ML20041A161

Evaluation of Potentially Adverse Environ Effects on Nonsafety-Grade Control Sys

ML20041A161
Person / Time
Site:	Midland
Issue date:	02/05/1982
From:	BABCOCK & WILCOX CO., CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:
Shared Package
ML20041A160	List: ML20041A159 ML20041A161
References
REF-SSINS-6820, REF-SSINS-SSINS-6 IEIN-79-22, NUDOCS 8202190189
Download: ML20041A161 (11)

Text

,.,

J LEVALUATION OF POTENTIALLY ADVERSE ENVIRONMENTAL-EFFECTS ON NON-SAFETY GRADE CONTROL SYSTEMS b

4 1'

1

+

1 Prepared by:

I Consumers Power Company i

Babcock & Wilcox Company 1

i t

1-r i

I '

t 9

.PDR

.a

-,_.-,,,-o.,--

y.,,

... -.--m- -, _, -, -..,- _,

, - _,,,.. _,_m,.

~,vm

~,-....,m,-,

TABLE OF CONTENTS

.P_ age I.

INTRODUCTION 1

II. I PIANT' LICENSING BASIS 1

A.

. Safety-Analysis Functions and Parameters B.

Plant Unique Features III.

SAFETY ASSESSMENT 2

A.

Potential Environmental Effects B.

-Impact on' Plant Safety Analysis IV.

SUMMARY

5 TABLES I.

Typical BEtJ 177 Fuel Assembly Plant Equipment-Response During High Energy Line Breaks.

II.

Control Systems / Components Related to Table I Equipment III.

Impact of Control System Effects.on the Midland Safety Analysis ACRONYMS j

LOCA'- Loss of Coolant-Accident SLB

--Steam Line Break FWLB

.Feedwater'Line Break f

l 1

..~ -......-.._.-,- -..

l' I.

INTRODUCTION This report is in response to Robert L Tedesco's letter of April 16, 1981 to James W Cook on the subject of "High Energy Line Breaks and

~

Consequential Control System Failures - Midland Plant, Units 1 and 2,"

(IE Information Notice 79-22). The concerns listed in Information Notice 79-22 are addressed utilizing the same review the B&W operating

-plants used in 1979 as a result of a meeting (September 20, 1979) between the NRC and B&W Operating Plant Owners. The ground rules for

-the review as stated at the meeting are:

Evaluate impact on Licensing basis accident analyses due to consequential environmental effects on non-safety grade control systems.

Identify Licensing basis accidents which cause an adverse environment for each plant.

Define afety Analysis inputs and responses used during Licensing basis accidents.

Verify Safety Analysis conclusions or recommend actions justifying continued operation.

It is important to note that the Midland Plant has the distinct advantage of_ utilizing safety-grade control system / components in place of many of the non-safety-grade control systems / components utilized by the typical B&W 177 fuel assembly operating plant.

The scope of this response includes a confirmation that the Midland Plant equipment performance is consistent with that used in the Licensing basis analysis.

Where non-safety grade equipment performance could be affected by the adverse environment, a safety assessment has been prepared. The safety assessment was used to define potential problems due to the effects of an adverse environment on non-safety-grade control systems.

II.

PLANT LICEN3ING BASIS A.

Safety Analysis Functions and Parameters The plant licensing basis analyses were reviewed to define the inputs, assumptions and responses used for non-safety grade control systems. This in' formation is summ'arized in Table I, which lists typical equipment actions and actuation times used in the safety analyses for B&W 177 fuel assembly plants. The data has been categorized to reflect the functional requirements as follows:

rp0182-0572a131

2 1.

Reactor Power Control and Shutdown 2.

Reactor Pressure Control

.3.

Steam System Isolation and Pressure Control 4.

Feedwater System Isolation and Control This categorization has been developed to focus upon those primary functions which have a potential for control system interaction.

Table I identifies the range of equipment actions and actuation times used in the plant safety' analysis for steam line break, feedwater line break and large and small LOCA.

B.

Midland Plant Unique Features Table I lists typical B&W 177 fuel assembly. plant non-safety-grade equipment response during high energy line breaks.

In the Midland Plant, many of these components are safety grade as listed below.

