ML20087N521

Proposed Tech Specs Changing Trip Setting for High Main Steam Line Flow Instruments from 120% to 140% of Rated Steam Flow

ML20087N521
Person / Time
Site:	Vermont Yankee
Issue date:	03/26/1984
From:	VERMONT YANKEE NUCLEAR POWER CORP.
To:
Shared Package
ML20087N517	List: ML20087N516 ML20087N521 ML20087N523
References
NUDOCS 8404030536
Download: ML20087N521 (3)

Text

._ . .

1 VYNPS ,

TABLE 3.2.2 PRIMARY CONTAINMENT ISOLATION INSTRUMENTATION i

Minimum Number of

, ' Operable Instrument Required Action When Minimum l Channels per Trip Conditions for Operations are System Trio Function Trip Setting Not Satisfied (Note 2) 2 Low-Low Reactor Vessel 182.5" above the' A Water Level top of enriched fuel 2 of 4 in each of High Main Steam Line $2120F B 2 channels Area Temperature 2/ steam line High Main Steam Line Flow $140% of rated flow B l

2/(Note 1) Low Main Steam Line Pr9ssure >850 psig B

High Main Steam Line Flow 140% of rated flow B 2/(Note 6) i 2 Low Reactor Vessel Same as Reactor A Water Level Protection System 2 High Main Steam Line 13 X background at B Radiation (7) (8) rated power (9) 2 High Drywell Pressure Same as Reactor A Protection System I

2/(Note 10) Condenser Low Vacuum 112" Hg absolute A 1 Trip System Logic - A Amendment No. 68 41 8404030536 840326 PDR ADOCK 05000271 PDR p

El VYNPS 3.2 (Cont'd)

The low-low'reactar. water level instrumentation is set lto trip when reactor water level is 82.5" H2 O indicated on the reactor. water. level instrumentation above the top of the enriched fuel.: This trip initiates closure of the Group 1 primary containment isolation valves and.also activates lthe ECCS and starts the standby. diesel generator system. This trip setting level was chorea to be low enough to prevent spurious operation, but high enough to initiate ECCS operation and primary system isolation so that no' melting of the fuel cladding'will occur and so that post-accident cooling can be accomplished and the limits of 10CFR100 will not be violated. For the complete circumferential break of a 28-inch recirculation line.and with the trip setting given above, ECCS initiation and primary system isolation are: initiated,in time to meet the above criteria. The instrumentation also covers the.

full range.of spectrum of breaks and meets the above criteria.

The high drywell pressure instrumentation is a backup to the water level instrumentation and in addition to initiating ECCS it causes. isolation of: Group 2, 3, and 4 isolation valves. For the complete circumferential break discussed above,.this instrumentation will initiate ECCS' operation at about the same time as the low-low water

~

level instrumentation, thus the results given above are applicable here also. Group 2 isolation valves include the drywell vent, purge, and sump isolation valves. High drywell pressure activates only these valves because high drywell pressure could occur as the result of non-safety-related causes such as not purging the drywell air during startup. Total system isolation is not desirable'for these conditions and only the valves in Group 2 are required.to close. Tha water-level instrumentation initiates protection for the full spectrum of loss-of-coolant accidents and causes a trip of all primary system isolation valves.

Venturis are provided in the main steam lines as a means of measuring steam flow and also limiting the loss of mass inventory'from the vessel during a steam line break accident. In addition to monitoring steam flow, instrumentation is provided which causes a trip of Group 1 isolation valves. The primary function of the instrumentation is to detect a break in the main steam line, thus only Group 1 valves are closed. For the worst case accident, main steam line break outside the drywell, this trip setting of 140 percent of rated steam flow in conjunction with the flow limiters and main steam line valve closure limit the mass inventory loss such that fuel is not uncovered, cladding temperatures remain less than 1295 0 F and release of radioactivity to the environs is well below 10CFR100.

i Temperature monitoring instrumentation is provided in the main steam line tunnel to detect leaks in this area.

Trips are provided on this instrumentation and when exceeded cause closure of Group 1 isolation valves. Its l

setting of ambient plus 950 F is low enough to detect leaks of the order of 5 to 10 spm; thus, it is capable of l covering the entire spectrum of breaks. For large breaks, it is a backup to high steam flow instrumentation i discussed above, and for small breaks with the resultant small release of radioactivity, gives isolation before the limits of 10CFR100 are exceeded.

f Amendment No. 58, 68 63 1

E________ __ __ __ _ _ _ . . _ _ _ _ _

VYNPS .

3.7 LIMITING CONDITIONS FOR OPERATION 4.7 SURVEILLANCE REQUIREMENTS (2) The instrument line flow check valves shall be tested for proper operation.

b. At least once per quarter:

(1) All normally open power-operated isolation valves (except for main steam isolation valves) shall be fully closed and reopened.

(2) With the reactor power less than 75 percent of rated, trip all main steam isolation valves (one at a time) acd verify closure time,

c. At least twice per week:

(1) The main steam line isolation valves shall be exercised by partial closure and subsequent reopening.

2. In the event any isolation valve specified in 2. Whenever an isolation valve listed in 4.7.2 is Table 4.7.2 becomes inoperable, reactor power inoperable, the position of at least one nther operation may continue provided at least one valve valve in each line having an inoperable valve in each line having an inoperable valve is in the shall be logged daily.

mode corresponding to the isolated condition.

3. If Specification 3.7.D.1 and 3.7 D.2 cannot be met, an orderly shutdown shall be initiated and the reactor shall be in the cold shutdown condition within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

Amendment No. 50 133 Ns __