ML18044A585

Forwards Response to NRC 800205 Request for Info Supporting Util Contention Re Lessons Learned Task Force Category a Requirements.Waste Gas & Chemical Vol Control Sys Need Not Be Included in Sys Integrity & Shielding Review Programs

ML18044A585
Person / Time
Site:	Palisades
Issue date:	02/27/1980
From:	Frost S CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
RTR-NUREG-0578, RTR-NUREG-578 NUDOCS 8003040550
Download: ML18044A585 (17)

Text

'\

tr_...,

consumers Power company General Offices: 212 Wan Michigan Avenue, Jackson, Michigan 4920! * (517) 788-0550 February 27, 1980 Mr James G Keppler Offi~e of Inspection and Enforcement Region III US Nuclear Regul~tory Commission 799 Roosevelt Road Glen Ellyn' IL 60137 DOCKET 50-255 - L!CDSE DPR PALISADES PLANT -

TMI JUSTIFICATION RESPONSli:

Consumers ?over Company was requested by le~ter dated Februar/ 5, 1986 to submit L~for:nation relative to the I:nplemen~ation of the Category A Lessons-Learned requirements.

The enclosed attachments prcvide further int'ormation to support our conten-tions of the following:

- the waste gas and chemical and Tolume control systems are not required to mitigate the conse-quences of a.ny accident illvolvi.ag :t'uel damage; and

• theretore, need not be included in the Systems Integ-rity and Shielding Review Programs

- j istii'ication for component cooling water isolation 1

logic

- high radiation signal as a diverse isolation signal

- allowing the shift supervisor to-leave the control room during accident conditions.

The other requirements outlined in the February 5, 1980 letter will be com-pleted as stated in Consumers Power Company's TMI NUREG-0578 Rev. 1 response.

The response time for the information requested by the TM! inspection team was extended to February 27, 1980 per phone conversation between Mr Richard D Silver (IiRC) and Mr S R Frost on February 19, 1980.

Steven R Frost Palisades Nuclear Licensing Engineer CC: Director, Office of Nuclear Reactor Regulation Director, Office of Inspection and Enforcement Attachments 16 pages

v COMPARISON OF TMI-2 WITH PALISADES .

Waste Gas Systems TMI-2 Sources/System Configurations Palisades Sources/System Configurations Swnmary Summary At TMI-2, leaks in the waste gas systems caused several At Palisades, if an accident occurred which did not result significant radioactive gas releases within the auxiliary in containment high pressure or significant fuel damage, building and off site. Gas from the RCS was allowed to gas from the PCS could leave containment through paths leave containment either dissolved in water or as free gas somewhat similar to TMI-2. These paths are letdown flow through four major paths through the letdown line in the in the chemical and volume control system (CVCS), sample makeup system, through the sample system, through the re- purge and PCS degas flow-through the NSSS sampling system, actor building vent header and through the reactor building possible but highly unlikely flow-through the containment sump pump discharge line. These paths would all have been vent header or the containment building sump drain line and isolated on a reactor building isolation signal, had one one additional path through the primary coolant pump seal ~

been received. At TMI-2, however, since reactor building controlled bleed-off line. Unlike TMI-2, however, these . . .

isolation only occurs on containment high pressure, no paths are all automatically isolated in the event of automatic containment isolation feature was available for significant fuel damage whether or not there is a breach the situation which existed. of the PCS.

The following provides a more detailed description of our understanding of TMI-2 gas release paths for comparison with Palisades.

1. Makeup System 1. Chemical and Volume Control System In the TMI-2 makeup system, gases in the reactor As at TMI-2, normal letdown flow will result in gases coolant being let down can come out of solution and collecting in the volume control tank, and manual collect in the makeup tank. This tank is manually venting will route these gases through the waste gas vented to the waste gas vent header, or, if pressure surge tank and compressors to the waste gas decay tanks.

increases sufficiently, will vent through the makeup The liquid relief on the volume control tank relieves tank liquid relief valve to transfer reactor coolant to the east dirty waste drain tank which, in turn, re- ~

and gas to the RC bleed holdup tanks. The RC bleed lieves to the waste gas surge tank. ~

tank vents also go to the waste gas vent header.

