NSD-NRC-98-5596, Forwards Westinghouse Responses to FSER Open Items on AP600. Summary of Encl Responses Provided in Table 1.NRC Should Review Encls & Inform Westinghouse of Status to Be Designated in NRC Status Column of Oits

Forwards Westinghouse Responses to FSER Open Items on AP600. Summary of Encl Responses Provided in Table 1.NRC Should Review Encls & Inform Westinghouse of Status to Be Designated in NRC Status Column of Oits

ML20217N457
Person / Time
Site:	05200003
Issue date:	03/02/1998
From:	Mcintyre B WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:	Quay T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NSD-NRC-98-5596, NUDOCS 9803090027
Download: ML20217N457 (13)

Text

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gm Westinghouse Energy Systems hx 355 Pmsburgh Pennsylvania 15230-0355 Electric Corporation -

DCP/NRC1278 NSD-NRC-98-5596 Docket No.: 52-003

. March 2,1998 Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION: T. R. QUAY

SUBJECT:

AP600 RESPONSE TO FSER OPEN ITEMS

Dear Mr. Quay:

Enclosed with this letter are the Westinghouse responses to FSER open items on the AP600. A summary of the enclosed responses is provided in Table 1. Included in the table is tne FSER open item number, the associated OITS number, and the status to be designated in the Westinghouse status I column of OITS.

The NRC should review the enclosures and inform ?,estinghouse of the status to be designated in the "NRC Status" column of OITS.

f Please contact me on (412) 374-4334 if you have any questions concerning this transmittal.

A!

Brian A. McIntyre, Manager .

Advanced Plant Safety and Licensing jml 1

Enclosures l I

r cc: W. C. Iluffman, NRC (Enclosures) ,y J. E. Lyons, NRC (Enclosures)

T. J. Kenyon, NRC (Enclosures) M I J. M. Sebrosky, NRC (Enclosures)

D. C. Scaletti, NRC (Enclosures) I N. J. Liparulo, Westinghouse (w/o Enclosures)

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. DCP/NRCl278 i NSD-NRC-98-5596 March 2,1998 Table 1 I List of FSER Open Items Included in Letter DCP/NRC1278 FSER Open Item OITS Number Westinghouse status in OITS 9.5.1-2 6619 Confirm W 9.5.1-3 6620 Confirm W ,

I 440.761F 6352 Action N  !

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1 Enclosure to Westinghouse Letter DCP/NRCl278 March 2,1998 I

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l NAC FSER OPEN ITEM i

l FSER Open item 9.5.12 (OITS 6619)

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1 The applicant has included the reactor head vents for consideration as a high/ low pressure interface in accordance j with the guidance provided in Generic Letter (GL) 81-12. However, only the power circuits inside containment have j been adequately protected from a hot short to prevent a spurious actuation. The applicant has not provided a i discussion of the protection provided for the power and control circuits located outside the containment, which can also result is a spurious actuation of the reactor head vents. Therefore, the applicants resolution of this issue is unacceptable. ,

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Response

We agree tFat the protection of head vent valve power and control circuits outside containment was not fully addressed in our previous response. We will add the following additional information to the SSAR. The red-line and strike-out changes shown include those previously submitted in response to FSER Open item 280.34F.

SSAR Revision:

The Reactor Coolant System Reactor Vessel Head Vent Valve Actuation subsection of SSAR Section 9.A.3.7.1.1 will be revised as shown below:

Reactor Coolant System Reactor Vessel llead Vent Valve Actuation The+eae:: : cr'"-'sys:e:n-reae:; ve: sd head ven: :dve:: a re: ec' ;idered :0 he high 'e ; pre:r :re i ::erfaee

• • When pastulating-ymrimeHee49atic- fr"^ "ng F , ne reae:c c=!=: sys ::r head ven* ".'ves diwharge-4e-the-in-contair nen: refue"ng "^';- N age :=h. Since reae:; c=!=: sys'e- head ven- 've twfuation ca m: d:anage a !c pressure sys:c:: and 4nce 'he sys:e:r . en:irely-within ec-> :inment-the

e depres:u-it ::= ::y:::e:r: /n!ves de -: repre en" Sigh !c pressure i->erfae : : descriNd i- NRG Genene Le: er S! !2.