Included below, where applicable, is the response time of these safety grade components to demonstrate they satisfy the response times in Table I.

1.

Safety-Grade PORV and PORV Controls 2.

Safety-Grade Main Steam Isolation Valves Valve Closure Time = 5 seconds (FSAR Table 16.3.6-1) 3.

Safety-Grade Main Feedwater Isolation Valves Valve Closure Time = 10 seconds (FSAR Table 16.3.6-1) 4.

Safety-Grade Auxiliary Feedwater Isolation'ralves Valve Closure Time = 10 seconds (FSAR Table 16.3.6-1) 5.

Safety-Grade Auxiliary Feedwater Initiation The maximum time for auxiliary feedwater to reach the steam generators for emergency operation, including diesel start time of 10 seconds, is less than 40 seconds (FSAR Section 10.4.9.2.3).

6.

Safety-Grade Main Steam Relief Valves III.

SAFETY ASSESSMENT A.

Potential Environmental Effects rp0182-0572a131 L-

3 The non-safety grade control. systems have been reviewed to determine

'if an s -ident environment could adversely affect the analyzed course e.

the event. Specifically, the approach taken was to use the safety analysis functions and parameters from Table I as a basis to identify where potential control system effects cou'd have an-impact. The results of this evaluation is summarized in Table II.

The matrix identifies, for six accident types, the control systems / components which could be affected by the environment caused by the event. Where a "_" entry is made-in the matrix, no potential for environmental effects exists due to the physical location of the equipment with respect to the high energy line break, ie, breaks inside containment do not affect equipment outside containment and vice versa. The entries X, Y, or Z are explained as follows:

X - The adverse environment caused by the break could affect the equipment and, equipment malfunction could affect safety analysis functions identified in Table I.

Y - The adverse environment caused by the break could interact with the equipment, but, the equipment malfunction would not affect the safety analysis function identified in Table I and does not require further analysis.

Z - Designates that the equipment is safety-grade in the Midland Plant and does not need to be addressed further in response to IE Information Notice 79-22.

This structuring of the potential effects matrix provides a focus on those non-safety-grade control systems which are important and identifies areas for further evaluation of the impact on the safety analysis (ie, X's).

B.

Impact on Plant Safety Analysis r-Potential environmental effects which could adversely impact the l

plant safety analysis are identified in Table II with an "X".

For each potential adverse effect, a safety assessment has been prepared i

to confirm plant safety or identify a potential problem area.

The results of the safety assessment are summarized in Table III, Impact of Control System Effects on the Midland Safety Analysis.

-These potential ef fects, due to en adverse environment, have been placed into two categories as follows:

1.

Equipment Performance Safety-grade equipment can be shown to perform the intended function, consistent with the safety analysis, in the adverse j

environment.

L rp0182-0572a131 s

4 2.

Pericd of Operability The required period of operability for the equipment (ie, time frame in which the equipment must function) is considerably shorter than the time it takes for an adverse environment to have an impact.

The impact on the safety analysis is presented below for the control systems / components with an X entry in Table II.

a.

CRDCS Under All Accident Environments A significant increase in initial power level as a result of spurious rod withdrawal prior to reactor trip has not been included in the SLB, FWLB or LOCA analysis in the Midland FSAR.

While it is likely that such an increase in power would'be offset by the reduction in the time-to-trip for each of these accidents, confirmatory analysis has not been performed.

The following summarizes the likelihood of significant rod withdrawal for each case.

1) For steam and feedwater line breaks, the time-to-trip is very short (up to 8 seconds for SLB and 13.4 seconds for FWLB).

Adverse environmental effects on any non-safety-grade equipment, eg, out-of-core detectors, which could result in spurious rod withdrawal, is considered extremely unlikely to occur prior to the reactor trip. After the reactor trip the control rods are prevented from withdrawing due to the CRDCS power supply breakers being tripped.

2) The same rationale applies to all but the very smallest LOCA's, ie, time to low RC pressure trip is short for the majority of small breaks.

Conversely, " leaks" (breaks too small to result in a low-pressure trip) are not expected to generate a severe environment.

