Failure Knowledge Database / 100 Selected Cases

The guillotine breaking of the secondary piping
in nuclear power plant
Dec. 9th, 1986, Virginia State United States
MURAKAMI, Hiroshiyo (Japan Atomic Power Company)
KOBAYASHI, Hideo (Tokyo Institute of Technology)(Summary)
At 14: 21 o n December 9th , 19 86, t he guillotine brea king ac cident show n in Fi g.1 occurred at th esecondary system p iping in Su rry Nu clear Po wer Plan t Un it No.2 . Th e Su rry Un it No .2 was owned andoperated by the Virginia Electric Power Company in Newport News, Surry County in the state of Virginia,
the USA. The commercial operation started in May 1973 and continued for a total operating time of 76,600
hours prior to the accident. The pipe failed in a 90°elbow located in the 18 inch (457mm) feedwater suction
line that feeds water to the feedwater pump as shown in Fig. 2. The material of the broken piping is carbon
steel (ASTM A234) with a wall thickness of 0.5 inches (12.7mm). The cause of the failure is wall thinning
due to erosion-corrosion. Four persons who were replacing thermal insulation nearby the line were killed
and two persons were injured.
1. Event(1) The main steam isolation valve failed to close while operating at 100% power on December 9th, 1986.
Therefore, the nuclear reactor tripped and the auxiliary feedwater pump started as shown in the outlineof the system given in Fig. 3.
(2) Since the auxiliary feed pump was also started in addition to the auxiliary feedwater pump after themain ste am isolat ion valve ha d been cl osed, a l arge am ount of water w as s upplied t o th e steam
generator, an d th e prim ary sy stem coolant tem perature fell to 290℃ or less. In order t o avoid
subcooling of the primary coolant temperature, a main feedwater supply control valve was closed.
(3) Since the feedwater pum p was working even though the main water supply control valve was closed,
the pressure i n front of an d beh ind th e fe edwater pump rose. A s a result, about 5 seconds aft er themain water supply control valve was closed, there was faint steam discharge sound, and the 90°elbow
part of the 450mm piping that branches from a 600mm header piping at a feedwater pump suction line
broke. Si x of eig ht persons w ho w ere re placing t hermal i nsulation nearby t he fra ctured e lbow partreceived serious burns. Four of them died, and two of them survived with serious burns.
2. Course(1) After the a ccident, a time series a nalysis was ex ecuted based on th e monitor re cord of a s econdary
system each equi pment bec ause of t he c larification of the pressure i ncrease s ituation of t he part ofconcerned.
(2) In or der to tr y to fin d the ca use of the brea king of the p art, sev eral i nvestigations including an1