The reactor vessel head vent valves are connected to the reactor vessel head and discharge to the IRHST. The head vent valves are not required to operatefollowing afre. There arefour head vent valves arrangedin two flow paths with two series valves in each path. One head vent valve is assigned to each of thefour Class !E electricaldivisions. The head vent valves arefail-closeddc-poweredsolenoid valves, and each valve ispo wered by a separate; safety relatedpower supply as shown on Table 9A 2. In the event that a spurious signal were to open a head vent valve, the flow path is blocked by the closed series head vent valve. In areas outside containment, the controlroom, andthe renwte shindo wn workstation; the po wer and controlcircuitsfor thefour l valves are routed in separate fre areas.

FSER Open item 9.5.1-2 -- 1 W- WestinEhouse

a NRC FSER OPEN ITEM inside cordainmert, the cables for the costrvi of one head vert valve in each pow path is enclosed in steel conduit up to the valve to prevent apre inside cordairunertfrom spuriously actuating two head vert ralves in y onepow path.

There are nofeatwes ofthe control systemfor autonatic opening ofthe head vert valves. Norrrelly, the head vert valves are trannally opened using sop cortrols in the controlroom orat the remote shutdown workstation.

These sop cortrols use encoded messages (nadtiple.ning) to cornmunicate with thefow divisionalI&C rooms.

There are no gre-irulucedfailwe modes ofsop controls that wil! lead to spurious actuation ofthe head vert ralres.

The head vent valves are also controlled from dedicated switches mounted on the dedicated safety panels in the control room. Each dedicated safety panel contains a switch for controlling each head vent valve (4 switches per panel). Each switch is a three-pasition, hold-in-position switch (open-neutral-close). If both switches are in the neutral position, soft control of the valve from the operator's console is allowed. If both switches are in the open position the valve will open. Either switch in the close position will close the valve.

If one switch is in neutral position and one in the open position, the valve will hold its previous position but soft control is defeated. The control circuitsfor opening the head rent valvesfrem the dedicated switches are two-pole, energize-to-actuate, dc circuits. During a fire, switches on one panel may be shorted but none of the l

head vent valves will he opened because the switches on the other panel will be deactivated before the fire- j shorts them.

l Therefore, a singlepre is not postulated to restat in an uncortrolled head vert actuation.

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l FSER Open item 9.5.1-2 -- 2 W-Westinghouse

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! NRC FSER OPEN ITEM i=

FSER Open Item 9.5.13 (OITS 6620)

Re:

The spurious actuation of ADS due to hot shorts of control circuits of motor operated valves from a fire in the remote shutdown workstation, DC equipment rooms, and Class IE penetration rooms has not been adequately addressed in the SSAR by the applicant. Spurious actuation of ADS results in a venting of the RCS in conflict with the fire protection of safe shutdown capability acceptance criteria specified above for the AP600. Therefore the applicants resolution of this issue is unacceptable.

Response

We agree to make the following SSAR revisions to address the protection of control circuits of motor operated valves from a fire in the remote shutdown workstation, DC equipinent rooms, and Class IE penetration rooms.

The issue of smoke control between the I&C rooms and the de equipment rooms will be addressed in our response to FSER Open Item 9.5.1-4 as part of our overall smoke control response.

SSAR Revision:

The fifth paragraph of SSAR Section 9.5.1.8. proposed in response to FSER Open Item 280.35F. will be revised as shown below:

The Combined License applicant will provide an analysis that demonstrates that operator actions which prevent irinimite the pmbability of the potential for spurious ADS actuation as a result of a fire can be accomplished within 30 minutes following detection of the fire.

The last subsection of SSAR 9A.2.7.1 on page 9A-8&9 will be revised as follows:

Spurious Actuation of Equipment Fire-caused damage is assumed to be capable of restilting in the following types of circuit faults: hot shorts, open circuits, and shorts to ground. Spurious actuation of componunts caused by these circuit faults are evaluated. Components are assumed to be energized or de-energized by one or more of the above circuit faults.