From the above, it is concluded that adverse interaction resulting in significant reactor power increases prior to reactor trip is extremely unlikely.

b) Turbine Trip / Turbine Stop Valves The concern for this system is related to operating plants that utilize the turbine stop valves as their primary main steam isolation system. The Midland design provides safety-grade Main Steam Isolation Valves as the primary main steam isolation system upstream of the turbine stop valves, rp0182-0572a 131

5 c) ' Turbine Bypass /ATM Relief Valves Under all Accident Environments The concern for these systems is.related to operating plants that'do not have a safety grade main steam isolation system upstream of non-safety grade Turbine Bypass / Atmospheric:(. TM)

A Relief Valves. The Midland design provides safety-grade Main Steam Isolation Valves upstream of the non-safety grade Turbine Bypass /ATM Relief Valves.

d) Main Feedwater Control

1) Large LOCA The large break Loss-Of-Coolant Accident relies upon safety-grade equipment for mitigation. Table I states the analysis conservatively assumes a loss of all feedwater for a.large LOCA. The Midland design provides safety-grade Main Feedwater Isolation valves which isolate the main feedwater during a large LOCA.

2) Small LOCA The small LOCA analysis and operating guidelines utilize OTSG level for RCS cooling and depressurization. At the Midland Plant the safety-grade auxiliary feedwater ontrol system is utilized to control OTSG level for small LOCA and the safety grade main feedwater isolation valves will' isolate the main feedwater.

3) FWLB Inside/Outside Containment - SLB Inside/Outside Containment To remain within the bounds of the safety analyses for these events, and prevent additional RCS overcooling,-

feedwater must be secured quickly to the affected OTSG and auxiliary feedwater initiated and properly controlled to the unaffected OTSG.

Section II.B on Plant Unique Features has shown that the main feedwater will be isolated, within the allotted time (1C seconds), to both Once Through Steam Generators (OTSG) by the safety-grade-Main Feedwater Isolation Valves, and that auxiliary. feedwater 'will be initiated within 40 seconds.

Auxiliary feedwater to the affected OTSG will be isolated by the safety-grade auxiliary fecdwater isolation valves via Midland's Feed Only Good Generator (F0GG) feature which is safety grade. The auxiliary feedwater is controlled by a safety grade control system.

IV.

SUMMARY

IE Information Notice 79-22 was issued to inform the nuclear industry that certain non-safety grade equipment, if subjected to an adverse rp0182-0572a131

r.

6 environment resulting from high energy line breaks inside or-outside of containment could complicate the event beyond'the FSAR analysis.

B&W reviewed the typical B&W 177 fuel assembly plant licensing basis analyses to define the non-safety-grade control-system assumptions and-

' responses used in the analyses.and listed them in Table I of.this report.

Next B&W did an evaluation to determine which of the licensing basis accidente (LOCA, SLB, FWLB)' analyses could be impacted by an adverse environment affecting_the equipment related to Table I.

The result of this evaluation is listed in Table II.

From Table II you can see that the Midland Plant has the distinct advantage of utilizing safety srade control systems / components in place of many of the non-safety grade s/ stems / components utilized by the typical B&W 177 fuel assembly operating plants.

Table III of this report is entirely Midland specific and demonstrates-that the IE Information Notice 79-22 concerns related to the. typical B&W 177 fuel assembly plant will not complicate the LOCA, SLB, or FWLB events beyond the FSAR analysis for'the Midland Plant Units 1 and 2.

rp0182-0572a131

TABLE I TYPICAL B&W 177 FA EQUIPMENT RESPONSE DURING 111C11 ENERGY LINE BREAKS s

Steam Line Feedwater Large Small Break Line Break LOCA LOCA-I.

Reactor Power Control and Shutdown Trip Function Utilized liigh $ or low

.lligh RC Pressure Reactor Trip Low RC Pressure RC Pressure Not Used Time of Reactor Trip 1.1-8.0 sec 8.2-13.4 sec II.

Reactor Pressure Control Time'to PORV Actuation PORV Not 4-8 see PORV Response PQRV May Be Actuated for Not Important Required for Time at which PORV Closes Steam Line

%20 see Depressurization Break In Long Term III.