Letdown can be and was also diverted directly to the Unlike TMI-2, however, if significant fuel damage RC bleed tanks. A key consideration here is that the occurs, letdown will be isolated auto~tically by the relief valves on the RC bleed tanks bypass the waste resulting containment high radiation (CHR) s~gnal.

gas system and the absolute and charcoal filters The CHR signal also automatically isolates t~e other and go directly to the station atmospheric vent. sources of primary coolant into the eve syst~m (dis-When at least one of these reliefs lifted on March 30 cussed later). Since these isolations stop the *r1ow-..,.-,*~**-:. -*7~*

in conjunction with the lifting of the makeup tank of primary coolant and, therefore, gases into~ *~p.e eves, ,.

---T--~-:* ..... ~-~- ...- . . --*~..

/I

2 TMI-2 Sources/System Configurations Palisades Sources/System ConfiSurations liquid relief, the result was the massive gas release this system cannot be a source of fission product gases which measured 1200 mR in the cloud above the plant. into the waste gas system.

The release was also made larger by leaks in the waste gas vent header and the remainder of the waste gas As discussed elsewhere in the comparison of Palisades system which released some of the gas being manually CVC system with the TMI-2 makeup system, letdown is not vented from the makeup tank at the same time. required to mitigate the consequences of any accident.

At TMI-2, then, continued letdown flow would have led directly to large off-site gas releases even if the remainder of the waste gas system had been leaktight.

In addition, as noted in NUREG 0600, lifting relief valves in the makeup system was considered to be a potentially significant source of the extensive releases of radioactive liquids into the TMI-2 auxiliary building. Again, these releases would have occurred even without leaks in systems or components.

No automatic features existed at TMI-2 ~o stop letdown flow in this type of situation .. ~

2. RCS Sample System 2. NSSS Sample System For RCS sampling, sample purge flow leaves contain- Under normal conditions, Palisades PCS sampling system ment goes through the nuclear sampling system and is similar to that of TMI-2. Primary coolant sample returns to the makeup system just upstream of the purge flow leaves containment, passes through the NSSS A makeup tank or returns to the auxiliary building sample system and returns to the volume control ~

sump. Sample system flow, therefore, contributes tank. Unlike TMI-2, however, another sample system to the RCS gas collected in the makeup tank or can effluent line is provided to the vacuum degasifier tank result directly in gases being released to the from which gases are returned to the w~ste,gas surge auxiliary building. tank. This path is used primarily. wheh. degassing I

the PCS in preparation for a cold shutdown. At lj~lisades

'l'ne RCS sample line reactor building isolation the normal degassing method is to vent the pr 1essurizer valves close on reactor building high pressure.

• vapor space through the NSSS sample system. Recent plant modifications have been accomplished to install an additional sample system effluent line which allows

)J I

.f:}"

3 TMI-2 Sources/System Configurations Palisades Sources/System Configurations

• ' I sample purge and degas flow to return to containment under accident conditions.

If significant fuel damage occurs, the resulting CHR signal automatically shuts the sample line containment isolation valves, CV-1910 and CV-1911, thereby stopping degas or sample purge flow, and eliminating this source of primary coolant and gas. As above, unless the CHR signal clears (highly unlikely), deliberate action must be taken to jwnper out CHR relay contacts in the valve control circuits in order to be able to reopen these valves. Palisades Plant Procedure ONP-11 contains specific instructions for this case to divert the sample system effluent back into containment before CV-1910 and CV-1911 can be reopened. This ensures that the fission product gases from sample or degas flow will remain inside containment and not be able to entey the waste gas system.

It should be noted at this point that Palisades has permanently installed hydrogen recombiners inside con-tainment. Hydrogen, therefore, whether from degas flow or from direct release into containment from the PCS,

'* will be controlled to prevent a flammable or explosive concentration.

