ML19098B449

Response to Letter of 5/20/1977, Furnishing Information Re Postulated Fuel Handling Accident in Containment & Submitting Revised Analysis Including Proposed Tech Spec

ML19098B449
Person / Time
Site:	Surry
Issue date:	07/05/1977
From:	Stallings C Virginia Electric & Power Co (VEPCO)
To:	Case E, Reid R Office of Nuclear Reactor Regulation
References
Serial No. 217A/052077
Download: ML19098B449 (16)

Text

July 5, 'l.977'. :

Mr. Edson G. Case, Acting Director Serial No. 217 A/052077 Nuclear Reactor Regulation PO&M/TAP/ALH:das U. S. Nuclear Regulatory Commission Docket Nos. 50-280 Washington, D. C. 20555 50-281 License Nos. DPR-32 Attn: Mr. Robert W. Reid, Chief DPR-37 Operating Reactors Branch 4

Dear Mr. Case:

This is in.response to your letter of May 20, 1977, in which you address-ed the postulated Fuel Handling Accident in Containment. The bases for our conclusion that the potential consequences of a fuel handling accident in con-tainment are well within the guidelines of 10CFRlOO are as follows:

1. The presently installed ventilation systems at Surry are such that only one of two diverse means need function to assure that 10CFRlOO guidelines are met during a postulated fuel handling accident in con-tainment.

a. The purge isolation system, which is actuated by any one of three seismic qualified radiation monitors, is capable of terminating a radioactive release before 10CFRlOO guidelines are exceeded. This is shown in attached cases 1, 2 and 4.

A loss of off-site power will render the purge isolation sys-tem inoperable, but would also cause all ventilation flow in and out of containment to cease. Since the containment is at atmospheric pressure during fuel handling, such a situation would not result in a radioactive release from containment.

b. The ventilation filter system which is analyzed in attached case 3 also serves to prevent exceeding 10CFRlOO guidelines during a fuel handling accident. A seismic event might affect the filter performance since the charcoal beds and the duct-ing between the outboard isolation valve and the filter inlet are not seismic qualified.

2. The probability of a seismic event at the Surry Station as stated in the Reactor Safety Study (WASH 1400 - NUREG-74/014). is between 10-4 and 10:-6 events per year. The largest period of time that fuel is

.being handled in containment is ten days per 18 months or.1.9 percent of *the time. This results in a conservative probability of a seismic event at the same time as fuel handling accident (given it has a 100%

probability) of 2 x 10-6 events per year.

• e e VIRGINIA ELECTRIC AND POWER COMPANY TO ~r. Edson.G. Case Page 2 We therefore believe that a containment fuel handling accident which results in exceeding 10CFR100 guidelines is not credible. We believe that increased sur-veillance to determine equipment operability.is. sufficient to assure that 10CFR100 guidelines will not be exceeded during the postulated accident. We therefore sub-mit for your study.the attached Technical Specification changes. (.These changes will be pursued through the normal channels if this concept is determined to be ap-propriate.) The changes address the following requirements:

1. The purge isolation system will be proven operable, with the closing of the valves in less than 30 seconds, .before and .weekly during fuel handling operations in containment.

2. The filters will be proven operable before fuel handling operations in containment.

The attached .revised analysis includes the proposed Technical Specification parameters and should justify all of our assumptions regarding the radioactivity released to the environment.

Very truly yours,

'77

• r/"* "

Cr2, )1),1. ':ffd&!c-.c,c')/.1/

C. M. Stallings Vice President-Power Supply and Production Operations Attaclnnents cc: Mr. Norman C. Moseley

Page 1 ~f 11 Revision 1 6-23-77 ATTACHMENT ANALYSIS OF REFUELING ACCIDENT IN CONTAINMENT Assumptions During refueling the contairnaent purge system is set up to exhaust through the ventilation filters in the Auxiliary Building. Both filter banks will be on 'line because the Fuel Building is also exhausting through the filters.