For example, air operated and solenoid operated valves are assumed to fail open or closed: pumps are assumed to fait running or not running; electrical distribution breakers could fail open or closed. For three-phase ac circuits, the probability of getting a hot short on all three phases in the proper sequence to cause spurious operation of a motor is considered sufficiently low as to not require evaluation, except for cases involving high-low pressure interfaces. For ungrounded de circuits, if spurious operation could only occur as a result of two unprounded hot shorts of the proper polarity, then no further evaluation is necessary, except for any cases t

l FSER Open item 9.5.1-3 -- 1 W Westinghouse

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NRC FSER OPEN ITEM involving a high-low pressure interface. Therefore, spurious operation of ac or de motor operated valves as a ,

result of power cable hot shorts is not assumed, except for cases involving a high-low pressure interface. J lt is assumed that a tire results in the loss of all automatic function (signals and logic) from the circuits located in the fire area, in conjunction with one worst case spurious actuation or signal resulting from the fire.

Spurious actuation of the redundant valves in any one high-low pressure interface line are postulated if the i circuits for those valves are located in the fire area.

Most control room controls use soft-controls which communicate over multiplexed data channels. There are nofre-inducedfailure modes ofsop controls that willleadto spurious actuation ofequdpment. Fire-induced spurious actuation from these multiplexed soft controls is not ==cd credible.

l 'lle probability ofsSpurious actuation from control room dedicated switches which could lead to a breach of reactor coolant system pressure boundary, loss of decay heat removal function, or loss of shutdown reactivity l control is prevented-minimized by the use of dual two-pole, energize-to-actuate, ungrounded de circuits, which require at least four simultaneous hot shons of proper polarity for spurious actuation. In the event of a fire in the main control room, control may be transferred to the remote shutdown workstation, depending on the extent of the fire. For a small fire which can be quickly extinguished, control is maintained in the main control room, and the potential for damage or spurious signals is limited. For larger postulated fires, the mair control room is evacuated and control is transferred to the remote shutdown workstation. Once control is transferred, the dedicated switches in the main control room are disabled by a transfer switch.

l The probability of sSpurious actuation of squib valves is fweven:cd dninized by the use of a squib valve controller circuit which requires multiple hot shons for actuation, physical separation of potential hot short locations, and provisions for operator action to remove power from the fire zone. No postulated fire can spread to the hot short locations before the operator can remove power from the fire zone.

Automatic depressurization system stages 1,2, and 3 consist of parallel paths, each path having two motor-l operated valves in series. The probability ofsspurious stage I,2, or 3 actuation is preve~cd mininized by the use of physical separation of control circuits for the two series valves and provisions for operator action to remove power from the fire zone. No postulated fire can spread to the hot short locations before the operator can remove power from the fire zone.

The fourth, lifth, and sixth paragraphs on page 9A-39 (Division A I&C and equipment rooms) will be revised as follows:

I The probability ofsSpurious actuation from control room dedicated switches which could lead to a breach of reactor coolant system pressure boundary, loss of decay heat removal function. or loss of shutdown reactivity l control is pden cd minimized by the use of dual two-pole, energize-to-actuate, ungrounded de circuits, which require at least four simultaneous hot shorts of proper polarity for spurious actuation.

l Following detection of a fire in the instrumentation and control room, the operators ean-shall close the automatic depressurizatior, system stage 4 block valve, then remove actuation power from this division using FSER Open item 9.5.1-3 -- 2 W-Westinghouse

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• NRC FSER OPEN ITEM

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the battery transfer switch located in the de equipment room to disconnect the battery and remote control from the control room to remove input power from the battery charger and regulating transformer. His operator l action will gevem-preclude spurious actuation of motor operated valves and squib valves resulting from multiple hot shorts in the instrumentation and control room.

Following detection of a fire in the de equipment control room, the operators can close the automatic depressurization system stage 4 block valve, then remove cabinet power from this division using the input l power switches on the instrumentation and control cabinets. This operator action will pevem-preclude spurious smoke-induced actuation of motor operated valves and squib valves resulting smoke-related integrated circuit failures in the instrumentation and control room.

The third paragraph on page 9A-41 (Division A penetration room) will be revised as follows:

l Following detection of a fire in this fire area, the operators enn-shallclose the automatic depressurization system stage 4 block valve, then remove actuation power from this division using the battery tnmsfer switch located in the de equipment room to disconnect the battery and remote control from the control room to remove input l att from the battery charger and regulating transformer. His operator action will geve,% preclude spurious m tuation of motor operated valves and squib valves resulting from multiple hot shorts in the penetration room.