3. Reactor Building Vent Header 3. Containment Vent Header At TMI-2, the reactor coolant drain tank (RCDT) vent The Palisades equivalent to TMI-2's reactor building connects to the reactor building vent header through vent header is the containment vent header. Two two normally closed valves. When the TMI accident potential sources of PCS gas are connected to this occurred, these vent valves were open. header, ie, the quench tank vent ana the 'I primary system drain tank vent. The quench tank can be vented to the When the EMOV opened, therefore, the entire reactor header through a normally closed valve'. Nor~~lly, the building vent header as well as the waste gas vent only potential source of PCS water and gas to! the quench headers outside containment were pressurized with the tank will be the pressurizer safeties since the PORVs RC drain tank. Since RCDT pressure peaked at 192 psig are isolated during plant operation.

before the rupture disc blew, the pressure in these Ii

4 TMI-2 Sources/System Configurations Palisades Sources/System Conf.igurations vent headers reached a value somewhere between the The primary system drain tank is vented to the contain-relief valve set point of 150 psig and peak RCDT pres- ment vent header through a pressure control valve. The sure. This caused an early minor release of activity only direct source of primary coolant into this tank is in the auxiliary building through waste gas system the relief valve on the primary coolant pump seal con-leaks. Two hours later when gross fuel failure trolled bleed-off line. This relief will not lift, occurred, this still open path resulted in signifi- however, unless the normal PCP bleed line to the chemical cant releases of gaseous activity through the waste and volume control system is isolated.

gas system leaks.

The containment building vent header is connected via the waste gas surge tank through compressors to the waste gas decay tanks. ~

Unlike TMI-2, however, if significant fuel damage occur-red with or without a breach of the PCS, the resulting CHR signal would shut the containment vent header isola-tion valves, CV-1101 and CV-1102, eliminating this source of gas from the waste gas system.

4. Reactor Building Sump Pump Discharge 4. Containment Sump Drain The reactor building sump pumps at TMI-2,.automatically At Palisades the containment sump gravity drain line pump water from the RB sump to the miscellaneous waste goes directly to the dirty waste drain tank through holdup tank or the auxiliary building sump tank out- normally closed containment isolation valves, CV-1103 side containment. Both tanks vent directly to the and CV-1104. When the sump level is high, an operator waste gas vent header. opens these valves to drain the sump and then recloses them. The valves do not open automatically. If by Automatic closure of the sump pump reactor building coincidence these valves were open when a safety injec-isolation valves did not occur because a reactor tion signal were received (caused by low pressurizer ~

building high-pressure signal was not received. pressure or containment high pressure) or if fuel Uncontrolled automatic pumping of the RB sump, damage occurred to give a CHR signal, these valves therefore, led to overflow of the auxiliary building would automatically shut. This line, therefore, would sump tank, flooding of the auxiliary building sump not be a source of highly radioactive jiqui'd or gas and flooding in various areas of the auxiliary outside of containment. ' )'

building as floor drains backed up. ,I This containment sump drain line has a second purpose which is pertinent to the matter at hand. This l_ine was recently modified to accept water from the engi-neered safeguards room sump pumps, sample purge water

.I/1

5 TMI-2 Sources/System Configurations Palisades Sources/System Configurations and pressurizer gas to give the plant the ability to return highly contaminated coolant and gas to containment.

Therefore, any leakage from HPSI, LPSI or containment spray as well as any water or gas intentionally brought out of containment will now be returned to containment to eliminate any need to process it in existing liquid or gaseous radwaste systems. If an abnormal condition develops which increases primary coolant gross activity to approximately 10 µc/ml, Palisades Plant Procedure ONP-11 requires that the containment sump drain line be isolated from other radwaste systems outside containme~

and that any leakage or sample/degas flow be directed , . ,

back to the containment sump. If an abnormal situation develops rapidly so that the CHR signal is received, this procedure requires that the above action be taken before the containment sump valves may be reopened and PCS sampling resumed.

5. NA 5. At Palisades, one other potential source of primary coolant and gases outside of containment is primary coolant pump seal controlled bleed off. This primary coolant flow of 4 gpm leaves containment through a separate penetration and goes to the volume control tank in CVCS. If this line is isolated, an alternate flow path totally inside containment would allow the pump seal flow to be maintained without operator ac-tion. If significant fuel damage occurs, the resulting CHR signal would shut the containment isolation valve on this bleed-off line and eliminate this source of e

coolant arid gas from the eve system without affecting the primary coolant pump seals.

11

• r '

I LJ.