The total flow rate for both systems is 66,000 cfm while the design flow rate for each filter is 36,000 cfm.

While the purge system is in operation, the air flow in the containment is as follows. Air enters the containment through two 15000 cfm fans (FS-F-4A & B), through two 36 inch butterfly supply valves (MOV-VS-100 A &

B) and is dispersed through the ring header outside the crane wall at EL-3 1 6". The air is continuously recirculated inside the containment by three 75,000 cfm recirc fans (VS-F-1 A,B;C). The air is purged from the contain1nent through the ring header at EL-20' outside the crane wall.

The air discharges through two 36 inch butterfly valves in series (MOV-VS-100-C,D). The air then passes through the Auxiliary Building Filter Banks (VS-FL-3 A & B) and the two 15000 cfm Purge Exhaust Fans (VS-P-5 A,B) o The-worst* single failure would be loss of the valve closing circuit which closes the valves and secures the purge fans en an alarm from either the crane monitor or the containment gas and particulate monitors. The two output relays are sufficiently redundant to secure purge flow; however, a loss of power to this circuit would cause them not to function. This would cause a total release through the filters with a boundary dose as calculated for case 3 of the dose calculations. This dose is still within the allowable limits, but our worst case.

Locations of containment gas and particulate radiation monitors The sample line ties . int~ 30" recirc, duct in containment at EL-9' 10".

The monitors are located in the Auxiliary Building at EL 45'10" along the west wall.

Sample line 1 11 ARC-2-21B which connects the containment particulate and gaseous monitor to the recirculation duct Length from 11448-FK-10 A & B 214 ft.

System flo~ from 11448-SN-207 10 cfm 3

Volume 0.870 ID Tube-= 1526.6in Response Time of sample to be detected in the containment articulate and aseous monitor 3 3 3 3 Flow == 10 Ft /min X miri/60 sec X l 728in /Ft = 288. in /sec Time= 1526.6 in 3

~ 288 in 3 /sec = 5.3 secondsfuse 30 seconds for conservatism

Page 2 of 11 e

. *--*t/ . *

• Air !Flow Rate 3QOOO cfm for purge system alone to calculate transit time of release in ducting Duct Area 2

= 9o62 Ft Duct Lengths I

Inlet to exhaust valve 130' *I I

Exhaust valve to filters 130' Velocity 3 3 V ~ve = 30,000 Ft /min X min/60 sec X Ft/9.62 Ft V = 51.9 Ft/sec Peak centerline velocity Umax ir 6 Umax

= 0.8 (Re=lc096Xl0 = Turb~lant Flow)

TT.--.~-,.

u1uu..n.. == 5le'): 0.3 = 64.9 FL/sec Transit Times

= 130 T 64.9 = 2 seconds Use le4 seconds to be conservative for transit time in exhaust ducting__

This analysis assumes that the .air flow path in the containment is continuous from the surface of the reactor cavity to EL-27. This is very conservative *as there is no velocity profile across the reactor cavity. Also,it is assumed that 50% of the area outside the crane wall is blocked with structures and equipment. This is a conservative assumption based on figures used in the LOCA analysis. The only mixing vol~me used is the volQme of air the release contacts in the transit from the cavity.to the exnaust inlet. .

Determine the open area outside the crane wall .. * - -* * - .z:. .. _:.. :-; * .

Containment diameter 126 1 Diameter inside crane wall 106 1 2 2 A= [ ~ (63) - 1r (53) ] 0.5 = 1822 Ft 2

Air Velocity Recirc air flow 225,000 cfm Purge air flow 3QOOO cfm Total 25~000 cfm for least possible transit time

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' Page 3 of 11 3 2 V = 255000 Ft /min X 1/1822 Ft X 1 min/60 sec = 2.33 Ft/sec which is also used for velocity across the cavity Air Transit Time Shortest distance from cavity surface to purge duct suction 70 Ft.

Time= 70 Ft~ 2.33 Ft/sec= 30 sec This is one-half the time assumed in our initial analysis.

