HITACHI GE Hitachi Nuclear Energy

Richard E. KingstonVice President, ESBWR Licensing

P.O. Box 7803901 Castle Hayne Road, M/C A-55Wilmington, NC 28402 USA

T 910.819.6192F 910.362.6192rick.kingston@ge.com

MFN 08-939 Docket No. 52-010

December 5, 2008

U.S. Nuclear Regulatory CommissionDocument Control DeskWashington, D.C. 20555-0001

Subject: Response to Portion of NRC Request for Additional InformationLetter No. 243 Related to the Design Control Document (DCD)Revision 5 - Safety Analyses - RAI Numbers 15.2-14 S01 and15.2-41

The purpose of this letter is to submit the GE Hitachi Nuclear Energy (GEH)responses to the U.S. Nuclear Regulatory Commission (NRC) Request forAdditional Information (RAI) sent by NRC letter No. 243 (Reference 1). GEHresponses to RAI Numbers 15.2-14 S01 and 15.2-41 are addressed in Enclosure1. DCD markups associated with the response to RAI 15.2-41 are provided inEnclosure 2.

If you have any questions or require additional information, please contact me.

Sincerely,

Richard E. KingstonVice President, ESBWR Licensing

MFN 08-939Page 2 of 2

Reference:

1. MFN 08-689, Letter from U.S. Nuclear Regulatory Commission to Robert E.Brown, GEH, Request For Additional Information Letter No. 243 Related ToDesign Control Document (DCD) Revision 5, dated September 4, 2008

Enclosures:

1. Response to Portion of NRC Request for Additional Information Letter No.243 Related to Design Control Document (DCD) Revision 5 - SafetyAnalyses - RAI Numbers 15.2-14 S01 and 15.2-41

2. MFN 08-939 RAI Number 15.2-41 DCD Markups

cc: AE CubbageRE BrownDH HindseDRFs

USNRC (with enclosures)GEH/Wilmington (with enclosures)GEH/Wilmington (with enclosures)0000-0088-0199 R1 for RAI 15.2-14 S010000-0092-5271 for RAI 15.2-41

Enclosure 1

MFN 08-939

Response to Portion of NRC Request forAdditional Information Letter No. 24.3

Related to Design Control Document (DCD) Revision 5

Safety Analyses

RAI Numbers 15.2-14 S01 and 15.2-41

MFN 08-939Enclosure 1 Page 1 of 10

NRC RAI 15.2-14 S01:

Provide the results of a bounding sensitivity analysis whereby the bounding sensitivityload rejection with bypass valve (LRWBP) event analysis is run from the limiting statepoint in the operating domain for the initial core using a constant feedwater temperature(FWT) boundary condition.

The results provided should include the sequence of events and transient plots similarto those provided for the analysis documented in NEDO-33338.

Background: For the LRWBP event the select rod insertion (SRI) mitigates the event byinserting rods in SRI groups to maintain low reactor power. The staff notes that theanalysis accounts for the reduction in FWT. GEH's response to the RAI states thatfeedwater temperature control (FWTC) would respond by maintaining or slowing therate of reduction in FWT thus mitigating the event.

However, the staff is concerned about the transient varying axial power shape (TVAPS)effect. The TVAPS phenomenon is a flow reduction effect. As the SRI groups insert,power is suppressed in the bottom portions of the core resulting in a reduction in theflow as the liquid water occupies the collapsed regions. As the flow traverses thereactor core it gains enthalpy and may result in critical heat flux conditions at the top ofthe core. While the staff agrees that the higher FWT (postulated under conditionswhere the FWTC is maintaining the FWT) may aid in the effectiveness of the reductionin gross core power during the SRI, the staff is concerned that the TVAPS effect may beexacerbated during the SRI if the FWT is maintained at a higher temperature during thetransient (thus a higher predicted flow quality during the SRI group insertions on abundle basis). TRACG04 has the capability to explicitly model the TVAPSphenomenon. The staff expects that the results of this sensitivity analysis would bebounding as the extraction is not modeled, thus maintaining the maximumpressurization and the FWT is held constant, thus treating the FWTC as instantaneousand the 7FWH/FWH bypass system as having an infinite capacity.

GEH Response:1. The analysis for the Generator Load Rejection with Turbine Bypass (LRWBP)

event as documented in NEDO-33338 Rev 0 (Reference 1) at SP2 (the limitingstatepoint) conditions (85% power, 4860F feedwater temperature) wasrecalculated with the same conditions, TRACG code version, and inputs with theonly exception of maintaining the feedwater temperature constant. Table 15.2-14-S0l-1 shows sequence of events for this event (Compare with Table 2.3-7 ofReference 1). Figures 15.2-14 S01-1a through lh show the results of thisanalysis (compare with Figures 2.3-3a through 2.3-3h of Reference 1).