Failure Knowledge Database / 100 Selected Cases

investigation of the material specifications, an integrity investigation of the material by metallography,
an investigation of the inside surface conditions of the piping, a micro and macro investigation of thefracture surface, and a piping wall thickness investigation were made.
(3) Since the phenomenon of wall thinning by erosion-corrosion was suspected from the condition of thebroken part, an investigation of the water chemistry record of the secondary system was conducted.
(4) Because a fracture had occurred, a fracture mechanics analysis was carried out.
(5) The Surry Unit No.1, that used a similar water chemistry management and had a similar piping layout
to the S urry Unit No. 2, was shutdown because it had been predicted that wall thinning of the piping
and elbow part by the phenomenon of erosion-corrosion had occurred as a result of the investigationsof the failed part. A measurement of t he pipe w all thickness at the Surry U nit N o.1 w as conducted,
resulting in observation of wall thinning similar to the Surry Unit No.2.
(6) The piping around the part where particularly severe wall thinning had been observed was replaced.
3. Cause
The part in w hich th e break occ urred was carbon steel that wa s expose d t o the s econdary waterchemistry environment of a pressuri zed water reac tor. In t he combination of th e secondary system waterchemistry (pH 8.8 - 9.2) by AVT (All Volatile Treatment), and carbon steel, it was not necessarily the waterchemistry for maintaining the c orrosion protection of carbon st eel. Since a c opper alloy was used i n t hesystem, prope r corrosio n pr otection of th e carb on ste el co uld not b e maintained un der th e hi gher pH .
Moreover, becau se th e p art t hat b roke was no t d esignated as a n object of the in-service i nspection, noinspection of the position where the break occurred had ever been conducted. In addition, the 90o elbow
where th e bre ak oc curred h ad be en installed as a res ult of an im proper pip ing lay out. For t his re ason, aturbulent fl ow occurre d i n t he e lbow part res ulting i n t he progression of s evere w all thinning b yerosion-corrosion. The break occurred after the scram of the nuclear reactor.
4. Immediate Action
After the fracture occurred, the Surry Nuclear Po wer Plant Em ergency Plan* was put i nto ef fect
immediately, and the notice of abnormal circumstances was issued. Then, this was changed to "Alert".
The owner of the plant star ted res toration ac tivities i mmediately. The plant owner c ontacted the U .S.
Nuclear R egulatory Co mmission (NRC) i mmediately a fter the a ccident. The NR C made the decision todispatch an inspection team from a nearby NRC branch. A specialist of the water hammer phenomenon wasadded to th e NRC ins pection team, form ing th e a ugmented inspection team. The a ugmented ins pection
team by the side of this re gulation carried out its own inspections independently fro m the elec tric powercompany that had caused the accident. On the other hand, the top level management of the Virginia ElectricPower Company responded by setting up the adjustment management group in charge of investigating thecause of the break, the safety of the plant, the operation, and the safety of the industry as shown in Fig. 4.
After the accident occurred, the Virginia Electric Power Company regularly reported the situation andother details of the accident to the media, explaining that it was not a serious accident such as one in which
a piping fracture causes the damage to the core of a nuclear reactor.
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Failure Knowledge Database / 100 Selected Cases*: A plan maintained as correspondence to a seri ous accident that results in damage to the reactor coreof a nuclear plant.
5. Countermeasure(1) An inspection of the wall thinning in the piping of the secondary system at the Surry Unit No.2 thatcaused the accident was performed. The piping in the part where the generation of wall thinning had
been observed was replaced.
(2) The piping was replaced according to the following conditions. (a) Adoption of stainless steel that hasa higher erosion-corrosion resistance than carbo n steel, for which t he corrosion resistance under thewater chemistry environment and flow velocity conditions was difficult to maintain, and (b) adoptionof l arger d iameter pi ping in ord er t o re duce erosion-corrosion a nd t o improve t he piping l ayout by
decreasing the flow velocity.
6. Knowledge
Even when the AVT (All Volatile Treatment) water chemistry in which ammonia and hydrazine is added
for the prevention of m aterial corrosion is adopted, if c arbon steel is used and a high flow velocity exists,erosion-corrosion c annot be pre vented. In t he par t w here t he flow v elocity be comes l arge, w all t hinningmust be m easured periodically and the wall thinning trend must be predicted. When relatively large wall
thinning is observed, it is n ecessary t o pr event eros ion-corrosion by (a) a dopting a material wi th greater
erosion-corrosion resis tance,(b) rep lacing th e piping w ith l arger d iameter pip ing, or (c) im proving t hepipe layout in order to avoid local occurrence of high flow velocity.
7. On the SideThe second design of the system of t he pressurized water reactor was based on a design of the turbine
equipment for a t hermal power pla nt. Therefore, the main system material adopted was carbon steel, andcopper alloys were used in the hea t exchanger tube of the heat exc hanger. M oreover, the s econd systemwater chem istry management w as als o b ased on t he water chem istry control of a therm al po wer plan t.
Therefore, the method of water chemistry control using the addition of hydrazine to phosphoric acid soda inorder to limit the decrease in pH even if the second seawater leaking from the c ondenser tube entered thesystem.
The design of the s econdary system of a pressuriz ed water reactor was based on the design of turbine
equipment of a thermal power plant. For this reason, a copper alloy was adopted as the material for the heatexchanger tube of a he at excha nger, a nd carbon s teel was mainly u sed f or t he material of the secondary
system. Moreover, the secondary syste m water chem istry control wa s also based on t he wat er chem istry
control of t he therm al power pl ant s o that, even if s ea wat er l eaked into t he secondary system fro m thecondenser tu be, th e pH w ould not easi ly decreas e. Sin ce w all t hinning w as obs erved i n ste am generator
heat exchanger tube by using the phosphoric acid soda, generally AVT processing which added hydrazine
to ammonia came to be car ried out. However, it was necessary to adjust the water chemistry control with
AVT processing of corrosion resistance so that both carbon steel and the copper alloy might be satisfied. In3