Mixing As the transit time of the release is 30 seconds from the cavity to the inlet to the purge and recirculation system, the volume of air contacted during the transit.is considered for mixing.

Total flow 255,000 cfm Transit time 30 sec. 127,500 cubic feet for mixing

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Page 4 of 11 CASE ANALYSIS PROBLEM BASIS of Supposed Refueling Accident inside of Containment Case 1: The manipulator crane monitor is functional and actuates the containment isolation valves and secures _the purge fans.

Case 2: The manipulator crane area monitor is not functional requiring the containment gas or the containment particulate wonitor to actuate the isolation valves and secure the purge fans.

Case 3: Neither the manipulator crane area monitor or the containment gas and particulate monitors are operational resulting in a total release.

Case 4: Assume worst case isolation (i.e. Case 2) and the filters are not available or the exhaust duct outside of containment and downstream of the isolation valves fails.

Physical Characteristics of Systems and Assumptions Item 1) As~ume a puff release of radioactivity from a ruptured fuel assembly in the reactcir fuel cavity. This puff release is as close to the nearest purge exhaust grill as is physically possible.

Item 2) The response of the area monitor is gamma radiation sensitive so that ir is not necessary for it to be immersed in a radioactive cloud to detect radioactiyity. It's position (i.e. approx. 10 feet) above Lhe fuel cavity, unshielded from direct /-rays from the pool reaffirms its capability to detect an accident release immediately.

Item 3) The travel time of a radioactive cloud from a puff release at a P,Oint on the pool surface to the purge duct suction and recirculation suction is 30 seconds which is twice as conservative as the-initial analysis.

Item 4) The closure time of the isolation valves (including all electrical impulses and p~ocesses) is 20 seconds. (Worst Case at Site 19.4 sec.

for vaives alone) for Tech. Spec. Case use 30 sec. for valves and circuitry.

Item 5) The response time from the recirculation suction to the gas and particulate monitors detection is assumed at 54 seconds., per calculation above. f Item 6) The purge rate is 30000 cubic feet per minute .. per system design and not considering reduced performance due to exhaust through the filter banks. f Item 7) Filtration of containment purge exhaust during refueling is assumed to be conservatively 70% efficient.

Item 8) The assumed volume of containment air with which the radioactive release is mixed, during the 30 second transit 1:ime from the reactor cavity to the purge duct equals 127,500 cubic feet.per calculations above. j*

Item 9) The time for air to travel through the purge duct to the inboard isolation valves is assumed to be 1.4 seconds.

Item 10) The delay time from reactor shutdown to initiation of fuel assembly transfer operations is at least 100 hrs (Tech. Spec.)

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Page 5 of 11 e e Item 11) The radial peaking factor is assumed to be 1. 65, Item 12) The number of fuel assemblies in the CORE is 157.

Item 13) Ten percent of the Iodine fuel assembly activities are assumed to be released into the reactor cavity water with 99.75% being inorganic and .25% in the organic form. The fuel pool D.F. for inorganic iodine is 133 while the DF for organic iodine is 1.

Item 14) Ten percent of the Noble Gases present in the fuel assembly are released to the reactor cavity* pool with the exception of Kr 85; 30% of Kr 85 is released. The DF of the Fuel Pool water for Noble Gases is 1.

Item 15) Dose calculational method from R.P. 13, section "Dose Conversion Factors and Equations" (includes average garrnna and beta energies for each isotope and thyroid dose conversion factors) 3 3 Item 16) ~Q = 2.1 X 10- sec/m (Latest meteorology)

Item 17) Breathing rate= 3.47 X 10- 4 m: 3 /sec Item 18) Site boundary distance= 1650 ft Item 19) Surry 1 & 2 CORE activities Calculation Method for activity for hottest fuel element Total core activity (µCi)) /. 1 - - ) Pea](ing factor )