A comparison of the subcooling plots between the two cases (see Figure 15.2-14-S0l-2) shows that there is no significant difference in inlet subcooling for almost 30 secondsbecause of the time it takes for the feedwater to enter into the core. Before this time,there is no appreciable difference between the two cases. The minimum CPR occurs

MFN 08-939Enclosure 1 Page 2 of 10

within the first 5 seconds; therefore, there is no difference in the ACPR/ICPR betweenthe two cases. The CPR for the constant-FWT case improves relative to the originalcase after about 36 seconds.

The TRACG model used for this RAI response is identical to the one used in NEDO-33338 Rev 0 (Reference 1) with the exception of feedwater temperature so that a clearcomparison can be made. Modeling that includes the updated channel pressure drop isnot considered in these analyses. Because core flows are very similar for the twoperformed cases (near 100%), the effect of the updated channel pressure drop on boththe original and constant FWT cases would not change the conclusion of this response.

References:

(1) GE Hitachi Nuclear Energy "ESBWR Feedwater Temperature Operating DomainTransient and Accident Analysis," NEDO-33338 (CLASS I) Revision 0, October2007.

DCD or LTR Impact:

No DCD changes will be made in response to this RAI.

No changes to the subject LTR will be made in response to this RAI.

MFN 08-939Enclosure I Page 3 of 10

Table 15.2-14-S01-1

Sequence of Events for Generator Load Rejection with Turbine Bypass

Time (s) Event

-0.015 Turbine-generator detection of loss of electrical load.

0.0 Turbine-generator load rejection sensing devices trip to initiateTCVs fast closure and main turbine bypass system operation.

0.02 Turbine bypass valves start to open.

0.06 Turbine control valves closed.

0.18 Turbine bypass opened at 80%.

0.20 SCRRI activated (no SCRRI rods assigned for this analysis.)

1.0 First SRI group inserts (one HCU, 2 control rods, fails to actuate).

10.0 Second SRI group inserts.

15.0 Third SRI group inserts.

25.0 Fourth SRI group inserts.

30.0 Fifth SRI group inserts.

35.0 Sixth SRI group inserts.

-40.0 Steam flow below 60% of rated.

-40.0 Core power reaches 50%.

0.0-400.0 FW temperature is constant.

-150 New steady state is established.

MFN 08-939Enclosure 1 Page 4 of 10

0 50 100 150 200 250 300 350 400 450

Time (sec)

Figure 15.2-14-SO0-la. Generator Load Rejection with Turbine Bypass - Constant FWT

Proc.ID:3470947627-Oct-2008 8:52:59

I L

90

80

70,L

E •a 60

250

~40

30

20

-m- SRV Flow (%)IC Steam Flow (%)

-- High Pressure CRD Flow (%)-4-- Bypass Valve Flow (%)--- IC Drainage Flow in Tank (%)

IC Drainage Flow in Vessel (%)

10

0 Irn . W _I0 50 100 150 200 250

Time (sec)

300 350 400 450

Figure 15.2-14-SO1-1 b. Generator Load Rejection with Turbine Bypass - Constant FWT

MFN 08-939Enclosure 1 Page 5 of 10

,F?8in5MP9165

15

14I-

0

1 3

j12

11

10

-- 1 1 1 I1

\"4-4-- NR Sensed Level above TAF

--- WR Sensed Level above TAFA Twv Phase Level above TAF

-.. LI Setpoint over TAF

- - - L2 Setpoint over TAF

.... L3 Setpoint over TAF

-- -- -- -- - L8 Setpoint over TAF1" -r k

0 50 100 150 200 250 300 350 400 450

Time (sec)

Figure 15.2-14-SOI-1c. Generator Load Rejection with Turbine Bypass - Constant FWT

Proc.ID:3470947E27-Oct-2008 8:52

9 0E+06

8.5E+06

8.0E+06

eL 7 5E+06E0

70OE+06

6.5E+06

6.OE+06

5.5E+06

I

____________ ____________ ____________ ____________ I ____________ I=i

- Dome Pressure (Pa)

- Steam Line Pressure (Pa)

TCV Pressure (Pa)

-+---Vessel Bottom Pressure (Pa)

...... SRV Opening Setpoint (Pa)

- - - - High Pressure SCRAM Setpoint (Pa)

- - - Low Steam Line Pressure Setpoint (Pa)

p - . -4---.

