Information Notice 1990-78, Previously Unidentified Release Path from Boiling Water Reactor Control Rod Hydraulic Units

Previously Unidentified Release Path from Boiling Water Reactor Control Rod Hydraulic Units
	ML031130145
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	12/18/1990
From:	Rossi C; Office of Nuclear Reactor Regulation
To:	;
References
	IN-90-078, NUDOCS 9012120148
	Download: ML031130145 (11)
	v • d • e

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 December 18, 1990

NRC INFORMATION NOTICE NO. 90-78: PREVIOUSLY UNIDENTIFIED RELEASE PATH FROM

BOILING WATER REACTOR CONTROL ROD HYDRAULIC

UNITS

Addressees

All holders of operating licenses or construction permits for boiling water

reactors (BWRs).

Purpose

This information notice is intended to alert addressees to potential problems

pertaining to a previously unidentified release path from the control rod drive

hydraulic systems in boiling water reactors that may lead to design basis

accident radiation doses significantly exceeding the values specified in the

Final Safety Analysis Report. It is expected that recipients will review the

information for applicability to their facilities and consider actions, as

appropriate, to avoid similar problems. However, suggestions contained in this

information notice do not constitute NRC requirements; therefore, no specific

action or written response is required.

Description of Circumstances

In June 1989, a design review for unmonitored release paths at Washington

Nuclear Power Plant Unit 2 resulted in the discovery of a previously unidenti- fied radiation release path in the control rod drive hydraulic system. This

path is postulated to result from the following sequence of conditions. The

two control rod drive pumps are shut down following a design basis accident.

There is a break outside of the reactor building (secondary containment) in

the non-seismically qualified piping or tankage to which the control rod

hydraulic system is connected (see Figure 1). Reactor coolant leaks past the

double seals in any of the 185 control rod drives and the valves in their

associated hydraulic control units. The leakage flows back through one or

more of the four headers connecting each of the 185 hydraulic control units to

the common control rod drive (CRD) pump header. The leakage then flows through

the CRD pump header and the control rod drive pumps to the break or the conden- sate storage tank located outside of the reactor building.

Much of the pathway to the condensate storage tank lies outside of the reactor

building and includes piping that is not seismically qualified. In addition, this piping passes close to the air intakes for the control room ventilation

system. Consequently, a failure of the supply piping for the drive pumps

s3 -1D8W- /'C

IN 90-78 December 18, 1990 during an accident would not only greatly increase the potential external

release, but could increase the radiation dose to the control room operators.

General Electric-Nuclear Energy performed calculations for the newly postulated

release path for a design basis accident with concurrent failure of the

non-seismically qualified supply piping for the control rod drive system at

Washington Nuclear Power Plant Unit 2. The calculations incorporated the

source terms specified in Regulatory Guide 1.3 and assumed that 10% of the

iodine would escape as a gas from the liquid release. These calculations

produced a 30-day thyroid dose for control room operators of 121 rem per gpm of

leakage, a 30-day thyroid dose at the outer boundary of the low-population zone

of 86 rem per gpm of leakage, and a 2-hour thyroid dose at the exclusion zone

boundary of 36 rem per gpm of leakage. A generic communication discussing this

concern was sent by General Electric-Nuclear Energy to each BWR utility in

July 1989.

Discussion:

For the control rod hydraulic systems at General Electric boiling water reac- tors, the inboard isolation for the primary containment is provided by the

double seals in the control rod drives, and the outboard isolation for the

primary containment is provided by valves within the hydraulic control units.

However, past leak tests of the rod drive seals that were performed by General

Electric produced a maximum of 5 gpm per drive. Leakage from the hydraulic

control units can also be significant.

As shown in Figure 1, four paths lead from each of the 185 hydraulic control

units to the common CRD pump header. Three of these paths, the accumulator

charging header, the drive header and the cooling header include check valves

to prevent the return of water from the hydraulic units. In addition, water

escaping through the accumulator charging header must leak through the insert

side scram valve, and water escaping through the drive header must leak through

one of the directional control valves. However, the check valve in the exhaust

header is oriented so as to permit the flow of water back to the CRD pump header.

The exhaust water then flows via the CRD pump header back to the reactor vessel

(or, as at Washington Nuclear Power Plant Unit 2, to the reactor water cleanup

system) along with the excess pump flow. Therefore, only one normally closed

valve prevents water that is leaking out of each of the 185 control rod drives

from returning through the associated exhaust header to the CRD pump header.

During startup testing at Limerick Unit 1, and at Susquehanna Unit 1, the total

leakage from all of the hydraulic control units combined was measured at 5 gpm

and 11 gpm, respectively. Both of these reactors include additional check valves

at the discharge of the control'rod drive pump (area A in Figure 1). A partial

audit by the NRC staff indicates that many of the newer BWR plants have check

valves installed in the discharge pipe of the control rod drive pumps. However, this audit also showed that other BWR plants, mostly the earlier ones, did not

have such check valves. The control rod drive system for BWR/6 plants is de- signed with a testable check valve and a motor-operated isolation valve. There- fore, this pathway is applicable to pre-BWR/6 plants only.