( after 100 hr. decay x ~57fuel assy X

( 1. 65

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Page 6 of 11 CASE 1 When a puff release results in airborne and direct gamma irradiation of the Manipulator Crane area monitor so that a prefixed dose rate setpoint is surpassed, activation of the isolation valves occurs instantaneously. It takes 20 seconds to isolate the contairunent. Thirty seconds is required for gaseous transit time to the purge duct. An additional 1.4 seconds is required from the purge duct grill to the 1solation valve. Therefore, if the Manipulator Crane Area Monitor is operational following a Fuel Handli~g Accident, zero release of radioactivity from the containment is expected9 Using the 30 seconds for valve closure (proposed for a Technical Specification Limit) to isolate the containment versus 31.4 seconds for the release to reach the inboard valve results in zero release.

e :pagf 7 __pf 11 CASE 2

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If the manipulator crane area monitor is not functional, following a fuel handling accident, the containment gas and particulate monitors will be used to actuate the containment isolation valves. The value* and site doses are as follows for a release of 74 seconds.which was ultra-conservative:

IsotQI>_!. Activity for hottest Activity Whole Bo21.(f) Whole Body(.8) Thyroid fuel element (},<~) Released Inorganic I 131 4.46 + 11 2.90 + 01 3.13 + 01 132 133 6.33 5.38

+

02 10 4.02 3o50 +

- 12 00 1.57 -

1. 02. +

13 00 134 6.93 - 23 4.51 - 33 8022 - 35 135 4.35 + 07 2o 83 - 03 2. 56 .., 04*

32.32 + 00 Organic I 131 4. 46 + 11 9. 71 + 00 1.05 + 01 132 6.33 - 02 1.38 - 12 5.38 - 14 133 5.38 + 10 1.17 + 00 3.41 - 01 134 6. 93 - 23 1.51 - 33 2.75 - 35 135 4.35 + 07 9.47 - 04 8.56 - 05 1.08 + 01 I 131 7.62 - 03 3.91 - 03 132 6.49 - 15* 1.10 - 15 133 1.56 - 03 9.09 - 04 134 7.93 - 36 1.62 - 36 135 2.90 - 06 8.67 - 07 9.18 - 03 rem 4.82 - 03 rem Kr 83m 85m 1.85 4.07

+

05 04 5.37 - 13 1.18 - 03 1.41 9.67

- 18 08 8.80

5. 77

- 18 08 85 6.06 + 09 5.27 + 02 5.80 - 04 5.80 - 02 87 4.03 - 12 1.17 - 19 5.27 - 23 5.70 - 23 88 89 L25 + 01 3.63 - 07 3. 80 - 10 5.40 - 11 Xe 131m 4.51 + 08 1.31 + 01 1.51 - 04 8.53 - 04 133m 9.99 + 09 2.90 + 02 3.63 - 03 2.68 - 02 133 8.54 + 11 2.48 + 04 __

9.60.,., ______

- 01 1.51 + 00 135m 2.60 + 00 + ---------

135 ______+.,,,_07 8.96 3.40 04 3 80 - 04 0

137 138

---

--------- 9.63 01 rem 1.59 + 00 rem Total 9. 72 - 01 rem 1.59 + 00 rem 43 .12 rem

Page 8 of 11 Case 2 (Continued)

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Case 2: Total Whole Body dose is 2.04 rem for Tech. Spec. valve closure Total Thyroid dose is 34. 38 rem and a total release of 59

• seconds r Case 2 assumes a 30 second transit time from the reactor cavity fuel pool to the purge duct during which time a certain amount of mixing occurs, as specified by suction off of the recirculation and purge fanso An additional 1.4 seconds is consumed in the purge duct prior to the isolation valve. The containment will be isolated ~O seconds after the radioactivity reaches the purge duct, resulting in a 5ff second release of the concentrations present at the purge duct grill 30 seco~ds following the fuel handling accident.