COMPARISON OF TMI-2 AND PALISADES LETDOWN AND GASEOUS WASTE SYSTEMS References

1. NUREG 0600 - Investigation into the March 28, 1979 Three Mile Island Accident by Office of Inspection and Enforcement

2. Flow Diagrams - Three Mile Island Unit 2 Dwg 2024, Rev 16 Dwg 2026, Rev 18 Dwg 2027, Rev 15 Dwg 2028, Rev 18 Dwg 2031. Rev 10 Dwg 2045, Rev 13 Dwg 2632, Rev 1

3. Piping and Instrument Diagrams - Palisades Plant M-201, Rev 20 M-202, Rev 21 M-203, Rev 16 M-204, Rev 16 M-210, Rev 14 M-211, Rev 27 (as Modified by FC-471)

M-219, Rev 10 (as Modified by SFC-79-075 arid FC-471)

E-17, Sh 3, Rev 7

4. Palisades Plant Normal Operating, Off~Normal and Emergency Procedures

5. NSAC-1, EPRI Report on the Three Mile Island Accident

. :?:*

i' COMPARISON OF TMI-2 TO PALISADES Letdown System

.. I TMI Condition/ TMI Design Features/Use of Palisades Design Features for Requirement for Letdown Letdown System Accomplishing Letdown Functions Swnmary Based on infonnation in NUREG 0600 and Letdown flow from the primary coolant sys-NSAC-1, the letdown system of TMI-2 provided tem to the chemical and volwne control the following functions during the TMI-2 system would be isolated in the event of accident: significant fuel damage by containment high radiation (CHR). Thus, normal let-

1. Reduction of primary coolant volume. down flow would not be available during an accident such as TMI-2. As discusseaA.

2. Reduction of primary coolant pressure. below, alternative design features exist,..,-

or have been added to the Palisades Plant

3. Sampling of primary coolant. which allow each of those system functions which are required during and following the

4. Degassing of primary coolant. the accident to be accomplished without letdown flow.

5. Cooling of primary coolant.

Each of these functions is discussed below:

1. Reduction of PCS Volwne

a. During First Letdown flow was used in conjunction with Letdown from the PCS to the CVCS at 15-1/2 Hours EMOV block valve discharge and makeup dur- Palisades would be isolated as a result ing the first 15-1/2 hours of the transient of containment high radiation when sig- ~

in an attempt to maintain a constant pres- nificant fuel damage occurs. The charg-surizer level. However, based on our ing pumps of the eves continu}: to operate review, it appears that letdown flow had after an SIS to inject 1oncentrated boric only a minor effect on level control and acid into the PCS. In ~ddition, the high-need not have been used. Measu~ed values pressure safety injection system, which of letdown flow rate are not available is independent of the eves, is available except at isolated times during the TMI for increasing PCS inventory by drawing accident. Nevertheless, based on the EPRI borated water from the SIRW tank.

analysis in NSAC-1, and from infromation in NUREG 0600, it can be inferred that the II I,

II

2

" I TMI Condition/ TMI Design Features/Use of Palisades Design Features for Requirement for Letdown Letdown System Accomplishing Letdown Functions letdown flow changed repeatedly between zero flow following reactor building isolation signals and maximum flows near 160 gpm with a most likely average near 70-90 gpm throughout the transient.

The primary coolant inventory increases at at TMI-2 during the accident were deter-mined by flow rates through the makeup (and safety injection) system. Typical sustained makeup flows ranged from approx-imately 150 gpm to approximately 720 gpm based on BWST level measurement and inferred letdown flow.

The PCS inventory decreases can be estimated by knowledge of the pressurizer relief (EMOV) and block valve positions (open or clo~ed) , and by the letdown flow.

Typical flows from the pressurizer were approximately 600 gpm, ie, much greater than the letdown flow.

Accordingly, throughout the first 15-1/2 During a Loss of Coolant Accident, rapid hours of the accident, primary coolant addition of primary coolant rather than inventory was controlled primarily by the inventory reduction is required. Reduc~

makeup flow and the :flow leaving the tion of primary coolant vol~e through ulr' pressurizer, rather than by the letdown of the letdown system in effe.ct increases flow. During this period, isolation of the size of the break ~pd cari increase the letdown flow would not have substantially severity *Of the transi~nt. '

changed the primary coolant volume. The effect of slightly reducing the coolant If coolant inventory reduction is desired loss rate if letdown were isolated would during an accident, this could be accom-have been beneficial early in the plished at Palisades by opening the PORVs transient. and block valves on the pressurizer, and discharging the primary coolant to the quench tank and into containment as at TMI.