5.0E+06

0 50 100 150 200 250 300 350 400 450

Time (sec)

Figure 15.2-14-SO1-1d. Generator Load Rejection with Turbine Bypass - Constant FWT

MFN 08-939Enclosure 1 Page 6 of 10

W'-2NW593

2

U

-2

-3

Time (sec)

Figure 15.2-14-SOI-le. Generator Load Rejection with Turbine Bypass - Constant FWT

0.35

0.25

0.25

0.

U-Control Fraction

fi A , %I ; C ;

900

800

700

600

500

400 •

200

100

I I i i 030 35 40 45 500 5 10 15 20 25

Time (sec)

Figure 15.2-14-S01-1f. Generator Load Rejection with Turbine Bypass - Constant FWT

MFN 08-939Enclosure 1 Page 7 of 10

Proc IDT3470947627-Oct-2008- 5259

2.3

2.2

2.1

2.0

. 91,9

o 1.8

S1.7

1.6

1.5

1.4

1.3

2420 ---v-- 2418

---- 2400 -- 2404

--0• 2422 ---- 2416

- 2410 - 2402

2428 2426 1

2412 2406

.2430 -- 2424

2414 - 2408

- _MCPR-!1IO(T) -4---_MCPR-140(T)

_MCPR-210(T) -- *---_MCPR-2400(2)0 50 100 -_ .... 250 3M0 350

Time (sec)

Figure 15.2-14-SO1-1g. Generator Load Rejection with Turbine Bypass - Constant FWT

Proc.lD :3470947627-Oct-2008 8:52:59

1.OE+01

9.OE+00

8.OE+00

7.OE+00

- 60OE+00

8 5.OE+00

4.0 E+00

2 OE+00

1.OE+00

0.0E+00

_ _ _ 6.0E+02

7 5. 0E +02

'A4Cl , e ).0E+02

-3.0E+02

.. ~2.0E+02 ,

*--Subcooling Cell 1 Level 3 (K)-'/--Subcooling Cell 7, Level 3 (K)*----Subcooling Cell 5, Level 3 (K) 1.0E+02"'-Subcooling Cell 11, Level 3 (K)

-'Feed Water Temperature (K)-Temperature FW in vessel (K)

0 o.OE+00

300 350 400 45050 100 150 200 250

Time (sec)

Figure 15.2-14-S01 -1 h. Generator Load Rejection with Turbine Bypass - Constant FWT

MFN 08-939Enclosure 1 Page 8 of 10

Figure 15.2-14-SO1-2. Generator Load Rejection with Turbine Bypass -Subcooling & CPR Comparison with and without Constant FWT.

Subcooling, Cell 7, Level 3 (constant FW case)Subcooling, Cell 7, Level 3 (original case)CPR-limiting channel 2400 (constant FW case)CPR-limiting channel 2400 (original case)

10.0 2.5

9.0 2.4

8.0 2.3__

7.0 2.26.0 2.150 ý-• . ... ....• :. 2.0 I

504.0 1.9

C) 3.0 1.8

1.0 1.6

0.0 ,1.5

0 10 20 30 40 50

Time (Sec)

MFN 08-939Enclosure 1 Page 9 of 10

NRC RAI 15.2-41:

DCD Rev. 5, Section 15.2.2.5, discusses the transient, Turbine Trip with a SingleFailure in the Turbine Bypass System. Fig. 15.2-7 is Bypass System terminated at 10seconds into the transient. At this time the feedwater flow is about 150% of normal,while the reactor vessel water level keeps going down. Table 15.2-11 notes (long termunspecified time) CRD activation to recover level. At this time the vessel void hascollapsed (as indicated by the reactivity change Fig. 15.2-7e) and feedwater flow shouldreturn to normal. Vessel steam flow reduces to zero at 10 seconds, Fig. 15.2-7d.Section 15.2.2.5.2 states that no operator action is required to mitigate the transient. Ifthe above condition continues in a very short amount of time, the water level will reachthe main steam line level but the operator is instructed not to take any action. RequestGEH extend this transient until the feedwater flow and the vessel water level have beenstabilized. Then, consider instructions to the operator.

GEH Response:

DCD Revision 5, Chapter 15.2, Table 15.2-11 incorrectly states that L2 is reached andthat HP CRD is activated to recover the level. The reference to CRD in the table wasinadvertently retained from a previous revision and will be removed in the next revisionof the DCD.

DCD Revision 5, Subsection 15.2.2.5, the Turbine Trip with a Single Failure in theTurbine Bypass System describes the event as similar to the Generator Load Rejectionwith a Single Failure in the Turbine Bypass System. The event diagrams of Figures15.1-5 and 15.1-7 are identical. The sequence of events in Tables 15.2-9 and 15.2-11for the two events are similar, including the fact that L2'is not reached.