Calculation Method-for Activity Released Time Release) (l~Filter efficiency)

X ( 5.°l/60 X 0.3( '>1.0 Calculation Method for Dose f Activity Released \ xi .23/J\x/E '

\ ) \ .25/"} \ mev/dis /

Calculation with Proposed Technical Specification valve closure time Release Detection 30 seconds to purge inlet 30 seconds to,Purge inlet 1.4 seconds to Isolation valve 30 seconds for release to transit sample line 31.4 seconds 30 seconds for valve closure (by T. S.)

90 seconds Release continues for (90 - 31.4 seconds) = 58.6 seconds prior to isolation Case 2 with actual valve closure time of 20 seconds Release Detection 31.4 seconds 80 seconds Release continues for 48.6 Sec.

Total Whole Body Dose 1. 68 rem Total Thyroid Dose 28.31 rem

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e Page 9 of 11

( CASE 3 If none of the radiation monitors capable of the containment isolation is functional or if a selective power failure occurs at the semi-vital bus, a.11 of the radioactivity released from the reactor cavity fuel pool is assumed to be released to the environment through the filters. This assumes no manual securing of the purge systemo The releases and site doses are as follows:

Isotope Activity Whole Body(f) Whole Bodyy.s) Thyroid Released Inorganic I 131 1.00 + 02 lo08 + 02 132 1.42 - 11 5.54 - 13 133 lo21 + 01 3.53 + 00 134 lo56 - 32 2.84 - 34 135 9. 76 ~ 03 8.82 - 04 111.5 r~;

Organic I 131 3.35 + 01 3.61 + 01 132  :+.75 -12 1. 85 - 13 133 4.04+00 1.18 + 00 134 5.20 33 9.47 - 35 135 3.26 - 03 2.95 - 04 37~28 rem

, nc- 1" 'l nl, , ,

Ki. G.Ju1 l.

• OJ - J..~ 4. 87 - le '-'* V'""t' .- .I.. I 85m 4.07 - 03 3o33 - 07 lo98 - 06 85 1.82 + 03 2o00 - 03 2.00 - 01 87 4.03 - 19 1.81 - 22 1.97 - 22 88 1.25 - 06 1.31 - 09 1.85 - 10 89 Xe 131m 4.50 + 01 5.20 - 04 2. 93 - 03 133m 1.,00 + 03 1.25 - 02 9.23 - 02 133 8.53 + 04 3.31 + 00 5.20 + 00 135m 135 8.97 + 00 1.17 - 03 1.31 - 03 137 138 3.33 rem 5.50 rem I 131 2.64 - 02 1.35 - 02 132 2.28 - 14 3 86 - 15 0

133 5. 38 - 03 3.13 - 03 134 2.74 - 35 5.61 - 36 135 9.96 - 06 2.98 - 06 3.18 - 02 rem 1.66 - 02 rem Total 8.88 rem 14-8.,8 rem Calculation Method for Activity Released Activity of Assy ) ( 1 ) * (Fraction Re.leased ) 1-Filter eff. )

( Curies X \ DF X to Cavity )C.. ( 0.3 Iodine

. . .0075<>1.0 0.1..: > 0.3 1. O All orhers

e Page 10 of 11 Case 4 It is assumed that the worst case purge isolation exists (i.e., Case 2) and the filters have zero percent efficiency or the exhaust duct down stream of the isolation valves fails and the purge rate remains constant. The releases would be Case 2 modified by:

The contribution by Kr and Xe would remain unchanged with a whole body 'f9 of 9.63 - 01 rem and a& 1.59 + 00 rem. The Iodine contribution to whole body would be: __ 9.18 - 03 rem = -r 3.06 - 02 rem q 0.3

4. 82 - 03 rem

= 1.61 - 02 rem 1-A 0 3 0

Totals "f = 9.936 01 Whole body= 2.60 rem Total Thyroid Dose 43.12 :cem 143.7 rem 0.3

.,,\.,

Page 11 of 11 Conclusion Dose at Site Boundary Rem Whole Bod-y: Thyroid Case 1 (Manipulator Crane monitor triggers isolation) 0 0 Case 2 (Containment gas or containment particulate triggers isolation) Tech. Spec. Valve 2.04 34.38 Actual Valve Closure 1. 68 28.31 Case 3 (No containment isolation but 70% filter) 8,88 148.8 Case 4 (Worst case containment isolation and 0% filter) 2.60 14307 10CFR100 Guidelines 25 300

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• - TS 3.10-1 3-17-72

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3.10 REFUELING Applicability I Applies to _operating limitations during refueling operations.