The fifth, sixth, and seventh paragraphs on page 9A-43 (Division B I&C/ penetration and equipment rooms) will be revised as follows:

l The probability of sSpurious actuation from control room dedicated switches which could lead to a breach of reactor coolant system pressure boundary, loss of decay heat removal function, or loss of shutdown reactivity l control is p=en:cd rdnimited by the use of dual two-pole, energize-to-actuate, ungrounded de circuits, which require at least four simultaneous hot shorts of proper polarity for spurious actuation.

l Following detection of a fire in the instrumentation and control / penetration room, the operators em-shall close the automatic depressurization system stage 4 block valve, then remove actuation power from this division using the battery transfer switch located in the de equipment room to disconnect the battery and remote control from the control room to remove input power from the battery charger and regulating transformer. This operator j action will gevem-preclude spurious actuation of motor operated valves and squib valves resulting from multiple hot shorts in the instrumentation and control room.

Following detection of a fire in the de equipment control room the operators can close the automatic depressurization system stage 4 block valve, then remove cabinet power from this division using the input l power switches on the instrumentation and control cabinets. His operator action will pevem-preclude spurious smoke-induced actuation of motor operated valves and squib valves resulting smoke-related integrated circuit failures in the,iastrumentation and control room.

The second, third and fourth paragraphs on page 9A-48 (Division C 1&C. penetration and equipment rooms) will be revised as follows:

FSER Open item 9,5.1-3 -- 3 W Westinghouse

o NRC FSER OPEN ITEM l The probability of SSpurious actuation from control room dedicated switches which could lead to a hreach of reactor coolant system pressure boundary, loss of decay heat removal function, or loss of shutdown reactivity l control is prevemed-rrinitri:ed by the use of dual two-pole, energize-to-actuate, ungrounded de circuits, which require at least four simultaneous hot shorts of proper polarity for spurious actuation.

Following detection of a fire in either the instrumentation and control room or the instrumentation and l control / division C penetration room, the operators eamshall close the automatic depressurization system stage 4 block valve, then remove actuation power from this division using the battery transfer switch located in the de equipment room to disconnect the battery and remote control from the control room to remove input power l from the battery charger and regulating transformer. This operator action will gevem-preclude spurious actuation of motor operated valves and squib valves resulting from multiple hot shorts in the instrumentation and control room or the instrumentation and control / division C penetration room.

Following detection of a fire in the de equipment control room, the operators can close the automatic depressurization system stage 4 block valve, then remove cabinet power from this division using the input l power switches on the instrumentation and control cabinets. This operator action will geve& preclude spurious smoke-induced actuation of motor operated valves and squib valves resulting smoke-related integrated circuit failures in the instrumentation and control room.

De fifth, sixth, and seventh paragraphs on page 9A-50 (Division D I&C/ penetration and equipment rooms) will be revised as follows:

l 7he probability ofsSpurious actuation from control room dedicated switches which could lead to a breach of reactor coolant system pressure boundary. loss of decay heat removal function, or loss of shutdown reactivity l control is gevemeerrinitrized by the use of dual two-pole, energize-to-actuate, ungrounded de circuits, which require at least four simultaneous hot shorts of proper polarity for spurious actuation.

l Following detection of a fire in the instrumentation and control / penetration room, the eperators e*+shall close the automatic depressurization system stage 4 block valve.then remove actuation power from this division using the battery transfer switch located in the de equipment room to disconnect the battery and remote control from the control room to remove input power from the battery charger and regulating transformer. This operator l action will prevenFpreclude rpurious actuation of motor operated valves and squib valves resulting from multiple hot shorts in the instrumentation and control room.

Following detection of a fire in the de equipment control room, the operators can close the automatic depressurization system stage 4 bhick valve, then remove cabinet power from this division using the input l power switches on the instrumentation and control cabinets. His operator action will Feve# Preclude spurious smoke-induced actuation of motor operated valves and squib valves resulting smoke-related integrated circuit failures in the instrumentation and control room.

The filth paragraph on page 9A-52 (control room) will be revised as follows:

FSER Open item 9.5.1-3 -- !

