified in the PTLR (T-1 interlock) and more than one reactor vent valve closed.

MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-11 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY (continued)

The Module Protection System instrumentation satisfies Criterion 3 of 10 CFR 50.36(c)(2)(ii).

Permissive and interlock setpoints automatically provide, or allow manual or automatic blocking of trips during unit evolutions. They are not explicitly modeled in the Safety Analyses. These permissives and interlocks ensure that the initial conditions are consistent with the safety analysis, before preventive or mitigating actions occur. Because these permissives or interlocks are only one of multiple conservative initial conditions for the safety analysis, they are generally considered as nominal values without regard to measurement accuracy.

Operating bypasses are addressed in the footnotes to Table 3.3.1-1.

They are not otherwise addressed as specific Table entries.

The automatic bypass removal features must function as a backup to manual actions for all safety related trips to ensure the trip Functions are not operationally bypassed when the safety analysis assumes the Functions are OPERABLE.

RTS and ESFAS Operating Bypass Interlocks and Permissives Reactor protection permissives and interlocks are provided to ensure reactor trips and ESF actuations are in the correct configuration for the current unit status (Ref. 4). This is to ensure that the protection system functions are not bypassed during unit conditions under which the safety analysis assumes the functions are OPERABLE. Therefore, the permissive and interlock functions do not need to be OPERABLE when the associated reactor trip and ESF functions are outside the applicable MODES. Proper operation of these permissive and interlocks supports OPERABILITY of the associated reactor trip and ESF functions and/or the requirement for actuation logic OPERABILITY. The permissives and interlocks must be in the required state, as appropriate, to support OPERABILITY of the associated functions. The permissives and interlocks associated with each MPS Instrumentation Function channel, each Reactor Trip System (RTS) Logic and Actuation Function division, and each Engineered Safety Features Actuation System (ESFAS) Logic and Actuation Function division, respectively, must be OPERABLE for the associated Function channel or Function division to be OPERABLE. MPS interlocks function automatically. If an MPS interlock fails to function correctly, then the corresponding MPS instrumentation channel is INOPERABLE and the ACTIONs for the affected MPS function are entered. The combination of the continuous self-testing features of the MPS and the CHANNEL CALIBRATION specified by SR 3.3.1.4 verify the OPERABILITY of the interlocks and permissives. Specification 5.5.10,

MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-13 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY (continued)

Power Range Linear Power Permissive/Interlock, N-2 The Power Range Linear Power N-2 permissive/interlock is an increasing power permissive/interlock, N-2L, and a decreasing power permissive/interlock, N-2H. This interlock is necessary to meet the single failure criteria for the operating bypasses.

The N-2L permissive/interlock is active above approximately 15% power and the N-2H permissive/interlock is active below approximately 15%

power.

1. When the N-2L permissive is active, a manual operating bypass is permitted for the High-1 Power Range Linear Power reactor trip and High-1 Power Range Linear Power DWSI. This increases the Power Range Linear Power reactor trip to the High-2 trip setpoint.
2. When the N-2L interlock is active, an automatic operating bypass is established for the High Intermediate Range Log Power Rate reactor trip and the High Intermediate Range Log Power Rate DWSI actuation.
3. When the N-2L interlock is not active, the operating bypass is automatically removed for the following:

the High-1 Power Range Linear Power reactor trip; the High-1 Power Range Linear Power DWSI actuation; the High Intermediate Range Log Power Rate reactor trip; and the High Intermediate Range Log Power Rate DWSI actuation.

4. When the N-2H interlock is active, an automatic operating bypass is established for the following:

the High Power Range Positive Rate reactor trip; the High Power Range Positive Rate DWSI actuation; the High Power Range Negative Rate reactor trip; and the High Power Range Negative Rate DWSI actuation.

MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-14 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY (continued)

5. When the N-2H interlock is not active, the operating bypass is automatically removed for the following:

the High Power Range Positive Rate reactor trip; the High Power Range Positive Rate DWSI actuation; the High Power Range Negative Rate reactor trip; and the High Power Range Negative Rate DWSI actuation.