Objective To assure that no accident could occur during refueling operatio~s that would affect public health and safety.

( Specification A. During refueling operations the folloking conditions are satisf.iecl:

I

1. The equipment door and at least one door in the personnel air

• 1ock- shall be properly closed;. For those systems. wh:i.ch provide a direct path from containment atmosphere to the -outside atmosphere, all automatic containment isolation valves,in the unit shall be operable or at least one . valve shall be. closed in each.line*

penetrating the containment.

2. The Containment Vent and Purge System;and the area and airborne radiation monitors which initiate isolation of this system, .shall

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be tested and verified to be operable innnediately prior to refueling operati~ns1 CVrief(

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9-13-76 b.

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The process vent gas monitor and particulate monitor shall be

. { operating.

6. All effluents to be discharged to the atmosphere from the waste gas decay tanks of the gaseous waste disposal system shall be sampled and analy~ed to demonstrate compliance with specification B-1 and B-3 138 above prior to releases via the process vent.

7. During periods* of primary to secondary leakage, the alar,Jl setpoint of< 1.3 µCi/cc will be based on actual isotopic content of samples obtained and analyzed on the multichannel analyzer.

8. Whenever the air ejector discharge monitor is inoperable and the steam generator blowdown monitors indicate a primary to secondary leak, the automatic divert feature shall be defeated and samples shall be taken from the air ejector discharge and analyzed from gross activity on a daily basis. If the gross activity reaches

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flow shall be manually diverted to the containment.

9. The maximum activity to be contained in one gas decay tank shall not exceed 95,400 curies equivalent of Xenon 133.

10. Purging of the containment shall be governed by the following conditions:

a. Containment purge shall be fil.tered through the high efficiency particulate air filters and charcoal absorbers whenever the co~centration of iodine and particulate isotopes exceed the occupational MPG inside the containment.

b. Containment purge shall be filtered through the high efficiency particulate air filters and charcoal absorbers whenever irradiated I. fuel is being handled or any object is being handled over irradiated Amendment No , 2L,

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' . e fuel in the containment. a.~~

• - 1 ' . ~~~

TS 3.11-5 3-17-72 Basis*,

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The releases of radioactive materials will be kept as low as practicable as required by 10 CFR 50 and will not exceed the concentration limits specified in 10 CFR 20. At the same time, the licensee js permitted the flexibility of operation, compatible with considerations bf health and safety, ta assure that the public is provided a dependable source of power under unusual operating conditions which may temporarily result in releases in excess of four percent of the conce*n tration limits specified in 10 CFR 20. However, all releases must be kept within the concentration limits specified in 10 CFR 20. It is ex-pected that using this operational flexibility under unusual operating conditions, the licensee shall exert every effort to keep levels of radioactive materials C:

released from the. pJant  ;:iR h1w as prartfr.ahle anr1 th::it ;:inn11;ii. rplP.;:ii:;pi:; will nn1-exceed a small fraction of the annual average concentration limits specified in 10 CFR 20.

The limiting conditions* for operation contained in specification A-3 _above, which relates to the total number of curies which may be released in liquid effluents in any year, is based on the expected perfonnance of the Surry Power Station assuming both units are operating with 0.25 percent leaking fuel and each unit is experiencing a 20 gallon per day primary to secondary system leak rate.

The formula prescribed in specification B-1 takes atmospheric dilution into account and assures that at the point of maximum ground concentration at the site boundary, the req~irements of 10 CFR 20 will not be exceeded. The limit

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is based on the highest annual avera~~ value of ?(/Q which will occur at the