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NRC'FSER OPEN ITEM l

l Most control room controls use soft-controls which communicate over multiplexed data channels. There are nofre-imiucedfailwe modes ofsop controls that willleadto spwious actuation ofequipment. Fire-induced spurious actuation from these multiplexed soft controls is not-ammeti credibic.

The fifth paragraph on page 9A-54 (remote shutdown workstation) will be revised as follows:

l Most remote shutdown workstation controls use soft-controls which communicate over multiplexed data chanr-is. There are no fire inducedfailwe modes of soy comrols that willlead to spurious actuation of equipment. Fire-induced spurious actuation from these multiplexed soft controls is not : .:.u::=d credible.

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1 FSER Open item 9.5.1-3 -- 5 W Westinghouse

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- NRC FSER OPEN ITEM Question 440.761F Supplemental Information (OITS - 6352)

Large Break LOCA Cases 2.2-A1. DECLG Break to IRWST Injection.

After the initiation of the DECLG LBLOCA the accumulators provide flow to downcomer through the DVI nozzles. Depressurization is accomplished mainly through the break. The water flows down through the downcomer and up the core. The downcomer refills with subcooled water during the LOCA reflood phase to a collapsed level of 21 to 22 feet that is to the DVI injection point. At the time the accumulators empty the water level in the vessel is about 6 feet. Pressure spikes produced from boiling in the core reverse the flow temporarily but the flow is predominantly upward. During the' core make up tank injection, the peak clad temperature (PCT) does not exceed 262 F. Water flow through the core and out the ADS-4 and the break provides adequate flushing to prevent concentration of boric acid in the vessel. The single failure assumed in this transient is that of a make up tank isolation valve, minimizing injection flow.

The results of the analysis indicate that the core remains adequately cooled with sufficient water flow to assure low boric acid concentration in the vessel. However, WCOBRA/ TRAC, which has been qualified for LBLOCA transients, was used in the calculation of this extended transient beyond core quench and before IRWST injection initiation (between about 120 s to 1500 s after LOCA initiation).

The code qualification documentation did not address the phenomena (core make up tank injection and vessel refill) present in this time frame. Although it is reasonable to assume that the code and the noding used for the LBLOCA are capable to address this time frame it is also true that the code has not been explicitly qualified for the phenomena beyond .: ore quench. Therefore, code qualification beyond core quench and before IRWST initiation is an open item.

Supplemental Response:

Reference I transmitted a response to the above FSER Open Item. Pursuant to discussions between Westinghouse and NRC Staff personnel, this submittal scpplements that response.

Following the Westinghouse response to FSER OI440.761F, an additional concern was expressed by the NRC Staff based on their review of certain CCTF and LOFT test data. The concern is that during the post-core quench period of a PWR DECLG break LOCA transient, steam binding from steam generator reverse heat transfer could lead to a repressurization of the RCS, to a level depression of the liquid covering the core, and possibly to a cladding temperature increase. This scenario is assessed below for the AP600, relative to the CCTF Test 58 results.

CCTF was a full-height,1/21 scale model of the primary coolant system of a Westinghouse PWR.

The CCTF facility simulated the overall primary system response and core thermal-hydraulic behavior during the reflood phase of a large cold leg break LOCA; CCTF contained two U-tube and shell heat 440.761F Supplement -1

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NRC FSER CPEN ITEM l

exchangers as SG simulators. ECC injection nozzles were provided at a number of locations in the CCTF facility. Run 58 is the CCTF test most representative of the AP600, because it simulates ECC injection directly into the downcomer with no downcomer vent valves operable. CCTF was designed using Trojan as a reference reactor, so the flow paths between the upper head and upper plenum and the upper head and downcomer are comparable to that specific PWR design. On the contrary, the LOFT facility configuration in the upper head region is atypical of PWR designs. Therefore, LOFT results are not considered herein.