Reactor Tripped Interlock, RT-1 The Reactor Tripped Interlock, RT-1 is active when both divisional reactor trip breakers indicate open. The RT-1 interlock is required to be active for the ESFAS interlocks T-2, T-3, and L-1.

FWIV Closed Interlock, V-1 The FWIV Closed interlock, V-1 is active when one FWIV indicates closed.

1. When the V-1 interlock is active, an automatic operating bypass is established for the Low Main Steam Superheat reactor trip.
2. When the V-1 interlock and the T-3 interlock are active, or the containment water level interlock, L-1, is active, an automatic operating bypass is established for the Low -Low Main Steam Pressure Secondary System Isolation actuation.
3. When the V-1 interlock or the L-1 interlock are active, the operating bypass is established for the Low Main Steam Superheat Secondary System Isolation actuation.
4. When the V-1 interlock is not active, the operating bypass is automatically removed for the Low Main Steam Superheat reactor trip.
5. When the V-1 interlock or the T-3 interlock are not active, and the L-1 interlock is not active, the operating bypass is automatically removed for the Low -Low Main Steam Pressure Secondary System Isolation actuation.

MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-15 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY (continued)

Wide Range RCS Tcold Interlock, T-1 The Wide Range (WR) RCS Cold Temperature (Tcold) T-1 interlock is active when Wide Range Tcold is greater than approximately 290 °F.

When the T-1 interlock is active, an automatic operating bypass is established for the Low Temperature Overpressure Protection actuation.

When the T-1 interlock is not active, the operating bypass is automatically removed for the Low Temperature Overpressure Protection actuation.

Wide Range RCS Thot Interlock, T-2 The WR RCS Hot Temperature (Thot) T-2 interlock is active when WR RCS Thot is less than approximately 200 °F and the RT-1 interlock is active.

1. When the T-2 interlock is active, an automatic operating bypass is established for the Low Pressurizer Level trip for Secondary System Isolation actuation
2. When the T-2 interlock is active, an automatic operating bypass is established for the Low -Low Pressurizer Level trip for the following:

CVCS Isolation actuation; and Containment System Isolation actuation.

3. When the T-2 interlock and containment water level interlock, L-1, are not active, the operating bypass is automatically removed for the Low Pressurizer Level trip Secondary System Isolation actuation
4. When the T-2 interlock and containment water level interlock, L-1, are not active, the operating bypass is automatically removed for the Low Low Pressurizer Level trip for the following:

CVCS Isolation actuation; and Containment System Isolation actuation.

Wide Range RCS Thot Interlock, T-3 The WR RCS Thot T-3 interlock is active when WR RCS Thot is less than approximately 340 °F.

MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-18 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY (continued)

Containment Water Level Interlock, L-1 The Containment Water Level Interlock L-1 is active when Containment Water Level is greater than approximately 45 ft. and the RT-1 interlock is active.

1. When the L-1 interlock is active, an automatic operating bypass is established for the following:

Low -Low Main Steam Pressure Secondary System Isolation actuation; Low Main Steam Superheat Secondary System Isolation actuation; Low Pressurizer Level Secondary System Isolation actuation; Low Low Pressurizer Level Chemical and Volume Control System Isolation actuation; and Low -Low Pressurizer Level Containment System Isolation actuation.

2. When the L-1 interlock and the WR RCS Thot interlock, T-2, are not active, the operating bypass is automatically removed for the following:

Low Pressurizer Level Secondary System Isolation actuation; Low -Low Pressurizer Level Containment System Isolation actuation; and Low -Low Pressurizer Level Chemical and Volume Control System Isolation actuation.

3. When the L-1 interlock and the WR RCS Thot interlock, T-3, or the FWIV Closed interlock, V-1, are not active, the operating bypass is automatically removed for the Low -Low Main Steam Pressure Secondary System Isolation actuation.
4. When the L-1 interlock and the FWIV Closed interlock, V-1, are not active, the operating bypass is automatically removed for the Low Main Steam Superheat Secondary System Isolation actuation.

MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-19 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY (continued)

Containment System Isolation Override Function, O-1, for the Containment Flood and Drain and CVCS Isolation Valves The manual override switches (one per division) allow operations to bypass the containment system isolation signal for the containment flood and drain isolation valves and the CVCS isolation valves to allow control of containment water levels with an active containment system isolation actuation or CVCS isolation signal (except High Pressurizer Level).