Failure Knowledge Database / 100 Selected Cases

order that to be referred to as high pH is required in order to improve corrosion resistance more for carbon
steel, but a copper alloy may dissolve, it is in the situation which is not made to high pH. As a result, if theflow velocity in the secondary system is high, wall thinning will occur in carbon steel. It is in the situation
which is not high pH, and it has been common sense as maintenance activities of the power plant that wall
thinning occurs in carbon steel on the conditions that the flow velocity is high. For this reason, the part thatthe flow velocity becomes high observes the wall thinning situation intentionally. Generally surveillance isthickness measurement of piping. It is necessary to carry out thorough wall thickness measurements during
periods when the power plant is shut down. Since the material and water chemistry control of the secondary
system in the Mihama Unit No. 3 are the same, wall thinning management was determined to be necessary,and th ickness measurements of pi ping were carrie d out d uring t he pl ant sh utdown. T he pipe rup tureoccurred in the Mihama Unit No. 3 because the time to put a fracture part on a maintenance list of wall
thinning to decide the part where the measurement of the pipe wall thickness was delayed.
In general, if a material that does not have excellent corrosion resistance properties is us ed for the part
where th e flo w velo city is hig h, er osion-corrosion w ill oc cur. Th e part i n w hich this er osion-corrosion
occurs most stron gly is th e part where t he flow veloc ity cha nges su ddenly. M oreover, when s evere wal lthinning is o bserved, it is good to inquire so tha t more suitable corrosive protection may be ready in t hecombination of the material currently used, since it may be possible to improve the water chemistry control.
Moreover, another ef fective counterm easure is to ad opt a m aterial wi th ex cellent corrosion re sistanceproperties so that erosion-corrosion will not occur.
*1: "a guillotine failure" involves "a fracture in which piping breaks into two separate parts and flows
out of both of fracture sides with out a coolant interfering , respectively" (fro m the nuclear dictionary ofNikkan Kogyo Shinbun and the nuclear library of the Internet library of the Japan Science and Technology
Agency JST http://mext-atm.jst.go.jp.) This technical term is currently used officially. "Guillotine" is a toolfor exe cution that w as in vented i n Franc e. Ma ny pe ople w ere e xecuted by gu illotine during the tim e ofterrorism that followed the French Revolution. Joseph Guillotine, a member of the Natio nal Assembly anda physician, proposed the use of the guillotine as an execution device in which the person executed did not
suffer and persons of all positions could be executed in a similar way, and his proposal was adopted in theNational Assembly.
Although the device was initially called "Louisette" or "Louison" after the name of Louis, the designerof th e d evice, Guil lotine, w ho greatly ad vertised the h umanity a nd equal nature of th is d evice, be came
famous, and the name "Guillotine" was given to the device. The official name of the guillotine is "Bois deJustice (pillar of justice)" in German reading. In addition, "Guillotine was ex ecuted by the guillotine" is amistake.
8. Information Source(1) USNRC Information Notice No. 86-106 Supplement 1: Feed Water Line Break 1987.
(2) Dr. Shibata, Dr. Miyazono, Ueda et al, "Piping failure accident of Surry Nuclear Power Plant" Ato mic
Energy Society of Japan, Vo.29, No.11, and p952-969 (1987).

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Failure Knowledge Database / 100 Selected Cases

9. Primary Scenario
01.Insufficient Analysis or Research
02. Insufficient Prior Research
03. Project Diversion
04. Ignorance
05. Insufficient Knowledge
06. Erosion/Corrosion
07. Production
08. Hardware Production
09. Machine/Component Production
10. Improper Piping
11. Usage
12. Maintenance/Repair
13. No Inspection
14. Failure
15. Abration
16. Erosion/Corrosion
17. Failure
18. Large-Scale Damage
19. Guillotine Failure
20. Leak
21. Bodily Harm
22. Death
23. Accidental Death5Failure Knowledge Database / 100 Selected Cases

Breaking position

Fig. 1Primary and Secondary Systems of Pressurized Water Reactor and Braking Portion.

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Failure Knowledge Database / 100 Selected Cases

90°elbow of 18 inches Breaking Position
Piping F ractured alo ng wit h t his li ne.

From the piping fractured
above drawing, piping blowout the following aspects.

Arrested crack

Fig. 2

Detail Drawing of the Breaking Portion.

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Failure Knowledge Database / 100 Selected Cases

External Shield Wall
Primary Containment Vessel

Closed Valve

Fig. 3

Schematically System Drawing of Pressurized Water Reactor.

Virginia Power
Nuclear Management

Industrial Safety
Independent
Investigation
Committee

U.S. Nuclear Regulatory
Commission (NRC)

Corporate andStation Nuclear
Safety andLicensing Stuff

Technical
Independent
Investigation
Committee

Fig. 4 Incident Response Organization Chart of Virginia Power.

8Incident
Coordination
andControl