Reasons why the effects of this repressurization phenomenon would be insignificant for AP600 are discussed below: I (a) SSAR subsection 15.6.5.3.4C.3.1 presents the results of an extended AP600 DECLG break calculation performed with WCOBRA/ TRAC. During the post-quench period of interest for this scenario { time 2100 seconds), the core is covered and the upper pienum contains a two-phase mixture (Figure 15 6.5.4C.3.1-8), while the downcomer liquid level is typically below the direct vessel injection nozzle location (Figure 15.6.5.4C.3.1-1), at a level more than two feet below the cold leg bottom elevation. The AP600 is equipped with flow holes between the upper plenum and upper head, through the upper support plate, that constitute a low resistance flow path of 0.72 sq.

ft. into the upper head; no such flow holes existed in the CCTF facility. The now path between  ;

the upper plenum and the downcomer through the upper head is designed to receive 1% bypass I flow during normal operation of the AP600; it will vent approximately 25 cfs of steam from upper l plenum to downcomer if this repressurization scenario were to occur with a i psi differential pressure. The flow path from the upper plenum through the upper head is less effective in the CCTF test facility than it is for AP600. Flow between the upper plenum and downcomer would equilibrate the pressure within the reactor vessel during the postulated steam binding scenario such that the AP600 upper plenum would not remain preferentially pressurized for an extended time period.

(b) Unlike CCTF, the AP600 hot leg is connected to a heat exchanger that provides heat transfer to a cold water heat sink. The PRHR heat exchanger in AP600 dissipates any pressure excursion resulting from sudden steam generation by condensing some of the additional steam that would be present in the hot leg / upper plenum region during such n scenario.

(c) In the reference SSAR analysis, the core makeup tanks drain to the ADS-1 actuation setpoint level at approximately 850 seconds transient time and to the ADS-4 actuation setpoint level at approximately 1700 seconds. Were this scenario to occur, the injection of CMT water into the AP600 downcomer by gravity would not be affected because the CMTs are connected to cold legs by the balance lines. Once the ADS Stage i valves (and sequentially the ADS Stage 2 and Stage 3 valves) open shortly after 800 seconds, RCS venting directly into the IRWST is available which limits any ste'am binding pressurization of the hot legs / upper plenum to the liquid head of approximately 4 psid at the ADS sparger outlet. The RCS pressure will be very close to containment pressure following ADS Stage 4 automatic actuation at 1700 seconds because the ADS Stage 4 Dow paths directly vent to containment the now exiting the core and upper plenum.

440.741F Supplement -2 3 Westinghouse

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. NRCESEh OPEN ITEM E 5 Furthermore, in following Emergency Response Guideline AE-1, "AP600 Loss of Reactor or Secondary Coolant," the plant operator will sequentially open all of the ADS valves manually based on the low RCS hot leg level indication which exists during a LOCA event. Therefore, the ADS Stage 4 flow paths could be opened by the operator within several hundred seconds of the inception of the LOCA event. Whether the operctor acts in accordance with ERG AE-1 or not, the long-term cooling phase, which begins with initiation of IRWST injection concurrent with ADS Stage 4 actaation, is not adversely affected by this scenario because the ADS Stage 4 flow paths are open and available to receive the core fl'iid outflow.

(d) The additional AP600 design features of (1) upper support plate flow holes, (2) PRHR heat exchanger, (3) ADS provide assurance the subject scenario is limited in magnitufe and is bounded by the CCTF Test 58 results. CCTF Test 58, which modeled downcomer injection, exhibits a short duration heatup at about 850 secoads transient time. In the unlikely event that a temporary fuel rod heatup would occur in AP600 following core quench, the duration of the scenario is considered to be bounded by the 20 second heater rod heatup time observed in CCTF Test 58, for the reasons indic ed above. Assuming conservatively that the highest power location in the AP600 undergoes a 20 second adiabatic heatup at 800 seconds into the DECLG break transient, a cladding temperature increase of 200 deg F would occur. The peak cladding temperature remains below 500 deg F during this temperature excursion, and the core will quench again following level recovery due to equilibration of the upper plenum and downcomer pressures.

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The process by which this postulated steam binding scenar:o occurs is self-limiting; any liquid t droplet flow into the steam generators that vaporizes to cause a repressurization will cease when the steam generator pressurizes. AP600 design features are such that the observed CCTF Test 58 results for the postulated scenario would be ameliorated, and this scenario will not lead to a large cladding heatup or to an inadequate ECCS performance condition.

References:

i 440.761 F-1: Response to FSER Open Item RA1440.761F-1, Letter from B. A. McIntyre, Westinghouse, to T. Quay, USNRC, DCP/NRCl229, January 26.1998. .

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l SSAR Revision: None '

440.761F Supplement -3

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