1. If an automatic Containment System Isolation or automatic CVCS isolation signal (other than High Pressurizer Level) is present and the RT-1 interlock is active, the operator can activate the override function O-1 manually with the Override switch. This override will allow manual control of the containment flood and drain, RCI Injection isolation, Pressurizer Spray isolation, and CES containment isolation valves from the module control system.
2. The Override switch must be manually restored when the override function O-1 is no longer needed.

If the reactor trip breakers are closed, the override function O-1 is not available.

Reactor Trip System and ESFAS Functions The specific safety analyses applicable to each protective function are identified below:

1. Excore Nuclear Power Neutron flux provides indication of reactor power and is measured at detectors located outside the containment vessel at the height of the core region. Wide range detectors are used at all power levels with continuous indication from subcritical conditions and startup to operating power levels. The neutron monitoring system provides indication from approximately 5 counts per second to 200% RTP.

Neutron flux signals that exceed their setpoints or the rate of change limits cause the reactor trip breakers to open and the demineralized water supply valves to be isolated. Four channels of neutron flux are required to be OPERABLE when the unit is in MODE 1; and MODE 2 and 3 when capable of withdrawing more than one CRA. A single CRDM may be energized in MODE 2 or 3 using an alternate power source while conducting CRA coupling and decoupling.

MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-28 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY (continued) this function is fulfilled. Four channels are provided to permit one channel in trip or bypass indefinitely and still ensure no single random failure will disable this trip Function.

b. Low Pressurizer Pressure - Reactor Trip, Demineralized Water System Isolation, Secondary System Isolation, and Pressurizer Line Isolation (Table 3.3.1-1 Functions 8.a, b, c, d)

The Low Pressurizer Pressure trip is designed to protect against RCS line breaks outside of containment, CRA drop, and protect the RCS subcooled margin against flow instability events.

The RTS and ESFAS Low Pressurizer Pressure setpoint is approximately 1850 psia. Actual setpoints are established in accordance with the Setpoint Control Program.

Four Low Pressurizer Pressure reactor trip and ESFAS channels are required to be OPERABLE when operating in MODE 1 with RCS hot temperature above the T-4 interlock. In MODE 1 with RCS hot temperature below the T-4 interlock and in MODES 2, 3, 4, and 5 the RCS temperatures are well below the T-4 interlock and with the reactor subcritical the heat input will be insufficient to reach the T-4 interlock. Four channels are provided to permit one channel in trip or bypass indefinitely and still ensure no single random failure will disable this trip Function.

The Reactor Trip and ESFAS actuation of the DWSI, and Secondary System Isolation by the Low Pressurizer Pressure trip function is automatically bypassed when the RCS temperature is below the T-4 interlock, and is automatically enabled when RCS temperature is above the T-4 interlock. Interlock and permissive setpoints are governed by the Setpoint Program.

Four Pressurizer Line Isolation channels are required to be OPERABLE in MODES 1 and 2, and in MODE 3 with RCS temperature above the T-3 interlock to limit inventory losses from postulated pressurizer spray and high point vent line breaks. The Pressurizer Line Isolation actuation is automatically bypassed when the RCS temperature is below the T-3 interlock, and is automatically enabled when the RCS temperature is above the T-3 interlock. In MODE 3 below the T-3 interlock isolation of the pressurizer lines is accomplished by other isolation signals. In MODES 4 and 5 the pressurizer line isolation safety function is accomplished.

MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-29 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY (continued)

c. Low Low Pressurizer Pressure - Reactor Trip and Demineralized Water System Isolation (Table 3.3.1-1 Functions 9.a, b)

The Low Low Pressurizer Pressure trip is designed to protect against RCS line breaks outside of containment and protect the RCS subcooled margin against flow instability events.

The RTS and ESFAS Low Low Pressurizer Pressure setpoint is approximately 1200 psia. Actual setpoints are established in accordance with the Setpoint Program.