Ie

IN 90-78 December 18, 1990 Combining the General Electric dose calculations for the postulated path with

the leak rates measured from the hydraulic units at either Limerick or

Susquehanna produces dose rates significantly in excess of the values in the

Final Safety Analysis Report. Independent calculations by the NRC staff pro- duced offsite dose values that were comparable to the General Electric results.

Radiation release by this path is not possible as long as the control rod drive

pumps are kept running. However, continued operation of these pumps following

an accident cannot be assured, particularly if the non-seismically qualified

suction piping were to fail.

This problem was resolved at Washington Nuclear Power Plant Unit 2 by the

installation of two check valves in series in the common discharge pipe from

the control rod drive pumps (at area A in Figure 1) to prevent backflow out of

the reactor building (secondary containment). The Washington Nuclear Power

Plant Unit 2 installation includes provisions for leak testing the valves and

a leak rate criterion of 0.01 gpm was established for these valves.

This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact one

of the technical contacts listed below or the appropriate NRR project manager.

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Charles R. Nichols, NRR

(301) 492-0854 Donald C. Kirkpatrick, NRR

(301) 492-1849 Attachments:

1. Figure 1. BWR Control Rod Drive System

2. List of Recently Issued NRC Information Notices

Note: At Washington Nuclear Power

Plant, Unit 2, the control rod drive

return water Is piped to the reactor w

water cleanup system

SvITE..t. .... \SECONDONDARY

OAin4Z( EXHAUST CWHIOL VALV(S CONTAINMENT

~I ~>*PCV "(E

S CU

OUTSIDE OF DRV

BUILDINGA-H

AREA

A SCIM VALVIE

6TaLQUT1 COTROL4MmuMRG

RMOO140MIX ROD

To OTHE

CONTARNEN R-OD -. I.-AJ___

CrI

DRIVEPUMPSM

0

~j

c

Figure 1. BWR CONTROL ROD DRIVE SYSTEM

Attachment 2 IN 90-78 December 18, 1990 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

90-77 Inadvertent Removal of Fuel 12/12/90 All holders of OLs or

Assemblies from the Reactor CPs for pressurized- Core water reactors (PWRS).

88-23, Potential for Gas Binding of 12/10/90 All holders of OLs or

Supp. 3 High-Pressure Safety Injection CPs for pressurized- Pumps During A Loss-Of-Coolant water reactors (PWRs).

Accident

90-76 Failure Of Turbine Overspeed 12/7/90 All holders of OLs or

Trip Mechanism Because Of CPs for nuclear power

Inadequate Spring Tension reactors.

90-75 Denial Of Access To Current 12/5/90 All Michigan holders

Low-Level Radioactive Waste of NRC licenses.

Disposal Facilities

90-74 Information on Precursors To 12/4/90 All holders of OLs or

Severe Accidents CPs for nuclear power

reactors.

90-73 Corrosion Of Valve-To- 11/29/90 All holders of OLs or

Torque Tube Keys In CPs for nuclear power

Spray Pond Cross Connect reactors.

Valves

90-72 Testing of Parallel Disc 11/28/90 All holders of OLs or

Gate Valves In Europe CPs for nuclear power

reactors.

90-71 Effective Use of Radi- 11/6/90 All NRC licensees

ation Safety Committees authorized to use by- to Exercise Control Over product material for

Medical Use Programs medical purposes.

90-70 Pump Explosions Involving 11/6/90 All uranium fuel

Ammonium Nitrate fabrication and

conversion facilities.

90-38, License and Fee Require- 11/6/90 All fuel facility and

Supp. 1 ments for Processing Fin- materials licensees.

ancial Assurance Submittals

for Decommissioning

OL = Operating License

CP = Construction Permit

IN 90-78 December 18, 1990 Combining the General Electric dose calculations for the postulated path with

the leak rates measured from the hydraulic units at either Limerick or

Susquehanna produces dose rates significantly in excess of the values in the

Final Safety Analysis Report. Independent calculations by the NRC staff pro- duced offsite dose values that were comparable to the General Electric results.

Radiation release by this path is not possible as long as the control rod drive

pumps are kept running. However, continued operation of these pumps following

an accident cannot be assured, particularly if the non-seismically qualified

suction piping were to fail.

This problem was resolved at Washington Nuclear Power Plant Unit 2 by the

installation of two check valves in series in the common discharge pipe from

the control rod drive pumps (at area A in Figure 1) to prevent backflow out of

the reactor building (secondary containment). The Washington Nuclear Power

Plant Unit 2 installation includes provisions for leak testing the valves and

a leak rate criterion of 0.01 gpm was established for these valves.

