Issue Date: 11/25/88 - 1 - 9900 STS 3.7.5

NRC INSPECTION MANUAL ILPB

PART 9900: TECHNICAL GUIDANCE

STS375.TG

STANDARD TECHNICAL SPECIFICATIONS

SECTION 3.7.5 ULTIMATE HEAT SINK

A. PURPOSE

To provide guidance on Standard Technical Specifications (STS)

Section 3.7.5 as it relates to determining the average water

temperature of the ultimate heat sink.

B. BACKGROUND

As a result of severe summer weather conditions, both Indian Point

Unit 2 and Unit 3 experienced an unforeseen increase in the

temperature of their ultimate heat sink and source of emergency

service water (Hudson River). When Unit 2 was faced with peak river

water temperatures exceeding the TS limit, plant personnel proposed

use of a time averaged temperature, which effectively reduced the

surveillance temperature in order to remain below the LCO limit.

C. DISCUSSION

The Westinghouse STS (3.7.5) on the ultimate heat sink, identifies

as part of the limiting conditions for operation, the requirement

that, "The ultimate heat sink shall be OPERABLE with: b. An average

water temperature of less than or equal to ( ) F." Under

surveillance requirements the TS read, "The ultimate heat sink shall

be determined OPERABLE at least once per 24 hours by verifying the

average water temperature and water level to be within their

limits."

The confusion referred to, stems from the language of the STS which

refers to an "average" water temperature. Some licensee's have

interpreted this to mean that an acceptable surveillance temperature

of the ultimate heat sink is a "time averaged" temperature based on

multiple measurements taken over a 24 hour interval. The use of a

time averaged temperature is not acceptable for demonstrating

compliance with the TS limits. The reference in the TS to an

"average" temperature, refers to a volumetric average or average

based on the readings of various individual thermocouples taken at

the same time. The TS do not allow a time average to effectively

dampen peak values occurring due to higher daytime temperatures or
9900 STS 3.7.5 - 2 - Issue Date: 11/25/88

tidal effects. The TS limits the temperature to that assumed in the

accident analysis or design of various components and systems. If

the use of a time averaged temperature means that for significant

periods of time the ultimate heat sink exceeds the TS limit or

greatly exceeds the temperature limit for short periods of time,

then for those intervals the plant is operating in an unanalyzed and

potentially unsafe condition. Since the
Issue Date: 11/25/88 - 3 - 9900 STS 3.7.5

ultimate heat sink is the long term mechanism for removal of reactor

decay heat and cooling of essential equipment loads, it is important

to maintain plant operation within design limits. Further, the

service water system and ultimate heat sink is often the source of

cooling for normal operating heat loads and provides margin against

unnecessary plant trips.

D. REFERENCE

The guidance provided in this directive was extracted from a

memorandum from John W. Craig, Chief, Plant Systems Branch, for

Frederick J. Hebdon, Chief, Inspection and Licensing Program Branch,

dated August 31, 1988, subject: Service Water/Ultimate Heat Sink

Temperature Surveillance (NUDOCS 69478/360).

END