Four Low Low Pressurizer Pressure reactor trip channels are required to be OPERABLE when operating in MODE 1 and in MODES 2 and 3 when capable withdrawing more than a single CRA above the T-3 interlock. In MODES 2 and 3 with no capability of withdrawing more than one CRA or below the T-3 interlock, and in MODES 4 and 5 the function is fulfilled because the CRAs are inserted.

Four Low Low Pressurizer Pressure DWSI channels are required to be OPERABLE when operating in MODES 1, 2, and MODE 3 above the RCS temperature T-3 interlock. In MODE 3 below the RCS temperature T-3 interlock actuation the reactor is shutdown.

The high subcritical multiplication signal and the low RCS flow signal provide the required protective functions below the RCS T-3 interlock temperature. In MODES 4 and 5 the demineralized water system is isolated from the reactor module.

3. Reactor Coolant System Level RCS Level is measured by four (one per separation group) detectors to detect the water level in the RCS vessel. The sensors are located such that they can monitor water level from above the reactor core to the top of the pressurizer.
a. High Pressurizer Level - Reactor Trip, CVCS Isolation, and Demineralized Water System Isolation (Table 3.3.1-1 Functions 10.a, b, c)

The High Pressurizer Level trip provides protection for system malfunctions that increase the reactor coolant system inventory.

Four High Pressurizer Level reactor trip channels are required to be OPERABLE when operating in MODE 1 and in MODES 2 and 3 when capable of withdrawing more than a single CRA. In

MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-32 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY (continued)

Four Low Pressurizer Level Pressurizer Heater Trip channels are required to be OPERABLE when operating in MODE 1, and MODES 2 and 3 with the pressurizer heater breakers closed. In MODES 2 and 3 with the pressurizer heater breakers open and in MODES 4 and 5 this function is fulfilled. Four channels are provided to permit one channel in trip or bypass indefinitely and still ensure no single random failure will disable this trip Function.

c. Low Low Pressurizer Level - Containment Isolation and CVCS Isolation (Table 3.3.1-1 Functions 12.a, b)

The Low Low Pressurizer Level trip provides protection for:

Failure of small lines carrying primary coolant outside the containment vessel; Loss-of-coolant accidents outside the containment vessel; and Four Low Low Pressurizer Level Containment Isolation and CVCSI trip channels are required to be OPERABLE when operating in MODES 1, and 2, and MODE 3 when RCS temperature is above the T-2 interlock and CNV level is less than the L-1 interlock. In MODE 3 with RCS temperature below the T-2 interlock, and in MODES 4 and 5, the reactor will remain subcritical.

The Low Low Pressurizer Level CIS and CVCS Isolation trip channels are automatically bypassed when the RCS temperature is below the T-2 interlock or containment water level is above the L-1 interlock. The Low Low Pressurizer Level CIS and CVCS Isolation trip channels are automatically enabled when RCS temperature is above the T-2 interlock and containment water level is below the L-1 interlock. Interlock and permissive setpoints are governed by the Setpoint Program.

4. RCS Hot Temperature Narrow Range RCS Hot Temperature is measured by one resistance temperature detector (RTD) per separation group (a total of four RTDs), located in the RCS flow near the top of the reactor vessel downcomer.

MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-38 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY (continued)

Four Low Main Steam Pressure reactor trip, DWSI, and SSI Trip channels measuring pressure on each steam line are required to be OPERABLE when operating in MODES 1 with RCS temperature above the T-4 interlock. In MODE 1 below the T-4 interlock and in MODE 2 the unit is protected by the Low Low Main Steam Pressure function. In MODES 3, 4, and 5 the reactor is subcritical. Interlock and permissive setpoints are governed by the Setpoint Program.

Four channels are provided to permit one channel in trip or bypass indefinitely and still ensure no single random failure will disable this trip Function.

c. Low Low Main Steam Pressure - Reactor Trip, Demineralized Water System Isolation, and Secondary System Isolation (Table 3.3.1-1 Functions 19.a, b, c)

The Low Low Main Steam Pressure trip provides protection for:

Increase in steam flow; Inadvertent opening of the turbine bypass system; Loss of feedwater flow; Steam system piping failures inside and outside the containment vessel; and Feedwater system pipe breaks inside and outside the containment vessel.

The Low Low Main Steam Pressure trip causes the reactor trip breakers to open and the DWSI and SSI to actuate.

