ML20207H921

SPDS Critical Safety Function Selection Summary Package, Catawba Nuclear Station

ML20207H921
Person / Time
Site:	Catawba
Issue date:	03/14/1986
From:	Lee H DUKE POWER CO.
To:
Shared Package
ML20207H868	List: ML20207H863 ML20207H890 ML20207H921 ML20207H933 ML20207H950 ML20207H954 ML20207H960 ML20207H965 ML20207H970
References
NUDOCS 8607250135
Download: ML20207H921 (5)

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Attachment 2 SPDS CRITICAL SAFETY FUNCTION SELECTION SUISEARY PACKAGE CATAWBA NUCLEAR STATION Section I: Description of Selection Process Section II: Summary of Results Section III: Listing of Applicable Correspondence H. J. Lee, Jr.

Nuclear Engineering i

Design Engineering Department

{ March 14, 1986

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8607250135 860715 PDR ADOCK 05000414 P PDR l

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i Attachment 2 1

j I. Description of Selection Process The following material is condensed from the Westinghouse

! Owners Group Emergency Response Guidelines Background

, information.

Critical Safety Function Identification For each of the barriers to the release of radioactive j material, there is a set of functions that must be maintained on a continuing basis if the barrier is to remain intact. The full set of functions that must be maintained in order to fully safeguard the general public from possible consequences of nuclear power plant operation is commonly referred to as

the set of safety functions. There are a variety of methods l available for identifying the components of a set of safety i functions and, as a result, the tabulations of safety l functions that are developed frequently appear to differ among i themselves. In reality, the differences are usually semantic, t The actual physical processes which must occur if the barriers

are to be kept intact are the same, regardless of the method

{ of analyzing the processes or the naming of the safety

functions. A second point to be considered in comparing sets j of safety functions is that a specific set may be intended only for a specific limited application and so may not include i certain safety functions that would be included in a more i general set. The only point of issue in comparing various l sets of safety functions having a common scope is whether

each of the sets is complete within that comon scope.

For purposes of developing symptom-based function related

restoration strategies for the operator, only the fuel matrix / cladding, reactor coolant system pressure boundary and containment vessel barriers need to be considered. The other l components of the general containment barrier can be i associated with the " distance" barrier and included within the scope of the Site Emergency Plan. The scope of application is I also limited to emergency operations in which the reactor is intended to be shut down. That is, normal power operations i are excluded from the scope of the set of safety functions

needed to address emergency transients. A set of safety i functions that is sufficient for the fuel matrix / cladding,

! reactor coolant system pressure boundary and containment l-vessel barriers in a plant that is intended to be shut down

consists of: i t

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Attachment 2 Maintenance of SUBCRITICALITY l

Maintenance of CORE COOLING Maintenance of HEAT SINK Maintenance of Reactor Coolant System INTEGRITY I Maintenance of CONTAINMENT Integrity Control of Reactor Coolant INVENTORY t This safety function set is defined as the critical Safety 7*

Functions. These Critical Safety Functions are associated with the barriers in the following manner:

1 i

Barrier Critical Safety Function l

' Maintenance of SUBCRITICALITY (minimize energy

production in the fuel)

Maintenance of CORE COOLING (provide adequate

~

Fuel Matrix reactor coolant for heat removal from the fuel) and Fuel Clad Maintenance of a HEAT SINK (provide adequate j secondary coolant for heat removal from the fuel)

Control of Reactor Coolant INVENTORY (maintain j enough reactor coolant for effective heat i

removal and pressure control)

! i

} Maintenance of a HEAT SINK (provide adequate l heat removal from the RCS)

Reactor Coolont Maintenance of Reactor Coolant System INTEGRITY l System Pressure (prevent failure of RCS)

Boundary l

Control of Reactor Coolant INVENTORY (prevent i

flooding and loss of pressure control) i l

Containment Vessel- Maintenance of CONTAINMENT Integrity (prevent failure of containment vessel)

I i

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Attachment 2 Situations can arise in which the integrity of a barrier is lost and cannot be restored even though all Critical Safety Functions are satisfied. The classic double-ended guillotine break of reactor coolant system piping constitutes an irrevocable failure of the reactor coolant system pressure boundary barrier. In this situation the reactor coolant system pressure boundary barrier is recognized to be failed, and all available resources are directed toward minimizing further degradation of the failed barrier and keeping the fuel matrix / cladding barrier and the containment barrier intact.

Critical Safety Function Prioritization Prioritization of the Critical Safety Functions is based directly on the barrier concept from which they are developed.

Since the first barrier to fission product release is the fuel matrix / cladding, the Critical Safety Functions related to this barrier are given the highest priority. Challenges to this barrier can come from inside and outside the barrier. The internal challenge comes from excessive core heat production resulting from fission power production (normal decay heat production is considered in safeguards system design) . Core heat production in excess of safeguard systems core heat removal capability is the most severe challenge to the fuel matrix / cladding barrier. If the ccre is at power, the energy production represents a potential additional significant challenge to the other barriers which may also be challenged or failed. Consequently, SUBCRITICALITY is the highest priority Critical Safety Function. The external challenges to the fuel matrix / cladding barrier come from inadequate decay heat removal due to either inadequate reactor coolant or secondary coolant. Even though the reactor core is shutdown, failure to remove the thermal energy from decay heat production can rapidly lead to sufficiently high core temperatures to fail the first barrier. CORE COOLING and HEAT SINK ate the second and third priority, respectively, Critical Safety Functions.

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j Attachment 2 1

I The second barrier to fission product release is the reactor

!- coolant system pressure boundary. Although challenges can again come from inside and outside, only the internal threats

are considered in prioritizing critical Safety Functions since

only they can be addressed by the operator. Potential 4

internal threats due to excessive core heat production and i inadequate core heat removal are addressed through the SUBCRITICALITY, CORE COOLING and HEAT SINK Critical Safety j Functions. The remaining internal threat to reactor coolant i

system pressure boundary results from a reactor vessel j pressurized thermal shock condition. Such a challenge can

' result from thermal stresses acting on a radiation embrittled

} reactor vessel in a low temperature reactor coolant condition.

! Reactor Coolant System INTEGRITY is therefore the fourth

priority Critical Safety Function.

s

' The third barrier, Containment, is analogous to the second barrier in that only internal threats are considered in prioritizing Critical Safety Functions. CONTAINMENT is the fifth priority critical Safety Function.

i 4 The sixth priority Critical Safety Function is Reactor Coolant I INVENTORY. This Critical Safety Function is actually a subset of the CORE COOLING Critical Safety Function but is considered j separately to facilitate Status Tree construction and ,

l prioritization of challenges. This Critical Safety Function addresses situations wherein reactor coolant inventory is

j adequate to satisfy the CORE COOLING Critical Safety Function i but not within the nominal operational limits. The challenges associated with the Reactor Coolant INVENTORY Critical Safety l Function are the lowest priority of all Critical Safety i Function challenges.

II. Susunary of Results I

The prioritization of Critical Safety Functions based on the barriers to fission product release results in the following i descending order:

i SUBCRITICALITY

! CORE COOLING l HEAT SINK  ;

! INTEGRITY  !

l CONTAINMENT l

INVENTORY III. Listina of Anolicable Correspondence l

f (none identified) f l

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