3 TMI Condition/ TMI Design Features/Use of Palisades Desi'gh Features for Requirement for Letdown Letdown System Accomplishing Letdown Functions

b. After 15-1/2 After 15-1/2 hours when the TMI plant had With a full primary coolant system Hours been brought under control, the letdown flow operating in a stable cooling mode at was continued and approximately matched the Palisades, charging flow to the PCS will makeup flow. In this mode, the letdown be limited to approximately 4 gpm for system was used to remove coolant volume makeup of seal leakage in the primary continuously added to the PCS by the makeup coolant pumps. In addition, the primary pumps for primary coolant pump seal injec- coolant pump seals do not require seal tion. injection for cooling or lubrication.

Instead, a controlled amount of primary As discussed below, letdown flow was also employed during this time period for coolant is allowed to bleed through the seals. This 4 gpm total flow (1 gpm per 9,

degassing the reactor coolant. pump} normally leaves contairunent through a separate penetration and returns to the volume control tank in the CVCS. The same signals which isolate letdown also isolate this controlled bleed off by shutting the containment isolation valve.

If this normal seal bleed-off line is isolated or blocked, seal flow would

-:~

still be maintained without operator actio~ through an alternate path inside.

containment. Isolation of letdown or the PCP seal controlled bleed-off line would not affect primary coolant pump opera-tion. Thus, reduction of primary coolant volume with the eves will not be require~

during an accident at Palisades. *

• It is noted that at TMI the makeup pumps The Palisades HPSI pumps have.a shutoff are used for both high-pressure safety head of 1,255 psig and, .1thus, cannot injection and normal makeup during plant overpressurize the syst¢m as long as operation. The design shutoff head is temperature is above 255°F (MPT consid-3,000 psig. Letdown flow during the eration). Consequently, using letdown accident may have been continued as a flow to avoid potential overpressuriza-normal precaution to minimize the potential tion by the safety injection pumps would for plant overpressurization. not be a concern at Palisades.

4 TMI Condition/ TMI Design Features/Use of Palisades Design Features for Requirement for Letdown Letdown System Accomplishing Letdown Functions

2. Reduction of a. First 15-1/2 Hours Primary Coolant Pressure The letdown flow can be used to reduce primary coolant pressure by reducing coolant volume.

At the' start of the TMr-2*accident Prior to significant fuel failure the letdown flow was increased in an letdown system at Palisades would not be unsuccessful attempt to reduce the rise isolated and would be availabe for re-in pressurized level. This had the adverse effect of increasing the ef-ducing pressure in the PCS if desired. 8:

fective size of the break.

Between approximately 5-3/4 and 7-3/4 Following significant fuel failure the hours in the accident pressure control letdown system at Palisades would be was accomplished by periodically isolated. If required, PCS pressure opening the pressurizer relief or reduction would be accomplished through vent lines. As discussed above, the the pressurizer PORVs as was done at TMI.

letdown flow was small compared to the flow from the pressurizer during this period and did not significantly contribute to pressure control.

During the sustained pressure reduction from 7-3/4 to 9-1/4 hours in the acci-dent the pressurizer relief line was left open continuously. Contribution of the letdown flow to the total pres-sure decrease was small. This attempt to go into the decay heat system was *1 unsuccessful and only after. the plant was repressurized and the primary 1 coolant pumps started was the plant brought to a stable cooling mode.

5

• ' I TMI Condition/ TMI Design Features/Use of Palisades Design Features for Requirement for Letdown Letdown System Accomplishing Letdown Functions

b. After 15-1/2 Hours After the plant was brought to a stable As discussed above under PCS inventory cooling condition, letdown flow was used control, primary coolant pwnp seal flow together with the makeup system to at Palisades is a PCS outflow and is indirectly control pressure by control- independent of the chemical and volume ling primary coolant inventory. This control system.

action was required at TMI, as discussed above, because of the net inward flow of coolant via the primary coolant pump seals. In particular, a minimum letdown flow of 28 gpm is required to balance the net inflow of 7 gpm per pump from seal injection.