Four Low Low Main Steam Pressure reactor trip channels measuring pressure on each steam line are required to be OPERABLE when operating in MODE 1 and MODES 2 and 3 when capable of withdrawing more than a single CRA. In MODES 2 and 3 with no capability of withdrawing more than one CRA and in MODES 4 and 5 the reactor is subcritical.

MPS Instrumentation B 3.3.1 NuScale US460 B 3.3.1-41 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY (continued)

Four Low Steam Superheat reactor trip, SSI, and DWSI channels are required to be OPERABLE when operating in MODE 1 with both feedwater isolation valves (FWIVs) open. With one or more FWIV closed, the reactor trip, SSI, and DWSI are not needed to mitigate any events.

Four Low Steam Superheat SSI channels are required to be OPERABLE in MODES 2 and 3 with the containment water level below the L-1 interlock, or with both FWIVs open.

In MODES 2, 3, 4, and 5 the reactor is subcritical.

Four channels are provided to permit one channel in trip or bypass indefinitely and still ensure no single random failure will disable this trip Function. Reactor trip and DWSI are automatically bypassed when the V-1 interlock is active (one or more FWIV closed). SSI is automatically bypassed when the V-1 interlock is active (one or more FWIV closed). SSI is also automatically bypassed if containment water level is above the L-1 interlock.

The bypass logic is necessary to permit unit startup without resulting in a Low Main Steam Superheat actuation.

9.

Containment Pressure Narrow Range Containment pressure is measured by four sensors (one per separation group) located near the top of the containment vessel.

a. High Narrow Range Containment Pressure - Reactor Trip, Demineralized Water System Isolation, Containment Isolation, Secondary System Isolation, Decay Heat Removal System Actuation, Pressurizer Heater Trip, and CVCS Isolation (Table 3.3.1-1 Functions 22.a, b, c, d, e, f, g)

The High Containment Pressure trip provides protection for:

System malfunctions that increase the RCS inventory; Inadvertent operation of the ECCS; Loss of containment vacuum; Steam system piping failures inside the containment vessel;

ESFAS Logic and Actuation B 3.3.3 NuScale US460 B 3.3.3-5 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES, LCO, and APPLICABILITY (continued) and 2, and in MODE 3 with the RCS temperature above the T-3 interlock.

9. LTOP Actuation The LTOP is designed to protect the reactor vessel integrity from postulated overpressure events that occur below the nil ductility transition (NDT) temperature below which the fracture toughness of the reactor vessel is reduced. Therefore the system must be OPERABLE in MODE 3 if the reactor coolant is below the NDT as specified in the PTLR and established as the LTOP enable temperature, the (T-1 interlock). Alternatively, the function is satisfied if one RVV is open. In MODES 1 and 2, the reactor vessel temperature is above the NDT temperature and the reactor safety valves provide overpressure protection. In MODE 4 the RVVs are de-energized and open which prevents pressurization of the reactor vessel. In MODE 5 the reactor coolant system is in open contact with the ultimate heat sink and cannot be pressurized.

The ESFAS logic and actuation satisfies Criterion 3 of 10 CFR 50.36(c)(2)(ii).

Operability requirements for manual ESFAS actuation are described in LCO 3.3.4.

ACTIONS When the required ESFAS logic for the Actuation Functions listed in Table 3.3.3-1 are inoperable, the unit is outside the safety analysis, if applicable in the current MODE of operation. Required Actions must be initiated to limit the duration of operation or to place the unit in a MODE or other applicable condition in which the Condition no longer applies.

A Note has been added to the ACTIONS to clarify the application of the Completion Time rules. The Conditions of this Specification may be entered independently for each Actuation Function. The Completion Time for the inoperable Function will be tracked separately for each Function, starting from the time the Condition was entered for that Actuation Function.