This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact one

of the technical contacts listed below or the appropriate NRR project manager.

Origina Signkd IN

Charles E Rossi

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Charles R. Nichols, NRR

(301) 492-0854 Donald C. Kirkpatrick, NRR

(301) 492-1849 Attachments:

1. Figure 1. BWR Control Rod Drive System

2. List of Recently Issued NRC Information Notices

12/11/90

NJDi*C/OGCB:DOEA:NRR

CHBerlinger

12/L~/jW 111/09/90

OGCB:DOEA:NRR *SPLB:DST:NRR *C/SPLB:DST:NRR *D/U ST:NRR *RPB:ADM

DCKirkpatrick CRNichols CMcCracken AThadani TechEd

08/17/90 08/20/90 09/24/90 10/30/90 08/06/90

DOCUMENT NAME: IN 90-78

IN 90-XX

August xx, 1990 for these and other plants produced offsite dose values that were comparable

to the General Electric results and that could also significantly exceed the

values specified in the Final Safety Analysis Report. Radiation release by

this path is not possible as long as the control rod drive pumps are kept

running. However, continued operation of these pumps following an accident

cannot be ensured, particularly if the non-seismically qualified suction piping

were to fall.

This problem was resolved at Washington Nuclear Power Plant Unit 2 by the

installation of two check valves in series in the common discharge pipe from

the control rod drive pumps to prevent back flow out of the secondary contain- ment. The Washington Nuclear Power Plant Unit 2 installation includes provisions

for leak testing the valves. Washington Nuclear Power Plant Unit 2 planned to

establish a leak rate criterion for these valves of 0.01 gpm.

The control rod drive system for BWR/6 plants is designed with a testable

check valve and a motor-operated isolation valve, therefore this pathway is

applicable to only pre-BWR/6 plants.

This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact the

technical contact listed below or the appropriate NRR project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Charles R. Nichols, NRR

(301) 492-0856 Donald C. Kirkpatrick, NRR

(301) 492-1849 Attachments:

1. Figure of Control Rod Hydraulic System

2. List of Recently Issued NRC Information Notices

Document Name: UNIDENTIFIED RELEASE PATH IN

SEE PREVIOUS CONCURRENCES

D/DOEA:NRR C/OGCB:DOEA:NRR

CERossi CHBerlinger

10/ /90 10/ /90

OGCB:DOEA:NRR SPLB:DST:NRR C/SPLB:DST:NRR D/DST:NRRK4 RPB:ADM

DCKirkpatrick* CRNichols* CMcCracken* AThadani TechEd*

08/17/90 08/20/90 09/24/90 10M /90 08/06/90

1990

Page 3 f 3 Combining the General Electric dose calculations for the postulated path with

at either Limerick or

the leak rates measured from the hydraulic units in excess of the values specified

Susquehanna produces dose rates significantly calculations by the NRC staff

in the Final Safety Analysis Report. Independent to the General Electric

produced offsite dose values that were comparable the values specified in the

results and that could also significantly exceed by this path is not possible

Final Safety Analysis Report. Radiation release running. However, continued

as long as the control rod drive pumps are kept cannot be assured, particularly

operation of these pumps following an accident were to fail.

if the non-seismically qualified suction piping

This problem was resolved at Washington Nuclear Power Plant Unit 2 by the

installation of two check valves in series in the common discharge pipe from

the control rod drive pumps (at area A) to prevent backflow out of the reactor

building secondary containment. The Washington Nuclear Power Plant Unit 2 and a leak rate

installation includes provisions for leak testing the valves

criterion of 0.01 gpm was established for these valves.

or written response. If

This information notice requires no specific action

in this notice, please contact one

you have any questions about the information appropriate NRR project manager.

of the technical contacts listed below or the

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Charles R. Nichols, NRR

(301) 492-0854 Donald C. Kirkpatrick, NRR

(301) 492-1849 Attachments:

1. Figure 1. BWR Control Rod Drive System

2. List of Recently Issued NRC Information Notices

Document Name: RELEASE PATH NOTICE ok 1vko .

D/DOEA:NRR *C/OGCB:DOEA:NRR

CERossi CHBerlinger

11/ /90 11/09/90

C/SPLB:DST:NRR *D/DST:NRR *RPB:ADM

OGCB:DOEA:NRR *SPLB:DST:NRR TechEd

DCKirkpatrick CRNichols CMcCracken AThadani

08/20/90 09/24/90 10/30/90 08/06/90

08/17/90

IN 90-XX

August xx, 1990 this path is not possible as long as the control rod drive pumps are kept

running. However, continued operation of these pumps following an accident

cannot be ensured, particularly if the non-seismically qualified suction piping

were to fail.