3. RCS Sampling For RCS sampling, TMI and B&W plants, in At Palisades, primary coolant samples are general, have two options for obtaining normally obtained directly from sample RCS sampling is reactor coolant samples. The normal sample point SX1023 on PCS loop 2 hot leg. Sam-required to deter- point is in t:pe letdown line upstream of ples can also be obtained from the pres-mine the extent of the letdown coolers through valve RC-Vl23. surizer liquid phase through SX-1034 on fuel damage. It should be noted that some later B&W the surge line. A primary coolant sample plants have this sample point in the let- may be obtained independent of letdown down line outside containment. The second flow.

TMI-2 primary coolant sample point is from the pressurizer liquid space through valve During normal plant operation, PCS sample RC-Vl22. water is returned to either the volume ~

control tank (normal lineup for purging)

Sample water.is returned to the makeup or to the vacuum degasifier tank. In system just upstream of the makeup tanks addition, recent plant mpdifications have 0

(used for purging) or through the catch been accomplished to ad4 a t hird sample basin in the swnple panel ~o the auxiliary system effluent line to:allow PCS sample building sump. With this system configura- purge flow back into containment under tion, the preferred path for purging sample accident conditions.

lines to obtain a representative sample would be to the letdown line. At Palisades, fuel damage with or without a breach of the PCS will cause sampling

' 6

.. I TMI Condition/ TMI Design Features/Use of Palisades Design Features for Requirement for Letdown Letdown System Accomplishing Letdown Functions At TMI-2 letdown was used to obtain reactor flow to be stopped when the resulting coolant samples early in the accident. containment high radiation signal closes containment penetration isolation valves, CV-1910 and CV-1911. These valves remain closed until deliberate action is taken by the operator to prepare to handle the highly contaminated coolant and then jumper CHR relay contacts in the valve control circuits to allow the valves to .m.

reopen. W If fuel damage occurs, Palisades Plant Procedure ONP-11 requires that the sample return lines to the volume control tank and the vacuum degasifier be isolated and that the system be lined up to direct sample purge flow back into containment prior to reopening CV-1910 and CV-1911.

This prevents contamination of unneces-sary systems outside containment with the highly radioactive fission products.

4. Reactor Coolant TMI-2 had tvo methods to degas: . At Palisades the normal degassing path is Degassing from the pressurizer vapor space through

1. Letdown PCS water through the makeup the sample system to the vacuum degasifier Degassing of reactor system and vent any gases from the tank. Degassing is independent of the CV. . .

coolant was required makeup tank. system. Degassing can also be accomplish~

following the accident by venting the volume control tank with to remove noncondensible 2. Use the feed and bleed mode for the ~akeup letdown flow, but this m~thod is very slow gases and to allow RCS system by letting down reactor coolant and is considered an alternate to the pressure reduction. directly into the reactor coolant bleed above. Recent plant mod'ifications have holdup tanks, WDL-T-1/A/B/C, Gas from been accomplished which also allow degas the relief valves on these tanks went flow to be returned to containment under directly to the station vent through the accident conditions.

relief valve vent header. Gas through the normal vents from the reactor At Palisades, fuel damage with or without coolant bleed tanks and the makeup tank a breach of the PCS will cause:gas flow

7

• • I TMI Condition/ TMI Design Features/Use of Palisades Design Features for Requirement for Letdown Letdown System Accomplishing Letdown Functions go through the WGS compressors to the to be stopped when the resulting contain-waste gas decay tanks. ment high radiation signal closes contain-ment penetration isolation valves, CV-1910 At TMI-2, the larges off-site release of and CV-1911. These valves remain closed noble gases occurred when the relief valves until deliberate action is taken by the lifted on the RC bleed tanks coincident operator to prepare to handle highly with gas system leakage during venting of contaminated coolant/gas and then jumper the makeup tank. CHR relay contacts in the valve control circuits to allow the valves to reopen~

If fuel damage occurs, Palisades Plant Procedure ONP-11 requires that the sample effluent lines to the vacuum degasifier and volume control tank be isolated, and that the system be lined up to direct sample system effluent *flow back into containment prior to reopening CV--1910 and CV-1911. This presents contamination of unnecessary systems outside containment with the highly radioactive fission products.

