ML20078N847

Forwards Response to NRC 830902 Comments on Unresolved Items Re Containment Purge/Vent Review.No Addl Tech Specs or Equipment Mods Warranted.Operability Requirement Met W/Compliance W/Tmi Item II.E.4.2

ML20078N847
Person / Time
Site:	Millstone
Issue date:	10/27/1983
From:	Counsil W NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	John Miller Office of Nuclear Reactor Regulation
References
RTR-NUREG-0737, TASK-2.E.4.2, TASK-TM A03501, TAC-42588, TAC-44864, NUDOCS 8311030019
Download: ML20078N847 (5)

Text

-

, . gggggggggg General OHkes e Seldon Street, Berkn. Connecticut

""S*""*"'C""

P.O. BOX 270 5

.am wra ma cow, HARTFORD. CONNECTICUT 06141-0270 g ase ur e cow- (203) 666-6911 October 27, 1983 Docket No. 50-336 A03501 Director of Nuclear Reactor Regulation Attn: Mr. James R. Miller Operating Reactors Branch #3 U. S. Nuclear Regulatory Commission Washington, D. C. 20555

References:

(1) 3. R. Miller letter to W. G. Counsil, dated September 2,1983.

(2) W. G. Counsil letter to R. A. Clark, dated March 28, 1983.

(3) R. A. Clark letter to W. G. Counsil, dated February 9,1983.

Gentlemen:

Millstone Nuclear Power Station, Unit No. 2 Containment Purge / Vent Review In Reference (1), the Staff identified several issues which were felt to be unresolved relative to containment isolation, purging and venting at Millstone Unit No. 2. Reference (1) provided Staff comments regarding our Reference (2) response to this issue. Northeast Nuclear Energy Company (NNECO) has addressed in this document the NRC comments and our response is attached. In so doing, NNECO did not reiterate the specific staff concerns, but rather refers the reader to these items as documerited in Reference (1).

NNECO has concluded that no additional Technical Specifications or equipment modifications to Millstone Unit No. 2 are warranted. Our technical basis for this conclusion is provided in both our response of Reference (2) and in this document.

We trust you will find this information resolves the outstanding items of the Millstone Unit No. 2 containment purge / vent review.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY 8311030019 831027 PDR ADOCK 05000336 - -

p PDR

.##. . go\

W. G. Counsil D Senior Vice President g)l l

J

w-

' ~

Response to item 1:

~

In the Staff's Reference '(1), Item 1 comments, ' Northeast - Nuclear Energy Company (NNECO) understaads the NRC expressed concern to be the following

. Items:

o ' The 6-inch _ butterfly valves have not been qualified to shut if a loss of coolant accident (LOCA) occurs while they are being used to vent the containment. For guidance in ' qualifying these 6-inch valves, the Staff provided enclosure (1) entitled " Operability Qualification of Purge ~ and Vent

' Valves."

o How is Millstone Unit No. 2 conforming to or plans to conform to the NRC '

Staff's " Interim Position for Purge and Vent Valve Operation Pending Resolution of Isolation Valve Operability?"

o Venting should be limited to a specific annual goal amount of -time commensurate with plant safety needs.

- Enclosure- 1 of Reference (1), " Operability Qualification of Purge _ and Vent Valves" states guidelines that are necessary to assure -containment isolation during a design basis ~ accident. This demonstration is required by Branch Technical Position CSB 6-4.' NNECO notes that these guidelines have already been met as -documented in the NRC's Reference (3), Enclosure 4 Safety Evaluation Report (SER) on purge / vent valve isolation dependability, NUREG-0737, item II.E.4.2 position 6 for Millstone Unit No. 2. The SER states

that the Staff " review of NNECO's response dated May 20,1981 and Sections 6.6 and 6.7 on Containment Post Incident Hydrogen Control System and Enclosure

- Building Filtration System, respectively," of the Millstone Unit No. 2 FSAR,

" indicates that the 6-inch hydrogen purge valves meet the intent of position 6.-

The performance, reliability and size (less than 8 inches) of the 6-inch hydrogen purge lines are acceptable."

NNECO points out that meeting the intent of position 6 of NUREG-0737 Item ILE.4.2 rests on the 6-inch purge-lines satisfying the operability criteria set

'forth in Branch Technical Position CSB 6-4 and the Staff Interim Position for Purge and Vent Valve Operation Pending Resolution of Isolation Valve Operability.

Thus, it is NNECO's opinion that the operability requirements of Enclosure 1 of Reference (1), " Operability Qualification of Purge and Vent Valves" have been met. -

This position is 'further supported by the Staff in Reference (3) wherein it is documented that multi plant issue B-24 is resolved for Millstone Unit No. 2 with the exception of specific concerns which NNECO addressed in Reference (2).

In our' Reference (2) response to Question Ib, NNECO presented design information on the 6-inch valves with an evaluation of valve ability to close against Edifferential pressures which would exist following a design basis accident. .. At ' that time, NNECO stated that the.m valves.will perform their intended function and close upon a Containment Isolation Actuation Signal (CIAS) against a differential pressure of 60 psig.

J

NNECO -would .like to clarify that the 6-inch valves close 'within 5 seconds following a CIAS as required by the Technical Specifications. Further, the design basis LOCA documented in .the: updated Millstone Unit? No. 2- FSAR includes the predicted containment pressure response as- a function of time during the event. For the worst case large break.. LOCA the maximum containment pressure during closure of the 6-inch purge valves is predicted to be

- approximately 25 psig. This value is well below the design limit of 60 psig for these valves. In addition, ~ the predicted peak pressure occurs 238 seconds following initiation of.this event and is below the containment design pressure of 54 psig. The containment' vent valves will be closed well before 'the peak containment pressure is reached.