RSVs B 3.4.4 NuScale US460 B 3.4.4-1 Draft Revision 2 B 3.4 REACTOR COOLANT SYSTEM (RCS)

B 3.4.4 Reactor Safety Valves (RSVs)

BASES BACKGROUND Two RSVs, in conjunction with the module protection system (MPS),

provide integrated overpressure protection for the RCS. The RSVs are spring operated, self-contained, self-actuating valves located on the reactor pressure vessel head. The RSVs provide overpressure protection based on the ASME Code,Section III pressure limit (ASME pressure limit) of 110% design pressure of RCS (Ref. 1). The RSVs are designed to prevent RCS pressure from exceeding the pressure Safety Limit (SL),

2420 psia. The RSVs also prevent exceeding 110% of Steam Generator System (SGS) design pressure during design basis accidents and anticipated operational occurrences (AOO) that challenge this system.

The lower setpoint RSV is capable of providing the full overpressure protection capacity and the higher setpoint RSV provides defense in depth relieving capacity.

Because the RSVs are self-contained and self-actuating, they are considered independent components. The minimum relief capacity for RSV 1each valve is [84,13,400 lb/hr] at the specified set pressure. The minimum relief capacity for RSV 2 is [87,500 lb/hr] at the specified set pressure. This capacity is based on a postulated overpressure transient of a turbine trip without turbine bypass capability, resulting in rapid decrease in heat removal capability. This event results in the maximum volumetric surge rate into the pressurizer, and defines the minimum volumetric relief capacity for each of the RSVs. An actuation of an RSV is indicated by RSV open position indication and by an increase in containment temperature and pressure because the RSVs discharge into the containment environment.

Overpressure protection is required in MODES 1, 2, and 3; however, in MODE 3 when RCS cold temperature is below the low temperature overpressure protection (LTOP) enable interlock T 1 temperature (T-1 interlock), overpressure protection is provided by operating procedures and by meeting the requirements of the LCO 3.3.1, "Module Protection System (MPS) Instrumentation," LCO 3.3.3, "Engineered Safety Features Actuation System (ESFAS) Logic and Actuation," and LCO 3.4.10, "LTOP Valves." In MODE 4 and MODE 5 with the reactor vessel head on, overpressure protection is provided by the ECCS reactor vent valves being isolated electrically from their controls causing them to open.

RSVs B 3.4.4 NuScale US460 B 3.4.4-3 Draft Revision 2 BASES APPLICABLE SAFETY ANALYSES (Continued)

Detailed analyses of the above transients are contained in Reference 2.

Compliance with this LCO is consistent with the design bases and accident analyses assumptions.

RSVs satisfy Criterion 3 of 10 CFR 50.36(c)(2)(ii).

LCO The setpoint of the two RSVs are established to ensure that the ASME pressure limit is satisfied. The ASME Code specifications require the lowest safety valve setpoint to be at or below vessel design pressure and the highest safety valve to be set so that the total accumulated pressure does not exceed 110% of the design pressure for overpressurization conditions. The upper and lower pressure limits are based on the +/- 1%

tolerance requirements for lifting pressures above 1000 psig (Ref. 1).

As-found acceptance criteria of +/- 3% meets the criteria of ASME OM code I-1320(c)(1) (Ref. 3).

The limits protected by this Specification are the reactor coolant pressure boundary (RCPB) SL of 110% of design pressure and 110% of external design pressure for the SGS. Inoperability of both RSVs could result in exceeding the reactor pressure SL or the 110% design pressure limit of the SGS, if a transient were to occur. The consequences of exceeding the ASME pressure limit could include damage to one or more RCS components, damage to the SGS components, increased leakage, or additional stress analysis being required prior to resumption of reactor operation.

APPLICABILITY In MODES 1, 2, and MODE 3 when RCS cold temperature is greater than the LTOP enable interlock T-1 temperature (T-1 interlock) specified in the Pressure and Temperature Limits Report (PTLR), the RSVs are required because the RCS and SGS are pressurized and limiting design basis overpressure transients are postulated to occur in MODES 1 and 2.

MODE 3 conditions are conservatively included although the FSAR Chapter 15 (Ref. 2) listed accidents and AOOs may not require the RSVs for protection. RCS cold temperature is considered to be greater than the LTOP enable temperature (T-1 interlock)enabling interlock T 1 temperature when three out of four RCS cold temperature instruments indicate greater than the LTOP enableing temperature specified in the PTLR. The T-1 interlock is described further in the Bases for LCO 3.3.1.