5. Primary Coolant At TMI the letdown flow passes through the At Palisades core cooling during an ac-System Cooling letdown heat exchanger before returning to cident will be accomplished by using the the PCS through the makeup pumps. It was steam generator as the heat sink at high noted in NUREG 0600 that this cooling of pressure and the shutdown cooling syst.

the letdown flow provided some cooling at low pressure. Additional core cool of the PCS throughout the TMI accident. can be provided by high-pressure injec-However, based on the nominal letdown flow tion and primary coolant removal from the.

rate of Bo gpm, this cooling was inadequate pressurizer, similar ~b tHe primary cool-to remove the decay heat generated in the ing, mode at TMI for the first 15-1/2 -

core until much later in the accident. hours of the accident.

Core cooling in the absence of effective natural or forced circulation at TMI was accomplished by makeup and relief from the pressurizer at flow rates of approxi-mately 600 gpm, much larger than the let-down flow of approximately Bo gpm.

.... j

• l._)

JUSTIFICATIOli FOR COMPONENT COOLING WATER (CCW) ISOLATION LOGIC Containment penetrations are presently divided into essential and nonessential systems with nonessential systems isolated on a containment isolation signal (CIS). The CCW system which presently isolates on a safety injection signal, SIS, is to be changed to a quasi-essential system, therefore, reducing the chance of primary coolant pump (PCP) seal failures caused by a lack of cooling water due to a spurious SIS. A seal failure could result .in a small break LOCA.

The new isolation scheme requires a safety injection signal and either a low level in the CCW surge tank or a containme~t pressure greater than 20 psi. The philosophy is that the CCW should be isolated on SIS in conjunction with the potential of a CCW line break. If the line does break and the containment is at a pressure of less than 20 psi, then water will flow from the system causing low level in the CCW surge tank. Thus, the logic for isolating.

If a SIS occurs and the containment is greater than 20 psi, and if a break should occur, gases and steam would flow into the CCW system instead of water flowing out because the CCW would be at a lower pressure. These gases could eventually find their way into the environment. To avoid.this from happening, the system is isolated under these conditions.

When the system is isolated, the valves are not latched closed as on the nones-sential systems, and the CCW is reestablished as quickly as possible for pump seal protection.

JUSTIFY THE USE OF CONTAINMENT HIGH RADIATION SIGNAL AS A DIVERSE CONTAINMENT ISOLATION SIGNAL The Palisades Plant radiation monitors operate primarily to provide isolation upon high levels of radiation. This provides for a means of containment isolation in the event of coolant loss to the containment volume which may be insufficient to cause isolation on the basis of high-containment pressure.

Location of each monitor is adjacent to an air cooler where radioiodines would condense along with water vapor in the event of even relatively minor breeches of primary system integrity. Radiation monitor locations in the lower level of containment also allow for response from abnormal sump or 590 level water accumulations of radioactive coolant. Such conditions could be hypothesized fo.r rupture of a letdown line after cooling by the letdown heat exchanger, leakage or overflow of the primary system drain tank, etc.

The NRC's THI inspection team concerns for ability to isolate containment on the premise that significant core damage might occur without loss of coolant have been reviewed. As a result of this review, relocation of one monitor is being undertaken in order to insure that a minimum of two monitors will be in the direct path of radiations emanating from abnormal concentrations of fission products passing through the letdown heat exchanger. This monitor will remain in close proximity, but moved to the other side of the air cooler which it was intended to monitor. This move as well as testing of the monitors will be accomplished prior to plant start-up .

• A'C'";. ,*'

'8.

j JUSTIFY ALLOWING-THE SHIFT SUPERVISOR TO LEAVE THE CONTROL ROOM DURING AN ACCIDENT During a condition in which the emergency plan is activated, the shift supervisor (SS) will be allowed to leave the control room for a brief period of time to make an evaluation of a problem that requires his attention and then immediately return to the control rQom. Justification for the SS to leave the control room is that if there is a problem elsewhere in the plant that needs his expertise, valuable information needed to make an evaluation may not be able to be explained in the detail needed using other communication techniques. An actual inspection may be required by the SS to make a quick evaluation based on his past experience and knowledge of the system as well as his overall knowledge of the present plant status during the accident condition.

Not allowing the SS to leave the ~ontrol room to make an evaluation of a problem, a quick solution may be avoided causing more problems and delaying the stabilization of the plant.