Given the similarities in the events, the DCD provides display of both the long-term (50seconds) stable conditions in the Generator Load Rejection with a Single Failure in theTurbine Bypass System, as well as the higher resolution of short term transient (10seconds) for Turbine Trip With a Single Failure in the Turbine Bypass System withoutunnecessary duplication. A comparison of the short-term event response in Figure15.2-7 with the similar time period in the long-term response curve in 15.2-5 showsclose correlation in that time frame. As indicated in the long term plot, feedwater flowremains high until feedwater flow is reduced by the setpoint setdown feature describedin DCD Subsection 1.2.2.2.3, Feedwater Control System, designed to preventexceeding L8 following a scram without operator action. A clarifying statement will beadded to the results section of DCD Subsection 15.2.2.5.3 Core and SystemPerformance referencing Figure 15.2-5 series for long-term response.

MFN 08-939Enclosure 1 Page 10 of 10

DCD Impact:

DCD Table 15.2-11 will be changed to remove the following "(1) L2 is reached and HPCRD is activated to recover the level".

DCD Subsection 15.2.2.5.3 Core and System Performance will be changed to refer toFigure 15.2-5 series for long-term response.

Enclosure 2

MFN 08-939

RAI 15.2-41 DCD Markups

26A6642BP Rev. 06ESBWR Design Control Document/Tier 2

Results

A turbine trip, assuming only 50% of the total turbine steam bypass capacity available, issimulated at rated power conditions as shown in Figure 15.2-7. Figure 15.2-7 presents trendresults for the first 10 seconds. Longer term results of a similar event, turbine generator loadreiection with a single failure in the bypass system, are shown in Figure 15.2-5. Table 15.2-4asummarizes the analysis results. The neutron flux increases rapidly because of the voidreduction caused by the pressure increase. However, the flux increase is limited by the partialactuation of the steam bypass system and the initiation of reactor scram. The peak simulatedthermal power does not significantly increase (< 10%) above its initial value. The number ofrods in boiling transition during this event remains within the acceptance criterion for AOOs incombination with an additional single active component failure or operator error. This event issimilar to the generator load rejection with a single failure in the turbine bypass system and doesnot need to be evaluated each fuel cycle.

15.2.2.5.4 Barrier Performance

Peak pressure at the SRVs is below the SRV setpoint. Therefore, there is no steam discharged tothe suppression pool. The peak pressure at the vessel bottom remains below the upset pressurelimit.

15.2.2.5.5 Radiological Consequences

Because this event does not result in any fuel failures or any release of primary coolant to theenvironment, there is no radiological consequence associated with this event.

15.2.2.6 Closure of One Main Sleamline Isolation Valve

15.2.2.6.1 Identification of Causes

Protection system logic permits the test closure of one MSIV without initiating scram from theposition switches. An inadvertent closure of one MSIV may cause an immediate closure of allother MSIVs, depending on reactor conditions. Closure of all MSIVs is discussed inSubsection 15.2.2.7.

15.2.2.6.2 Sequence of Events and Systems Operation

When a single MSIV is closed in conformance with normal testing procedures, no reactor scramoccurs and the reactor settles into a new steady state operating condition. Closure of a singleMSIV at power levels above those of the normal testing procedure may cause closure of all otherMSIVs. There is no operator action required to mitigate the event.

Table 15.2-12 lists the sequence of events for Figure 15.2-8.

15.2.2.6.3 Core and System Performance

The neutron flux increases slightly while the simulated thermal power shows no increase. Thenumber of rods in boiling transition during this event remains within the acceptance criterioni forAOOs. The effects of closure of a single MSIV are considerably milder than the effects ofclosure of all MSIVs. Therefore, this event does not need to be reanalyzed for any specific coreconfiguration.

15.2-10

26A6642BP Rev. 06ESBWR Design Control Document/Tier 2

Table 15.2-11

Sequence of Events for Turbine Trip with a Single Failure in the Turbine Bypass

System

Time (s) Event *

0.0 Turbine trip initiates closure of main stop valves.

0.0 Turbine trip initiates bypass operation.

Turbine bypass valves start to open to regulate pressure (Half fail toopen).

0.1 Turbine stop valves closed.

Not enough turbine bypass availability is detected and the plant isscrammed

0.45 Control Rods begin to enter in the core.

L2 is not reached, new steady state (1) L2 is reaced and HP CRD-iLong term ,a•ivated to r.eover. the lev..

• See Figure 15.2-7.

15.2-39