Steam System Isolation and, Pressure Control (1)

Steam Line Isolation Time 1.6-8.5_sec' 6,0-12.0 see Code Safety Code Safety a ves are sed alves a (2)

Time to Steam Releif Valve Opening 7.0-16.0 sec 7.0-7.5 sec g,

A 1 (2)

Time for Steam Relief Valve Closure 20-30 sec 25-30 see for Conservatism for Conservatism IV.

Feedwater System Isolation and Control

{1)

Main Feedwater Isolation Time 19-34 see S18 see Analysis Con-Manual Level se vatively (1)

Auxiliary Feedwater Isolatica Time 19-34 sec N18 see g

oss R

ments (2)

Auxiliary Feedwater Initiation Time N40 sec

%40 sec of All Feed-Based Upon (2)

Main or Auxiliary Feedwater Control Maintain Maintain-Minimum Minimum E*#"

"E ui e ines OTSG Level-OTSG Level (1)

Aff ected Steam Generator for SLB and FWLB (2)

Unaf fected Steam Generator for SLB and FWLB a

wa

TABLE II CONTROL SYSTD1/ COMPONENTS RELATED iO TABLE I EOU1PMFST Licensing Basis Accidents SLB Inside SLB Outside FWLB Inside FWLB Outside Large Small Non-Safety-Grade Control Systems Containment Containment Containment Containment LOCA, LOCA I.

Reactor Power Control and Shutdown Control Rod Drive Control System x

x x

x x

x II.

Reactor Pressure Control Power Operated Relief Valve Z

Z Z

Z Z

Z Pressurizer Heaters Y

Y Y

Y Y

Y Pressurizer Spray Y

Y Y

Y Y

Y III.

Steam System Isolation and Pressure Control Turbine Trip / Turbine Stop Valves x

x Steam Line Isolation Valves

• Z Z

Z Z

Z Z

Turbine Bypass /ATM Relief Valves **

x x

x x

x x

IV.

Feedwater System Isolation and Control Main Feedwater Contro1**

x x

x x

x x

Main Feedwater Isolation Valves

• Z Z

Z Z

Z Z

Auxiliary Feedwater Isolation Valves

• Z Z

Z Z

Z Z

Auxiliary Feedwater Initiation **

Z Z

Z Z

Z Z

Auxiliary Feedwater Level Control **

Z Z

Z Z

Z Z

• Affected Steam Generator for SLB and FULB

- Environmental Effects Cannot 9ccur Due to Location of

• • Unaf fected Steam Generator for SLB and FNLB Equipment (Inside containment vs outside containment)

Y Environment will not affect Safety Analysis Results x Environment could affect Safety Analysis Results 2 These ore safety-grade systems at the Midland Plant NOTE: The Z entries are !!idland specific while _ all other entries are for the typical B&W 177 Fuel Assembly Plants.

TABLE III IMPACT OF NON-SAFETY-GRADE CONTROL SYSTEM /COFfPONENT EFFECTS ON THE MIDLAND SAFETY ANALYSIS Licensing Basis Accidents SLB Inside.

SLB Outside FWLB Inside FWLB Outside Large-Small Containment Containment

' Containn.ent Containment LOCA LOCA I.

Reactor Power Control and Shutdown Control Rod Drive Control System (2)

(2)

(2)

(2)

(2)

(2)

II.

Reactor Pressure Control Power-Operated Relief Valve Pressurizer Heaters Pressurizer Spray III.

Steam System Isolation and Pressure l

Control Turbine Trip / Turbine Stop Valves (1)

(1)

Steam Line Isolation Valves Turbine Bypass /Atm-Relief Valves (1)

(1)

(1)

(1)

(1)

(1)

.IV.

Feedwater System Isolation and Control l

Main Feedwater Control (1)

(1)

(1)

(1)

(1)

(1) l Main Feedwater Isolation Valves Auxiliary Feedwater Isolation Valves Auxiliary Feedwater Initiation Auxiliary Feedwater Level Control (l')

Safety-Grade equipment can be shown to nerform intended function at the Midland Plant.

(2)

Required period of operability is short.

i l

, NOTE: All open entries are either a (-) or a Y or a Z on' Table II and will.not impact.the safety analysis.

L D>

.. _ _