In' Reference (1), the Staff requested that venting be limited to a specific annual goal amount of time commensurate with plant safety needs. It is NNECO's understanding that the Staff's SER, Enclosure 1 of Reference (3), stated that e although the 6-inch hydrogen purge lines meet the requirements of Section B.I.c .

l1 of Branch Technical Position CSB 6-4, Revision 1, " Containment Purging During -

j Normal Plant Operations," it is the Staff's view that venting should be limited.

I NNECO recognizes that the plant is inherently safer with closed purge / vent isolation valves. As such, the plant is operated according to this philosophy, with purging / venting through the 6-inch valves in accordance with plant safety needs.

As stated, in Reference (3),' these valves are operated in order to comply with i the Limiting Condition for Operation for containment pressure delineated in Section 3.6.1.4 of the Millstone Unit No. 2 Technical Specifications.

' However, it is NNECO's position that while the licensee should limit purging commensurate with plant safety needs, there is no valid technical basis for restricting the use of the 6-inch hydrogen vent lines to a specified annual time limit. Therefore, NNECO intends to vent through the 6-inch lines according to

. plant safety needs. Based upon accumulated operational data it is expected that these valves will be cpen approximately 300 hours0.00347 days <br />0.0833 hours <br />4.960317e-4 weeks <br />1.1415e-4 months <br /> per year and thus will allow l adequate plant operational flexibility without compromising plant safety.

i i-i~

t i )

Response to item 2:

NNECO's position regarding leakage integrity testing has been communicated to the Staff in our response to Question 2 in Reference (2). In summary, NNECO -

concluded that for both the 42-inch seals and 6-inch seals the present leak rate testing requirements were adequate to determine seal integrity. NNECO

. believes that these intervals are justified. Millstone Unit No. 2 Technical Specifications Section 3/4 6.1.2 requires periodic testing of both size valves.

These valves have been tested individually (Type C-local leak rate test) at every refueling outage since plant operation began in December,1975. Also two additional (Type A) integrated leak rate tests have been performed. Test results -

to date have confirmed no failures due to degradation of the resilient seals. For over seven years of plant operation, there has been no degradation of the resilient seals more rapid than stated by the manufacturer. 'The maintenance and repair of these resilient seals are per the manufacturer's instructions and are assured by plant procedure.

Therefore, additional Technical Specifications are not necessary for adequate resilient seal -testing ' and maintenance. - Furthermore, requiring additional technical specifications solely for the purpose of purge / vent valve seal testing would not conform with the intent of the Commissian's proposed rule published in the Federal Register (47 FR 13369). Northeast Nuclear Energy Company emphatically endorses the concepts embodied in the proposed rule, and reiterates the view that the volume and complexity of the current technical specifications is not conducive to focusing the attention of plant operators on matters -of authentic safety significance.- The existing situation should not be exacerbated with the inclusion of additional testing requirements of secondary importance.

L J

Response to Item 3 In Item 3, the Staff expressed concem that a small break LOCA might not generate CIAS signals rapidly enough to preclude release of radioactive material through the 6-inch purge lines and therefore containment should be isolated on a high radiation signal. NNECO notes that this item was addressed in our response to Question 3 of Reference (2) and that although our analysis, summarized in Reference (2), did indeed address a large break LOCA coincident with containment venting through the 6-inch lines, our position remains valid.

NNECO maintains that high radiation auto-closure of 6-inch valves is not required since the valves auto-close on either high containment pressure or low pressurizer pressure signals for both small and large break LOCAs.

- In order for significant amounts of radioactive material to be released to containment, and subsequently to the environment, thrcugh the open hydrogen vent valves, one must assume significant core damage has occurred. The Millstone Unit No. 2 licensing basis small break LOCA analysis models such a scenario. This analysis conservatively predicts that the Safety Injection Actuation Signal (SIAS) and CIAS occur within 60 seconds following the design basis small break LOCA. A SIAS automatically initiates containment isolation, thereby closing any potential leakage path from containment. Furthermore, Millstone Unit No. 2 Operating Procedure 2506, " Loss of Coolant Incident",

requires verification that all equipment receiving a Containment Isolation Actuation Signal is in its accident mode. This includes the 6-inch purge / vent valves being verified closed.

NNECO also points out that the 6-inch lines do not provide a direct path to the environment but vent through charcoal, particulate and absolute filters and then discharge through the monitored 375 foot Millstone Unit No. I stack. Reference (3), Enclosure 1, states that it is the Staff's judgment that those lines that provide a direct path frcm the containment atmosphere to the environment should be isolated on high radiation signal. This is not the case at Millstone Unit No. 2 as described above and therefore this position is not applicable to the 6-inch vent valves.

Additionally, Northeast Nuclear Energy Company has performed a cost / benefit evaluation concerning the Staff request to modify the 6-inch butterfly valves to receive an isolation signal from containment radiation monitors. A total expediture of approximately $130,000 would be required for such a modification.

NNECO has concluded that the cost of such a modification exceeds its safety value as described above and in Reference (2).

NNECO believes that requiring high radiation auto-closure of the 6-inch lines at Millstone Unit No. 2 is contrary to the NRC plan for management of plant specific backfitting. There is not adequate justification that such a modification would contribute effectively and significantly to the health and safety of the public and lead to utilization of both NRC and licensee resources in as optimal a fashion as possible in the overall achievement of protection of public health and safety.

4

. .