RSVs B 3.4.4 NuScale US460 B 3.4.4-4 Draft Revision 2 BASES APPLICABILITY (Continued)

The LCO is not applicable in MODE 3 when RCS cold temperature is below the LTOP enable temperature because overpressure protection is ensured by LCO 3.3.1, "MPS Instrumentation," LCO 3.3.3, "ESFAS Logic and Actuation," and LCO 3.4.10, "LTOP Valves." In MODES 4 and 5, overpressure events are precluded by open ECCS reactor vent valves providing a relief path from the RCS to the containment and isolation of the module from credible sources of system overpressure (e.g., CVCS injection and pressurizer heaters).

ACTIONS A.1 With one RSV inoperable, the remaining OPERABLE RSV is capable of providing the necessary overpressure protection. Because of additional design margin, the ASME pressure limit for the RCPB and SGS can also be satisfied with one RSV inoperable. However, the overall reliability of the pressure relief system is reduced because additional failure of the remaining OPERABLE RSV could result in failure to adequately relieve primary or secondary system pressure during a limiting event. For this reason, continued operation is permitted for a limited time only.

The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Completion Time to restore the inoperable RSV to OPERABLE status is based on the relief capability of the remaining RSV and the low probability of an event requiring RSV actuation.

B.1 and B.2 If the Required Action of Condition A cannot be met within the required Completion Time or if two RSVs are inoperable, the unit must be placed in a MODE in which the requirement does not apply. To achieve this status, the unit must be brought to at least MODE 2 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and to MODE 3 with RCS cold temperature below the LTOP enable interlock T-1 temperature (T-1 interlock) within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. RCS cold temperature is considered below the LTOP enableing temperature when two or more RCS cold temperature instruments indicate below the LTOP enableing temperature specified in the PTLR.

The allowed Completion Times are reasonable based on time to reach the required unit conditions from full power conditions in an orderly manner. The change from MODE 1, or 2, to MODE 3 reduces the RCS energy (core power and pressure), lowers the potential for large pressurizer in-surges, and thereby removes the need for overpressure protection by the RSVs.

LTOP Valves B 3.4.10 NuScale US460 B 3.4.10-2 Draft Revision 2 BASES APPLICABLE Safety analyses (Ref. 3) demonstrate that the reactor vessel is SAFETY adequately protected against exceeding the Reference 1 P/T limits.

ANALYSES In MODES 1 and 2, and MODE 3 with RCS cold temperature exceeding LTOP enable temperature (T-1 interlock) specified in the PTLR (T-1), the reactor safety valves will prevent RCS pressure from exceeding the Reference 1 limits. Below the T-1 interlock temperature specified in the PTLR, overpressure prevention falls to two OPERABLE or one open ECCS RVV.

The PTLR contains the acceptance limits that define the LTOP requirements including the setpoint for the T 1 LTOP enable T-1 interlock.

Any change to the RCS must be evaluated against the Reference 3 analyses to determine the impact of the change on the LTOP acceptance limits.

Transients that are capable of overpressurizing the RCS are categorized as either mass or heat input transients, examples of which follow:

a. Inadvertent operation of the module heatup system,
b. Excessive CVCS makeup, or
c. Spurious actuation of the pressurizer heaters.

The Reference 3 analyses demonstrate that one open RVV can maintain RCS pressure below limits. Thus, the LCO requires each closed RVV to be OPERABLE or one RVV open during the conditions when a low temperature overpressure condition could occur.

Fracture mechanics analyses established the temperature of LTOP Applicability at the LTOP enableing T-1 interlock specified in the PTLR.

The fracture mechanics analyses show that the vessel is protected when the RVVs are set to open at or below the limit shown in the PTLR. The setpoints are derived by analyses that model the performance of the MPS instrumentation and actuation and the RVVs assuming the limiting low temperature overpressure transient of spurious actuation of the pressurizer heaters in the RCS. These analyses consider pressure overshoot resulting from signal processing and valve stroke times. The LTOP setpoints at or below the derived limit ensures the Reference 1 P/T limits will be met.

The MPS setpoints in the PTLR will be updated when the revised P/T limits conflict with the LTOP analysis limits. The Bases for LCO 3.4.3, RCS Pressure and Temperature (P/T) Limits, discuss these updates.

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